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  :  FAQ 

Interview with John Stronczer by Steve Lees of Stereo Audio (Australia)

Text and Image courtesy of Wicked Digital, Australia

Steve Lees: John Stronczer is the owner and product designer at Bel Canto. Starting out designing tube based amplifiers, John has moved his company firmly to the forefront of audio with a range of digital control centers (DACs) and Class D amplification. In this interview I ask John about that progression.

SL: How did you get into designing audio products?

John Stronczer: I started designing audio products as a hobby while I was working at the Honeywell Research Center in the early 1980s. Iíve been interested in audio and music since I was 12 years old and built my first Dynakit system at that age.

SL: Which aspect do you enjoy the most, digital or analog product design and why?

JS: My background is in analog design. Although I am getting more into DSP design for custom FIR filters and loudspeaker crossover and EQ. The critical focus in digital audio design for high performance playback mostly comes down to analog issues of jitter, power supply and the analog input or output stages anyway so my analog background serves me well here.

SL: You started using tubes for your amplifiers, why the switch to transistor and why class-D?

JS: I actually designed my first tube amp in 1986. It was a single ended 845 triode with about 20 watts of power. Iíve owned push-pull triode and pentode audio amps but they never performed to the level that I wished. There always seemed to be a veil between me and the music with push-pull amps.

The SE operation of the output transformer goes a long way to removing this veiling effect. I also like the inherent elegance of the SE amplifier and called these amps my Physics Experiment. My first exposure to a modern class-D amp was the Tripath architecture. My initial impression was that through the bass and lower mid-band it came close to that direct connection to the music that SE triodes offer. I also was attracted to the elegance and efficiency of class-D and saw that it would be the future of audio amplification.

SL: Class-D compared to other amp designs, is there still a way to go in terms of development or are we seeing the pinnacle of their performance levels now?

JS: The performance level of the latest crop of class-D amps is very high indeed with reduced sensitivity to load impedance, reduced HF distortion and very wide dynamic range plus low distortion levels. I still think that any class-D amp has some advantages in performance compared to traditional amplifiers relating to thermal modulation, lack of bias wander and the elegance of the circuitís operation.

SL: How do the Bel Canto Reference amplifiers differ to other class-D (IcePower) amplifiers?

JS: We put our own electronics in front of the power supply and the analog input of the power modules. This allows us to achieve higher levels of performance from the modules. Theyíre operating in a better environment and achieve their potential for performance more effectively with our circuits. Also details of wiring, chassis design, and connectors all contribute to the final results.

SL: You have a preference for Burr Brown DAC chips, what is it about them that you prefer over say Wolfsen, ESS Sabre and others?

JS: Iíve evaluated the alternative architectures and found that I could go farthest with the BB devices. Surprisingly it comes down to their analog performance. The way the BB architecture connects to and biases the analog output electronics leads to higher performance and the BB DACs still have the lowest noise with performance approaching 130dB of dynamic range. I also found that the distortion characteristics of the ESS architecture was not very ďanalogĒ in that the distortion components at low signal level were still visible above the noise floor. More traditional BB, Wolfson, AKM or Crystal DACs behave in a more analog way: Low level distortion components disappear below the noise floor as the signal level is reduced.

SL: Bel Canto DACs seem to have a very neutral sonic signature compared to some others using the same DAC chips, so clearly the DAC chip is not the main determining factor on sound quality. Would you agree with that statement?

JS: Yes, just like the IcePower amp modules the DAC is just a starting point. Details of clock design, jitter rejection, power supply, PCB layout, parts selection and chassis design all contribute to the final result.

SL: In terms of the chassis design having an influence, is it simply the shielding factor, or is there more to it?

JS: The chassis design has more to do with microphonics and vibration. The size, strength and weight all effect this. This is more important than shielding.

SL: How do you achieve that BC signature?

JS: We pay close attention to all of the factors I just mentioned. For example our power supply designs are quite unique and contribute greatly to the final results. Controlling jitter at the internal clock that produces the final DAC output is also critical to the performance.

SL: Jitter, it is all we hear about lately when digital audio is talked about, can you explain exactly what it is and how it affects the audio quality of D/A conversion?

JS: Jitter is noise on the clock used for converting the digital signal to analog. The noise shows up as errors in the timing of the clock used for the conversion process creating unwanted signals in the analog output that arenít necessarily related to the original analog signal. Itís easily perceived as a reduction in clarity and in some cases annoying glare.

In extreme cases the jitter squashes dynamic contrasts and removes inner definition suppressing the sense of life in the music and rendering the sound boring and unpleasant. In subtler cases it would be perceived as a reduction in the life-like qualities that high-performance audio achieves; the sound may still be pleasant but the emotional impact of the performance is reduced.

SL: In view of the VBS power supply technology, can you explain how that works and the influence it has on the sound quality?

JS: The VBS represents the peak expression of our unique approach to powering Bel Canto products. Itís an extreme filter -- 100dB by 100Hz! -- that isolates and filters any noise on the AC line. The VBS achieves lower noise levels on the 12VDC power than appears at the output of most preamplifier circuits, around 6 microvolts RMS over a 30 KHz bandwidth. It also can supply high peak current as needed. Itís close to an ideal power supply, a Virtual Battery, although there are NO Batteries in the design. Itís also a very efficient power supply as are all of our designs. The top-of-the-line DAC3.5VB with a VBS1 uses a combined power of merely 7 to 8 watts under full operation! The effect of extremely clean power on the sonic performance of a DAC is similar to removing jitter. Very dynamic, clear and natural sound results when you reduce extraneous signals delivering an outstanding ability to hear deep into the performance.

SL: The C5i Integrated Amplifier, a successful product combining DAC and amplifier, is this the way forward for audio do you think?

JS: Eliminating the preamp is one way forward! For peak performance there are still advantages in separate mono amplifiers and even mono DACs.

SL: I know of only one manufacturer offering a mono DAC, what is it in that architecture that appeals to you from a technical point of view?

JS: I have tried a pair of old DAC3's in mono and was surprised at the performance gains...kind of like mono amps!

SL: Where do you see the future of audio heading?

JS: More and more digital content with very high dynamic range ADC and DAC ports as needed, computer-based audio streamers and wireless or power line Ethernet networks are all coming. Further out I think weíll see more improvements in power supplies and amplifiers, DSP applied to the system and perhaps active loudspeaker applications. Efficiency is also going to remain an important factor. Iím proud that we can provide a complete high performance system that uses less than 60 watts of power!




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