Passive Graphic Equalizer

[reubensm]

Was taking a look at the NAD C320's passive preamp. Was thinking of trying out a passive equalizer. This is an interesting circuit, take a look:

 

[IndianEars]

With an Op Amp delivering gain, hardly a passive circuit, na ?

 

[reubensm]

With an Op Amp delivering gain, hardly a passive circuit, na ?

The actual design is intended without the OP amp.

 

[greenhorn]

you would need a gain stage somewhere to compensate for the attenuation from the network right ?

 

[IndianEars]

Also will require a very low Driving impedance at the input, if it were Passive.

But yes, its a simple and elegant design where the Equalisation is done in the forward path rather than in the feedback loop.

I suspect that there will be a (undesirable) fairly large interaction between the various bands, as the Potentiometers in one Freq band are varied.

 

[reubensm]

I think, its more of a circuit idea than something which is workable, forward path eq results in gain loss to a greater degree. Would be interesting to use this with a preamp with the variable output levele (some preamps have separate preamp outs with hi level and low level options.

 

[kanwar]

Was thinking of trying out a passive equalizer. This is an interesting circuit, take a look:

Hi Reubensm,

The circuit shown by you is flawed, the 470k resistors driving a 100k pot................ a very impedance node loaded by low impedance

Much better to use a buffer and then drive the volume pot.




If you really want to see a proper passive EQ then have a look at this:

These are one of best ones from Pultec and are considered as rare gems among classic studios freaks. Many few possesses them.

Some Pro audio gear built using similar concept

REQ-2.2 Resonance Mastering Equalizer - Buzz Audio