UTC 3AX Passive EQ

[River]

Is anyone familiar with this unit. Or the UTC 3A?

I've got one here but I'm not really sure how it should be hooked up.

This unit has an older 3 pin jack for both the inputs and outputs with dual Daven T Pads on the Inputs and Outputs. According to the only info that I can find online it's supposed to not have the loss that the 3A has.

Does anyone know what the hookup for this thing should be? I've tried every combination of pins but can't seem to make it work. I must be doing something wrong.

A Schematic would be fantastic, but I won't hold my breath...

Thanks!

Riv

 

[NewYorkDave]

Are the pins marked? Since it's three pins, they'll be Input, Output and Common. Even if they're not marked, it shouldn't be hard to trace them out.

The only info I could find on the 3A and 3AX is this catalog page:

http://www.festivalprojections.com/UTC/UTC_3AX.gif

 

[kato]

This thread may not help but it might interest you.

 

[Twist Turner]

The link to the resonant eq above(which I never did figure out how to hook up right) and the 3a are totally different Eq's. The 3a is my favorite Kick drum eq for getting a nice solid thump. Mine came converted with 1/4 jacks on it so I really couldn't tell you how it hooks up. I'll dig around and see if I have the manual in my files somewhere. I know I have some info on it somewhere.

Great find, hope you are able to figure out the hook up

BTW- I just checked my hard drive and all i have is a flyer for the 3a no hook up info.

 

[emrr]

[quote author="NewYorkDave"]Are the pins marked? Since it's three pins, they'll be Input, Output and Common. Even if they're not marked, it shouldn't be hard to trace them out.

The only info I could find on the 3A and 3AX is this catalog page:

http://www.festivalprojections.com/UTC/UTC_3AX.gif[/quote]



For that matter, it's very likely the device doesn't care which you use for input versus output. So you may only have to find the common, which may be attached to the chassis.

 

[tardishead]

revisiting an old thread.
I have just got a UTC 3AX eq and wanted to ask if anyone else out there is using these units.
They are awesome - they have a unique tone especially in the top end.

The insertion loss seems to be very big - in the region of 40-50db I believe.
Both bass and treble have 25db boost. I think the circuits are in series.
So I need a gain makeup amp to use these ideally. Is it better to put an amp before the eq or after. If after would you have a problem with NOISE?

 

[emrr]

after. think about it; +40db over 0 db at 600 ohms is +/-10 watts, and you are certainly blowing up the EQ at that point.

 

[Twist Turner]

A cool way to get around the insertion loss is get a couple of V74's. I bought a pair just to use with my passive eq's, kinda like instant Pultec on a budget.

 

[tardishead]

Just looked into the UTC eq again.

The bass and treble circuits are wired in series. There is 25db boost on each.
50 db insertion loss.
Can anyone recommend a really clean 50db make up amp??

 

[tardishead]

Dont know if anyone has dug up some more info on these - a schematic???

I have 2 of these each followed by RCA BA2c preamps for gain makeup.

There's one strange thing which happens with using this eq. When you dial in more treble the bass gets attenuated. Looking at the brochure it says that change in volume should be negligable due to compensating pads. I still dont know if I have this hooked up right. I have tried many different ways of connecting - out of phase, common tied to ground but nothing gets rid of this problem. Both my units came with the same wiring inside - a few years apart - as a stock unit it operates with common not tied to chassis.

Also I noticed with both bass and treble turned to unity - the unit is slightly brighter than it is out of circuit.

I have tried putting 600ohms from hot to common on the output. No effect.

Both act almost identical - frequencies are slightly different.

Should I put 600:600 transformers on the input and output??

Is it possible that these circuits are not in series but parallel and have some effect on each other. The ammount of treble definitely affects the ammount of bass aswell.

 

[emrr]

Don't know what is defined as unity with these, but can say that many EQ's like this measure most flat somewhere away from the designated 'flat' position. Not uncommon. Treble increase could be leakage, too.

Have you drawn it out?

Are your BA-2 circuits home made, and connected with 600 ohm windings? Or feeding a stock 250 ohm winding? Are the inputs terminated in 600 ohms, or do the EQ's take care of that? I see you played with 600 ohms.

 

[tardishead]

So it is a boost only eq - high and low with 2 davens 25db.

everything is encapsulated in wax so it is pretty hard to see exactly what is going on? I am working a few long days so i will attempt to trace it out sometime in the next few days.

 

[emrr]

Anyone know what the attenuators are for the 3A version (no compensating pads for unity eq reference)?  Are they simply Daven 500/600 ohm T's, in 1 dB steps?    I have the filters for one of these (simpler versions that only do 10dB max), but not the attenuators.  I would assume, when used between 500/600 ohm devices, a 5K rheostat with a disconnect switch would work fine for dialing up the resonant boost.

 

[tardishead]

Hey Doug
Yeh I think mine have 10k lin Davens as I remember - they are clickless.

 

[rackmonkey]

Did anyone ever get around to tracing either of these out? I’m racking up my 3A, and there are no connectors - just bare wire where the jacks/plugs once were. I played around with this unit and tested it a few years ago when i got it. But I was never quite sure I had it wired up as intended.

I think it’s safe to assume it expects 600 ohms in on the gain makeup amp. I remember i connected it to both an Altec 9475 and an RCA BA-2A strapped for 600 and it behaved more or less as I thought it might. Any experiences with it would be appreciated.

 

[!rob!]

I am wishing to swap out the pots for switched attenuators. Has anyone done this or have any insights regarding this?
Love the tone of these!
Thanks,,,