Quick cathode bypass cap question

Started by HeavyFog, April 20, 2017, 08:16:42 PM

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HeavyFog

So i'm building a valvecaster and i decided to add cathode bypass caps to increase the gain. Rather than add a gain control between the 2 stages the plan is to wire the gain control the same was its usually wired in a valvecaster except with the bypass cap, and that's where i'm stuck. Would i wire it with the cap coming off lug 2 to ground (like in a fuzz face gain control), or would i bypass the pot completely with the cap?

antonis

Depending on cap & pot values, if you bypass the pot you may have no gain control..  :icon_wink:
(especially at high frequencies..)

"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

merlinb

Yes, you would do it like a FuzzFace. Works exactly the same way.

HeavyFog

I'm using a 50k pot with a 1uf electrolytic (will socket that if I need to change it). So I should be good if I wire it like a fuzz face pot?

antonis

1μF cap appears a resistance of about 2k at lowest frequency of interest which is about 2.5% of gain pot value..(50k)

On original FF there are 1k pot & 20μF cap on a 1/100 analogy, so if you want to keep the same gain setting "taper" you have to place a 1000μF cap..

You have to make some compromise between valve anode/cathode resistors and bypass cap values.. :icon_wink:
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

HeavyFog

Just got my valvecaster up and running with the 50k pot wired with a 10uf cap and wow what a difference it made. The gain is much tighter and a bit less bass than before. IL post a shcematic as soon as I get a chance