Film-Tech Forum ARCHIVE: DCA 1622 hum

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Posted by Anhtu Vu (Member # 7689) on 12-05-2014, 06:50 PM:

Hi all,

I'm right in the middle of a huge and very important film fest and the center channel started emitting some hum. I narrow down to the center channel amp (DCA 1622) by unplugging the input cable.

Any suggestions as to what can cause an amp to suddenly start humming ??? we're kind of stuck as it's friday and there's no way i can can a replacement before monday. Thx

Posted by Marcel Birgelen (Member # 6801) on 12-05-2014, 07:00 PM:

Did you already try to swap it with another amp from e.g. your front left or right channel to check if the culprit is the amp or the input signal itself?

Posted by Marco Giustini (Member # 4544) on 12-05-2014, 07:02 PM:

If the amps hums with NO inputs (both channels) then you need a new amp!

Posted by Anhtu Vu (Member # 7689) on 12-05-2014, 07:55 PM:

@Marcel

As i mentioned in my message, i UNPLUGed the input signal cable….so without input signal and if the speaker still hum, the only culprit is the amp….

Posted by Marcel Birgelen (Member # 6801) on 12-06-2014, 03:17 AM:

Sorry, I misread this. Sometimes you'll get a noticeable hum if you mix balanced and unbalanced inputs, but if the hum is also there without an input, then the amp is indeed the only likely culprit.

How are you using the amp? Are you bi-amping the center speaker or do you also have another channel connected to the amp?

Is it a typical 50/60Hz hum? Did you check for obvious sources of a ground loop already?

Posted by Carsten Kurz (Member # 5396) on 12-06-2014, 05:04 AM:

What processor do you use?

First, swap the center input cable from your processor into an L or R amp and see if the hum goes with it. When you connect an L/R cable into the center amp and the hum stays on the center, then it's most probably a faulty amp.

How are the input connections to these amps made - connectors, TRS/XLR, or bare wires?

If the hum is there without any input connections being made, I suppose a capacitor went dead, which is sort of a typical issue.

- Carsten

Posted by Steve Moore (Member # 4753) on 12-06-2014, 05:59 AM:

It sounds like potentially a capacitor has failed in the amp. If you can't get it replaced before Monday, the only real solution is to swap if for one of the other amps (i.e a surround or sub amp) if they are the same model or approx. same power output. If they have gain controls, make a note of where they are set on each amp and swap them over.

In an emergency situation, I guess the dialogue is more important than surround.

Posted by Marco Giustini (Member # 4544) on 12-06-2014, 06:03 AM:

Did you unplug *all* the inputs?

Posted by Jarod Reddig (Member # 6363) on 12-07-2014, 02:42 PM:

If the speaker is still humming without a signal cable plugged into the amp try using a plug adapter on the amps power wire that omits the ground.

Posted by Marcel Birgelen (Member # 6801) on 12-07-2014, 04:08 PM:

quote: Jarod Reddig
If the speaker is still humming without a signal cable plugged into the amp try using a plug adapter on the amps power wire that omits the ground.

A word of caution about this: If your device isn't properly shielded (as in double shielded, like required in most countries to be allowed to work without a grounded power connector), you're creating a risk of electric shock here. And it's not just some stupid warning, like don't pull a plastic bag over your head. I've had the "pleasantry" of touching equipment that, if properly connected, would have caused the RCD to trip.

Posted by Jarod Reddig (Member # 6363) on 12-07-2014, 05:41 PM:

Its one way to isolate the amp to tell if it is the source of the hum. If one decides to operate his equipment hook-ed up that way then thats his own deal.

Posted by Anhtu Vu (Member # 7689) on 12-07-2014, 09:57 PM:

I replaced the amp with a 1222 re-calibrated the rig and finished the festival that way. A new 1622 is on order.

Posted by Jarod Reddig (Member # 6363) on 12-08-2014, 09:24 PM:

Nice to hear.