Explorations in Audio

Karsten Hein

Are you ready to Explore?

In 'Explorations in Audio' I aim to share some practical insights on setting up and optimising an affordable HiFi system. Although one would think that, really, all has been said about HiFi, some surprisingly simple questions still remain, e.g.: 'Is digital superior to analogue?' 'Do cables matter?' 'Can digital cables pick up interference?' 'Should speakers be placed on spikes?' 'Has evolution in HiFi made older gear obsolete?' 'Where should I place my sub?' 'Which room correction works best?' - On the other hand: 'Are these really the right questions?' - We shall see.

What’s new in eiaudio?

While the entries in this blog are divided into the three distinct categories above, you will find a mixed listing of the most recent postings below. The most recent article is shown first. If this is not your first time visiting, the listing below is a good place to quickly check if anything is new.

Your input is more than welcome, as long as you follow the basic audiophile rule of ‘ear over mind’. This means that you do not comment based on what you think you know, but only on the basis of your own listening experience. Please feel free to suggest gear for testing as well as leave comments on the descriptions provided here.

  • Shure 701 Pro Master

    Shure 701 Pro Master


    Author: Karsten Hein

    Category: Gear & Review

    Tag(s): Loudspeakers

    “What on earth…!?” you might be thinking when stumbling across this article, and even more so if you have been following this blog and perhaps thought you had me pegged as a straightforward audiophile who just happened to be into vintage gear. What on earth is a pair of Shure 701 Pro Master (that was obviously built for public address) to do on an audio blog that is dedicated to the enhancement of domestic listening pleasures? Well, to be absolutely honest, I was a little surprised by this acquisition myself. I guess, some little voice had whispered to me that these anno 1979 PA speakers would be worth the effort of exploration, simply because they would yield new experiences on many levels.

    For one thing, the Pro Masters featured a 15-inch paper-cone woofer that was similar to some highly relevant Tannoy and Altec classics. From experience, I had learnt that paper was a decent enough construction material to build natural sounding dynamic drivers. On the other hand, more often than not, I had been warned by my audiophile friends that 15-inch drivers would be far more difficult to integrate with the room, as their greater dimensions could more easily excite room modes that would in turn limit placement choices. I had therefore thought it best to first experiment with speaker placement on the affordable level of the Shure Pro Masters before finally taking the plunge on their more expensive domestic cousins.

    In addition to the new bass experience, the Shures featured a radial horn driver with adjustable angle that would offer fresh insights into horn-loaded designs as they were found on many renowned Hi-Fi and studio loudspeakers built by Altec Lansing, JBL, TAD, Electro Voice, Fostex, among others. Horn designs offered the benefit of high sensitivity output even at the low voltages produced by small tube amplifiers. In fact, the Pro Masters’ 102dB in sound pressure (measured at one watt power input and at one meter distance from the speakers) could mostly be attributed to the horns of the high frequency drivers. While the Shures’ horn principle may not have been the most delicate on the market back in the 1970s, it would allow me to learn more about the sonic characteristics of horns in terms of minimum distance, sweet spot, room modes and reflections, and other parameters which would be difficult to judge without first-hand experience.

    For the pair of 1979 Pro Masters presented here, I ended up driving all the way up to the infamous Marburg “Hinterland”. Their previous owner Micheal was an ageing audiophile and collector of loudspeakers himself and in the advertisement had described the speakers as being fully functional. Hence, I was quite optimistic when I arrived. I found the speakers set up in a furnished garden hut, in which Micheal had compiled his third or fourth system. A quick listening tests showed them to play music. However, neither the positioning on a table nor the room itself allowed for a deeper tonal analysis. There was pretty much a lack of everything, and so I decided to trust his verdict that they were still fully intact. We carried the Pro Masters to my car and spent the next few minutes listening to his current basement horn system.

    Back at home, Sabina helped me carry the heavy speakers up our winding stairwell. I quickly found a spot for them, and we ended up parking them there for a few weeks to finish some other projects. When I finally came back to the Shures, I quickly set them up on two stubby stepladders. I connected them to our Dynavox VR-70 tube amplifier which was fed from our Marantz CD-17 and Cambridge DAC on Restek V1 combo. Having been fully broken in, the Dynavox VR-70 (still with original Chinese tubes) was capable of producing a tonally and spatially accurate musical image. The big question was, if the amp would be able to offer the same dexterity with the Shure Pro Masters connected instead of our EPI 500 loudspeakers. Having limited experience with PA speakers myself, I really had no idea what to expect next, but I was prepared to keep an open mind.

    Our upstairs listening room was a little special in terms of dimensions. It was almost 13 meters deep, 10 meters wide, and over 4 meters high in its centre. There were no two walls running in parallel. With all this space available, it may come as a surprise that the only area reserved for listening was a unilateral triangle of about 2 meters in length with a thick piece of carpet laid out at its centre. Somehow the juxtaposition of short listening distance and the massive delay of the room made it relatively easy for the brain to filter out reflections from the music source. Hence, this was usually not a poor choice of venue for testing loudspeakers. However, when setting the Shure PA horn-loaded speakers in motion for the first time, I realised that listening at this short range would be a real challenge.

    The horn’s design principle naturally caused high levels of compression at short range that could easily overstrain the ears. Luckily, some previous owner had added Visaton LC57 attenuators to dial back the horns. This worked quite well, indeed. I then started experimenting with the horns’ dispersion angles and adjusted them from formerly 120 to now 60 degrees. At short range, this made the treble sound less bloated and more musically effortless. It was possible that this observation would have been different at greater distance from the speakers or other room dimensions. To my utter surprise and delight, the Shures’ horn drivers did not only sound large and impressive but were also tonally sensitive and dimensionally accurate. The Pro Masters were capable of natural transients and even tonal nuance despite delivering the output to entertain an event.

    A lot has been said (and written) on the discrepancy between the relatively small size of horns in relation to their 15-inch woofer companions, as found on many professional audio and domestic designs. This naturally takes us to the subject of bass performance. It seems that on PA loudspeakers, 15-inch drivers with rippled cone surrounds were used as 'midrange' chassis that were also capable of extending into the upper bass frequencies. This was a significant finding when it came to the expectations one might have towards such designs. Coming from domestic speakers, I would have suspected a 15-inch driver to act as a subwoofer that would only with great difficulty reach the higher crossover frequencies when coupling to the horn. However, listening to the Pro Masters perform, I quickly understood that I would have to dial down my expectations in terms of bass extension. 

    The Shures played an excellent treble and even created a believable midrange, perhaps as one might expect from listening to a home concert, and yet bass was more hinted than it was fully executed. This was also the moment when I started to feel confined by my up-close listening position. I wanted to have a solid back wall behind me to more fully appreciate the slapping of the large cones. In order to find out more about the Shures’ tonal balance, I would need to give them an audition in our main listening room in which my listening distance was at five meters, with the back wall about 90cm behind me. To make this happen without getting in trouble with my wife for aesthetic reasons, some dedicated stands would need to be built first. I drew up a quick design and went to buy some wood and paint from a local DIY store. On my way home with my bundle of carpenter board and solid wood beams, another question came to mind: What made these horns sound so great, and what was the crossover design for the woofer?

    Back at home, I decided to first open the speakers to find out what was inside. The large woofers were held in place by eight screws that were professionally countered from the inside by threaded drive-in nuts. This would make woofer replacements an easy task, and I could already see why. As it turned out, one of the woofers had a crack in the cone and had already been taped from the inside. The crack had hardly been visible from the outside, and I had a strong sensation that Michael the pensioner and loudspeaker collector from Marburg's Hinterland had in fact sold me a damaged loudspeaker without telling me about it. In my years in Hi-Fi, I have come to understand that there is a generation of people who have learned to twist the truth in any way they like, even to the point where they start to believe it themselves.

    Luckily for me, the damage did not render the bass driver useless. With a fresh strip of black tape in place, the driver could still be trusted to perform for a number of years. And, to my surprise, I saw that the woofer was attached straight to the terminal without passing any kind of crossover. While this would leave it up to the driver's cone and its spider's mass and tension to reduce unwanted high frequencies, it also lessened the likelihood of phase issues, as long as the drivers were positioned correctly to begin with. I was strangely reminded of the Orbid Sound Pluto's (kit) design, which seemed to go by the same method, even though their much smaller bass drivers had great difficulty in losing the higher frequencies and therefore contributed to a squeaking midrange.

    Following the inspection of the woofer (seemingly a 15" Eminence-type with the typical square magnet and three magnet screws), I unmounted the Shure's horn driver and noticed that a number of audiophile improvements of the crossover and mounting had been made in comparison to the original design. The capacitors had been replaced with modern audiophile foil caps. In addition, a variable Monacor DSP-1 resistor had been installed to protect the horn from damage in the event of unintentional power spikes. The horn was no longer screwed onto the cabinet's rear wall. It was instead placed on a wooden support with foam cushion. This would minimise some of the back wall resonances and prevent these from afflicting the horn's diaphragm.

    Some prior owner had also attached self-adhesive bitumen mats to the interior walls; however, they had already become loose in many places and had begun to slide down the sides. I decided to take them out completely in order to once again reach that warm, vintage, cabinet sound of a resonating wooden box. If the original intension had been to reduce cabinet resonances, some simple internal struts would probably have done a better job anyway. I decided to hold on to the bitumen mats just in case I would change my mind upon hearing the speakers perform.

    Building the stands for the Shures was a simple enough task. We started out from two 16mm carpenter boards that would form the bottom plates of the stands (32mm in thickness) and to this attached three 360mm beams of 80x55mm in strength in a triangular position. We then screwed the top plate onto the beams, again made from two sheets of 16mm carpenter board. I was hoping that this construction would allow for more freedom on the side of the speakers which would in turn result in a more pleasant tonal representation. Three spikes would isolate the stands towards the floor. And, on the side of the speakers, I would replace the four original plastic feet with three rubber cushions made for professional music gear. I had already noticed that three supporting points often produced a better defined coupling between materials and was therefore easier to execute than four spikes or cushions on which the weight distribution could be less than ideal.

    When I set up the speakers in our main listening room just a few days later, I was actually feeling hopeful that the combination of greater listening distance and better stands would also lead to superior imaging, and that the boxy shape of the room would do well to accentuate bass response. To my surprise, however, the Shures did not sound any more bass-heavy than they had done before. Unless they were used for public address, where they would be called upon to transport vocals over a great distance, these speakers needed a subwoofer in order to capture all aspects of natural instruments. My next task would be to find a sensible sub to pair with the speakers, and thus I found myself crawling even deeper down the rabbit hole. In order not to get lost on the way, I decided to see an expert on professional audio solutions, hoping that he would aid me with my difficulties.

    As I found out from running a few web searches, there was an audio enthusiast by the name of Rainer Weimann who operated a part-time sales office southeast of Darmstadt in which he sold affordable audio gear to small-time local musicians, entertainers, and organisers of events. Over the years, he had established a reputation as distributer for the Chinese brand Dragon Audio. Founded in Shenzhen in 2004, Dragon Audio had grown into a major OEM producer of audio gear with over 1,400 staff working in 14 factories. I was specifically interested in an active Hi-Fi subwoofer made by DA that Rainer had listed on an auction site. The other product I had seen on sale in Reiner's shop was an active 15-inch Vonyx PA subwoofer. Vonyx was another audio company that had made a name for itself serving the lower end of the market. Ideally, it would be possible for me to listen to the two subs in direct comparison.

    Upon arriving at 'ProSchall', as Rainer's shop had been named, I was given a warm welcome and invited inside. I immediately recognised some of the products I had seen offered online. The two subwoofers were standing side by side, right next to some even larger specimen. Rainer explained that the 15-inch Vonyx PA subwoofer was designed to power public venues and would sound best when driven at high levels of sound pressure. It had a rigid suspension that could handle high volume music program but would sound flat and overly dry when played at living room volume. The Dragon Audio woofer, on the other hand, had been designed to be played in a household environment. It had a softer suspension that would allow the driver to operate accurately even when played at low volume.

    Seeing that I was not yet fully convinced, he quickly connected the 12-inch DA woofer for me. The sound it produced was instantly familiar from listening to Hi-Fi gear. I could imagine that this would play well with many types of speakers. Rainer then connected the 15-inch Vonyx woofer, and immediately the room sounded too small for the hard and dry bass of the woofer. The music could be physically felt in the room more than it could be heard, and it was easily conceivable that the neighbours would derive greater benefits from the output of this woofer than we could in the listening room. It was at that moment that I could quite literally feel the difference between Hi-Fi and PA speakers. Either of them would perform like a fish out of water if it was employed outside of its intended venue. I thanked Reiner for the wonderful experience and, with a deeper understanding of the matter (and one Dragon Audio subwoofer called 'The Art of Sound' in the trunk), I made my journey back to Frankfurt.

    From Reiner, I had also learned that professionals often preferred to have the vocal section separate from the bass drivers, because this would reduce the load on the amplifiers, decrease the likelihood of damage to the delicate top-end, and allow for the perfect number of bass drivers in relation to the size and sonic characteristics of the venue. This made sense of course, considering how long it took me to integrate simple 3-way speaker systems in our listening rooms. PA speakers could be used for a whole range of venues, from outside gigs on which massive amounts of bass were needed, to boxed-in basements in which low frequency waves were accumulated from being reflected back from the walls. In our living room, the 12-inch DA woofer turned out to be more than sufficient for filling in the Shures' missing bass. For the first time, the tonal balance was as one would expect from speakers of this size. As you might imagine, the following movie night turned out to be a real treat for the whole family, with the Pro Masters effortlessly rising to breath-taking volume at an instant and the subwoofer giving the sound effects their palpable bass dimension.


    • Type: full-range public address speaker
    • Principle: 2-way, front-ported bass reflex
    • High frequency section: radial horn driver
    • Low frequency section: dynamic 15-inch woofer
    • Special features: 60° / 120° adjustable horn
    • Power handling: 150 watts RMS / 55V peak
    • Sound pressure level: 102 dB (at 1W / 1m)
    • Frequency response: 50 Hz to 15,000 Hz
    • Crossover frequency: 2,000 Hz, 18dB
    • Nominal impedance: 8 Ohms
    • Horizontal sound distribution: 60° or 120°
    • Vertical sound distribution: 90°
    • Operating temperature: -7°C to 43°C
    • Cabinet: 15.9 mm multiply wood, vinyl coated
    • Original weight: 26,4 kg per speaker
    • Dimensions: (H) 700mm; (W) 585mm; (D) 405 mm
    • Country of manufacture: USA
    • Year: 1979


    • Terminals for bananas and spades
    • Visaton horn volume attenuator
    • Audiophile horn crossover
    • Monacor DSP-1 resistor

    Jörg Hegemann
  • Orbid Sound Pluto (kit)

    Orbid Sound Pluto (kit)


    Author: Karsten Hein

    Category: Gear & Review

    Tag(s): Loudspeakers

    Our family had just returned from living in the United States and was coming to terms with the adjustments of living in Germany, when a friend of mine introduced me to Mr Beyersdorffer’s infamous Orbid Sound loudspeaker company. Seeing that I had an interest in audio gear, he handed me a brochure that seemed to give away lots of secrets regarding the production and sale of loudspeakers. In this, Mr Beyersdorffer claimed that the established audio companies were ripping off their customers by packaging cheap drivers into fancy-looking boxes, hoping that enough paying customers would be attracted by their paid-for (and therefore always positive) reviews in the audio press.

    Mr Beyersdorffer explained that Orbid Sound could work with superior drivers at a far lower price point than the audio establishment, since his company did not advertise in expensive magazines, and instead had built its reputation on word-of-mouth from its happy customers alone. His claims were not without truth, of course, with Hi-Fi stores selling speakers based on their high wattage figures, increasingly dubious frequency curves, and accentuated treble response—the latter being directed at affluent pensioners who were happily smiling that they could once again hear the upper ranges of the frequency spectrum. These were the days in which low-budget speaker manufacturers would paint large shiny rings around their smallish drivers in the attempt to make their speakers look more impressive through the cloth.

    However, these brands—mostly from mail-order outlets and department stores—were not the primary target of Mr Beyersdorffer’s campaign. His rantings were directed at established Hi-Fi stores, and in his audience were emerging audiophiles on a tight budget. If he could convince the youth of the day that they could play with the big boys by being cleverer than the audio establishment, he would be able to earn enough money with his company to make a living for himself, and perhaps even some more. As it turned out, my friend, my younger brother, and myself ended up buying our first ‘real’ loudspeakers from Orbid Sound.

    To save money, my brother and I chose assembly kits from the company. My brother’s Pluto kit came with prefabricated cabinet parts and was easy to assemble. I decided to go one step further by building the speaker cabinet from scratch. With more than 30 years having passed since then, I have forgotten what my loudspeakers were called, I just remember that they had four small woofers each, instead of one larger one. And these woofers were paired with the Pluto’s midrange driver and tweeter. Although I liked the idea of benefiting from the reduced time-lag of four smaller bass drivers and could even follow Mr Beyersdorffer’s ideas on this, I found that the concept did not work so well in practice—perhaps due to differences in timing between the drivers—and so I sold my speakers again, just a few weeks after finishing them.

    My brother, on the other hand, kept his Orbid Sound Pluto kit speakers and finally left them behind at my parents’ house when he moved out in 2006. This is precisely where I found them just the other day. I called my brother to ask if I could take them home for a listening test on our system, to which he agreed. There was a moment of pause in which we both had to snicker at the improbability of running Orbid Sound speakers on a 'grown-up' stereo system. How would they compare against the high musical standards set by our vintage classics, let alone the modern Tannoy XT8f dual-concentric towers, the Epicure EPI 500, or even the Martin Logan SL-3 electrostatic speakers? We decided that we could not know until we tried, and I took the Plutos home with me later that evening.

    Upon further inspection, I could see that the cabinets and drivers were still in surprisingly good shape, even if the glue of the veneer edging had become a little brittle in some corners, revealing plies of multi-ply underneath. This came as a surprise to me, as I had misremembered them to be made of cheaper pressboard. Multi-ply had the added advantage that it was not as sonically dead as the MDF board that is typically used these days. So, I whipped out a bottle of Ponal wood glue to solve the issue. The drivers themselves were still sonically sound, and I could not detected any scraping when moving them by hand.

    Some people had reported that Orbid Sound designed their crossovers without using coils, simply by combining resistors. However, with the crossovers being cast in hardened resin, it was difficult for me to find out how much truth there was to this claim without breaking them. In my early youth, I had also built speakers without coils in their crossovers and learnt that such designs could actually be beneficial to phase correctness in some setups. Without the low pass function of a coil choke, the woofers were simply allowed to play lower midrange frequencies. And while this may have been an option on a two-way system, I was a little suspicious in respect to a 3-way design. Some sceptic listener had even x-rayed the crossovers and suggested in an online forum that they were in fact quite conventional. Be that as it may, in the end, I decided that it was worth finding out what Orbid Sound had cooked up thirty years ago.

    Following some time listening to our Epicure EPI 500 speakers, I connected the Plutos to our Dynavox VR-70 tube amplifier, which had already been well run-in at this time. The music source was our Marantz CD-17 paired with a Cambridge DAC. I positioned the Plutos in the exact position where our EPI 500 had been, with the chassis at about 105cm distance from the room's front wall, only to find that this practically eliminated all bass frequencies from the rear-ported speakers. As intended book shelve speakers, the Orbid Sounds had been designed with the room's front wall to act as bass support. This itself was not necessarily a shortcoming in real-world applications; hence, I slowly began moving the stands closer to the room's front wall. As the chassis were approaching 62cm distance, bass notes finally began to sound right.

    And yet, there was a second quirk that I had noticed right from the first minute of the speakers performing. Something was off balance in the Plutos' midrange. Female voices sounded squeakier and more compressed than I was previously used to, from our other speakers (and from real-life). At first, I had thought that this effect would lessen once the bass had locked in with the room, but sadly this was not the case, and I began to wonder what the level attenuation panel at the Pluto cabinet's rear wall was actually used for: the tweeter or the midrange? When first setting the speakers up many years ago, my brother and I had chosen to install a simple wire bridge, instead of using one of the included attenuation resistors. (I think there had initially been two, but who knew where they were now?) Listening to the Plutos today, this proved to have been a mistake. I admit that back in the 90s, we used equalisers to augment speaker performance, a practice that would be seen as an unspeakable blunder in the world of audiophile listening today.

    Another phenomenon that I had noticed upon first listening to the Plutos was their eagerness to cast frequencies deeply into the room. This could have even been considered a positive effect if it had also served to create a stage impression with identifiable width and depth. For some reason, however, the Orbid Sounds did this at random and with no apparent coherence. This made only three basic stage positions discernible: left, centre, right. Snare drum, high hats, guitars, and piano notes found themselves loosely afloat in the listening room, strangely devoid of all form and position. Of the Plutos' three difficulties, this last one would probably be the most difficult to fix, as it seemed to stem from timing issues between the three chassis.

    If tonality could be fixed through midrange attenuation, this might be a step in the right direction. To find out, I would first need to confirm that the attenuation clamps had actually been attached to the midrange. If they had instead been connected to the tweeters, it would probably be best to give up on these speakers. But if the midrange could be reduced in volume, this might actually reduce the midband squeakiness and create some listenable speakers. The rear terminal looked large enough to house a standard Visaton attenuator. The next morning, I unmounted the woofer to have a look inside. My findings were twofold: The midrange driver really was connected to the attenuator clamps, and, even better, it was housed in a separate internal cabinet. Feeling reassured by the results of my exploration, I ordered two Visaton attenuators, thus hoping to rein in the sqeaky midrange.

    The Visaton LC57 attenuators arrived just three days later and easily slotted into the existing cabinet holes of the resistor clamps. I connected pins two and three of the L-pad, thus reaching maximum resistance (minimum midrange volume) with the attenuators turned left, as was described on the face plate. And yet, a first listen to the Orbid Sounds with the new L-pads in place reminded me of an issue from first placing the fixed resistors thirty years ago: There was hardly any difference in sound...! — But how was this even possible? Normally, one would think that taking the midrange drivers out of the sonic equation should also affect the speakers' ability to perform in this area. Were the Plutos' woofers perhaps allowed to extend into midrange frequencies after all? And what may have been the point of having dedicated midrange drivers, if their presence would be hardly detectable?

    Over the course of the next few days, I experimented with various distances to the listening room's front wall and also tried different settings on the attenuator dial. Even in their most becoming position—out75/in70cm front wall distance, 2/3 midrange-volume, placed at 2m distance to form an equilateral triangle with the listening position—the Pluto (kit) speakers still sounded compressed in the midrange. And although the applied attenuation did produce a mildly positive effect in terms of tonal balance, this proved less significant than expected. Granted, the Plutos were capable of producing excessive amounts of sonic information. However, they presented this in an overly eager and in-your-face fashion that would take some getting used to. Considering their entry-level priced competition of the 1990s, the Plutos' capability to present a great wealth of musical detail may even have been a welcome feature. Their ability to radiate notes deeply into the room surely was perplexing, until it also became apparent that this mostly came at the expense of losing precise musical dimension. From their very beginning, Mr Beyersdorffer's Orbid Sound had banked on the notion of setting themselves apart from the Hi-Fi mainstream, and these speakers certainly lived up to the expectation.

    Note: Martin Beyersdorffer died on 1 November 2020, just a few days before reaching his 87th birthday, and the company is currently maintained in its second generation by his son Daniel Beyersdorffer and Thomas Feil.


    • Type: 3-way dynamic ported speaker
    • Features: midrange adjustment via resistor
    • Frequency range: 33 Hz - 20,000 Hz
    • Impedance: 4 Ohms
    • Power handling: 60 watts (RMS)
    • Tweeter driver: 3.0 cm, soft-dome 
    • Tweeter model: Peerless of Denmark, SKO10 DT
    • Midrange driver: 10 cm, coated paper
    • Midrange model: WDH of Germany, BMT 130/19-120
    • Woofer driver: 15 cm, poly-compound
    • Woofer model: Peerless, 830228 (dual voice coil)
    • Cabinet: Laminated multiply wood
    • Cabinet volume: 27 litres
    • Dimensions: (W) 23.5 cm; (D) 24.5 cm; (H) 52.5 cm
    • Country of origin: Germany (kit)
    • Weight: 11 kg
    • Year: 1992

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  • Dynavox VR-70E II (Part 2)

    Dynavox VR-70E II (Part 2)


    Author: Karsten Hein

    Category: Explorations

    Tag(s): Power Amplifiers

    When I wrote my first review of the affordable Chinese import tube amplifier back in January 2022, I promised that I would write an update on my impression of the VR-70E II after it was returned to me following some modifications. My reason for having the amplifier revised had been the level of humming, its lack in audiophile frequency extension, as well as poor transients and imaging, which altogether resulted in a certain blandness of sound. My original tests had been conducted with our Dynaco PAS-4 tube preamplifier and the formidable 8 Ohms Tannoy XT-8f tower speakers.

    Upon my handing in the amp, the tube specialist had offered a speedy service within a couple of weeks, to which I had agreed. Then, however, he had somehow gotten caught up in other projects and seemed to have forgotten about me. When he then started to ignore my phone calls—after five months of patience on my side—I decided that enough time had been wasted and picked the VR-70E II up in close-to-original condition. I think we were both surprised and sad that I should have taken such resolute measures, but it seems that I had simply run out of patience with him. On my drive home, with the amp in the back of our car, I was wondering what could be done next: Sell it? Keep it for a later project?—I would need to listen to it one more time to make my final decision.

    Now, I am not sure if you sometimes have a sonic memory of the things that you have listened to. We commonly have this gift when it comes to scents or smells. As we often connect scents with emotions, we tend to remember them for a long time. This is especially true for the early experiences in our lives, and we might remember the smell of our kindergarten, or school, or perhaps of the house of your grandparents. Well, it seems that some people have a sonic memory.

    For instance, I vividly remember the sound signature of my first CD player. This was a 1988 JVC XL-Z444, and I recently even purchased this unit again, just to enjoy the sound one more time. This was not an audiophile CD player by any means and it does not need to be discussed in this blog, but its stoic crudeness and pitch-black backdrop certainly had its charm and served to set it apart from vinyl records, cassettes, and radio broadcasts at the time. I really celebrated listening to it again and having my juvenile memories confirmed. In a similar way, I still held a sonic memory of VR-70, and I was a little bit frightened of having this revived the second time around.

    With five months having passed since my original test, the set-up environment of our smaller system had meanwhile changed. The Dynaco tube design had given way to our Restek V1 solid state preamplifier. The speakers, too, had been replaced. Instead of the Tannoys, a pair of Epicure EPI 500 had found its way into the lineup and had just been optimised in terms of coupling towards the hardwood floor. In the meantime, I had learnt from trying to match the Dynaco with our B&K ST-140 amplifier that this preamp could easily have a lowpass effect in some set-up combinations. In my first test, I had all too hastily attributed the experienced loss in top-end to the Dynavox amp. This had happened, because I had been as yet unaware of the PAS-4’s shortcomings in terms of compatibility.

    Hence, when I sat down to listen to the VR-70 E II this time around, the treble was more open and spacious with improved transients right from the start. I was also happy to find that the original tube-hissing that I had heard from the amp had disappeared. The reason for this was twofold: first, the Restek V1 was a dead-silent preamp to begin with, whereas the PAS-4 produced a mild tube hissing on its own; second, the technician had found a grounding problem with the VR-70 itself. He saw that the properties of its pharadeic cage had been compromised by the bottom plate being paint-coated. He had consequently removed the paint to include the floor plate with the chassis grounding scheme. This had a significant effect on the VR-70's noise floor, which was now hardly audible, even with the ear held near the tweeter.

    The original lowpass effect in combination with the Dynaco had also made me overly hasty in turning the amp in for service—after just 40 hours of listening. Since then, the technician had adjusted the amp’s bias to 350 mV and allowed it to run for a few more hours. This, too, had given the factory-new amplifier some time to homogenise its frequency response (break-in time) and helped to take some of the initial harshness off the critical vocal section. With the top-end having opened up and the bottom end having gained power due to reduced grounding noise, there was now more depth and dimension to the music in many ways. In direct contrast to the B&K ST-140 solid state amp, which had performed to our satisfaction in this position before, the VR-70 E II presented a considerably larger stage with very similar tonality. 

    Vocals seemed grainier on the Dynavox, an impression that did not lessen even when the tubes were at full operating temperature. At the same time, voices seemed slightly more distant on some recordings. I especially noted this effect on Tony Bennett & Diana Krall’s album “Love is here to stay”. This may have been intrinsic to the Chinese tubes that had surely not been chosen for their superior tonal characteristics but rather for their bang-for-buck regarding their use on an entry-level amp. At the Dynavox’s current quality of output, I was fine with the idea of having to upgrade the tubes in some not-too-distant future in order to fulfil the promise of audiophile bliss.

    From my original four complaints about the amp: bland top-end, tube hissing, poor imaging, and grainy voices, only the last point remained. And this—surprisingly—despite all original parts still being present. I felt a little silly for not having tried matching a different preamplifier in the first place, but then again, I probably would not have learnt about the chassis grounding issue on my own. The experience only shows why it is so important that this page is called “Explorations in Audio” and not 'Facts' or 'Truths' in Audio. Life means ever learning, and only the mindset of the Explorer can expect and appreciate the surprises that the journey brings. To prove the point, and also to treat myself to today’s Father’s Day present from my wife, I will stop writing and focus my attention on the 1970s album “New Skin For The Old Ceremony” by Leonard Coen on vinyl.

    Back to Part 1 | [to be continued with new tubes…]


    • Power output (RMS, 8 ohms):  2 x 40 watts
    • Input impedance:  20 kOhm
    • Pre-amplifier tubes:  2 x 6F2 (ECF82)
    • Power amplifier tubes:  4 x EL34 (ultra-linear)
    • Tube bias:  300 - 350 mV
    • Frequency response:  10 - 40,000 Hz
    • Total harmonic distortion:  0,1%
    • Signal to noise ratio:  >88 dB
    • Damping factor:  N.N.
    • Output terminals: 4/8 Ohm, gold plated, for spades or bananas
    • Dimensions:  (W) 35,0 cm x (D) 30,0 cm x (H) 18,5 cm
    • Weight:  14,5 Kg
    • Year:  2013 - 2022

    80s night
  • Turntable Cover Restoration

    Turntable Cover Restoration


    Author: Karsten Hein

    Category: Explorations

    Tag(s): Restoration, Turntables

    We might as well face it: Turntable covers have always been little more than a necessary evil. It seems that manufacturers—while suffering great pains in designing their beloved machines—were unable to think of anything more exciting than simply slapping a semi-translucent dustcover on top. And, typically, this cover was made of some easily scratched acrylic compound. For those of us searching for or selling vintage turntables these days, a scratched dustcover often meant a substantial degradation, not only in terms of attractiveness, but also in price.

    Since the non-profit nature of my eiaudio testing series had made me rather price-conscious myself, I could not help but wonder just how much effort it would take to restore a scratched dustcover to its original splendour. The idea of being able to do so myself did seem attractive to the explorer in me. After all, this would enable me to take advantage of the potential price discount granted on the scratched cover, while being able to do the restoration myself. Hence, I contacted a friend, who also happened to be a specialist in automobile restoration, to help me find the best strategy for my project. Thomas was intrigued by the idea of restoring acrylic plastic and took the badly scratched dustcover of our Thorens TD 320, a turntable I had purchased some weeks earlier, to his repair shop.

    Thomas returned the cover to me in mint condition just two days later and informed me which equipment I would need to purchase in order to complete this type of restoration by myself. I took note of his advice and placed my order on the same day.

    Inventory Needed

    • orbital sanding machine
    • sanding paper, grades 240 - 3000 (240 / 320 / 400 / 600 / 800 / 1000 / 1500 / 2000 / 3000)
    • orbital polishing machine
    • polishing pastes in grades fine & extra fine (e.g. 3M ‘Green cap’ / 3M ‘Yellow cap’)
    • one large microfibre cloth

    The total tab would have set me back around 300.00 EUR, but, since we already had an orbital sander in the household, I only needed to purchase the various grades of paper and the polisher with the corresponding pastes and cloth. Thomas thankfully offered to keep me company during my first sanding attempt. On his advice, we took our little sanding project outside. This gave us cleaner air to breathe and protected our household furniture from the fine sanding dust.

    The dustcover to be restored was of a 1978 Dual CS 721 turntable. Next to the typical house cleaning scratches, it also showed two lines of approximately 1mm in depth and 20cm length which had most likely come from piling other items on top of the unit during its years of storage. We discussed the most appropriate choice of sanding grain and decided to start from 320. If the scratches had been any deeper, we would have probably started from grain 240 to be on the safe side.

    We positioned the turntable cover on an even non-slip surface and placed the sander firmly on top of it. The speed dial was set to medium revolutions in order to keep the temperature low during the process. If the temperature became too high, the cover could easily become stained or deformed. The sander was placed on the surface with the motor turned off, and it was turned on only when securely in place. This way, there was less chance of the paper’s sharp edges accidentally cutting new scratches into the surface.

    Thomas explained to me that the machine would need to evenly sand the whole surface until reaching a ‘level 320 sanding result’. (Note: Be sure to keep your fingers away from the paper edge, as this can indeed be quite sharp and easily cut into flesh.) Starting from grain level 320, the turntable cover did become opaque at an instance, and we knew that it would take some time for it to become translucent again. On the positive side, we could watch the deep scratches gradually disappear. We had peeled the Dual logo off with a screwdriver before sanding, and we made a point not to polish the edges of the small cavity where the logo had originally been placed.

    Thomas insisted that we take the time to fully complete each step of the sanding process, thus working our way up from 320, to 400, and then to 600, until all the steps to 3000 had been completed. At each level, we made sure that the surface was fully restored to the level characteristic of that grain. We stayed out of the sun and took breaks to keep the material temperature low. At grain level 3000, the surface started to become translucent once again. We inspected the final result by wiping the surface with the large microfibre cloth.

    Once we were happy with the sanding result, we exchanged our sander with the polisher. Thomas explained that it was best only to use small amounts of polishing paste, as this would otherwise splash about in a circle. As we had done during sanding, we turned the machine on and off while it was in contact with the turntable cover. Thomas showed me how to apply even pressure in order to achieve a uniform result over the whole surface. I saw that one small scratch we had missed in the early stages of sanding also managed to survive all the stages of further treatment. To me, this only highlighted the importance of a very thorough first sanding.

    We checked the polishing result from time to time, until no further progress could be made using the '3M Green' cap paste. It was only then that we changed to the '3M Yellow' cap paste for that final high-gloss polish. Pleased with the result of our work, we found ourselves ready to tidy up the scene of the action approximately one hour after we had started. One hour’s work is probably a good estimate for anyone doing this the second or third time around. I was lucky that I had the help of my professional friend who had made sure I took the correct time and followed all the steps necessary. First time polishers would probably be best off to calculate with 2-3 hours of manual labour.

    I hope you will find this account of events helpful in your own restoration project, even if it is only to help you better appreciate the prices charged by professional restorers. Do feel free to leave a personal comment below. With 'Hyvor Talk', we have recently made social engagement on this platform far easier. — Enjoy.

    Click here to see the full video

    Digitising Records
  • Epicure EPI 500

    Epicure EPI 500


    Author: Karsten Hein

    Category: Gear & Review

    Tag(s): Loudspeakers

    Although the brand has largely been forgotten by today’s Hi-Fi enthusiasts, there are few names in vintage Hi-Fi that make the audiophile heart grow fonder than that of Epicure. The company’s focus in loudspeaker design was on providing natural tonality and imaging, and it often went to great lengths in the pursuit of this aim. Its founder, Winslow Burhoe (a former apprentice at Audio Research), had originally set out from a 2-way speaker design, which he named ‘the module’, and designed a whole range of loudspeakers around this. The Epicure 'Model 20', for instance, used two sets of 'the module', which were positioned invertedly to form a dipole and resemble live-stage characteristics. The idea was to incorporate the listening room’s front wall for acoustics effect. A similar design was also used in the EPI 'M 201' loudspeakers. These early specimen were well-received by the audio world and aimed at the higher end of the market.

    The EPI 500 were among the first Epicure loudspeakers to break with the traditional module design. Instead of being based on Epicure’s tested 2-way principle, the EPI 500 were a classic 3-way tower speaker featuring specialist drivers to cover: the high notes, the critical midrange, and the bass frequencies. While essentially being of a closed-cabinet design, the EPI 500 extended their cabinet volume with the help two passive radiators, one placed on each of the speakers' side walls. These served to absorb the woofer’s inward energy and also supported it in the area of low-frequency extension. (Passive ratiators have again become attractive in modern times, in the sense that they provide considerable bass extension to Bluetooth convenience gadgets made by JBL, Bose, etc.) The Epicure's top-end was based on their signature inverted-dome gold ring tweeter. Where other high frequency drivers would have their domes facing outwards, Winslow Burhoe had made a name for himself using an inverted face-plate design, which gave the tweeter some horn-like compression characteristics. The tweeter on our specimen was of the second generation air-cushioned, oil-dampened design, a fact that would have placed the most likely construction year of our pair in the mid to late 1970s.

    I purchased our EPI 500s from a private vendor in Nürnberg, who had in turn bought them a few years earlier in order to listen to his extensive vinyl collection. Having had troubles with the engine of our car on the way to Nurnberg, I arrived there in some disarray, kept wondering about my risky journey home, and therefore found it rather difficult to focus on the music. We listened to two or three songs, I held my ear on the drivers to check for potential noises that should not have been there, and concluded that they worked just fine. I did notice that one of the midrange drivers showed a slight smell of burnt coil-resin, but since I could not detect any scraping sounds emanating from it, I decided to trust the seller’s own verdict that he had not noticed any faults with the speakers himself. Epicure speakers were well known to stand the test of time, unless they had been over-driven for extended periods. The 40-something-year-old woofers looked as though they had been re-coned, and I was relieved to see that the work had been done with care.

    While heaving them into the car for my ride back to Frankfurt, I noticed that—despite their modest size for tower speakers—they were surprisingly heavy, and I was grateful for the helping hand offered by their previous owner. 250 kilometres distance could seem long when seen from the perspective of a broken car that was blowing black diesel fumes out its back. As one might imagine, I made good use of my time going through different scenarios of having the car and speakers towed home that day. Luckily enough, I managed to make the journey back with the engine in its last twitches and unloaded the speakers before finally taking our vehicle to be serviced. This was commitment to the cause all the way through, of course. But then again, I was confident that the Epicures deserved no less.

    When I finally returned home to further investigate the EPI 500, I noticed that they had one additional feature that I had noticed in the very beginning of my research and then somehow forgotten about: There was a wooden base screwed in place that formed a closed acoustic frame underneath the cabinet. This raised each speaker off the ground by about 8.6 cm. The base was needed to elevate the tweeter to ear-level, but it also prevented the speaker terminals from touching the ground. There may have been a number of reasons for positioning the terminals underneath the loudspeaker, e.g.: to make the back of the speakers look cleaner; to allow for the attachment of invisible sub-floor cabling; or simply to make unobstructed use of the cabinet's resonances. Holding my hand to the side and rear walls of the EPI 500, I could feel that this cabinet had been designed to naturally incorporate resonances with its sound signature, instead of bracing against internal and external vibrations in the way modern speaker designs would.

    Understanding how the EPI 500 dealt with inherent resonances would be vital to finding the correct placement and integration in the room. However, with the whole cabinet and passive radiators set in motion at once, I also saw that success would not come easy. I would have to put myself in the position of the designers and imagine the most probable environment that they had envisaged for their speakers to perform in. This, of course, was likely to have looked and sounded differently from our sleek office with white high-gloss furniture and scant carpeting. Luckily, the underlying architecture of our building itself was not all too different from the typical American home of the 1970s and 80s, in the sense that our room was located under the roof of the building and of poorly insulated wooden beams that were planked with gypsum and plywood boards. This would most likely help to absorb some of the excess bass energy, if needed. I also discussed the matter with my audiophile friend Luigi who reminded me that the base had probably been designed with American highfloor carpets in mind.

    The base of the EPI 500 had a small hole describing a semicircle towards the floor through which one was to run the speaker cable. To keep the base from touching the ground, some previous owners had glued small rubber pads of 1mm thickness and 20mm width into all four corners. I did not know if this had been found a good idea and decided to listen to the speakers in this condition first. Our testing system consisted of the Restek V1 preamplifier with upgraded Kassel power supply and the B&K ST-140 power amplifier. As sources, I used our Technics 1310 turntable and Marantz CD-17 player paired with Cambridge DAC. The interconnects were of solid core silver, and the speaker cable was our affordable but effective Belden 9497. This was a Hi-Fi setup that I could trust in terms of sonic integrity, having listened to each of the components in many different constellations. Naturally, I was intrigued to learn what the EPI 500 would add to or take away from the balance of sound.

    Perched on the hardwood floor with the 1mm thick rubber plates in place, the speakers sounded dull and lifeless. I felt compelled to visually inspect the tweeters just to see if they had perhaps been damaged during transport. They looked fine. I also noticed that the ground in our office was not perfectly even so that the base did not manage to press down firmly enough on all sides. As I had expected, the smallish pads could neither offer a defined coupling nor decoupling from the ground. They somehow did both, and this confusion was audible. To learn more about the situation, I scraped off the pads and placed the speakers directly on the floor. With wood piled ontop of wood, the whole floor was turned into a resonator, and the resulting sound was overly wooden and muddy. To experiment with the opposite direction, I then placed our ultra-hard metal ball Aucharm absorbers underneath the base. This did serve to accentuate treble, but, consequently, the EPI 500 now sounded overly analytical and were lacking bass.

    At this stage, I could already hear that the speakers had some potential, and that the optimum solution would need to provide the right mixture of dampening and stability. To make this possible, I lined the bottom of the base with felt towards the floor. This improved tonality, but I still had problems with imaging, possibly resulting from the slightly uneven floor. Thinking about how to address this issue, I added three 5mm-thick and 40mm-wide felt cushions: two on each side at the front, and one in the back. The hole for the speaker cable got in the way here, but I decided that a few centimetres off axis would not matter to the rear support. I then sat down to listen and was relieved to find that both soundstage and tonality had much improved. The EPI 500 produced a full and open sound that was also tonally rich. The double-bass on Diana Krall’s album “Turn up the quiet” now had lots of zest and dimension. I was not yet happy with the depiction of Diana's voice which was represented softer and less assertive than I was otherwise used to. Placing a second felt cushion on the other side of the speaker cable hole in the back went some way of solving issue. Possibly, the enhanced sound could be attributed to the improved balance in the support between the speaker's front and back.

    In positioning the speakers, I found them to work well with the mouth of their drivers at 109cm distance to the front wall of the listening room. This was a placement that should also be possible to achieve in most listening scenarios. The speakers were placed just under two meters apart, measured from axis to axis, and my listening position was similarly at around two meters distance measured in diagonal. I found the tweeters and midrange to work best with the tweeter’s output axis crossing at least one third behind the listening position, instead of being pointed directly towards the listener. I have found this to be the most enjoyable setup with many speakers, but this might just have to do with my own listening tastes.

    In this setup, I found the EPI 500 to offer a highly natural and informative mid-band. Their ability to reveal lots of nuance and layering in this tonal segment would have made them an instant darling with audiophile listeners. More generally speaking, the Epicure’s ability to incorporate their cabinet's resonances and passive radiators into the music output made them an excellent companion for natural instruments as found in Jazz, Folk, Country Music, etc. However, I found that the obvious strengths of the mid-band did not automatically translate into an outstanding depiction of voices. From my own perspective, our more modern Tannoy XT8F managed to offer the tiniest bit more in terms of believability in the midrange. I would have had to run further tests to learn if voices could be improved by adding solid steel plates inbetween the base structure and the felt pads in order to increase stability. I had a strong feeling that structural instability towards the ground might have been the culprit here.

    Going through forums, I had read that some people suffering from tinitus were complaining about listening fatigue in connection with Epicure speakers. This phenomenon may have had to do with faulty coupling to the ground, with high feequency infiltration, but also with the shape of the inverted-dome tweeter itself. I noticed that this could produce a slight compression effect and thereby make the music seem quite dense in the treble. I also noticed that I tended to listen to music louder than I would have done with our other speakers. It was easy to get carried away while listening to these speakers, as I found out when putting on our 2009 pressing of Fleetwood Mac's 1977 album "Rumours". I simply enjoyed listening to the intense tonal richness that I had sometimes missed before.

    In comparison to my first experiments with the EPI 500, bass performance had trippled, thus providing me with the realistically full sound and satisfying punch of an excellent tower speaker. Imaging was excellent, with a naturally wide and unconstrained center image. The music was well-spaced: from front to back and from left to right. Voices were still a touch on the sweet and soft side, but we would need to see about this aspect in the long run. From my experience, the EPI 500 should be easy to drive from a 20 watts tube amp, as well as a beefy solid state amp. They took some time in setting up properly, but the additional effort was well-worth it. Perhaps the aspect that I enjoyed most about them was their ability to provide a Jazz club atmosphere with freely breathing natural bass—but without the smell of cold cigarettes and stale beer.

    Sound Sample on Youtube


    • Type: 3-way dynamic speaker
    • Design: closed cabinet with passive radiators
    • Impedance: 4 Ohms
    • Power handling: 250 watts (max.)
    • Frequency range: 45 Hz - 20,000 Hz (+/-3dB)
    • Tweeter: EPI gold ring (2nd generation)
    • Tweeter principle: 2.6cm invert-dome, air-cushioned, oil-dampened
    • Midrange driver: 10.5cm, paper cone (1st generation)
    • Bass driver: 25.4cm, paper cone
    • Passive radiators: 30.4cm
    • Crossover freq.: 750-3,000 Hz
    • Cabinet finish: walnut
    • Dimensions: (H) 91.44 cm, (W) 30.48 cm, (D) 35.56 cm
    • Weight: 28.12 kg (each) 
    • Country of manufacture: U.S.A.
    • Year(s): 1973 - 1981

  • Let's explore together

    Let's explore together

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    If you happen to live in the greater Frankfurt / Rhine-Main area and own vintage Hi-Fi Stereo classics waiting to be explored and written about, I would be honoured to hear from you!

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