Possible to change a presence pot to work as a mid cut knob?

[Anonymous]

On my 2 channel TR I rarely, if ever, have the presence pot out of 0. At this level, is that equivalent to taking it out of the circuitry? If so, I'm curious if it's possible to find a pot voiced at around 480Hz that can function as a mid cut. That would be incredible!

If it isn't equivalent to taking it out of the circuit, and if such a pot exists, would it be possible to daisy-chain a knob in somewhere? I have the Diezel Herbert in mind when I ask this, and I don't want to use the FX loop because I've never been satisfied with the coloration it brings to my tone. Also, it would be less things to worry about when transporting the amp...

If you don't know, do you know where I might be able to find this out, or if a call to Mesa might be helpful?

Thanks!

 

[Chris McKinley]

That would definitely require a custom rewiring....not only of that pot, but of the sequence of all the pots in the tone stack. I would strongly advise against it, not because it would require radical customization, but because you are choosing one frequency in the low-mid range. If you absolutely had to have the mod done, at the very least I'd pick a different frequency like 200Hz to kill the mud, or 800Hz to replace the singing mids, or even 3.2kHz to clarify the overall mids and string attack. Preferably, I'd convert that knob into a parametric EQ so you could tailor it on the fly to each song rather than just have a low-mids boost/cut.

 

[coppa]

turning your presence all the way UP would be close to taking it out of the circuit so leave that knob there if you like the sound when the presence is all the way down.

leave it alone

I would sooner have the loop modded to get rid of the undesirable coloration, and run an eq in the loop if thats the effect your looking for.

 

[Anonymous]

turning your presence all the way UP would be close to taking it out of the circuit so leave that knob there if you like the sound when the presence is all the way down.

That's the way the presence pot functions for both channels? I know it's out of the loop when dimed on the orange, but I thought it was different on the red.

If you absolutely had to have the mod done, at the very least I'd pick a different frequency like 200Hz to kill the mud, or 800Hz to replace the singing mids, or even 3.2kHz to clarify the overall mids and string attack.

On a recording, use a parametric EQ with a high Q value and try cutting ~480 - 500 Hz. That's the kind of tone I'm looking for.

Thanks for the replies. Seems like it might be complicated, but I'm not really worried about that.

 

[coppa]

turning your presence all the way UP would be close to taking it out of the circuit so leave that knob there if you like the sound when the presence is all the way down.

That's the way the presence pot functions for both channels? I know it's out of the loop when dimed on the orange, but I thought it was different on the red.

That the way any passive control works. a pot is a variable resistor turning it up reduces the amount of resistance. Supposedly the only difference between the red and orange channels is that the presence pots are different values.

 

[Anonymous]

turning your presence all the way UP would be close to taking it out of the circuit so leave that knob there if you like the sound when the presence is all the way down.

That's the way the presence pot functions for both channels? I know it's out of the loop when dimed on the orange, but I thought it was different on the red.

That the way any passive control works. a pot is a variable resistor turning it up reduces the amount of resistance. Supposedly the only difference between the red and orange channels is that the presence pots are different values.

Right, but last I recall hearing, Mesa uses active controls. Or is presence different...?

 

[KH Guitar Freak]

Right, but last I recall hearing, Mesa uses active controls. Or is presence different...?

Never heard of Mesa using active controls on the Rectos before... :?

 

[coppa]

its passive

the presence cuts the highs after the preamp in the power amp section. I suppose you could replace the presence pot with a resistor of the same value then it would be locked in place in that one setting. it would free up the presence knob....

it sounds like you are talking about adding a contour control like the express amps that mesa makes have.

Why dont you email Voodoo mods or FJA or something and ask them what they can do for you.

I still think its a stoopid idea, but if you got the cash and you don't care. give er! :twisted:

 

[mr_fender]

The presence circuit in the Rectifier series is an interesting bird. Orange channel presence uses negative feedback in the power section to bleed off high frequency content before the phase inverter. The Red channel uses a simple low pass filter just after the tone stack to bleed off highs to ground and is not part of the power amp section at all. This is because the modern mode disconnects the negative feedback completely for a brighter and more agressive tone. In both channels, it's wired up as a variable resistor, so it would be fairly simple to replace the pot with a fixed resistor. You can't just cut the pot out in this case, because when the pots are set to "zero", the variable resistor is actually at its maximum value. The presence pot in both channels is a 25K pot, so you could simply solder a 1/4 or 1/2 watt 25K resistor in place of the pot to hard wire it to "zero". Just be sure to tape up any bare connections, or use heat shrink, to prevent any shorts.

As for a mid cut knob, you'd have to wire up a notch filter and insert it into the signal path somewhere. Could be done, but you're looking at quite a bit of work. It would be MUCH easier to just use an EQ pedal in the FX loop. Unless you use an active and properly buffered notch filter, you'll have much more tone loss than just using the FX loop. Using an active filter means you'll have to contend with the signal levels in that portion of the amp to avoid any clipping. By the way, unless you have the loop active master bypassed on the amp, all the FX loop components are already in your signal path.

 

[Anonymous]

The presence circuit in the Rectifier series is an interesting bird. Orange channel presence uses negative feedback in the power section to bleed off high frequency content before the phase inverter. The Red channel uses a simple low pass filter just after the tone stack to bleed off highs to ground and is not part of the power amp section at all. This is because the modern mode disconnects the negative feedback completely for a brighter and more agressive tone. In both channels, it's wired up as a variable resistor, so it would be fairly simple to replace the pot with a fixed resistor. You can't just cut the pot out in this case, because when the pots are set to "zero", the variable resistor is actually at its maximum value. The presence pot in both channels is a 25K pot, so you could simply solder a 1/4 or 1/2 watt 25K resistor in place of the pot to hard wire it to "zero". Just be sure to tape up any bare connections, or use heat shrink, to prevent any shorts.

As for a mid cut knob, you'd have to wire up a notch filter and insert it into the signal path somewhere. Could be done, but you're looking at quite a bit of work. It would be MUCH easier to just use an EQ pedal in the FX loop. Unless you use an active and properly buffered notch filter, you'll have much more tone loss than just using the FX loop. Using an active filter means you'll have to contend with the signal levels in that portion of the amp to avoid any clipping. By the way, unless you have the loop active master bypassed on the amp, all the FX loop components are already in your signal path.

Thanks, that's exactly what I was looking for. Seems like it would be easy to remove the presence pot, but very difficult to get a mid cut in. I thought it would be "cut and paste" in the signal chain, which it clearly isn't. I do have the loop set to bypass if that's what you meant.

Anyway, that definitely answers my question. Thanks again!

 

[fluff191]

Channel 2 pot is 25k and Channel 3 is 100K. I just changed mine out to match the 2nd channel.

 

[mr_fender]

This was for a 2 channel Triple Rectifier. In the older version, both pots are 25K (unless my schematic is wrong). The three channel heads are wired up quite differently with respect to the presence controls.

 

[mr_fender]

I do have the loop set to bypass if that's what you meant.

Yep. With it bypassed, the entire loop circuit is removed from the signal chain, including the 4th preamp tube. I see how you would notice a difference. I suppose you could swap a few components in the tone stack to tailor the midrange control to be closer to your desired frequency. However if you want the 400HZ cut in addition to the midrange control setting, that wouldn't work. You'd really have to add another filter section. Out of curiosity, what don't you like about the effects loop?

 

[Anonymous]

Yep. With it bypassed, the entire loop circuit is removed from the signal chain, including the 4th preamp tube. I see how you would notice a difference. I suppose you could swap a few components in the tone stack to tailor the midrange control to be closer to your desired frequency. However if you want the 400HZ cut in addition to the midrange control setting, that wouldn't work. You'd really have to add another filter section. Out of curiosity, what don't you like about the effects loop?

Seems to make the tone a little muddier. It's probably more that I have a lousy tube in V4 than anything else, but the reason I'd want to go with a pot swap is because though more difficult and permanent, it's cleaner and less circuitry. Plus, it would mean less things I would need to worry about in a gig situation.

I did mod my loop to serial, so I should probably give it another chance. I think once I switch out the tube to something a little better, and maybe even to a 12AY7 to give it less gain, I'll be in better shape.