Reducing bass in my Plexi clone

ledvedder

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Hi guys! I've built a Ceriatone Plexi 51. I've been reading up on some ways to tame the bass on a plexi. Even with my bass on zero, I still feel it could use less at times. Would reducing the cap I've circled from 0.022 to 0.01 be a simple method to accomplish this? Has anyone ever done it? 20220722_091343.jpg
 

Amadeus91

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Hopefully, more knowledgeable members will chime in, but I'll give it a shot.
Lowering the value of the cathode bypass cap for the V1a will tighten up/reduce the bass.
Right now, looks like you have a 330uF in that position.
 

ledvedder

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Hopefully, more knowledgeable members will chime in, but I'll give it a shot.
Lowering the value of the cathode bypass cap for the V1a will tighten up/reduce the bass.
Right now, looks like you have a 330uF in that position.
Yeah, I'm considering trying 22uF there.
 

playloud

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Before you do that, make sure you've exhausted all the options with the amp as-built.

If you plug in to the bright channel, and choose the following settings, is there still too much bass with the knob at 0?

Cathode - split
V2A - 0.68uf
V1B - 0.0022uf
 

ledvedder

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After playing it extensively yesterday, I think what I'm looking for isn't necessarily less bass, but tighter bass. Not as mushy, if that makes sense. One small test that I did was parallel a 1k5 over the 1k v2a cathode resistor. I think this gets me closer to where I'm trying to go.
 

paul-e-mann

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Hi guys! I've built a Ceriatone Plexi 51. I've been reading up on some ways to tame the bass on a plexi. Even with my bass on zero, I still feel it could use less at times. Would reducing the cap I've circled from 0.022 to 0.01 be a simple method to accomplish this? Has anyone ever done it? View attachment 111666
I would email Nik he will know exactly what to do.
 

junk notes

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I think what I'm looking for isn't necessarily less bass, but tighter bass. Not as mushy
Now, that possible issue could target the power tubes.
A recent example that I had was trying out EHX 6CA7s for the SV20H - mud; pulled them out in less than a hour after trying to dial in a desirable tone. I do not think a big bottle tube agrees with this particular Marshall circuit. YMMV
 

ledvedder

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Now, that possible issue could target the power tubes.
A recent example that I had was trying out EHX 6CA7s for the SV20H - mud; pulled them out in less than a hour after trying to dial in a desirable tone. I do not think a big bottle tube agrees with this particular Marshall circuit. YMMV
I have JJ 6CA7s in it right now.
 

tallcoolone

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The non invasive solution would be the right OD in front...you are describing the classic issue with those amps. And the classic way to fix it is an OD in front. Makes the amp more flexible onstage as well.
 

Emiel

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The filtering (32+32, 32+32, 50+50) looks like '69 spec to me. You might want to up it to '70 spec (50+50 all around).

Try reducing V1B to 0.0022uf as well. I did it in my clone and it removed most of the mushy bass that you get at higher volume / gain settings.
 

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