Sv: [sdiy] parametric eq schematic ?

[Michael Schulze]

Also check out Tom Jung's book IC OpAmp cookbook for a full explaination
with schematics.  May be out of print but I think it's a SAMS publication...

> From: <cfmd at swipnet.se>
> Date: Mon, 15 Jul 2002 17:55:54 +0200
> To: markus <n0nspaz at mindspring.com>, synth-diy at dropmix.xs4all.nl
> Subject: Sv: [sdiy] parametric eq schematic ?
> 
> Dear Mark,
> 
>> someone has asked me to make a three-band parametric EQ optimized for
>> guitar. as i am not skilled enough to design one, i am having trouble
>> finding a suitable design to work from.
>> 
>> could anyone direct me toward a schematic (preferably with explanation or
>> instructions) that is public domain or that i could license for this
>> purpose ?
> 
> A fully parametric EQ can you build by using a number of parametric bandpass
> filters, such that you can adjust the frequency and Q value. State variable
> filters have become popular in professional EQs. If you look at my page
> 
> http://home.swipnet.se/cfmd/synths/schematics/
> 
> You will find at the bottom a simple SVF which can be used. The schematic is
> over at
> 
> http://home.swipnet.se/cfmd/synths/schematics/svf1.pdf
> 
> Feel free to use! It's a crude schematic which isn't optimized. I put it up
> since people where nagging that these things where SO difficult to make, when
> they infact are not. I've cooked up things according to similar design with no
> major problem.
> 
> To make a 3-band full parametric EQ you take three SVF, use only the bandpass
> output. Feed all three of them with the same input signal. Feed the bandpass
> output to the central tapper of a pot, and each end is wired through a
> resistor to either the positive or negative mix-bus. The mixbuses is built by
> using resistor in negative feedback over an op-amp and the input of this
> buffer is from the three bands of each side. You feed the output of one buffer
> through a resistor to the other buffer, so a diffrentiation is achieved. The
> input signal is feed to one of the buffers through a resistor. An input buffer
> should naturally be used.
> 
> The pan-pots on the output of each band will set the peak/dip amount for that
> band, the Q-pot will naturally set the Q-value for the range and the
> double-ganged frequency pot of each band naturally sets the peak/dip
> frequency. The resistors at each end of the pan-pot will naturally set the
> maximum peak/dip values.
> 
> I am not back at home, so I can't draw a fancy schematic, but if you can hold
> your horses some, I could calculate some good values for you at least.
> I'll be back at home at least for the weekend.
> 
> Cheers,
> Magnus
> 
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