Modding 2204: Background noise help

[lgehrig4]

Hello!

I recently built a 2204. It worked out well and sounded very good, but now I've begun modifying it.

My first mod was to convert it to JEL specs (below) and it came out very good, but my goal is to have something closer to a #34/#36 modded Marshall. Just in that range and tweaked to my tastes. I have now a JEl/#34 mod mix and though the tone and gain are in line with what I was expecting, the amp got noisy after the last few changes. Note, my original 2204 did not have a bright cap on the gain pot nor did I have a piggybacked 470K/500pf running from the normal input to gain pot.

Due to home construction, I don't have the luxury of adding one component and testing. To make this bearable, I have to solder in a few components, hope for the best, and then take the amp downstairs to test. I'm getting a workout

The noise is a fast ticking and a squealy squirrely sound. It's not over the top, but definitely not something I would want.

Changes I made before noticing this
2200pf bright cap on gain pot
470K/500pf from normal input to gain pot (using shielding wire) *I also tried 470K/2200pf here. Same noise
.68uf piggybacking 820R to V2 pin3 (this was a .22uf with the JEL mod)
330pf piggybacking 100K to V2 pin6

What I had from JEL mod and still have
.0022uf coupling cap to V1 pin 6 (replaced .022uf)
.68uf/2.7K (replacing cold clipper to V1 pin3)
470pf piggybacking 100K to V2 pin8
Neg feedback: 100K to 47K on board >> 220k/4n7 >> 4ohm tap


Jake E Lee
https://drive.google.com/drive/folders/ ... ek5m96uNtV

#34
https://drive.google.com/drive/folders/ ... w_5hpSBlK1

I'm not totally surprised given the changes I made, but I took good care with the lead dress and used shielded wire where called for. Could it be a tube issue and the new mods are just exposing them? I'm testing it with the chassis back in the headshell, which has shielding tape on the bottom. Any suggestions are most welcome!

As a bonus, which can I try for more mid to upper mid punch? I'm happy with the low end and there are more highs than I need. I'm missing (for my taste) that punchy, solid kerrang right down the middle. The amp as a whole has punch, but not exactly in the frequency range where I would prefer it to be. I'm not sure what component(s) to manipulate for this.

[cdemike]

Does the amp make these weird noises with no guitar plugged in and with the volumes at maximum? Could be a tube issue, but I'd also want to rule out some unforeseen oscillation. If you don't have extra tubes to roll and rule out a tube fault, it couldn't hurt to just shuffle the 12AX7s you already have in between positions to see if that would change the situation. Ticking makes me think either oscillation and/or that it's picking up environmental noise, especially with the construction happening and with the amp not having a noise issue before the mods. My wifi router also makes a ticking noise (no squealing though). I know space is an issue with your current situation, but have you tried moving the amp to different places in the same room?

Regarding the sound fine tuning, did you have a preference between the peaking network running from the low-gain input to the volume pot? I'd guess the 470k/500pf was closer to the goal, but it sounds like we might both be struggling with "tone words" here. Maybe it'd be better if you had clips of the amp now or can reference another recorded amp that it sounds like as well as a recorded amp that's closer to what you'd like your amp to sound like. I'm thinking you might like a big .68uF presence cap like some of the mid+70s JMPs had. I also have found that reducing NFB takes away some of the upper midrange bite that I associate with Marshalls, so reducing the NFB resistor and/or moving the NFB feed to the 8- or 16-ohm taps might help. If the amp is closer to how you like it in its current form, changing the amount of NFB vs the NFB cap's value would be my starting point.

[lgehrig4]

Does the amp make these weird noises with no guitar plugged in and with the volumes at maximum? Could be a tube issue, but I'd also want to rule out some unforeseen oscillation. If you don't have extra tubes to roll and rule out a tube fault, it couldn't hurt to just shuffle the 12AX7s you already have in between positions to see if that would change the situation. Ticking makes me think either oscillation and/or that it's picking up environmental noise, especially with the construction happening and with the amp not having a noise issue before the mods. My wifi router also makes a ticking noise (no squealing though). I know space is an issue with your current situation, but have you tried moving the amp to different places in the same room?

Regarding the sound fine tuning, did you have a preference between the peaking network running from the low-gain input to the volume pot? I'd guess the 470k/500pf was closer to the goal, but it sounds like we might both be struggling with "tone words" here. Maybe it'd be better if you had clips of the amp now or can reference another recorded amp that it sounds like as well as a recorded amp that's closer to what you'd like your amp to sound like. I'm thinking you might like a big .68uF presence cap like some of the mid+70s JMPs had. I also have found that reducing NFB takes away some of the upper midrange bite that I associate with Marshalls, so reducing the NFB resistor and/or moving the NFB feed to the 8- or 16-ohm taps might help. If the amp is closer to how you like it in its current form, changing the amount of NFB vs the NFB cap's value would be my starting point.

Thank you! Since posting this I decided to go with the #36. I already have an extra preamp socket installed so I figured I would give it a go. I am pretty much following the #36 done by Headfirst Amplification. I have to order parts, but I managed to somewhat complete what would be the #34. I tried that out and I go like the tone. I no longer hear the "squirelly squeaky" I described, but the ticking is still present.

I agree that it might be a preamp tube. Due to home construction, my testing spot is right near my wifi router so it's funny you mentioned that. I will switch out the preamps sometime this weekend and report back.

[lgehrig4]

It did actually turn out to be the wifi router So funny that you happened to mention that

[Colossal]

That annoying ticking is a telltale sign of a router

Glad you found it.