overall muffled sound on an amp

[EKDENTON]

The "overall" tone on one of my old 6v6 plexis has a much darker tone ....or maybe i should say it sounds constipated or like it is under the laundry pile. LOL


So i have tried replacing the cathode capacitors on V1A from 22u to a 10u. I left the .68u on V1B. I had a .047u coupling cap on the normal channel and changed it to a .02u, the bright channel has a .002u. Changing to the 10uf and going down from a .047u to a .02u did not change the tone enough to hardly notice a change. All the other coupling caps and the caps at the tone stack are all as per the amp plan. The little tone caps are the 500pf


I think the range between the normal and bright channel is pretty good but i would like the overall tone of the amp a lot brighter, so I can at least use my neck pickup on my guitar.  Should i keep going smaller on the first stage of coupling caps? Or should i work further along in the signal path at other coupling caps or tone caps?


Any ideas?

[sluckey]

Have you tried jumping the two channels together?

I have two plexi style amps, my November and a 6V6 plexi. Both have preamps that are an exact copy of the JMP 1987 plexi circuit. The bright channel is very bright, almost brittle, ice pick kinda bright. The normal channel is too dark and muffled. Neither channel sounds good to me until I jump them together. Then I can blend the bright with the dark to get a really full sound, plenty of tight bottom and plenty of top end highs too. Both of these amps now only have one input jack and the channels are permanently jumped together.

[PRR]

You seem to be changing bass response.

I wonder if you may be losing treble. "under the laundry pile" sure sounds like loss of highs. (And "icepick" is excess highs, which is why Sluckey's mix technique is one work-around.)

[EKDENTON]

Hey Sluckey, yes it's the exact same build I have been doing. I have them jumpered together with one input, a bright and normal volume.  The bright volume is about where the normal volume should be and the normal volume is not much use its too dark.


PRR. I think you are right i just cant seem to figure out where. Let me pull the chassis back out and re-check everything even the pots, maybe i put the wrong size pot in or something. All the coupling caps, tone caps, and cathode caps are the values i have used on other builds that work great.


Can I tell if the issue is in the tone stack if i lift the ground of the tone stack?

[tubenit]

The speaker can sure make a big difference.  Have you tried it with another speaker?

Other factors I've found that muffle the tone are too much shielded wiring and (at times) Mallory caps in the preamp section.  The Mallory caps seem OK to me more often in OD or LTPI and power amp. I usually don't care for them in the first two gain stages or sometimes in tone stacks.

Maybe try Hoffman's yellow Jupiters in the first several gain stages and tone stack area?

With respect, Tubenit

[EKDENTON]

Thanks Tubenit, I will try different speakers and see what happens. I didn't use the sheilded wire but i did use Mallory caps. I think I may have a few orange drop caps. I may  change a few caps tonight and see if i like it better.

[hesamadman]

Two things that has caused it for me.

1. Speaker.

2. OT. I've had a 30 watt OT from a Marshall 30 watt in my ac30 build. Two completely different power amps. The impedance was wishing 50% of specs but it just made for a way too dark tone. Swapping it with a more appropriate OT yielded wonderful results.