Active EQ

Stompboxes circuits published in magazines, books or on DIY electronics websites.
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caspercody
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Post by caspercody »

If I wanted to use this tone control, but as a pedal, would I need to put say a buffer or something at front and end of this circuit?

Thanks
Rob
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Ichabod_Crane
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Post by Ichabod_Crane »

Yes, it's better put in front of it any input stage to set the impedance. A jfet preamp, an NPN or opamp stage should be ok.

Manfred
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Post by Manfred »

For which input level should the preamp in the front end designed, instrument or FX level?
I would recommend that you also hook in an output buffer circuit.

phatt
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Post by phatt »

Caspercody EQ circuitstock.png
Hi Casper,
a couple of observations and options you might like to try;
1/ This is a passive tone circuit.
2/ input buffer is not that important as it's a hi Z tone circuit anyway and as it's highly likely there will be pedals in front the buffer is not important.
3/ That extra treble control is of little use as it just fights the first treble control. A waste of parts.
If inserted *After* the opamp it can work much more effectively as a pressence control.
(See pics for clues)
Start with a 47nF cap and a 10k pot (might need log)
That way the treble will still boost at around 2~3kHz and presence will cut or boost above that freq. Much more useful. :secret:

4/ Add a ~470pF cap in the feedback loop otherwise you will have too much bandwidth at full treble and presence.
the 1uF at the input of opamp needs to be ~10nF which will help get rid of excessive bass.

5/ you can always add a 47nf cap at input to tilt the tone even more to cut excess bass.

Adding screen shots of what I'm talking about. I've over laid the mods curve on the stock pic to show how the presence works if inserted after opamp.
Of course breadbord it all before you commit as I've not built this ,, but I've built a heck of a lot of tone circuit so I'm fairly certain it will be an improvement. :thumbsup

Oh there are other mods but too late tonight,, bed time.
Phil.
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caspercody
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Post by caspercody »

Thanks Phatt.

Just so everyone knows, this is a tone stack from Baja on his ENG pedal. Not my design.

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