loud sound coming from haedphone out on mixer

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loud sound coming from haedphone out on mixer

Post by I'm Painting Again » Thu Mar 19, 2015 10:41 am

it's sending out a continuous full volume, very loud, sort of lowish tone

( 500 - 1kHz) I'm estimating..some random noise as well

it's there faintly when the mater faders are up, gone when down, no change when the channels are up or down..

any ideas of hat this could be?

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Post by Darlington Pair » Thu Mar 19, 2015 1:46 pm

From just the headphone, but not the main outs?

Possibly an oscillation from the headphone amp? Bad solder joint on a decoupling cap/bad cap somewhere around the headphone amp? Blown headphone amp? Depending on how the headphone amp is implemented (discrete, op-amp...) it could be any number of things.

The model and a schematic would be super helpful.

Shouldn't be too hard to find with that information.

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Post by I'm Painting Again » Thu Mar 19, 2015 7:40 pm

there's a little of it on the main outs but the headphone out is LOUD like generating a solid tone above +4 I'd reckon

its the Hill Multimix 16

http://www.oocities.org/thecongostudio/ ... manual.pdf

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Post by Darlington Pair » Fri Mar 20, 2015 6:47 am

Is there any change in volume with the headphone volume control? Is it in both channels?

I'm trying to figure out if it's happening before the headphone amp and being amplified by the amp or if the noise you hear in the main outs is just some crosstalk from what's happening with the headphone out.

Is the noise kinda broadband white noise or is it a solid tone? Also, are these the same headphones you've always used or are they new? The datasheet talks about oscillation with inductive loads, which headphones are.
Last edited by Darlington Pair on Fri Mar 20, 2015 7:06 am, edited 1 time in total.

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Post by Darlington Pair » Fri Mar 20, 2015 7:01 am

I would look for a bad solder, open resistor, or bad cap at C30, R55 and at C33, R52 from looking at the application note on the 2030 datasheet.

You can also look for a power supply oscillation at C40, C41, and C42 for the headphone amps.

Do you have an oscilloscope?

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Post by I'm Painting Again » Fri Mar 20, 2015 3:14 pm

no change in volume..only on the left side..nothing on the right with signal present..

it's a low pitched high amplitude tone that kind of purrs and clicks rhythmically even if that makes sense..

The scope I have is no good anymore IIRC

If techs did guess they might guess crosstalk

tried two pairs of phones both do the same exact thing..

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Post by I'm Painting Again » Fri Mar 20, 2015 3:16 pm

it's full volume no matter where the pot is and when the 1/4" is half clicked in it jumps to the right can for that brief moment..

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Post by I'm Painting Again » Fri Mar 20, 2015 3:18 pm

it's the same noise in the main out but you have to crank the output quite high to hear it..definitely seems like a symptom of crosstalk..you can hear a sound signal on another channel in the same manner.

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Post by I'm Painting Again » Fri Mar 20, 2015 3:19 pm

you can hear the sound faintly when you crank your monitors when the master faders are completely down as well..

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Post by Darlington Pair » Fri Mar 20, 2015 5:32 pm

I think we've narrowed it down to IC7.

Look closely at all the solders around it, my bet is on cracked solder on a resistor or cap leading to oscillation, possibly a open resistor, or bad cap, maybe a bad IC7

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Post by I'm Painting Again » Fri Mar 20, 2015 8:18 pm

I'll give it a peep..

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Post by I'm Painting Again » Sat Mar 21, 2015 2:57 pm

just gave a quick look to discover the master board is actually revision 3 not 2 lik ein the posted schematic.

also upon taking it apart and putting it back the problem went away and the jack functioned properly then after a while it came back..

I did not see any cold joints but I'm assuming that this could be the problem if it's intermittent like this, no?

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Post by Darlington Pair » Tue Mar 24, 2015 10:34 am

I'm Painting Again wrote:just gave a quick look to discover the master board is actually revision 3 not 2 lik ein the posted schematic.

also upon taking it apart and putting it back the problem went away and the jack functioned properly then after a while it came back..

I did not see any cold joints but I'm assuming that this could be the problem if it's intermittent like this, no?
Yeah, intermittent tells me it's a bad connection of some sort, most likely cold or cracked solder. If there's molex or ribbon cables try reseating them and see if it goes away, if it does then give them a good cleaning.

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Post by Drone » Tue Mar 24, 2015 5:36 pm

Anything where something is mounted to the chassis AND a PCB is a likely suspect too, physical stresses on these parts is higher.
The previous statement is from a guy who records his own, and other projects for fun. No money is made.

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Post by Darlington Pair » Fri Mar 27, 2015 8:58 am

Drone wrote:Anything where something is mounted to the chassis AND a PCB is a likely suspect too, physical stresses on these parts is higher.
What he said.

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