MOTM

Hi,

while asking around about filters to be included into my proposed "famous 
fixed filters" PCB,
another idea came up, which has caused a lot of resonance so far:
People want a Moog(TM) parametric EQ.
(Moog is the registered trademark of Moog Music. The Moog Parametric EQ was 
based on a - now expired - patent of Dr. Moog and Norlin. AFAIK)

But just cloning that circuit woud be boring, and would require very special 
potentiometers.

So why not design something that is even better than the original, while 
still preserving the original's behaviour?
This leads to the voltage controlled M-Para-EQ.

The PCB would contain the electronics for the EQ, including the voltage 
controlled frequency sweep.
Everybody has the choice to build it as a voltage controlled device, or just 
like a "simple" Moog-style parametric EQ.

Options for Frequency control:

(F1) Voltage controlled sweep, either of individual bands, and/or of all 
bands with one CV. Manaul control of frequencies with ordinary linear 
potentiometer.
(F2) Manual frequency setting with dual 100k reverse audio taper (-log) 
potentiometers
(F3) Manual frequency setting with dual 100k audio taper (log) 
potentiometers.EMS-HiFli style front panel labeling that allows for high 
frequencies to be on the ccw end of pot.
(F4) 23-position rotary switch (as used in High End Audio Amps) for precise 
setting and recall of frequency, but without continuous sweep.
(F5) 23-position rotary switch for precice manual frequency setting, plus 
voltage control for continuous sweep.

Options for Bandwidth control:

(B1) 6-position rotary switch. (You can use a 23-position as well, but that 
would be overkill, IMO.)
(B2) Build your own special pot from a dual 50k log and a single 500R lin 
pot, and some adventurous transplantation.

Options for Cut/Boost control:

(G1) Potentiometer (no special type required)
(G2) Rotary switch (11-position or 23-position)

Any combinations of F, B and G options are possible, by just connecting 
different front panel parts to the same PCB.

Interested?

JH.

Interested, yes, but I have some questions:

1. Would it be possible to have voltage control of Bandwidth and Boost/Cut too?

2. How many bands per board? The original had 3 bands for the whole 
unit. Are you planning to do 3 bands on one board? Or is there any 
interest in 1 band per board (then builders can make up as many bands 
as they want)?

> 1. Would it be possible to have voltage control of Bandwidth and Boost/Cut 
> too?

This would be possible, but I'd leave the original Signal path, with all its 
special side effects, then.

>2. How many bands per board? The original had 3 bands for the whole
>unit. Are you planning to do 3 bands on one board? Or is there any
>interest in 1 band per board (then builders can make up as many bands
>as they want)?

I'll see how many bands will fit on a PCB. Hard to tell in advance.
Probably more than 3. But no promises.

JH.

At 8:20 AM +0100 11/30/07, JH. wrote:
>So why not design something that is even better than the original, while
>still preserving the original's behaviour?
>This leads to the voltage controlled M-Para-EQ.

Hmmmm. Wouldn't that naturally lead to the UN-fixed filter bank? What 
about a voltage-controlled "fixed" filter bank. It would have all 
eight bands of the fixed filter bank, but have the frequencies and 
maybe resonance of each be voltage controllable. It would end up 
being a pretty big module, what with all the pots and jacks, but 
think of the motion you could give to a sound with one of those!


        Seth