This headamp has lot of power, 2 x 2 Watts @ 32 Ohms, pure Class-A, powered from a +/-17V dual supply. With 100db sensitive IEMs noise is almost non existent (default NE5534 opamps in voltage gain).
However, I felt like sticking my scope inside, and here's what I found.
The +17V has less than 1mV AC RMS, a decent figure, especially when thinking it's coming from a boost-converter 12V-to-17V with an SMPS of 12V/6A in front.
The -17V instead has over 7mV of AC RMS ripple and noise, kinda big for my taste. The spikes are really there, scope measurements were done @10Mhz with spire around the probe, to minimize interferences. So, almost 10 times more noisy than the +17V rail...interesting.
After adding few more caps (six actually: 2x1000uF + 4x100uF) AC RMS decreased about 4-5 times and now it's about 2 times more noisy than the +17V, quite acceptable I'd say.
Noise spectrum @ headphones output plug seems OK to me, no wonder there's almost no noise, even with sensitive cans. So, probably the PSRR/CMRR is able to reject most of this noise, so good news.
2 x 1000uF/35V Nichicon FC + 4 x 100uF/35V Nichicon Audio KA are able to settle down the ripple & noise.
However, I felt like sticking my scope inside, and here's what I found.
The +17V has less than 1mV AC RMS, a decent figure, especially when thinking it's coming from a boost-converter 12V-to-17V with an SMPS of 12V/6A in front.
The -17V instead has over 7mV of AC RMS ripple and noise, kinda big for my taste. The spikes are really there, scope measurements were done @10Mhz with spire around the probe, to minimize interferences. So, almost 10 times more noisy than the +17V rail...interesting.
After adding few more caps (six actually: 2x1000uF + 4x100uF) AC RMS decreased about 4-5 times and now it's about 2 times more noisy than the +17V, quite acceptable I'd say.
Noise spectrum @ headphones output plug seems OK to me, no wonder there's almost no noise, even with sensitive cans. So, probably the PSRR/CMRR is able to reject most of this noise, so good news.
2 x 1000uF/35V Nichicon FC + 4 x 100uF/35V Nichicon Audio KA are able to settle down the ripple & noise.
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