Aphex EQF-2 Transformer issue

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Marcocet

Well-known member
Joined
Sep 27, 2004
Messages
241
Location
Brooklyn, NY
So I picked up a bunch of Aphex EQF-2 500 series eqs. None of them have the optional transformer. Online I saw Avedis post about adding 2503s to his so I figured I'd give that a shot and ordered some Ed Anderson clones. In retrospect I could have gone with stock or a matching cinemag but I figured I'm throwing them in an API desk lets see how they like the API iron.

They don't, and I can't see why. Basically I'm getting a ton of low end roll off on the one I modded. I've included the manual which has directions for wiring up the transformer but I followed them exactly. Right now I just modded it back to spec but I'm hoping someone here will have some hints for a relative newbie like myself.

Thanks.

-marc alan

http://www.pupcostudios.com/documentation/PDF/EQF-2docs.PDF
 
What is the output impedance of this Aphex unit prior to the transformer?

If that's ok, then make sure you have your primaries and secondaries wired in phase.
 
Schematic here:  http://timbryson.com/images/linked/EQF-2docs.PDF

I'd reckon it should be ok probably, although I don't know the exact specs of the transformer in question.
 
It looks like the original Jensen it calls for was 66.7:600 and 1:3. Knowing very little about transformers is there any way I could make the 2503s work in this configuration?

Thanks so much

 
Okay, I'm starting to figure this out. It appears that it's possible to wire the 2503 as 75:600. However I haven't been able to track down what I need to do wiring-wise to change the secondaries impedance. Any help would be extremely appreciated. Thanks again so much.

 
api01.jpg


look at the diagram for the 2503 - the colors on the 2503 match the colors for the original part.  wired like that it should be ~75:600, but it is a very inexact spec.

[edit]

looks like marc probably has the transformer hooked up as suggested in the schematic, which is pretty much identical to the output of a 312.  first thing to check: is there any DC present at between R146 and ground?  that could cause the bass droop problem.  if there is any DC, stick a ~1000uf/16v cap between r146 and the brown lead.  this seems unlikely, as it would put DC on the unbalanced output without the transformer.  but maybe there is a cap there already, not indicated on the schematic?

if there is no DC, it may be that the output stage simply doesn't have enough current to drive the transformer.  you might be able to get away with using two windings in series for primary and two for secondary (all four windings are identical, so it doesn't really matter which ones you use).  this would give you a 1:1 ratio output.

ed
 
Ed, as always you rule. That's exactly what I've been looking for. Thanks so much!

-marc alan

EDIT: yes, there is a cap not on the schematic and yes I was leaving it. Glad to know why it's there though.

 
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