coupling cap to block some bass?

[dmartn149]

I got an early 60's Epiphone Pacemaker amp a few weeks ago. It is basically Gibson/Epiphone's version of a Fender 5F1 Champ. After replacing the caps, and power cable, It sounds really good in the higher register, but lower notes, and especially open position chords sound too muddy. I am thinking I could replace one of the coupling caps with a .01uf to block some bass. Should I replace the one between the preamp stages? or the one between the pre, and power tube? I'm thinking the one just before the 6v6 tube. I could try it both ways, but it is so much easier to ask the experts.
Thanks, and thanks for not making me take a test to join the forum.

[tedmich]

is this its schematic?
http://www.ampwares.com/schematics/e...maker-trem.pdf

or this one?
http://www.ampwares.com/schematics/e...-pacemaker.pdf

I might try to put a lower value cathode bypass cap on the 1st stage, so the boost won't go so low.

[Tom Phillips]

...I might try to put a lower value cathode bypass cap on the 1st stage, so the boost won't go so low.

Agree. With that change the first stage of the amp will generate less bass. I think it's a better approach than starting with more bass response and then blocking it / filtering it out in a later stage.

[dmartn149]

It's like this
ga5.pdf
It differs from the Fender Champ in that the first stage cathode is bypassed. So should I just remove that cap?

Yes I know that's gibson schem. It's just like the 61 Epi. ea50

I just looked through my stuff and found some 10uf 35v tantalum caps. Would one of these work as a smaller cathode bypass on the first stage?

[pdf64]

There was a recent thread in which the concensus seemed to be that a fully bypassed (ie at line frequency) 1st stage cathode should help to mitigate hum interference between the heaters and signal path..
Clearly many amps don't conform to that, eg many Marshall models.
And the lack of balanced heaters makes such good practice potentially wasted.
But 20nF coupling to >1M (corner frequency of >8Hz) seems a needlessly extended low end.
In the first instance I would move the corner frequency of the 1st to 2nd stage coupling up; if say 2n2F, cormer frequency ~79Hz, the heater induced hum may be further reduced.

If it's the original speaker and is alnico, a tired magnet may be responsible for flubby bass and muted top end.

[dmartn149]

Pdf64. So if I'm understanding you right. You would be in favor of changing the first coupling cap instead of altering the bypass cap value, so as not to induce hum into the signal. It is very quiet now.

The speaker is the original Jensen, but while the bass is flubby, the top end sounds great

[Enzo]

Other than the filter caps, there are only four caps in the amp - two couplers and two bypass. You can unsolder one end of a bypass cap and lift it, then play the amp, then try it with the other bypass cap. Your could sub a smaller coupler into the first position, then try it in the second position. All than could be done in a half hour of poking around, and then all the questions would have answers.

[eschertron]

Since the ball's in play, I suggest making the second coupling cap (between the preamp and the 6V6) and the 6V6's cathode bypass cap smaller. In a champ build I went with 4n7 coupling cap [edit: about 5x higher f3 than with the stock cap]. that gave me a corner freq of about 150Hz. I further affected the LF with the 6V6's cathode bypass cap.

Use Enzo's rule and try what your SWAG predicts. I know it's an old amp and you want to keep it mostly unmolested, but the best course of action is action.

[dmartn149]

No, I'm not worried about keeping it unmolested. I've already changed all the caps and both cathode resistors. I just want it to sound good. I really was hoping to avoid lots of trial and error. The cathode resistors are soldered to the leads of the bypass caps, so it's not quite as easy as just lifting a leg of the cap.
So what about replacing the first stage bypass cap with a 10uf 35v tantalum cap (I already have a couple of these) The cap there now is a 25-25.

[Tom Phillips]

...So what about replacing the first stage bypass cap with a 10uf 35v tantalum cap (I already have a couple of these) The cap there now is a 25-25.

To make a significant difference that you can hear you will need to change to 2.2uF or smaller as mentioned by pdf64.

[dmartn149]

Okay, Thanks everybody. I'll see if I can find some caps locally next week.

[Tom Phillips]

Okay, Thanks everybody. I'll see if I can find some caps locally next week.

Keep in mind that you can make series & parallel groupings of various caps to experiment. Use anything that you have laying around or can salvage out of junked equipment to experiment. When you determine the value that gives you the sound you like then you can purchase a single new cap of the nearest standard value.

[dmartn149]

Keep in mind that you can make series & parallel groupings of various caps to experiment. Use anything that you have laying around or can salvage out of junked equipment to experiment. When you determine the value that gives you the sound you like then you can purchase a single new cap of the nearest standard value.

Thanks, but I really don't have much laying around. I've only worked on a few amps, and I usually order only what I need. There is an electronics store in town. They should have my cap.

[dmartn149]

Okay, I've tried a couple of different cathode bypass caps on the first stage. I'm down to 1uf there, and also changed the last coupling cap from .02uf to .01uf. I still can't get a good sound using neck pickup on any of my guitars. Should I just forget using the neck pickup with this amp? It sounds great with a bridge position humbucker. Maybe that's it's one trick.

[Tom Phillips]

Achieving "one good trick" is great progress.
There are lots of other combinations of parts to try but then you might just trade one trick for another.
All your testing to date has been with the one speaker. Correct?
The response of different speakers can make a significant difference. Some people also like to play a small amp into a larger speaker cab. Something to try if you have other speaker cabs available.