Fully parametric EQ schematics
« on: October 09, 2017, 09:08:00 PM »
I'm looking for schematics for fully parametric EQ's from high end audio gear. I'm attempting to build a 5 band EQ with controls for frequency, bandwidth, gain and individual band bypass switches. Thanks!


L´Andratté

Re: Fully parametric EQ schematics
« Reply #1 on: October 10, 2017, 01:51:34 AM »
Check Steve Dove´s Studio Sound articles I think they are in the in the GDIY archive!
"Why not get an assistant to work the faders? Real vintage! And maybe cheaper... ;)"

iampoor1

Re: Fully parametric EQ schematics
« Reply #2 on: October 10, 2017, 02:56:24 AM »
Fred Forssell has a paper on it, and the Urei 545 is a good state variable schematic to follow thats pretty easy to mod. Barry Porter
s Net Eq is fantastical as well. :D

Re: Fully parametric EQ schematics
« Reply #3 on: October 11, 2017, 08:51:53 PM »
Grabbed the Steve Dove articles, that mostly appears to cover mixer design which is a useful subject to read about anyway. The Urei 545 schematic is a great resource. I can't seem to find a schematic of the Barry Porter NetEQ. I'd prefer to stay away from switched knobs and use a potentiometer instead for sweepable control over each parameter.

bruno2000

Re: Fully parametric EQ schematics
« Reply #4 on: October 11, 2017, 10:13:49 PM »
Grabbed the Steve Dove articles, that mostly appears to cover mixer design which is a useful subject to read about anyway. The Urei 545 schematic is a great resource. I can't seem to find a schematic of the Barry Porter NetEQ. I'd prefer to stay away from switched knobs and use a potentiometer instead for sweepable control over each parameter.

If you can't find the wonderful Barry Porter EQ schematics, you're not looking very hard. 
My $0.02.
Best,
Bruno2000
https://groupdiy.com/index.php?topic=33256.0
« Last Edit: October 11, 2017, 10:16:55 PM by bruno2000 »

abbey road d enfer

Re: Fully parametric EQ schematics
« Reply #5 on: October 12, 2017, 12:58:59 AM »
I'm looking for schematics for fully parametric EQ's from high end audio gear. I'm attempting to build a 5 band EQ with controls for frequency, bandwidth, gain and individual band bypass switches. Thanks!
All good parametric EQ's use the SVF topology, with the exception of the GML/Sontec/MEP that uses bridged-T.
I suggest you have a look at the dbx 905 that solves elegantly the issue of RevLog pots, by usin law-steering on linear pots. Only the SVF topology allows that.
The only flaw in the 545 is the use of 4741's, which was all that was available at the time. Today there are much better opamps; noise is a serious issue in SVF filters.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

L´Andratté

Re: Fully parametric EQ schematics
« Reply #6 on: October 12, 2017, 01:35:47 AM »
The Steve Dove articles contain exactly what you asked for: fully parametric five band eq schematic including individual i/o, based on negative impedance converters, which Fred Forssell also mentions in his paper. ;)
"Why not get an assistant to work the faders? Real vintage! And maybe cheaper... ;)"

abbey road d enfer

Re: Fully parametric EQ schematics
« Reply #7 on: October 12, 2017, 03:43:41 AM »
I'm attempting to build a 5 band EQ with controls for frequency, bandwidth, gain and individual band bypass switches.
I've always felt individual bypass switches to be useless in practice. EQ ON/Off is much more useful IMO.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

Re: Fully parametric EQ schematics
« Reply #8 on: October 13, 2017, 09:38:06 AM »
I found this page after a bit of looking around Google: http://sound.whsites.net/articles/state-variable.htm#s30
In figure 5 there's a schematic that would suit my needs, but I'm a bit unsure how to calculate the values for C2 and C3 to adjust the frequency range.

abbey road d enfer

Re: Fully parametric EQ schematics
« Reply #9 on: October 16, 2017, 01:58:56 PM »
I found this page after a bit of looking around Google: http://sound.whsites.net/articles/state-variable.htm#s30
In figure 5 there's a schematic that would suit my needs, but I'm a bit unsure how to calculate the values for C2 and C3 to adjust the frequency range.
the highest frequency Fmax (frequency pot Full CW) is governed by f=1/2.pi.RC (R being R9/10, C being C2/3).
The lowest frequency is a fraction of the highest frequency
Fmin=Fmax(R12//R9)/(R12//R9+R10), with R12//R9= (R12.R9)/(R12+R9)
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.


gyraf

Re: Fully parametric EQ schematics New
« Reply #10 on: October 23, 2017, 11:15:32 AM »
I think the Focusrite ISA's worth mentioning here, as she also uses linear pots for frequencies - https://groupdiy.com/index.php?topic=44818.0

The (attached here) Tantek (HomeStudio recording DIY rack module from late 1980'es) is on same principle..

Background: http://www.muzines.co.uk/articles/stack-in-a-rack/1949

Jakob E.
« Last Edit: October 23, 2017, 11:23:08 AM by gyraf »
..note to self: don't let Harman run your company..