Presence pot after the tone stack vs treble response

[temol]

I have a Marshall type tone stack that works in a normal way untill I connect presence potentiometer after the tone stack. Presence of a "presence" affects treble response.
What's the best way to prevent this? Output buffer or rescaling the tone stack?



T.

[JustinFun]

That's not a presence control. I don't think you can do a presence control without an output transformer (though others who know more may be able to prove me wrong).

What are you trying to achieve?

ETA - it does look similar to the dual rectifier presence control - maybe follow that more exactly?

[GibsonGM]

Traditionally, the Presence control was a feature of the Long Tailed Pair, and worked with (negative of course) feedback taken from the output of the OT.   

There are a few work-arounds, mainly to avoid needing feedback so you can simulate this...but what you're showing, Temol, looks to me just like a 1 knob tone control (hi cut).  So, it is naturally going to affect treble response in the tone stack before it!  I mean, you COULD throw a buffer right before it, but that really seems like a lot of work for little payback - it's not going to do much more than your guitar tone control!

The idea of presence controls has to do with attenuating high and upper mid freq's from the feedback path, allowing the PI to then achieve its normal gain for them and accentuate them.  Can't do that here, no matter how you slice it.

[teemuk]

IMO, when talking about "presence control" in general, one can't really make any assumptions about the control's circuit topology. The term merely refers to a control that operates at certain range of (upper higher) frequencies that enhance the sense of sound source's "presence". In acoustic terms we can even pinpoint an effect that attenuates higher frequencies more than lower frequencies when distance to sound source increases. So it all makes perfect sense. Sound source sounds more "present" with enhanced upper higher frequencies and less present when those frequencies are attenuated. All mixing engineers are aware of this effect too.

Naturally there are dozens of circuit topologies that can be employed to control upper higher frequencies and yes, the active one in negative feedback loop of a power amplifier is an extremely popular one. But equally we can find several good examples of "preamp-based" presence controls, whether active or passive. Even combinations.

---

Back to the topic. The impedance of the Presence control in OT's post is very, very low compared to output impedance of the tone stack circuit. Basically the 1M ground reference resistor is in about proper range, but the presence control presents only an approximately 20K and up (frequency-selectively) impedance and thus severily "loads down" the tone stack circuit, effectively causing a shift in its frequency response.

If you want these controls to have less interaction the presence control shouldn't load the tone stack circuit, so yes "rescaling" one of the circuits is one option, a buffer stage between the presence control and the tonestack is another one.

[PRR]

Names aside: you have a 20K pot hanging off a 250K pot. You are sure to have a lot of "interaction", and probably in the direction of "tone suck".

FWIW: I would call that a plain treble-cut. Not even a cut/"boost" like the main stack does.

In wide-band audio, "presence" is between Mid and High. Guitars are narrow range and it is hard to slot more curve-kinks in there. The 5F6a "presence" does bend the highs a little different than the tonestack Treb knob, AND it screws-up the power driver balance in the top of the audio band giving a change of distortion flavor. I don't think there is any simple way to emulate a 5F6a's Pres knob without stealing large chunks of 5F6a (including the glass).

[GibsonGM]

IMO, "Presence Control"...Historically...Fender...long tailed pair, feedback loop.  Not just "extremely popular", that is where it started.  The rest descend from it.   That's all.

Yes, you can jam another control after a tone stack and call it presence if you like, as long as you ensure they won't interact.  As shown, they interact.

[thermionix]

Temol, who is that in your avatar?

[JustinFun]

Temol, who is that in your avatar?

It's Peter Sellers in Dr Strangelove, isn't it?

[temol]

thermionix - it's Dr. Strangelove

Back to main topic..

I'm not sure how to call this type of additional tone adjustment. On most of the schematics I  have, it's just "presence". I attach parts of a schematics.The one I've asked about, it's upper left schematic (seventheaven). Below, there is a tone stack from dr Boogie. The other two... do not remember (I've made this comparison some time ago, and simply forgot to post it here).
I've built all of them and only 7thvn is problematic. I think I'll try both - rescaling and a buffer.




T.

[J0K3RX]

Try this
https://www.dropbox.com/s/0d4pimt44x8o39i/Tonestack%20-%20Presence.jpg?dl=0

[thermionix]

It's Peter Sellers in Dr Strangelove, isn't it?

thermionix - it's Dr. Strangelove

C'mon now...Duck?!  Help me out!