Anyone tried a treble boost with opamps?

[Steben]

You know....
Inverting stage, low input impedance with typical cap,.... some single-ish diode in the loop etc ?

[Processaurus]

As drawn the the input impedance would be much too low for guitar, the "virtual ground" you see at the inverting input means the guitar would see a 5K impedance.  You don't see a lot of inverting opamp configurations as the front end of effects for that reason- to get a modern high impedance input you would need at least 500K apiece for the pair of resistors setting the gain, which tends to get noisy.

I guess you could intentionally load the pickups with a low impedance input, like the Rangemaster (50K for R in, 1M for gain pot in feedback loop), and get what amounts to an interesting eq curve doing a muddy sound (tone sucked pickups loaded by the low Z input) into a treble boost (the rest of the circuit), but, the sound totally changes if you run any effects or buffered pedals ahead of it, or you change guitars.  There are more consistent ways to get that sound, without torturing the guitar  signal.

Easy enough to use a non inverting opamp for the input, and get a high Z input. You could do a little input cap on an MXR microboost (non inverting opamp configuration with variable gain) and get a treble boost.  Or do a unity gain non inverting buffer in front of your circuit here.

[anotherjim]

What you have may also be a radio receiver - a feedback cap <100pF is probably called for to counter that.

An input cap "may" be sized to have some k-ohm of impedance below 5Khz. A 470pF is worth over 60k ohm at 5Khz and can only have higher impedance below that -  some MegOhms down at 50Hz!

As I understand it, the Rangemaster is more of an upper mids peak booster. At the very high end, the input cap impedance is low and the pickups Hf output is loaded down by the low resistive impedance so it's not in practice a simple high pass boost.

[Steben]

I guess you could intentionally load the pickups with a low impedance input, like the Rangemaster (50K for R in, 1M for gain pot in feedback loop), and get what amounts to an interesting eq curve doing a muddy sound (tone sucked pickups loaded by the low Z input) into a treble boost (the rest of the circuit), but, the sound totally changes if you run any effects or buffered pedals ahead of it, or you change guitars.  There are more consistent ways to get that sound, without torturing the guitar  signal.

Indeed. Rangemaster is the target.
I get what you mean. But striving for more consistent ways usually lead to a dominance of digital. And a fuzz face is all about inconsistency.
On the other hand, why not stick to a BJT I hear you thinking.... 

[ElectricDruid]

It should be possible to copy the Rangemaster's frequency response with an op-amp. And you could even copy the response you get when connected to whichever guitar is supposed to work best, since they won't all be the same.

About the only thing you wouldn't get would be the subtle (ok, sometimes not so subtle) distortion. But there's ways to do that too, if required. A really clean Rangemaster-style booster might be a good thing though.

[Steben]

It should be possible to copy the Rangemaster's frequency response with an op-amp. And you could even copy the response you get when connected to whichever guitar is supposed to work best, since they won't all be the same.

About the only thing you wouldn't get would be the subtle (ok, sometimes not so subtle) distortion. But there's ways to do that too, if required. A really clean Rangemaster-style booster might be a good thing though.

Asymmetrical clipping is possible, in the positive "half" of output as drawn in my sketch.
The non-linear curve in the negative "half" is something else.

The main reason behind my thinking is consistent design. A generic opamp and generic diodes will give similar results in each "build".
If only scarcity was the reason, a silicon equivalent may suffice. One could even lower the bias resistor values slightly to aim for same input Z.

[Gus]

do a search for "brown source guitar effect""

[fryingpan]

Do a non-inverting buffer, then a low-pass filter with a 3-5kHz corner frequency (you could even make it sweepable), then the actual "treble boost" with some clipping built into it. You still only need one opamp chip (a dual opamp, of course).

[Steben]

Do a non-inverting buffer, then a low-pass filter with a 3-5kHz corner frequency (you could even make it sweepable), then the actual "treble boost" with some clipping built into it. You still only need one opamp chip (a dual opamp, of course).

You will loose the volume roll off effect ...

[fryingpan]

True. But you will gain much better versatility.

[Steben]

True. But you will gain much better versatility.

Or you can make the buffer switchable 

[Elektrojänis]

How about using non inverting opamp setup and make the resistor to ground variable? (Or "Vr"/"bias" or whatever it is called if using single supply.) That way you could tune the pickup loading for how you like it with whatever guitar you are using. It would still have to be the first in your effect cahin though to work meaningfully.

The suggested filter after the opamp stage would allow you to place it anywhere in the chain and control that top end. Is a simple filter the same as low impedance loading the pickup? There is always the cable capacitance and guitars tone control cap which could produce a resonant peak with the pickup and loading taht combination down could possibly affect that resonance in a different way than just a filter after the preamp stage. The difference is probaly very subtle though. (How low impedance input affects the guitars volume control is not though.)

[iainpunk]

heavy loading of a system, like with low input impedance, will negate any resonance by lowering the Q factor by a lot.

i build an opamp-based treble booste a few years ago, called it the 'terrible treble' booster. it had only one useful setting (maxed out), the rest was too fat and muddy.
it used a all-pass filter topology to boost frequencies above 1kHz, while also inverting those frequencies, resulting in a bit different sound to keeping the phase normal while boosting with the same amount. well, they sound the same clean, but the clipping characteristic of what comes next changes enough to make it ''open up'' in a cool way.

ill look for the schematics if i still have them.

cheers