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In Reply to: RE: Valve preamplifier biasing posted by Tre' on February 26, 2021 at 10:23:13
Not sure where you're getting your numbers from, but the 1ufd cap into a 10k load would yield about 16Hz cut-off. Could be better, but at 8ufd as you suggest, you're down to 2Hz.
Pretty meaningless.
Dan Santoni
Follow Ups:
I'm not sure how important it is but if you want 20Hz to be phase shift free and at 100% amplitude, then the -3db point of the high pass filter created by the coupling cap and the impedance that it sees needs to be at 2Hz.
A -3db point of 16Hz means the phase is disturbed all the way up to 160Hz.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Some folks say F 3 needs be a decade (2 Hz.) away from the passband, while other people think 2 octaves (5 Hz.) away is OK. That makes the absolute minimum value for working into that blasted IHF "standard" 10 Kohm load 3.3 μF.
My price/performance suggestion is a 4.7 μF. metalized polypropylene part bypassed by a 0.47 μF. 716P "orange drop". An improvement is a 0.33 μF. PPFX Multi-Cap as the bypass, but costs escalate.
Eli D.
In some rooms, with some speakers, the higher F3 can be better but if the room is tamed properly and the woofers (and woofer amps) are up to it, then the lower F3 can be better.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
The 7.5 uF, 330V ASC are not the worst linestage coupling caps. Not even close. They'll tolerate any reasonable B+ required, are easy to get and are not very big... :)
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
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