Plexi amp channel mixing…

[brewdude]

What is the point of using a tone stack and/or volume/gain knobs at all… just hard bypass the pots and put them all on “11”

[Reeltarded]

Uhh stop wanting your eyes to be happy and the amp will sound great. This is not a thing. You are obsessed with a not a thing.

If you see an amp that sounds perfect to you dimed on all controls.. buy that amp. You'd seriously spend your time better chasing cars.

Now, if you mean to say your amp isn't making you happy and explained what your amp doesn't do that you think other amps do.. that isn't where the controls are set..

WE CAN HELP!!

I have played 4 holers since uhh.. they were new. The first thing I stopped doing was jumping channels!

[Reeltarded]

What year are your amps?

The latest similar model has something called a WHAT THE EFFING HELL ARE YOU THINKING 4700pf bright cap. That thing is similar to the WHAT REALLY IN T3H EFFIN HELL WERE YOU THINKING 5000pf bright cap. These are the things that make the volume I come on so fast the amp is in full drive by 3. (not 3 o'clock.. I don't play a clock.. I play amps.. dials have numbers. 3.) This thing matters, but not to you because the bright cap stops doing anything over about 7.

Dimed amps mean collapsed NFB. NFB provides sizzle and bump. If you are dimed there is a throat. If you lower the volume into the 7 area you are about to hit the knee on that curve... then,. then... 7.1.. 7.2.. eeeee.. NFB collapse. My prefered volume settings are based on a balance where the power tubes aren't all the rage, just lots of it.

So, your presence is null, and your bright cap is null, and you are splitting signal across two inputs to drive a channel that sounds like your great grandfather plunking a broadcaster through an early harvard.. ewwww

Are you dumping into load boxes? What are you looking for?

[Mastershon]

This is without jumping channels. Straight into input 1 high. The second volume adds girth to the sound and is ‘ideal’ at 7. Was curious to know circuit wise why it falls flat past 7 or 8 or so and turns into a mess. Certainly there is a circuit reason why, and therefore a circuit change that can be implemented to prevent it. Perhaps you are correct that it’s due to bypass capacitor and/or negative feedback, however I have altered and/or removed those values and the phenomena remains. It still ‘feels like’ the signal out of V1a&b combined at maximum ‘over overdrives’ v2a but I could be wrong so that’s why I was hoping for some input from you guys as to how to tame that. The whole mixing resistor over ground thing. And yes as soon as I find one that doesn’t I will buy it to analyze!

[Mastershon]

Also another reason I believe it to be too much signal going into V2 is that when a lower gain tube is placed there (like a 5751), the issue goes away. So I was looking for a simple logical way of altering the circuit to reduce signal into V2 so that a standard 12AX7 can be used. Change the mix resistor values? Add a voltage divider prior to V2? Idk

[Reeltarded]

I see.

My answer is that this is a technical issue with loading that is unimportant because the thing you actually wish is that the I channel just sounded awesome with the II channel on 0.

Are you positive you like Marshalls?

You can change the response of dead channel 2 bypassing the mixer, the splitter (mixer) is a pair of 470k resistors with a 470pf cap over the bright side and none on the normal. You would have to experiment but I am thinking 100-250pf range.. wild ass guess. The PCB makes it a little harder to do things but replacing the mixer pair with a 1m variable resistor thingy (no ground) would allow you to dime both channels and limit the effect of the dead channel being raised by exactly the amount under the headroom that makes it sound like its on 7 when its on 10.. or 11.. or whatever. You could swap just the normal side to a 500k that was a little over and instead of balancing them just turn II down.. But this is just an accounting trick. We're going to jail if the ampthorities audit this mod. Oh no!

You like low MU tubes in your Marshall? Lemmy is having a fit! (mods we need a puke emoji.. stat)

You can swap out the II cathode bypass with something MUCH smaller and that is a better idea. You can roll tubes through V1 until you find one with a forward B side and a gentle A side. (Marshalls drive on the left side of the lines)

Plate resistor values.

You could do a couple tricks on the input that (virtual) bandpass the signal feed to II. You might find that a bypass around 5kpf (ironically) would ignore enough low and feed enough mids to make it feel better..

Who drives this Marshall with all the controls dimed that you love so much? If I can hear what sounds ridiculous to your fingers I can imagine how to do that and it's not more than 4 or 5 fairly simple things. I'm better with hearing a thing.

Stewardess.. I speak jive!

[sluckey]

... or you could set the knob to 7, loosen the setscrew, slip the knob to 10, and tighten the setscrew.

[pompeiisneaks]

... or you could set the knob to 7, loosen the setscrew, slip the knob to 10, and tighten the setscrew.

This is EXACTLY what I thought of, but didn't say anything I'm glad you did steve hehehe

wait what if he wants it go to to eleven?

~Phil

[Reeltarded]

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[sluckey]

wait what if he wants it go to to eleven?

Nope. He only wants 10.

[Reeltarded]

you can pull the cap off the knob and replace it with no adhesive so you can dial only the pointer in once you get the sound happening

i'm still looking for a way to do it remotely over bluetooth without having to pair it to my car

[Mastershon]

Thanks for all the responses guys. And yes it seems humorous I get that, but there’s a method to my madness!

It is funny to maybe just reset the knob on 10 by removing the cover and regluing it, or resetting the set screw so it appears on 10 haha

Reeltarded those are great suggestions, and yes I love Marshall’s I have 10 or 12 of them. Lost count. I’m not running volume 2 on zero, the amp sounds thinner with volume 2 on zero. Volume 2 on 7 (and volume 1 on 10) sounds excellent. Just would like to knock down the voltage divider effect going over 1 Meg over ground when above 7.

[Mastershon]

Reeltarded you hit the nail on the head that a 500k pot on volume 2 in lieu of 1 Meg would resolve the issue. Was looking for some other circuit way of achieving the same thing.

[pdf64]

Oscillating? Can you tell me more about this?

What is your understanding of ‘oscillation’?
Maybe this might help https://robrobinette.com/Tube_Guitar_Am ... itar_Audio

[Reeltarded]

I had a WAY better idea in my sleep. A 100pf bright cap on volume II. Seriously its a couple bucks and try that for the sound. Ignore rotation. It will get the thickness without woofing and a little boost..

Pot limiting:

Don't change the pot. strap a 500k across the outside lugs of the extant volume II.

There are excellent tonal variations you are missing by having this one goal.