Woops.... So the AC input voltage was lower than required? That would cause ripple... 🙂
48 mV ripple is quite excellent, actually. I'd say that if it isn't audible, don't mess with it. But if you insist, you can insert some resistance between the last two caps in the supply. If you make the LC filter 29H/60uF and the RC 1kOhm/40uF you'll end up with a 3rd order filter with a cutoff around 4 Hz. That should result in -70 dB at 60 Hz and -88 dB at 120 Hz. I think you mentioned that the current draw was 12 mA. So you'll drop 12 V across the resistor, hence, have 12 V lower B+.
With a 10H inductor in place of the 1 kOhm resistor -- resulting in an LC-LC filter -- you'll get 13 dB better attenuation at 60 Hz. Whether that justifies the additional expense of the inductor over the resistor is for you to decide.
~Tom
48 mV ripple is quite excellent, actually. I'd say that if it isn't audible, don't mess with it. But if you insist, you can insert some resistance between the last two caps in the supply. If you make the LC filter 29H/60uF and the RC 1kOhm/40uF you'll end up with a 3rd order filter with a cutoff around 4 Hz. That should result in -70 dB at 60 Hz and -88 dB at 120 Hz. I think you mentioned that the current draw was 12 mA. So you'll drop 12 V across the resistor, hence, have 12 V lower B+.
With a 10H inductor in place of the 1 kOhm resistor -- resulting in an LC-LC filter -- you'll get 13 dB better attenuation at 60 Hz. Whether that justifies the additional expense of the inductor over the resistor is for you to decide.
~Tom
I guess it all depends on what sounds best. Also getting a small enough physical choke. Since I'm only dealing with 12mA it could be small. The smallest I found was a 10H 65mA from Hammond.
I have a multi-tap choke I can test it with and just add the resistor on the other channel and listen.
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