Excelsior! Objective Complete.



I finally fingered it out and I may be able to reduce the hum by 2/3
or more. So far I got my ripple on the rail from 1.56 VAC 120Hz to
about .63 VAC and I got the ripple on the bias from 172 mVAC 60 Hz
to 68 mVAC - measured at the divider feeding pin5 on both tubes. Each
tube is seeing 34 mVAC.

I read a very thin book produced by Radio Shack concerning building
regulated power supplies. There was a section about fixing ripple at
the input filter.

Simple fix: add more Caps. I did the same thing for the bias circuit,
conceptually. Different values, Every cap has a different ESR even
within the same size, type, and brand.

The concept is that if using one big cap the ESR may not be sufficient
to filter because of the rise and fall time aka RC constant. To be
sure to smooth it out using multiple caps adding up in parallel to the
target value and even exceeding it.

The important part is that the voltage is better naturally regulated
against current draw and provides a lower ripple overall because they
avg a better rise and fall time.

In my case it also lowered the floor and cleaned up the distortion a
bit due the various values able to effectively filter out other
frequencies and noise. I suppose some might say that I lost some freq
response. I will know more as I try to get the preamp hotter and more
distorted. I generally like a clean sound so I can always add more
distortion via a pedal. I'll know more when hook up the rest of my
rig and see what happens.

X
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