EVH5150 III 50 Reducing Gain Red Channel

DADA

Member
Would like a second opinion or confirmation that this idea will work.
The idea I read on another forum is to have a second Blue Channel.
To do so he lowered the 3 resistor values to matching that of the Blue Channel
Would putting a second resistor of 220K in parallel over R72 / R80 / R82 reduce it each to 110K?

Thank you all

Following is from another Forum.

So I had some free time last night and decided to tinker with the amp a little. I put some lower gain tubes in the channel 3 path. The gain was easier to control, but It really screwed with the tone. Amp felt thin and brittle and just didn't sustain like I was hoping so 12ax7's went back in.

After my initial disappointment, I decided to take the plunge and change out the plate resistors. I have modded my own amps for a decade and have built a few amps of my own, so I felt comfortable with making the changes. First note, This is probably one of the easiest amps I have ever worked on. Everything is labeled and is schematic correct. I wish Mesa and Peavey would get on board with this kind of clarity in design. Channel 3 has 3 plate resistors that are 220k (massive dirt/gain) so I decided to start there.

I changed out the first gain stage plate resistor first (R72 220k to 100k) It was a definite improvement but still insane amounts of gain. Was more touch responsive and cleaned up better but still light years more gain than channel 2, so on to the next 220k plate resistor.

R80 and R82 are both 220k plate resistors in channel 3's stages. I decided to change both at once and see where it put me. For me this is the ticket. Channel 3 ends up feeling a lot more like channel 2. There is more gain and a little more compression, but the gain is much more touch sensitive and you can clean up the channel if you want with just the volume knob now.

This mod probably is not for the metal head crew, but for rock & roll or classic VH, this is a huge difference. I think I will leave it for now.
 
Interesting. Subscribed.

I lowered the Red with a tube change but the characteristic is still decidedly Red. I like the Red a lot but often think the Blue is so awesome that it might be nice to have (2) Blue :confused:
 
The modification is still being altered.

Still tinkering around with the red channel a little. Changed out a filter cap (c16) from a 1uf to a 22uf, which is the channel 2 value for that same stage. It got rid of the nasal sound. It sounds really close to channel 2 afterward, enough so I was playing and half paying attention and was adjusting the wrong eq thinking I was on the 2nd channel.
 
Thanks, Jamme61!

Here some more results:
That 22uf coupling cap really brought the 3rd channel to life. I may end up changing out one or two of the plate resistors for 150k to see how it responds. Right now, tone wise, the amp reminds me of an older bogner ecstasy head I played years ago but not quite the gain push of the bogner. It definitely has those thicker, chewy mids though. If the 150k plate resistors get that extra shove gain wise without the full blown insanity that the 220k provided, that would be great.

So the 22uf (C16) coupling cap is a major part of the mod.
And for reducing the amount of gain reduce the plate resistors (R72 / R80 / R82) to your liking (between 110K and 150K)
 
Agreed, lower gain preamp tubes are by far the easiest and reversible way. You also can try a variety of combinations. V2, V3 and V4 are solely relegated to the RED channel. So you can tweak those without impacting the GREEN or BLUE channels. Try 12AT7 or 12AY7 versions in a couple of those spots. I bet you'll find something you like.
 
Tried that with the tubes and did not like the sound of it.

The mod is further fine tuned by the guy. Might try this in the future ;-)

Still tinkering around with the red channel a little. Changed out a filter cap (c16) from a 1uf to a 22uf, which is the channel 2 value for that same stage. It got rid of the nasal sound. It sounds really close to channel 2 afterward, enough so I was playing and half paying attention and was adjusting the wrong eq thinking I was on the 2nd channel.

I already found the 3rd channel to be tighter, thinner and more compressed sounding than the second channel. For bringing the heavy, that is great, for me however, not so much. Of the mods I performed, the capacitor change was the bigger tone change than the plate resistors truthfully. It gave the third channel more girth and warmth and less of that djent mid range "whomp". Tone wise it is near identical to channel 2, but there is a little extra gain(15% more than the blue channel if I had to put a number on it).

In a tube circuit, the cathode bypass cap adds gain to a stage and a filter on the tone. The smaller the cap, the tighter the tone. It had a 1uf originally, I added a 22uf. I only changed the one cap since it was the one that was a smaller value than the corresponding gain stage in the blue channel. When modifying an amp, I try to change only one part at a time in most cases and then test my changes. Makes it easier to troubleshoot if there are issues. Value wise it was a 22uf polarized can cap 50 volt.

The plate resistor, determines how much distortion the tube stage is creating. 100k is the standard value Marshall has used forever, while 220k is the value you see in 5150's, soldano's, rectifiers, etc. If I ever go back inside the amp, I may try some 150k as a middle ground value to see how they would affect the gain staging. I don't mind having the extra gain as long as its controllable. The plate resistors I used currently were 100k resistors 1/2 watt.

No problem. I have played the amp at two gigs since the mods and have determined that it sounds near perfect for what I want. That 22uf coupling cap really brought the 3rd channel to life. I may end up changing out one or two of the plate resistors for 150k to see how it responds. Right now, tone wise, the amp reminds me of an older bogner ecstasy head I played years ago but not quite the gain push of the bogner. It definitely has those thicker, chewy mids though. If the 150k plate resistors get that extra shove gain wise without the full blown insanity that the 220k provided, that would be great. As it stands, it nails some 90's AIC and Tool type sounds.
 
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