LC >
May you tell our readers a brief history of your HiFi Company?
VT >
At Symfonia, our philosophy is to apply the latest developments in solid state electronics to the design and manufacture of advanced audio equipment.
Symfonia was founded by Stanley Berkley and Vince Testa in 1992. The pair have a long and distinguished association with the audio industry with extensive backgrounds in working with esoteric equipment.
While Stanley has specialised in digital telecommunications and the design of audio equipment, I have concentrated on the importing, marketing and retailing of high end equipment across Australia.
LC >
You're currently proposing a new amplifier design technology, called Zero-Delta, may you briefly explain us what is it all about?
VT >
For a typical output stage, the devices used change their parameters with temperature and signal level. Output devices consist of a chip of semiconductor material bonded to a metal case.
The case protects the chip and provides a means of mounting the device to enable extraction of heat. Heat flows from the chip to the case and then on to the heatsink.
During operation of the amplifier, the current flowing from the power supply through the semiconductor chip creates heat, and this heat causes the temperature of the chip to change.
The temperature of the semiconductor chip changes the bias of an amplifier, not the temperature of the case, and not the temperature of the heatsink. It takes time for the heat to escape from the chip to the metal case and then to the heatsink.
The heatsink temperature is thus only a long term average of the chip temperature.
These changes are very fast, in fact at the speed of the audio signal, and especially on musical transients, and here lies the problem.
The chip temperature is varying wildly and instantaneously with the output signal but the heatsink temperature is a very long term average of chip temperature. Thus conventional bias circuitry that monitors the heatsink temperature cannot track the chip temperature.
This problem is referred to as Fast Dynamic Bias Shift.
Class Zero Delta eliminates Fast Dynamic Bias Shift by controlling the instantaneous bias condition rather than the long term bias control that regular amplifiers employ.
Additional circuitry is added to the amplifier which senses when one of the output devices is beginning to turn off and prevents it from doing so completely by "pushing" that device on again by just the right amount.
At the same time, the opposite device which is being turned on to provide the signal output current is also "pushed" by the same amount. Therefore neither output device is turned off and they retain the ability to turn on rapidly when required.
Overall, the output stage bias current is held at a constant value, regardless of junction temperature or changes in the power supply rails.
As a super critical test of the effectiveness of this approach, application of a single half-wave pulse at full power for any duration will return the output stage to the correct bias value within 2 or 3 microseconds of the load being removed!
This is many orders of magnitude better than the figures for conventional amplifier designs that are of the order of seconds to many minutes for recovery, and not accurately qualified.
Some of the other benefits Class Zero Delta offers:
LC >
It seems you strongly believe in the solid-state technology for reaching
hi-end musical performances. Which is your point of view regarding
thermoionic tubes?
VT >
Thermonic tubes have a number of drawbacks some of them are:
their device parameters deteriorate from the moment they are switched on.
Unless you employ many tubes in parallel you cannot directly connect them to the loudspeaker. Thus output coupling transformers must be employed.
Transformers limit the frequency response of the amplifier and introduce distortion.
By nature of design, tubes are inherently microphonic (are vibration sensitive).
LC >
Which are, according to you, the fields of HiFi design where one can
expect the most relevant innovations in the years to come?
VT >
With the evolving world of digital audio we will see more manipulation of audio by DSP chips (Digital Signal Processors). As DSP technology and software evolves (we need more MIPS) it will be possible to include the acoustical environment in a global feedback loop i.e. one or more microphones in the listening room feeding an analogue to digital converter as input to a DSP together with the original source material for comparison.
The possibilities with this scheme are limitless.
LC >
We at TNT-Audio believe that every HiFi component is very sensitive to
vibrations and to the quality of the AC that feds it.
These are fields mainly disregarded by a large part of HiFi designers.
Your opinion and views on this topic?
VT >
Mechanical vibration have been a problem for many years especially in situations where electrical -mechanical devices are used to extract information MUSIC, ie Turntable (tonearm-cartridge) CD players/Transport or equipment using valves.
Any external vibration that causes a valve to become microphonic can create an additional signal that will have an effect on the music that is heard. The same can be said of a styli if moved other than the record groove or a laser diode reading a CD or a laser disc.
In record players some manufacturers such as Linn, Sota, Thorens, AR, use a floating suspension to help isolate the turntable from its environment, thereby minimising audible and inaudible feed back that is caused by the signal returning to its original source via the loudspeakers.
There are many different systems/methods that are promoted to minimise vibration. I prefer isolation platforms that employ springs to isolate equipment from its enviroment. With the exception of loudspeakers.
AC power can have an effect upon the sound that you hear. This is caused by the AC mains being contaminated by RFI and the mains frequency not being precisely 60/50 Hz.
There are many mains power conditioners on the market. I recommend that any person contemplating purchasing one of these unit to have a home demonstration.
In the Symfonia PSL-1 we incorporate a line filter to minimise this problem.
LC >
As usual, something about your plans for the future: new gear, ideas etc.
VT >
We are in the process of designing a new active crossover that does the frequency splitting in the digital domain with a DSP rather than the conventional analogue techniques.
The active crossover can be connected to a home PC running Windows or OS2 to control the filter characteristics. We are also busy working on a new range of amplifiers all based on Class Zero Delta Technology.
Courtesy Vince Testa for TNT.
Copyright © 1998 Lucio Cadeddu