Filters in series (which capacitors to change for tweeking bass)

[AndreasA]

I am going to ask my tech to tweek my 5E3 clone for less and tighter bass response. He already put a switch to chose between .1uF and .022uF for bright chanal coupling cap. That made a big difference. Now I am curious about how the other caps affect the tone.

High pass filters: As I understand, the bright chanal .1uF and the post-PI coupling caps each constitute a high-pass filter, hence we have two high-pass filters in series. Now, what would be differece be between

- tweeking the bright chanal coupling cap?
- tweeking the post-PI coupling caps?
- tweeking both?

The cap determines the frequency onset of the attenuation. Now, if I have two ".047uF filters" in series (for example by changing all .1 to .047), wouldn't the onset be lower than say a .022uF after V1 and .1 post-PI? Also, is it best to kill unwanted frequencies early in the amplification process so that the amp doesn't have to struggle with these? I can see that the tweed tremolux has the smaller cap later in the curcuit unlike the other tweeds...

Shelving filters: Each cathode bypass cap is part of a shelving filter. What would the difference be between

- tweeking the V1 cap, the V2 or tweeking both?

OBS: I use V1 = 12AY7, V2=12AX7

I would really like to experiment myself and report back to you however, I haven't got the skills or courage to mess around inside an amplifier.

Andreas A

[MWJB]

Start off by replacing the 25/25 cathode bypass cap at V2, pin 3 with 0.68uf (or you could try subbing both 25/25 preamp cathode bypass caps with 5uf each).

The tremolux probably uses smaller PI coupling caps to prevent excessive noise/general funkyness with the tremolo circuit.

If you use humbuckers you could try a 12AU7 in V1?

[AndreasA]

MWJB, thanks for your reply. I mainly use a strat with stock pu's. Once in a while I use P-90 equipped guitars.

What would the point be of changing the V2 bypass cap instead of V1? (or vica versa)

As I wrote, I am not qualified to messing around inside amps, so what I am trying to get is some guideline conserning what tweeks I should have my tech do. All tweeks will be made switchable so that I can find the right combination and perhaps make that one permanently.

[MWJB]

You might find that going to 5uf at both preamp cathode bypass caps makes the tone too skinny with a Strat? Ultimatlely the change that sounds best to you is the one you want...

Changing cathode bypass caps is pretty straight forward, observe polarity of any electrolytic caps (waisted end towards tube, arrows to ground), 0.68uf will be easier to find as a non-electrolytic. Caps should be >25V rating. As long as you don't touch anything else you'll be fine, drain caps with a jumper wire from pin 1 or 6 of any preamp tube to the chassis if concerned, remove jumper before powering up.

Use a solder sucker to clean out the eyelets before fitting the new cap.