leitmo

Dual SS Pultec style EQ
« on: November 05, 2015, 01:03:26 PM »
Here's one of my last builds: a dual channel solid state Pultec style EQ.

The parts:

- https://www.don-audio.com/Classi-PEQ-Filter-PCB-Passive-Equalizer, Aaron is such a great guy and his products are top notch

- http://www.jlmaudio.com/shop/dingo-kit.html, trusty DINGO for I/O interface

- http://capi-gear.com/catalog/product_info.php?cPath=71_72&products_id=136, 2520 input opamp

- http://capi-gear.com/catalog/product_info.php?cPath=71_72&products_id=169, 1731 output opamp followed by

- http://capi-gear.com/catalog/product_info.php?cPath=21_37&products_id=437, great output transformer. Rich and dense sound

Front panel came from Schaeffer (FPE for US guys)

Knobs from http://www.musikding.de/ and http://www.banzaimusic.com/

I really like how sweet it sounds, everything sounds better and more finished through it even with subtle cut and boost.

This EQ is really good handling harsh recordings (i mean this kind of harshness that bites you in the ear).






leitmo

Re: Dual SS Pultec style EQ
« Reply #5 on: November 05, 2015, 01:07:11 PM »
switchable PEAK / SHELF hi boost...really makes a difference

weiss

Re: Dual SS Pultec style EQ
« Reply #6 on: November 05, 2015, 02:36:36 PM »
Very nice! :)

groselicain

Re: Dual SS Pultec style EQ
« Reply #7 on: August 12, 2019, 08:40:48 AM »
switchable PEAK / SHELF hi boost...really makes a difference

Hi there! Could you ever explain how you're getting shelving? I've searched and searched but I can't seem to find an explanation anywhere. Thank you!

Re: Dual SS Pultec style EQ
« Reply #8 on: August 13, 2019, 11:17:04 PM »
Hi there! Could you ever explain how you're getting shelving? I've searched and searched but I can't seem to find an explanation anywhere. Thank you!

Take a look at the Helios EQ high boost section of the schematic.  It's shifted up in impedance from the Pultec, but you'll see the general idea for a passive high shelf.   Another one to look at might be Ian's REDD type EQ  which is shelving.
Basically, you would end up not using an inductor.  The response is created with the cap acting against the increasing resistance from the pot (10k on a Pultec) creating a "pole", albeit one that is moving around as the pot value is changed.    However, in order for it to be a "shelf" response and level off at some determined frequency, rather than continuing to rise indefinitely, there needs to be a "zero" added to the pole created by the cap and pot.  This is done with a resistor in series with the cap.

Someone may come along who's done this and can give you values etc. but a good way to get the info, without doing all the maths, would be to use some sort of simulating software on your machine and start plugging in values. 
 

leitmo

Re: Dual SS Pultec style EQ
« Reply #9 on: August 14, 2019, 01:49:08 AM »
Hi there! Could you ever explain how you're getting shelving? I've searched and searched but I can't seem to find an explanation anywhere. Thank you!

For peak/shelf just bypass inductor in hi boost


Re: Dual SS Pultec style EQ
« Reply #10 on: August 14, 2019, 10:26:37 AM »
For peak/shelf just bypass inductor in hi boost

Yes, that's the jist and short form of it.
Keep the bandwidth control to use as the "zero" for the shelving off.  Adjust to taste.  Hit "record".