Angry Charlie presence mod

Started by harrisxr650, December 15, 2021, 04:15:09 AM

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harrisxr650

Hi people,

I'm building and angry Charlie clone with a pcb from Pedalpcb and i would like to add a presence control,

Can someone clarify that the resistor needs to be replaced with a pot is the R19 (6k8)?
Also what value and type the pot should be? 10k or 25k and A or B?

Thanks




antonis

#1
Usually, 5k/100nF product works well, so make R19 20k (combined with 22nF cap)

P.S.1
Isn't 3band Bax EQ enough for tone setting..??

P.S.2
IMHO, presence controls are more effective when inserted to NFB loop..
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

iainpunk

QuoteP.S.2
IMHO, presence controls are more effective when inserted to NFB loop..
better yet, they ''actually'' aren't presence controls at all if they aren't in a feedback loop of a power amp, they are just extra HIGH treble controls. a ''true'' presence control doesn't only control the top end frequencies, but it also determines the amount of negative feedback, and thus the onset point and knee of clipping in said amplifier.

cheers
friendly reminder: all holes are positive and have negative weight, despite not being there.

cheers

eh la bas ma

Here is a thread about presence control with links for more information :

https://www.diystompboxes.com/smfforum/index.php?topic=128126.0

Hope it helps
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"We must not confuse what we are and what society has made of us." Theodor W. Adorno.

pinkjimiphoton

i'd take the 22n on the end of it, and replace it with a faked variable cap.
put the 22n on pin 1, put like, a 100p or so on pin 3, join the ends together. take the node at r19 to the free ends of the caps, and the wiper to ground.
ya may have to reverse the outer pot pins.
that way, you can "fake" a presence control. as you turn it up, it will seem to get brighter. all the way down will be the stock circuit. you could also do this in the feedback loop of ic1 or 2, but it would sound more like a tone control than presence at that point.

you don't have enough stages to really do a presence control. normally, you'd take r19 and make it variable feeding back to the second stage,  but ya need another stage added i believe to keep the phasing right.
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iainpunk

Quoteyou don't have enough stages to really do a presence control.
the number of stages doesnt matter, its the kind of stage that turns a 'negative feedback control' into a presence control.
generally a gainstage with an early onset of nonlinearity and much midrange, so if the negative feedback gets increased, the output will clip later and with less midrange.

cheers
friendly reminder: all holes are positive and have negative weight, despite not being there.

cheers

pinkjimiphoton

Quote from: iainpunk on December 18, 2021, 02:58:53 PM
Quoteyou don't have enough stages to really do a presence control.
the number of stages doesnt matter, its the kind of stage that turns a 'negative feedback control' into a presence control.
generally a gainstage with an early onset of nonlinearity and much midrange, so if the negative feedback gets increased, the output will clip later and with less midrange.

cheers

i dunno bro, as i recall, the reason some tube amps don't have presence is there needs to be a couple stages difference to keept the phasing right, but i dunno if that applies here too.
otherwise, any kind of pot in a feedback loop would be a presence pot, no?
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iainpunk

Quote from: pinkjimiphoton on December 18, 2021, 03:02:57 PM
Quote from: iainpunk on December 18, 2021, 02:58:53 PM
Quoteyou don't have enough stages to really do a presence control.
the number of stages doesnt matter, its the kind of stage that turns a 'negative feedback control' into a presence control.
generally a gainstage with an early onset of nonlinearity and much midrange, so if the negative feedback gets increased, the output will clip later and with less midrange.

cheers

i dunno bro, as i recall, the reason some tube amps don't have presence is there needs to be a couple stages difference to keept the phasing right, but i dunno if that applies here too.
otherwise, any kind of pot in a feedback loop would be a presence pot, no?
no, not any pot, but any pot that takes a ''curvy'' nonlinear power amp, takes out some mids and makes it more linear without affecting to much of the overall gain, is a presence control. its this ''without affecting the overall gain to much'' part that makes a presence control what it is.

there are also lots of tube amps with feedback, but without a presence control. (vintage Fender Champ comes to mind)

lets not get hung up in these details and agree that a simple LPF is not a 'presence' control?

cheers
friendly reminder: all holes are positive and have negative weight, despite not being there.

cheers

pinkjimiphoton

a fender champ has presence? i don't even see a feedback resistor in it bro ;)



presence is just feeding back some of the output of the amp to a prior stage to help minimize distortion, last i checked.

In an amplifier, a presence control boosts the upper mid-range frequencies to make the sounds of voices and instruments with similar tonal ranges seem more "present". ... Increasing the presence resulted in there being less and less negative feedback on high frequencies. The effect varied according to amplitude.

Presence (amplification) - Wikipedia


What does a negative feedback switch do?
In a nutshell, negative feedback is incorporated in an amp design as a way to minimize distortion in the output stage of an amplifier. This is done by sending an out-of-phase signal into the phase inverter circuit, reducing its gain and, thereby, distortion.Jan 4, 2018

Ask Amp Man: Positively Negative Feedback - Premier Guitar


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iainpunk

Quote from: pinkjimiphoton on December 18, 2021, 05:12:06 PM
a fender champ has presence? i don't even see a feedback resistor in it bro ;)
what i said was that the champ (bar the 5C1) does have feedback, but no Presence control. that 22k from the output transformer going back to the 2nd half of the preamp tube, its even called ''R13 negative feedback''

presence is not the existence of NFB, its a specific form of negative feedback where high mids / treble is fed back less than the rest of the signal, which results in more high mids / treble coming out of the power amp. often this is done with a single variable LPF in the feedback loop

what im saying is directly based on what i have seen in schematics of amps and how i interpret the functioning of those parts.

for a NFB control to work like a presence control from a real amp, it needs to have influence over both high mids/treble and the onset of distortion.

also, to harrisxr650, sorry for derailing this thread. :icon_redface:
the cheese rolls downhill again

cheers
friendly reminder: all holes are positive and have negative weight, despite not being there.

cheers

pinkjimiphoton

hahah yer right ian, i didn't even notice that resistor on that one. it wasn't on the first example, but its all good. not picking on ya at all in any way, just sayin'

yeah, it works on the treble and mids cuz of being reversed in phase, it helps cancel frequencies out. a pot instead of a resistor just lets ya vary it. you can literally control the sound of the whole amp with that one resistance.
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"When the power of love overcomes the love of power the world will know peace."
Slava Ukraini!
"try whacking the bejesus outta it and see if it works again"....
~Jack Darr

iainpunk

Quoteyeah, it works on the treble and mids cuz of being reversed in phase, it helps cancel frequencies out. a pot instead of a resistor just lets ya vary it. you can literally control the sound of the whole amp with that one resistance
almost right, if i were to add a presence control to a champ:


(sorry for crude drawing, a touchpad isn't really meant for this)

cheers
friendly reminder: all holes are positive and have negative weight, despite not being there.

cheers

pinkjimiphoton

absolutely no worries ever, brother ian ;)
  • SUPPORTER
"When the power of love overcomes the love of power the world will know peace."
Slava Ukraini!
"try whacking the bejesus outta it and see if it works again"....
~Jack Darr

harrisxr650

Quote from: antonis on December 15, 2021, 07:02:54 AM
P.S.2
IMHO, presence controls are more effective when inserted to NFB loop..
My amp doesnt have a presence control so i thought it might be a good idea to fit one here :)


Quote from: iainpunk on December 18, 2021, 06:07:23 PM
also, to harrisxr650, sorry for derailing this thread. :icon_redface:
the cheese rolls downhill again

cheers

Naahh...just go on.. valuable information to a diyer with only basic electronics knowledge :)