5E3 clone with too much bass

[Rhodesplyr]

A client of mine bought a 5E3 clone on craigslist that appears to have been built by someone on the learning curve of amp building, judging from the odd mish-mash of boutique and generic parts, i.e., someone who's read that certain parts should be used at certain circuit points, but doesn't really know why.

My client's complaint about the amp can be traced to the fact that the frequency response goes too low, giving it a bloated sound and causing the speaker (a 1960 Jensen P12Q) to flop back and forth at frequencies that aren't that musically useful. (It's not oscillation, just over-emphasis of the lower notes.)

All the major coupling caps in the amp are 0.022uF Sozos. The first filter stage is 33uF, and the two following stages are each 10uF. The 12AY7 and 12AX7 cathode bypasses are both 47uF rather than 25uF.

I'm planning to trim the cathode bypasses back to 25uF, and I'm wondering if it might also help to return the circuit to the stock 16uF-16uF-16uF filter values.

Or, to put it another way, if you were faced with a 5E3 clone with bloated bass, where would you limit the bandwidth? The Hi-Fi side of my brain tells me to do it at the input stage, but this isn't Hi-Fi :-) I figured I should ask the 5E3 experts :-)

[d. spree]

A client of mine bought a 5E3 clone on craigslist that appears to have been built by someone on the learning curve of amp building, judging from the odd mish-mash of boutique and generic parts, i.e., someone who's read that certain parts should be used at certain circuit points, but doesn't really know why.

My client's complaint about the amp can be traced to the fact that the frequency response goes too low, giving it a bloated sound and causing the speaker (a 1960 Jensen P12Q) to flop back and forth at frequencies that aren't that musically useful. (It's not oscillation, just over-emphasis of the lower notes.)

All the major coupling caps in the amp are 0.022uF Sozos. The first filter stage is 33uF, and the two following stages are each 10uF. The 12AY7 and 12AX7 cathode bypasses are both 47uF rather than 25uF.

I'm planning to trim the cathode bypasses back to 25uF, and I'm wondering if it might also help to return the circuit to the stock 16uF-16uF-16uF filter values.

Or, to put it another way, if you were faced with a 5E3 clone with bloated bass, where would you limit the bandwidth? The Hi-Fi side of my brain tells me to do it at the input stage, but this isn't Hi-Fi :-) I figured I should ask the 5E3 experts :-)

Is this a typo when you say "The 12AY7 and 12AX7 cathode bypasses are both 47uF rather than 25uF." A mod is often done (I just did one) to reduce bassiness and boom by using a 4.7uF cap, or even a 2.2 uF in teh first cathode bypass. I would think a 47uF cap would increase the problem?

[Jazz P Bass]

Try this first.
Remove the first bypass cap altogether.
If the boomy notes are now missing, add a capacitor.
If you have an assortment, try them all.
ie: 25, 15. 10. 4.7 & 2.2

[Chuck H]

+++

FWIW this is a common complaint with stock 5e3 clones. You mention that "All the major coupling caps are .022uf" (Is the difference between a major and minor coupling cap the third ) I would make sure they are all .022uf. And reduce the first cathode bypass cap to 4.7uf. JPB is right that trying the amp with the bypass cap removed will tell you if this mod will "fix" the problem. I would probably actually increase the filters to 47/20/20. But that's not part of the problem your having.

[d. spree]

Bruce at Mission amps has a mod kit that will reduce that bass woofiness - it allows the player to shift between the original amp values (which I like when playing my starts - i.e.e not playing with humbuckers) and lower value caps in the cathode bypass position and in one of the coupling cap positions. It helped one of my tweeds. On another tweed I simply replaced the cathode bypass cap with a lower value and the first two coupling caps with 4.7uF instead of 22 uF. This fixed the problem completely - but of course isn't switchable.

Is the speaker still good?

[Rhodesplyr]

Is this a typo when you say "The 12AY7 and 12AX7 cathode bypasses are both 47uF rather than 25uF." A mod is often done (I just did one) to reduce bassiness and boom by using a 4.7uF cap, or even a 2.2 uF in teh first cathode bypass. I would think a 47uF cap would increase the problem?

No, it's not a typo. This amp was built by someone either had no 25uF caps handy or, for some reason, thought that 47uF would be better.

[Rhodesplyr]

The speaker is basically good, but has its own issue separate from the woofiness problem. It's a Jensen P12Q with a whizzer cone. It behaves just fine on a sine wave sweep, but actual guitar tones generate some odd resonances. I have a repaired standard Jensen P12N that we may try instead.

[Jazz P Bass]

Later model SF Fenders (ultra linear?) used a 330uf bypass cap.

Sheesh!

[d. spree]

No, it's not a typo. This amp was built by someone either had no 25uF caps handy or, for some reason, thought that 47uF would be better.

Wow! Given the fact that many people seek far smaller values than the 22uF it is no surprise it would boom away! Have you made any changes yet? If so let us know how it has worked out. As I posted earlier I had good luck with a MIssion amps mod kit - I like it becuase you can switch to the original configuration when you want.