Onboard Parametric EQ

Hi all,

I'm looking to cobble together a few circuits to approximate a Zappa-style onboard parametric EQ with a Dan Armstrong Green Ringer. I'm thinking of using this schematic from Electronic Soundmaker: http://www.muzines.co.uk/images_mag/articles/es/ES_83_09_parametric_e_4.jpg

And inserting the Beavis Audio Green Ringer: http://beavisaudio.com/schematics/Green-Ringer-Schematic.htm

I'm not sure if the Green Ringer should go before or after the EQ's input buffer. I'm also wondering how to power the Green Ringer at 9v when the EQ will use two 9v batteries for +18/-18v. Is it as simple as running the the positive and negative from one of the batteries?

Would anyone have any recommendations for a lower noise modern equivalent for the opamps? Would it be better to use a Jfet buffer from a noise standpoint?  Thanks in advance for any advice.[

SaintMangoes said:

I'm not sure if the Green Ringer should go before or after the EQ's input buffer..

Click to expand...

Try it first before EQ.

I'm also wondering how to power the Green Ringer at 9v when the EQ will use two 9v batteries for +18/-18v.

Click to expand...

EQ is powered with two 9V bateries. For GR powering just use +9V after SW1a.

Would anyone have any recommendations for a lower noise modern equivalent for the opamps?

Click to expand...

NE5532 and TL064 are just fine, IMO.

Thank you for your response! I'll try it out and see what happens.

SaintMangoes said:

I'm not sure if the Green Ringer should go before or after the EQ's input buffer.

Click to expand...

Note the input impedance of the parametric EQ is only 10k; a passive electric guitar pick-up will not like it.

Would anyone have any recommendations for a lower noise modern equivalent for the opamps?

Click to expand...

I think the original combo of 5532 and TL064 does not make sense. The TL064 has a very low current draw on the battery but is quite noisy. The 5532 is a low-noise type but has a large current draw. I think it would make more sense to use TL072's everywhere. The overall current draw would be similar and the noise level much better.
RC4559 is a better option, half the current draw and half the noise than TL072.

SaintMangoes said:

I'm not sure if the Green Ringer should go before or after the EQ's input buffer.

Click to expand...

It depends very much on what you expect in terms of sound. Since the Green Ringer is a non-linear circuit, its sound depends on how it is driven by the signal. OTOH putting the EQ after the octaver could help taming harshness.
All stompbox designers know that EQ is needed both pre and post processing. You need to experiment.
My typical set-up for this is a pair of graphic EQ's (Boss GE7) that I tweak till I get the desired result.
Most often I end up with a more or less fixed input EQ and a variable output EQ.