Lower chipamp distortion through better PCB routing
I wanted to apply to chipamp design what I learned from Bruno Putzeys' article "The G Word, or How to Get Your Audio off the Ground", originally published in Linear Audio Vol.5. The key learnings for me there were:
Attached are the spectra of the NOS ChipAmp.com's LM3886 board and two of my boards giving 18V RMS @ 1kHz into 8ohm resistive load. To give you an idea of my measurement setup noise and distortion, I also include the loopback (a.k.a GenMon) performance of my test setup with no amplifier connected (E-MU 0204 sound card with Pete Millett's sound card interface - see the photo of my test bench). The spectra were taken by ARTA software.
Note how a different PCB layout affects the THD performance. Not only the overall THD level is affected, the proportion of higher-order harmonics (which are bad for subjective performance) also changes. Same general layout, same parts, chips form the same batch. Also, note that the distortion and noise of my boards are not that much higher than my measurement floor...
UPDATE: a couple of spectra with a lower noise floor are attached to the post #26 below.
UPDATE2: boards are now available at HiFiOcean.com.
I wanted to apply to chipamp design what I learned from Bruno Putzeys' article "The G Word, or How to Get Your Audio off the Ground", originally published in Linear Audio Vol.5. The key learnings for me there were:
- Each signal has its own reference;
- A single GND pour not a good reference for any signal;
- The signal and its reference should travel together; and
- The signal and its reference should look into balanced impedances.
Attached are the spectra of the NOS ChipAmp.com's LM3886 board and two of my boards giving 18V RMS @ 1kHz into 8ohm resistive load. To give you an idea of my measurement setup noise and distortion, I also include the loopback (a.k.a GenMon) performance of my test setup with no amplifier connected (E-MU 0204 sound card with Pete Millett's sound card interface - see the photo of my test bench). The spectra were taken by ARTA software.
Note how a different PCB layout affects the THD performance. Not only the overall THD level is affected, the proportion of higher-order harmonics (which are bad for subjective performance) also changes. Same general layout, same parts, chips form the same batch. Also, note that the distortion and noise of my boards are not that much higher than my measurement floor...
UPDATE: a couple of spectra with a lower noise floor are attached to the post #26 below.
UPDATE2: boards are now available at HiFiOcean.com.
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ChipAmp.com 1kHz 18Vrms @ 8ohm.png59.4 KB · Views: 1,198
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MyGC TH 1kHz 18Vrms @ 8ohm.png60.8 KB · Views: 1,143
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MyGC SMT 0.1% 1kHz 18Vrms @ 8ohm.png61.1 KB · Views: 1,126
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EMU0204+IF 1kHz loopback.png60.7 KB · Views: 379
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