Distortionless Variable Equalzier

[mjrippe]

Found this file on my drive.  Passive "distortionless" EQ.  Don't know what book it came from but thought I'd post it here for discussion.

 

[ruffrecords]

Interesting circuit. I notice it has separate boost and cut controls for both bass and treble much like the Pultec EQP1A. Thanks for posting it.

Cheers

Ian

 

[thomasdf]

Interesting!
Since it is passive, I guess there is quite a level loss... Why use a pad on top of that?
Do you guys know what frequencies it would be working on?

What book does it come from?

Enough questions for today
Thanks

 

[Michael Tibes]

It is also interesting why it was considered 'distortionless'? At first glance it doesn't seem to be less distorting than any other passive eq? Maybe there's more information about it?
To me the pad seems to provide the necessary level reduction that is needed in order to 'boost' frequencies. a passive 'boost' in such an eq is effectively a 'cut less of certain frequencies'-function.

Michael

 

[ruffrecords]

Interesting!
Since it is passive, I guess there is quite a level loss... Why use a pad on top of that?

I think the pad is an integral part of it and represent the insertion loss when the controls are in the flat position. Parts of the pad get frequency selectively bypassed to decrease or increase the attenuation to provide boost and cut. That's basically how all my passive EQs work anyway.

Cheers

Ian

 

[gyraf]

1H2, 4uF - 72Hz

820mH, 2uF - 125Hz

6.6mH, 18nF - 4.6KHz

5mH, 14nF - 6KHz

Yes, the attenuator is for getting 16dB down, so there's room for 16dB boost.

It looks like high boost goes towards shelving at gentle boost settings and towards bell at high ditto..

"Distortionless" is probably the exiting name for "passive" - from a time where passive wasn't posh...?

Jakob E.

 

[mjrippe]

Jakob, my calculations gave the same values for Bass boost, but Treble boost came out as 14.6k and 19k.  Mine seem too high for typical EQs of the time, yours seem too low.  Is there another factor at work?

 

[gyraf]

I think your frequencies are at shelving (cap-only) and mine are LC. The circuit seems to go from shelving towards bell, following high boost amount setting..

Jakob E.