Class-D amps - a different re view

Kijanki, On my 1 ohm speakers, there is very very little resistance in the way of the signal. The signal is beautiful and natural when it is left alone. Oversampling, as elegant a circuit as is, cannot operate without introducing some timing error. That flaw is painfully obvious on my Scintillas.

These amps are so good at being faithful to the signal, minute distortions, usually deaf on listeners, work their way through. I have found speaker cables must be bereft of insulation, DACs must be simple.

Muralman - I have no experience with high end DAC circuits but my Benchmark has surprisingly clean and transparaent sound. Part of this is due to anti-jitter circuitry. Jitter produces sidebands of very low amplitude (typicaly -80dB) but very audible since not harmonically related to root signal. It sounds less clean (hash) but often people prefare sound with some amount of hash or thd. They often call clean systems "analytical". Sombody even said, after listening to hi-end system, that everything (instruments) sound separate and he preferes all mixed together. I suspect I have similar hearing limitations with my audio experience.

I will search for more info on oversampling. I just don't know how they can filter out carrier of 44.kHz. With the ratio of 2:1 Bessel filters just start attenuating - no matter how many poles. Usage of other filters will affect the sound.

Kijanki, I hear you. I know someone who told me they feel music should be blended because that is how he hears it in the audience. He went out and bought the same speakers as I, and put a Krell on them. Talk about opposing forces.....

My DAC has no anti jitter circuitry. I believe that is the clock, the same thing that is scalping the crud off the signal supposedly. There is no clock that can get the signal perfectly aligned. There are too many complexities. It's sort of like electron studies. It can't be done, because that which is observing unavoidably effects the outcome of the measurement. It is all explained under Quantum Theory.

Like I said before, I can get right to the ribbons and hear nothing but pure music.

By the way, try a naked wire for your speaker cable, then try a wide ultra thin cable. This is a very interesting experiment.

Oops, I meant to say, "Ultra thin ribbon," and not cable.

Muralman - people are often confused and becuse they like guitar sound on 30W Vox (remeber The Beatles)with tubes and no feedback (high thd) and want their home system to be like that - close to real performance. Home system of course should not change sound - even if clean jazz guitar does not sound as lively as distorted one. Issue of real life performance is very interesting because real life performance is often very poor (poor acoustics, bad seat etc) - not the studio level what becomes clear after you compare sound from the studio and the concert records.

Jitter is resolved by means of PLL - single loop in cheaper and double in more expensive CD players. DAC spits out with the rate from the disc (to be exact from internal clock phase lock looped to CD and going thru FIFO buffer at this rate). Good transport means lower jitter but is costly. Another method is to completely reclock signal to DAC's clock, upsample it and send to DAC in corrected intervals. Benchmark is trying to do it (correct)acurrate to 5ps. Both methods produce great results - reclocking gives better supression of the jitter and allows to use cheap DVD player as a transport.

I checked audio DACs at Analog Devices website - almost all of them are sigma-Delta (oversampled). There is still few with traditional architecture carrently being discontinued. All Dacs shown as 24-bit are sigma-delta. Traditional Dacs go only to 18-bit (maybe 20-bit).

Dielectric in the speaker wire is evil (even teflon) - I agree. Latest trick is to use foams (lower dielectric constant than solid material) and wide tubes so that wire has only contact with one wall. Another problem is to compromise between low resistance and low inductance (thick wire) and skineffect free (thin wire). Skin effect starts at gauge 20 at 20kHz and splitting wire into many helps only a little (more surface area but still in the sum of magnetic fields). Tapes are wonderful but not practicall solution. I replaced coils in my cheap speakers with the "tape coils". It sounds better - at least I'm telling myself. Capacitor in series with the tweeter is the reson for brigtness in many speakers. Mylar caps are horrible (high dielectric constant) but Teflon are too expensive. Polypropylene paralleled by small teflon is the ticked. I also changed resitors to non-inductive. Every bit helps.