Caruso Pre Amp Feedback

[ilovedrums247]

hello,

Going through recalibrating my caruso preamp to a new PAS Audio 2002 Amplifier and running across a funny problem, maybe someone else has experienced it..

After setting gain with DRV to -10db on meter, when I increase FB i'll get a small gain reduction before it shoots into the red. It occurred with both dummy head and actual head and in both left/right channels.

I had help building the pre-amps from a forum member, whos a better electrical engineer then myself, and they were able to set it correctly with the old QSC GX3.

Also, Its noted in the PAS manual to "connect (2) signal and (3) ground in the XLR connector of the cable", but the back of the amp says (pin 1 ground, pin 2 +, pin 3 -)


Any ideas?

thanks

[leemichael]

Back of the amp is correct.

It’s industry standard for

Pin 1 Ground
Pin 2 Hot +
Pin 3 Cold -

This amplifier also seems underpowered for a cutter head.

[ilovedrums247]

Thanks leemichael for confirming the output wiring, the amp was recommended by Flo so giving it a shot…

More baffling to me is the feedback behavior, maybe there’s something I don’t understand. Why is it that adding more gain would cause to shoot into the red?

[flozki]

The PAS2002 performs very, very successfully in various studios. One of the best ones off the shelf for little money.
I cannot recommend the GX-3 anymore. Too much power, quality completely inconsistent. There were very good ones, very bad ones.
Often the devil is in the detail: cabling, RC network, quality of fuses, etc.
Did you check with the official dummy head? You should easily get –10 to –12 dB at 5 kHz and –28 to –29 dB at 1 kHz.
If you don’t reach this, don’t even think about trying with a real head.
but it could be that somewhere the phase is inverted. so a quick one to check.

[Loris]

Yes you should check if the phases are inverted first. I also had that kind of issue. I exchange + and - wire at the output of the power amp and that solved the problem.

Hope it helps.
Loris

[ilovedrums247]

swapping the speaker output +/- worked

thank you all for the helpful suggestions

[ilovedrums247]

While calibrating with the dummy head I’m only getting about 16db of feedback in both channels. (-10db from daw, amp gain max, going in steps of 10db as recommended)

From what I’ve read in previous posts this could be a phase issue, among other things..

Does anyone have suggestions where to look or what to try or measure?

[ilovedrums247]

For anyone else who's using a PAS 2002, what value did you use for R410?

[ilovedrums247]

Answering my own question, a 43k resistor solved the problem and now i'm getting -26db of feedback.

But now a new issue comes up...

When turning off the head via switch, is it normal for the amplifier to to suddenly get overloaded with signal?

The feedback meter is not showing signal but my overload LED on the amp lights up..

[flozki]

how is cutter off switch implemented?
maybe you send me a picture, schematic how you did by mail .
as long as you disconnect the drive line the head is always safe.

happy cutting f .