Yet another DIY EQP-1A equalizer

[Paul Fawcett]

Hi Again All,

Some of you may remember me posting here way back in the spring http://www.groupdiy.com/index.php?topic=44071.0 a build log about a DIY LA-2A compressor that I did as commission for a local music studio here in Richmond, VA.  It turned out working really well!!  And so, as it turns out,  I have been recently putting together a companion piece for the same folks... this one is a DIY version of the Pultec EQP-1A equalizer...also, I realize, well-trod territory around here... but at least I used a totally new layout for this, and incorporated (yes, I know it's probably overkill) DC heaters for the tube filaments.

The build went really smoothly, and I'm very pleased with the way the layout has came together -- it's rather different from (though intentionally not as compact as) Cayacosta's layout on RecProAudio. At any rate, I thought it was worth showing off a bit. I haven't been as good about posting the build log as I was with the LA-2A, but if you have an interest in this circuit, keep an eye on my blog (url down below)... with luck I'll have some sweeps and sound samples posted in a few days --- but for now, there's some exterior pictures and some gutshots of the assembled but not-yet fired up build. This has been really a fun one... What do you think?

Cheers,

Paul

http://wombatamps.blogspot.com/2011/12/black-iris-eqp-1a-complete.html

 

[radiance]

True DIY! Love it!!

 

[Paul Fawcett]

I had a chance to fire this up the other day, and it seems to be working really well, although the Hammond 270CAX transformer ends up delivering voltages about 25v lower than the specification. It's within less than 10% of nominal though, so nothing to get too bent out of shape about.

Naturally, the first thing I wanted to do was characterize the frequency response.  I'd like to give a shout-out to Holm Acoustics for their really fine HolmImpulse http://www.holmacoustics.com/holmimpulse.php freeware, which I discovered when poking around for tools to do this with just my sound card at home.

This software is evidently intended for characterizing speaker setups, but was pretty much ideal for this purpose.

I'm happy to report that the frequency response of the repro unit came very close indeed to the old ones that pultec published in the original users manual!

 

[evilcat]

Man it's a beautyful built ! Congratulations. I'd love to hear some samples...

Ben

 

[Paul Fawcett]

Man it's a beautyful built ! Congratulations. I'd love to hear some samples...

Ben

I'm working on that. I know that Cam started using it for work on a TV commercial spot the same day it was delivered.  The LA-2A I made for them before I know has been extensively used on a bunch of television commercials that have aired recently or are coming out soon - I really should start collecting a list and see if they are online.

 

[Paul Fawcett]

I had a chance to post a more complete wrap-up on the blog.... now guys, what piece of classic tube studio gear should I tackle next?  The EQP-1A and the LA-2A have whet my appetite! 

Blog entry: http://wombatamps.blogspot.com/2011/12/eqp-1a-delivered.html

(is there a way to in-line the links on this site?)

 

[Paul Fawcett]

A final update on this long completed project...

Evidently both the EQP-1A described here and an LA-2A-inspired compressor I did earlier for Black Iris have been seeing heavy use in recording music for television commercials.  My favourite though are the ads for Toyota's "Hum" campaign for the Prius.  Check out the complete update on my blog. I confess that it's quite gratifying to see & hear equipment I built being used in the hands of working professionals.