[Rippy]

I own a BP-25 (a very enjoyable product) and would like to know if the dc offset is low enough to remove the output caps? All my power amps have blocking caps on the input. The reason is that when I compare the spectral response into the amplifier load, the Bryston+Benchmark dac looks quite a bit different than the Benchmark alone does going into the same load.  The main differences seem to be in the bass region.

As the system is set now, the best sound and flattest spectral graph is with the Benchmark alone. Will removing the output caps get me any closer? I need to have the BP25 in for switching and so on.

Thanks in advance.

[brucek]

Will removing the output caps get me any closer?

If I quickly look at the schematic for a BP25, I see it uses 100uf output capacitors and a ~50 ohm series resistor.

If you do the math, assuming a 10K load, I calculate the capacitor offers a difference of -0.068dB across the load at 20Hz in relation to 20KHz.

I can't imagine that would be considered audible.....

brucek

[Rippy]

I agree, it should make no difference. However, SOMETHING is, so of course, I blame the lowly electrolytic cap first! At any rate, if I can do without an output cap, I would perfer to in any case. Seems a much better idea than spending great gobs of money on exotic caps... providing the preamp is up for it.

Actually the bigger overall bass problem, that of a rather overwhelming bass compared to the source, started when I acquired the bigger power supply for the BP25. My unit is a 1999 model, which is supposed to be able to take the MPS1 supply, but there is quite a bit of difference in the bass output compared to the original. It is flat with the little power supply and bassy on the newer one. The obvious solution, go back to the original power supply, is not acceptable because the sound, while bassier, is also cleaner on the new one.

[Rippy]

Since no one replied to my question, I will post what I discovered for what it is worth. I measured the offset voltage, and the worst case offset was 6 milli volts and the best was .1milli volt.  Well within limits, especially considering that all my present gear has input caps.

The output caps are high quality non-polar electrolytics under no biasing voltage. According to Jung and some others, electrolytics are fine caps...if they are under some bias voltage greater than the signal swing. Otherwise, according to them, electrolytics create some distortions and noise. Removing them certainly has removed whatever it was that was annoying the hell out of me. The soundstage is noticably deeper and the already great perceptual noise level of the preamp has improved considerably. The focus on things seems much better, and has more ease to it all. Nothing to make one proclaim the second coming of audio, since the preamp is pretty darn good already, just a nice finish to it all.