Treble and Bright caps

[Paradox]

Okay . . .so I finally found a 22uf for C13 and it really is a big difference from the .68uf i put in a cpl weeks ago. Really smooth.The .68 seems a hair brighter than the 22 tho'. And now I'm wondering what would happen if I put a 22 in C7 to match C13. . . .or maybe taking C7 out ?Anyone think this would be a bad idea ? I mean possible damage ? And could anyone tell me what C6 is for ?

C6/C7/C13 are cathode bypass caps. You can experiment with them without damaging anything. Changing C6 will have a stronger effect than changing C7. Changing C7 will have a stronger effect than changing C13. You can get into mud really quick with too high values early in the signal chain.

http://www.ampbooks.com/home/amplifier-calculators/cathode-capacitor/

 

[Deisel401]

Thank you very much. That info will help me a lot. Have a good evening.

 

[Kapo_Polenton]

I found 22uf to have more high mids and definition than .68 uf... guess it all depends on the ears. I just seem to be a fan of something in that position on almost all the modules I have.

 

[Jaded Faith]

I found 22uf to have more high mids and definition than .68 uf... guess it all depends on the ears. I just seem to be a fan of something in that position on almost all the modules I have.

Technically speaking, this finding is the opposite of what's occurring. Plug the two cap values into that calculator and see the difference. It's quite different. I will say the 22uF will have a lot more of everything, but that shouldn't be perceived as a high mid/definition thing. If you could A/B the two in real time you would probably hear the difference better.

 

[Paradox]

My personal preference is smaller cathode bypass and coupling caps early in the signal chain. Smaller is subjective and my personal preference certainly won't agree with everyone else.

 

[Kapo_Polenton]

Technically speaking, this finding is the opposite of what's occurring. Plug the two cap values into that calculator and see the difference. It's quite different. I will say the 22uF will have a lot more of everything, but that shouldn't be perceived as a high mid/definition thing. If you could A/B the two in real time you would probably hear the difference better

This is what I keep hearing.. you are probably right because it does seem that everything has come up here when compared to the brahma that has a .68 in that position. I think I just left it because it sounded different than the brahma stock and I really didn't need 2 brahmas! :roll:

 

[Jaded Faith]

Not a bad decision and it makes a lot of sense to me. :wink:

I can certainly confirm either one will sound fantastic. That's a great stock module and a great place to start for experiments.

 

[Deisel401]

The way Paradox explained it, C6 having more effect than C7 and C13, and C7 having more effect than than C13, I'm thinking about trying a 22 in C6 instead of using caps in C7 and C13. I'm not trying to make my SL+ into a Brahma, although I would love to have one, I was looking for more Marshally "sparkle" and "shine" in the upper mids. So leaving the .68 in C7 and adding a 22 in C13 def did it for me. Maybe I should just leave well enough alone. I'm wondering if I should try this with my PLEXI. I also read on here somewhere about changing R25 from a 33k res to a 39k res to change the mid freq. But I can't figure out if all the resistors on the SL+ pcb and the PLEXI pcb are all 1/2 watt resistors. And even tho' I'm good with my soldering gun, I don't understand everything I need to know about gain staging and the preamp circuit. But I'm learning. There's a lot of info and links in these threads for ppl like me that want to learn.

 

[Jaded Faith]

C6 will have no effect on a Brahma or Plexi, but you will be fine on the SL+. It wasn't really clear which module you were going to try that on.

A 33K at R25 is very traditional Marshall.

When in doubt, use 1/2 watt resistors in any position on the module. There is no benefit to going any smaller and larger is always the safer bet.

 

[Deisel401]

Thanks. I'm working on my SL+ but was thinking of trying the same mods on my Plexi. But now I know I should leave C6 alone on the Plexi. Thanks. And I'm glad you told me about the use of 1/2 watt resistors cuz when I changed out R25 from 10k to 33k I assumed all the res's were 1/2 watt. Later I found on the Module parts list (Graham Pearson, i think?) "all vales 1/4 watt unless otherwise noted". So I don't have to go back in and change any of my new resistors from 1/2 watt to 1/4 ?

 

[SacredGroove]

Thanks. I'm working on my SL+ but was thinking of trying the same mods on my Plexi. But now I know I should leave C6 alone on the Plexi. Thanks. And I'm glad you told me about the use of 1/2 watt resistors cuz when I changed out R25 from 10k to 33k I assumed all the res's were 1/2 watt. Later I found on the Module parts list (Graham Pearson, i think?) "all vales 1/4 watt unless otherwise noted". So I don't have to go back in and change any of my new resistors from 1/2 watt to 1/4 ?

You had a 10k in R25? I'm guessing that the resistor you're referring to is directly behind the Mids pot? I'm really just curious, is all.

FWIW, C6 is a bypass cap for (gain) stage two, and on the Plexi, Brahma, and some other mid-gain modules, stage two is bypassed. :wink:

 

[Kapo_Polenton]

FWIW, C6 is a bypass cap for (gain) stage two, and on the Plexi, Brahma, and some other mid-gain modules, stage two is bypassed. Wink

So with no value there in C6, a gain stage to that first tube on the module board is bypassed much like the standard plexi would do? (so no cascade)

I'm really puzzled when I compare these pcb's to my PTP plexi and 2204 I worked on/built. I'd like to know, where the very first cap C3 appears in a real 2204?

 

[SacredGroove]

FWIW, C6 is a bypass cap for (gain) stage two, and on the Plexi, Brahma, and some other mid-gain modules, stage two is bypassed. Wink

So with no value there in C6, a gain stage to that first tube on the module board is bypassed much like the standard plexi would do? (so no cascade)

Yes, but on a standard Plexi there are only two tubes and all stages are used, whereas the MTS has three tubes and two stages are bypassed: one on the input tube and one on V1 of the module.

I'm really puzzled when I compare these pcb's to my PTP plexi and 2204 I worked on/built. I'd like to know, where the very first cap C3 appears in a real 2204?

C3 is the coupling cap from the first stage, which is in the preamp/head.

I'm really tired, so I hope this made sense...:lol:

 

[Kapo_Polenton]

Roger that. I think I know where I am but there are def. differences between the circuit flow. I think changes are best left to the pros like you guys.

What about C1 on the preamp tube board. What does that affect? I'm also interested in areas of the circuit that add brightness/tightness. I look at my GTO judge and to me it sounds wayyyy different than any of the other modules I have. I'm trying to wrap my head around why that might be.

C6,C12,C8... all empty in the judge. That means they must have bypassed that whole stage!

C3, .022 uf which is not any different than a SL+ or most of the othe modules out there.

C1 - empty (this might be the "bright" cap on a plexi or JCM800 pot i assume)
C2- 471pf cap

C7, C12 are .68 uf.

So what is the judge lacking? High end.

I think Randall might have blown it here. They could have left the mode switch in and added an additional switch which would add in the bypassed gain stage and had a real fire breathing monster.I'm also wondering whether or not Randall had some quality control issues. Maybe on some modules the cap has gone in C2 rather than C1 and thus accounts for why some people say it is dark while others say they have to ensure it isn't too bright. Perhaps only George Lynch knows the answer to this! :roll:

 

[SacredGroove]

Roger that. I think I know where I am but there are def. differences between the circuit flow. I think changes are best left to the pros like you guys.

What about C1 on the preamp tube board. What does that affect? I'm also interested in areas of the circuit that add brightness/tightness. I look at my GTO judge and to me it sounds wayyyy different than any of the other modules I have. I'm trying to wrap my head around why that might be.

C6,C12,C8... all empty in the judge. That means they must have bypassed that whole stage!

C3, .022 uf which is not any different than a SL+ or most of the othe modules out there.

C1 - empty (this might be the "bright" cap on a plexi or JCM800 pot i assume)
C2- 471pf cap

C7, C12 are .68 uf.

So what is the judge lacking? High end.

I think Randall might have blown it here. They could have left the mode switch in and added an additional switch which would add in the bypassed gain stage and had a real fire breathing monster.I'm also wondering whether or not Randall had some quality control issues. Maybe on some modules the cap has gone in C2 rather than C1 and thus accounts for why some people say it is dark while others say they have to ensure it isn't too bright. Perhaps only George Lynch knows the answer to this! :roll:

Could you send me a gut shot? I believe the Judge has a newer pcb and I don't want to get into specific parts locations without knowing what their actually labeled on the board.

[email protected]

 

[Kapo_Polenton]

Sent! Just don't get in to trouble with your family for spending too much time on this !! But if we can help the MTS community enjoy their GTO more, that would be fantastic. It is soo close!

 

[SacredGroove]

Sent! Just don't get in to trouble with your family for spending too much time on this !! But if we can help the MTS community enjoy their GTO more, that would be fantastic. It is soo close!

Thanks...LOL. It's not like I've been condemned from MTS. I just need a serious break and reassess what I'm doing, so it doesn't effect family as much as it did.

R16, R22, C6, C8, C12 are all part of stage two, which is bypassed, like you mentioned.

Leave C2, but remove R8. C2 is more like a bright cap on a Plexi. When the Bright switch is engaged, C2 is switched on in parallel to the Gain pot.

Remove the cap on the tube board. That's rolling off some highs. You could also try putting that cap at C2 to replace the 470p ceramic cap.

Do you know the value of the pots? These could have a dramatic effect on overall tone and gain.

I think if you traced the module, you'd see how similar they are to other amps. Recto/Grail then XTC are my preferred boards to use.

Try a .0015p at C3. That will tighten it up a bit.

 

[Kapo_Polenton]

POTS values are not written on the pots so i figure i'd have to pull them to measure the sweep to know.. I'll post back with my findings once i try some of your tips. Thanks!

 

[Kapo_Polenton]

Eureka.. MUCH better! 2 value changes and bam. Usable module. excellent mid range crunch and fatter sounding than my brahma. This thing has now earned it's spot among the rotation. Friedman should have consulted you before releasing this thing! Now that mode switch, who knows why it has such a volume drop, sounds great though. :idea:

 

[Deisel401]

@ Sacred Groove. Yes , there was a 10k resistor in R25 and R31. And those are stock values in my PLEXI i just bought a few weeks ago from M.F. And it's dated " 1104R1146 ". Kinda weird, huh? I changed both of those to 33k and can't hear any difference . . . . . . . This is NOT a great sounding module.