Deeper voicing on EVH5150iii

[Tahoebrian5]

Hi, I'm hoping to get a bit better sound out of the high gain, Channel 3, of my EVH. To me the low end sounds kind of brittle and I would like a deeper tone. I'm considering playing with the values in the tone stack. I'm happy with Channels 1 & 2 so trying to keep any mods to just Ch3.

Here is a schematic of the tone stack. Beyond this would it be recommended to change coupling caps instead or in addition to the tone stack?

[Tahoebrian5]

The input part of the preamp circuit

[Tahoebrian5]

Center part of the preamp circuit

[Jazz P Bass]

I would work with V1A at first.
That 470pf coupling cap (C16) looks like they are trying to limit the low frequencies.
Your on your own here so try a larger cap. (.001 maybe)

The cathode bypass cap could also be made larger.

[Tahoebrian5]

470pf is a bit low. On looking at the rest of the coupling caps, V4a has a .001mF. This seems like it would block most of the lows and mids. It's right before the cold biased stage so maybe something to do with that?

[Gaz]

470pf is a bit low. On looking at the rest of the coupling caps, V4a has a .001mF. This seems like it would block most of the lows and mids. It's right before the cold biased stage so maybe something to do with that?

470p is reasonable for this many gain stages. Have you ever built an amp with this many? Bass build-up is ridiculous. Raising it to .001uF is not absurd, however emphasizing bass later on in the path is preferable since it won't have the chance to get amplified into a muffled mess. I think your intuition to play with the tonestack was a good one. I would first try changing the slope resistor from 47K to 39K or 33K for more low mids. Next I would try lowering channel 3's resonance cap (not sure if it's c2, c3, or c4 without examining the switching too much) to .0047uf all the way down to .002uF. This will beef up the low mids too. I don't know if I would call any of the mods "deeper", but they will warm it up for sure and beef up the low midrange. I personally think the 47K can sound a little anemic and nasal, although it is a very tight and at this point iconic sound borrowed from the SLO. Of course it depends on the whole circuit...

[Tahoebrian5]

470p is reasonable for this many gain stages. Have you ever built an amp with this many? Bass build-up is ridiculous. Raising it to .001uF is not absurd, however emphasizing bass later on in the path is preferable since it won't have the chance to get amplified into a muffled mess. I think your intuition to play with the tonestack was a good one. I would first try changing the slope resistor from 47K to 39K or 33K for more low mids. Next I would try lowering channel 3's resonance cap (not sure if it's c2, c3, or c4 without examining the switching too much) to .0047uf all the way down to .002uF. This will beef up the low mids too. I don't know if I would call any of the mods "deeper", but they will warm it up for sure and beef up the low midrange. I personally think the 47K can sound a little anemic and nasal, although it is a very tight and at this point iconic sound borrowed from the SLO. Of course it depends on the whole circuit...

Some good thoughts there, thank you. I don't have much experience with high gain amps with lots of stages so any feedback is very appreciated. I am familiar with the idea of keeping low freq's minimized until later in the circuit though.

I'm considering replacing the slope resistor with a trim pot. Seems like the best way to dial it in by ear. Any downside to leaving it in?

I'm not sure I followed your comment about the resonance cap. Are you referring to the resonance feedback loop similar to the presence control but for low freq's? If so this is an older model (rev C) and does not have that feature.

Can you comment about the .001mF coupling cap on V4? Is this common before a cold biased stage in high gain amps?

Thanks a bunch

[Pedro Vecino]

You can raise the value of 470pF capacitor without problem. The same applies to the 6505+ (5150 II) compared to original 5150: has limited lows at that point. It will not spoil the texture if done discreetly.
I use a 1000pF plastic capacitor added (1470p) and the low content remains very fluid and fuller.
However, I leave the original value of the slope resistor because the change to 33K shifts the typical center frequency of the 5150.

[Tahoebrian5]

Interesting. I'm not sure how close the schematic is for the 6505 but adding a parallel cap is easy enough to try. I'll give it a shot. So are you saying you tried changing the slope but did not care for the results?

[Pedro Vecino]

Has different effect since one is "pre-overdrive" and another is after him.
Reducing the slope resistor to 33K you will find a emphasis between lows and mids but also shifts up the middle center frequency and alters the original balance of mids and highs. You can try it simply installing a 100K resistor in parallel over it and get 32K but I think that the original value, as in the SLO and Rectifiers, is part of the presentation of his sound.

[Tahoebrian5]

Ok I spent some time really listening to CH3 yesterday and I think a bigger problem than the thin low end is actually the lack of clarity. Looking at the schematic, it has six gain stages. I'm wondering if it would be worthwhile to bypass V5a and V5b which would bring it down to 4. This would be closer to a Soldano SLO.

[Tahoebrian5]

Ok, Ive got V5a and b bypassed. Wired the input to v5a directly to V6a and disconnected V5 from the signal path. What is surprising is I'm not getting much saturation even with the gain all the way up.. Kinda sounds like a jcm800 without a boost at bedroom volume. IT seems that this means most of the saturation was coming from the late stages. I would have thought the cold biased stage would be contributing more. So now trying to figure out where to find more gain.

[Tahoebrian5]

After studying the SLO schematic, and given that I need more signal strength. I think my next move is swap R63 out to a 1meg ohm.

[tedmich]

I find a nice adjustable NFB resonance presence circuit (like from a PV JSX) can do a lot of tone shaping, and its not the minefield that changing gain stages in an ultra high gain amp can be. Other people love a graphic EQ in the FX loop and that's totally noninvasive, tweakable and reversible.

[Tahoebrian5]

Some good thoughts there, I'm trying to keep changes to ch3 for now.