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Inter.View to Tommy Jenving - Supra Audio

by Lucio Cadeddu

Italian version

LC > When the first special Hi-Fi cables appeared in the market it seemed that the material of the conductors and the cross section were the most important issues.
Then the research evolved and the designers started to use different dielectric materials and fancy lacing geometries.
According to you which aspects of cable designing (materials, sections, dielectrics etc) have more influence -today- in audio performance?

TJ > When we launched our first high end loudspeaker cable in 1976 the concept was based upon -exactly as you say- material and cross section area.
Since then we have developed both ourselves and our products. That is not to say that our initial concepts were wrong, but quoting our own '97 catalogue, page 6, tells where we stand today:
'Before considering more special esoteric 2nd and 3rd-order effects, such as conductor metallurgy, the performance of audio cables is principally determined by their series loop resistance, their loop inductance.....' i.e. the geometry of the cable.
Our concept is simple and physically realistic: 'For low impedance be aware of the inductance whereas for high impedance be aware of the capacitance!'
That is translated into application, a low inductance for speaker cables and a low capacitance for interconnects. Our Supra Ply loudspeaker cable is an example of this thinking.
When we launched the Ply two years ago it was highly controversial as it is made with flat conductors as close to each other as possible in a flat surface to flat surface design (thereof the name Ply). That makes a low loop inductance, whereas most hi-fi cables were wide spaced cables with high inductance and focussed on choice of material, such as long crystal copper, etc.
We could prove by measurements that our concept was the correct, so what did the long crystals help when the geometry of the wide spaced design made high dynamic losses?
Today, already after two years, all cable manufacturers have followed after and stress the importance of low inductance. Nobody developes wide spaced speaker cables, anymore.

Following our concept for interconnects the capacitance has to be low. Therefore we started developing an interconnect with an insulation material of a very low dielectric factor. That ended up into Supra DAC, with the gas blown Poly-Ethylene foam for insulation. The lowest capacitance of a hi-fi interconnect on the market, as far as we know. This answers your question about the importance of dielectric. Teflon is highly spoken of, among audiophiles.
Yes, for an interconnect it has good properties but for a speaker cable it makes only a meaninglessly high price. However, even better is our gasblown PE-foam. This can be explained: The velocity factor is to be as high as possible for a digital interconnect as well as for a video interconnect and this velocity factor is directly depending on the capacitance of the insulation.
This is easy to understand if you consider the switching surges in the material.
Thereof we can easily see the direct connection between high frequency properties, propagation velocity and dielectric properties.
So, why do we not use Teflon? Simply because our gas blown PE is of an even lower capacitance and is much more economic to process in production.
We simply make a better cable at a lower price! The propagation velocity of Supra DAC is 78% of the speed of light. With Teflon it would be 69%.
Another parameter of importance at high frequencies is the characteristic impedance which is also directly depending on the geometry and dielectric of the cable.

LC > Silver and OFC copper are the most used materials for Hi-Fi cables. New materials such as carbon fiber, titanium or metal matrix seem to have interesting audio properties.
Is R&D at Supra moving towards new conductors?

TJ > Even here we have practiced lateral thinking and done the opposite to the common designing.
The facts that silver has a lower resistance than copper and that the silver oxide is conductive do not make it a suitable material for wire plating in speaker cables. The OFC copper is fine, but how long time does it stay Oxygen Free, unless you protect it by plating? A PVC- insulation is for example emitting chloride ions that make copper-chloride on the copper wire surface, a process that accellerates with current flow through the cable in use. (Is that the burn-in of a cable?) This problem is increased by the fact that the strands of a wire are twisted, leading to the current jumping from strand to strand when trying to go the straightest runway. Thus, the current passes the oxide of the the surfaces of the strands thousands of times per metre run in a cable.
So, what is the use of the OFC? Silver plating is a no good solution to this as it even increases the surface run, by means of its lower resistance. And the silver oxide, although conductive, makes diodicity thresholds and non-linearity. So, again, we choosed the opposite way. We tin-plated the strands, instead, as tin has a higher resistance, hence, making the current mainly be kept inside the copper which stays OFC, with less jumps and less oxide. Again, a better result at a lower price.
In application this is the Supra Ply speaker cable. Silver is, however, good for high frequency applications. Regarding other materials we use carbon fibers in our screens on a strong nylon base, but Titanium we have not tried in production, as yet.

LC > Besides speaker and signal cables even power (AC) cables seem to influence the overall performance of an audio system. We have tested commercial (that is, not designed for Hi-Fi) shielded power cables and have discovered huge improvements with respect to the standard stock AC cords that come with every Hi-Fi equipment.
What is the position of Supra with respect to this new trend?

TJ > Yes, AC cables definitely influence. The alternating magnetic field that is radiated from a mains cable which is placed close to the line level circuits will certainly induce disturbing signals into these. Besides the mains frequency there are not only transients from other equipment such as refrigerators etc but also the music itself causes current transients when the amplifier sucks the reservoir capacitors of the power supply along with the music signal surges.
In idling position the reservoir capacitors are filled at a level which corresponds to the root mean square value of the mains voltage, but when there is a surge, by for example a percussion beat, the capacitors will be filled up by only the top part of the sine wave, i.e. just lightly more the part that exceeds the idling level. Only a maximum of 70% of the sine wave is used to compensate the power supply for the heavy power surges.
This means considerable current transients in the mains cable.
It also makes it important that the mains cable is of a low inductance and consequently a sonicly good mains cable should be designed as per the concept of a loudspeaker cable, if safety rules would allow it.

LC > Besides cables - interconnects, plugs and bananas play an important role in good signal transfer.
Many audiophiles complain about the overall quality of RCA plugs.
What is the position of Supra?

TJ > Yes, connectors play a significant role. We have designed some RCA plugs as well as banana plugs.
The RCA plugs are lath turned in one piece in order to avoid increased number of contact points. The insulation is of Teflon. The banana plugs are of a smooth an spring forced type for perfect contact surface. It can be connected to the cable either on axis or 90 degrees of axis. They are direct gold plated, although we are not convinced that this makes any big difference. However, the opinion among audiophiles is that this is better owing the the electro- chemical properties.

LC > Are there serious differences one should take care of when designing signal cables for CDs and for analogue equipment?

TJ > There are certain parameters to pay attention to for digital audio transference but if a cable is good enough for digital audio it is very well suitable for an analogue interconnect application. I do not think we have to consider any difference in design demands between CD and other analogue applications. Give me a reason and we will do some research.

LC > Some special devices called cable enhancers promise to improve the cable performances by using as hoc electric signals to minimize break-in of the conductors.
Some test CDs claim to do the same following the same principle. We do believe that cables need some break-in (especially power cables) so these devices seem to work in this way, more or less.
Have you tested any of these devices? Is there any explanation to the strange phenomenon of cable break-in?

TJ > I wish to avoid making comments on these cable enhancers as I have too little knowledge about these items.
In general I believe that the less influence on the signal the purer it stays.
I believe that the music itself is enough random to prevent from break-in, i.e. I do not believe very much in break-in.
However, I dare not to say that the phenomenon does not exsist. We are down-to-earth profiled cable designers and as long as there is no sufficient technical relevance in the theories we keep a careful position.
It is said that the break in phenomenon depends on the instrument tones always starting with a positive wave. Has anyone studied if that really is the case?
Take a guitar player as an example; he sometimes hits the string in direction against the microphones and sometimes in direction from the microphones.
Then, in what phase position the front wave is when it hits the microphone ?
Does it depend on the distance ?
You see, I am not convinced.
There might be an electro-chemical process, however, that creates a change in the copper surface by influence of the insulation as I mentioned previously on your second question.
There might develop some copper chloride or silver chloride, or other chemical components depending on materials used. But if so, then the burn-in is a malfunction.
History shows, however, that any difference can be interpreted good even if it technically is bad, owing to the expectations and psychological climate. Let me compare to the wrongly designed wide spaced speaker cables: There is a significant difference in sound between such a cable and a cheap bulk cable of ordinary 8-cross view design. Since the wide spaced cable is an expensive speaker cable from a famous brand you take for granted that the correct sound is by this cable.
Is that the case with burn-in? I do not know.
This also leads me to say, please do not misunderstand me, I do appreciate personal taste and it is, indeed, allowed to like a sound that is not measuring a perfect curve.

LC > Any secret plans at Supra? New designs, other than cables and connectors?

TJ > Yes, we are continously researching and developing. I can reveil a little bit of a secret of a coming product: We have a worldwide patent on a shielded mains cable, which is under safety approval. There will be more, so keep your ears open.

Courtesy Tommy Jenving of Supra Audio for TNT
Copyright © March 1997 Lucio Cadeddu

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