Dead time is part of the design of the amp, not something that arises from its ’harmonic structure’.Haven’t found a digital which can compete.Most digital are to clean for my ear.Sterile with no decaying harmonic structure, creating too much dead time, are the words I believe you should be using.
Judging by the measurements I keep seeing, great class D amps still haven’t arrived. Most of them have issues with ringing. All of them have ultrasonic noise that sits on the outputs like standing DC. Upwards of .8 volts of noise!?!?!? That’s hifi, is it? A 1kHz sinewave looks horrible through those things. For all intents and purposes, it’s made entirely out of high frequency noise.@kosst_amojan
Actually a 1KHz since wave looks good on most of them, without any noise. The ultrasonic noise to which you refer is the residual and is itself a low distortion sine wave at the switching frequency.
Show me where it is stated that the Merrill uses higher than 500K for its switching frequency. In fact, Merrill stated (on this site) that higher frequencies for switching were harder to do. I hope Mr. Merrill steps in here and clears this up. What he seems to claim is that the zero dead time using GaNs plus his zero feedback circuit are what makes the great sound.
The advantage of such high performance output devices is that they allow one to build a circuit that has no dead time circuitry in it. This means the circuit is a **lot** simpler! Of course, there is always some shoot-through current, so by going with a lower switching frequency a lot of consequences of that are avoided- one can use a slightly larger heatsink and the shoot-through heating is controlled. But the advantage of reduced distortion via no dead time is profound. So this should be a very nice sounding amplifier.
Go to Stereophile and look at the last 5 or 6 class D amps they’ve measured. Unless JA applies a low pass filter on the AP the output signals look horrendous.@kosst_amojan
I did and found the review at the link below.
I think you may have misinterpreted something in JA’s measurement comments. The filter to which you refer above has to be there because all class D amps have a residual sine wave component, which has to be filtered in order to prevent the analyzer from having difficulty; in JA’s words:
As class-D amplifiers produce RF noise that could drive my analyzer’s input circuitry into slew-rate limiting, between the test load and the analyzer I inserted Audio Precision’s auxiliary AUX-0025 passive low-pass filter, which eliminates noise above 200kHz.Note the cutoff frequency of the filter- 200KHz, and why it needs to be used. Nowhere in this article does JA say or imply anything that you suggest above. He seems to think the waveforms look pretty good.
https://www.stereophile.com/content/mytek-brooklyn-amp-power-amplifier-measurements
You need to understand better, it’s not the switching frequency "so much" but the "output filtering" needed to get rid of it that ’s problem, which gives phase shift problems right down to 3-5khz (the mids and highs of the audio band).@georgehifi
This statement is incorrect.
Many such filters are 12db, but if only 6 db, that is where you use the rule of thumb that the phase effects extend to 1/10th the cutoff frequency. In the case you state above that would be 45KHz, not anywhere in the audio passband! If 12db, the effects are more constrained; IOW 6 db is a worst-case scenario.