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electronicsman 15th May 2020 03:07 PM

EQ circuit modification
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So I have this parametric eq or bandpass type circuit. I am quite happy with the sound, but i would like to change one thing. I would like it to function in a way, so that when the potentiometer is set to zero (maximum value) sound comes trough unaffected ( no cut or boost). But when you start to turn the pot clockwise, you start to get a boost at the desired frequency. I would like a boost at 2 - 6 khz(somewhere in there) with a low to medium Q. (not so critical for my application).

I was wondering if any of you skilled gentlemen could help me make the modifications, so the circuit would suffice my needs. If you have some other circuit in mind that would do this i am open to suggestions.

Many thanks in advance.

wgh52 15th May 2020 03:23 PM

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Hi electronicsman,

the most simple and straight forward solution that springs to my mind is to "cut the 500k Pot in half", make one half variable, the other half fixed. Means in detail: Take a 250k Pot and a 250k fixed R in series and you're done. See edited picture attached. The order of Pot and R may have to be changed, I did not think that through...

Best Regards,

electronicsman 15th May 2020 03:29 PM

1 Attachment(s)
Thanks for a quick reply. If i understand correctly, means i need to do this.(in the schematic)

wgh52 15th May 2020 03:35 PM

Nope my friend, please review the attachment just posted.

electronicsman 15th May 2020 03:39 PM

Thanks 100 times. I am sort of new to electronics, so i really appreciate any help.

Best regards

wgh52 15th May 2020 03:48 PM

Well, no issue! My pleasure!

As you may see, by the fixed resistor you just enable the parameter Gain to only be varied over a certain range. In this case beginning "flat" at rightmost turned Pot position. If you reverse the R/Pot order, the flat response is at leftmost turned Pot position. In the case of the 500k Pot "flat" was at the middle position! You see: No rocket science here ;):D


electronicsman 15th May 2020 04:58 PM

Thanks for everything. One more question. As i understand this circuit will produce an output with a 180 degree phase shift. How could i make the output in phase with the input?

rayma 15th May 2020 04:59 PM

You can't, it inverts polarity by the topology. Follow it with a unity gain inverter to invert the polarity again.

electronicsman 15th May 2020 05:01 PM

Something like this?

rayma 15th May 2020 05:03 PM

That's a non-inverting unity gain circuit. This one inverts. Use equal resistors for unity gain.

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