Crossen Streams Studio

Classic audio recording, equipment restoration and construction

Andy Crossen
info@crossenstreams.com

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Crossen Streams Pultec EQP-1A Program Equalizer

This is my first tube project. My goal was to find as many of the original components as possible to duplicate the look and feel as well as the sound.




Transformer/inductor lineup:

Note that the Sowter is a repro Peerless S-217-D, which I plan to A/B test with the original.
The S-217-D is impossible to find with any regularity, so the A/B test should determine the original's contribution to the sound and whether it's in the "gotta have it" category.

UPDATE (03/19/08): David Geren from Cinemag noted that I had the part number incorrectly labeled for the inductor above.
CML-150T is the part number for the bare inductor, and CML-150T/TB (pictured above) is encapsulated in a shielded mu-metal can with threaded bushing.
The CML-150T/TB costs significantly more than the unpackaged version.
The unpackaged version is fine for most applications and should have no problem with interference from stray magnetic fields unless it's placed very close to a power transformer. I opted for the mu-metal can mainly for looks and ease of mounting.


Painting the chassis (hammered finish bronze for the chassis, and a custom paint color for the front panel):


7/1/07: Components mounted on painted and engraved front/back panels:

Unfortunately, though you can't see it well in the photo, my front panel paint was incompatible with FrontPanel Express's milling and engraving process. Some of the paint around the lettering has flaked off, while it's gotten blotchy from excess heat in other areas. Not to mention the metal shavings that embedded themselves all over the panel. All in all though, it's not too bad and I'm going to move forward with it after some detailing. :-)

Here are my FrontPanel Express design files for the front and rear panel templates: Pultec FPD templates.

Inside the rear chassis:


I've used turret boards like Cayacosta did for his Pultec clone, and per his design mounted the amplifier circuit on a pair of these on the back panel. The passive filter components will go on a long turret board mounted to the bottom of the case. The big 40uF/450V caps will get mounted similarly.




In the above photo the amplifier section is basically complete, and the filter section and PS electrolytics have been laid out in the bottom of the case.






The above photos show two views of the amplifier and filter sections completed. While unpictured, the front panel controls are also wired. Time to fire it up!




The front panel looks pretty good, despite my earlier concerns. I touched up some trouble spots with white paint, and gave the front panel a few coats of semi-gloss clear.
That evened out some of the smudging that occurred as a result of the FrontPanel Express milling process. I'm happy with it, and would even probably chance it again knowing I like this paint color.






Not having a real Pultec (and at last eBay's auction price of $7,700, I never will), it took some trial and error to lay out the rear panel correctly so that everything fit.
I modeled my rear panel after a photo of Dr. Pat's Pultec rear panel.




Here's a DIY'ed copy of the Pultec-style label they used to put on the rear. This will go on the back as a finishing touch.




Here it is in a homemade pine rack I built a while ago. It sounds great in initial tests. Check back soon for sound samples and listening tests pitted against an original!


NEXT UP:
1) Sound clips
2) A/B comparison between the Peerless original and Sowter repro output transformers.