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Low distortion Class D amplifiers for mastering? What to expect?
Old 3 weeks ago
Gear Head
🎧 10 years
Low distortion Class D amplifiers for mastering? What to expect?

Hi, I was wondering what sorts of distortion numbers people have measured in their Class D (and related) amplifiers, measured at full power? Both DIY and commercial, in the ~300-500W range. I'm looking over the docs for my Bryston electronics and I'm thinking of an upgrade at least for the LF and LFX drivers, and Class D was my first thought. The amplifiers drive a set of PMC MB2 XBD main monitors which I will be using for mastering. The Brystons achieve around 0.0015% across the frequency range. That's roughly -40dB (on a power scale). The Brystons (3B, 4B, 7B, from the SST 2 series) are a bit of an older design (Class AB) and I guess modern Class D/T/etc designs can be much more efficient and more linear, and I wonder what performance numbers I should be looking for when replacing them. I want something good but also something that's reasonable.

The numbers measured during final checkout as supplied on the certificate by Bryston for my units are as follows:

Distortion percentages at full rated output power

ID                     20 Hz       200 Hz      2K Hz       20K Hz      Rated power
3BSST2 CH1 (HF L)      0.00177%    0.00161%    0.00153%    0.00498%    150W/channel
3BSST2 CH2 (HF R)      0.00232%    0.00193%    0.00187%    0.00414%    150W/channel
4BSST2 CH1 (MF L)      0.00138%    0.00132%    0.00153%    0.00485%    300W/channel
4BSST2 CH2 (MF R)      0.00191%    0.00177%    0.00139%    0.00493%    300W/channel
7BSST2 unit #1 (LF L)  0.00125%    0.00105%    0.00144%    0.00444%    700W/unit (mono)
7BSST2 unit #2 (LF R)  0.00117%    0.00098%    0.00138%    0.00438%    700W/unit (mono)

Relative levels of distortion to signal
(calculated using P=10 log_10(X) with X from above, eg 0.00177% -> X = 0.0000177)

ID                     20 Hz       200 Hz      2K Hz       20K Hz
3BSST2 CH1 (HF L)      -47.52 dB   -47.93 dB   -48.15 dB   -43.03 dB
3BSST2 CH2 (HF R)      -46.35 dB   -47.14 dB   -47.28 dB   -43.83 dB
4BSST2 CH1 (MF L)      -48.60 dB   -48.79 dB   -48.15 dB   -43.14 dB
4BSST2 CH2 (MF R)      -47.19 dB   -47.52 dB   -48.57 dB   -43.07 dB
7BSST2 unit #1 (LF L)  -49.03 dB   -49.79 dB   -48.42 dB   -43.53 dB
7BSST2 unit #2 (LF R)  -49.32 dB   -50.09 dB   -48.60 dB   -43.59 dB

noise levels for balanced input are all -116 dB to -113 dB
So I'm primarily looking to get a lower distortion unit while keeping or improving the power handling (especially on transients) and keeping or improving the noise levels.

How do those numbers compare to more modern designs? Alternatively - what would you say are the lowest distortion and noise amps you've tried that I can look up these numbers for?

One thing - I'm not really interested in talking about how you should be listening to the amplifiers rather than looking at numbers etc - I appreciate this train of thought and find it's valuable but this is not what this thread is for. I'm looking for measured numbers to have an objective comparison, long before I start doing all sorts of listening tests. Always feel free to start your own thread and I'll be glad to contribute Thanks
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