low volume from mixer amp

[jimbo123]

Hi all. got a problem with my well loved studiomaster mixer amp.

its all working ok, But the sound output from the unit is very low. I have to push all the volume sliders up to get any volume , But the peak lights come on

have sent line in to the amps from a mixer & cd player and the output is ok, I have sent line out from the studiomaster to another amp & that seems ok

so why am I not getting the correct out put from the studiomaster

Its a studiomaster vision 8 mixer amp simular to the 708,

 

anyone got any clues please

[jamesperrett]

Dirty contacts on the connectors perhaps? I would guess that they are switched so that you can separate the mixer and power amp by plugging a lead into the appropriate socket so this switching could be faulty. Although I'd expect only one channel to go down at a time if this were the problem.

[S&L]

these sorts of mixers usually have amp volume/attenuator controls on their rear and separate from the faders.

I can't find any photos or details of the mixer mentioned but weirdly there doesn't seem to be separate amp and mixer output control. some do have overides to direct the amp output to auxs/alts/phones so it's worth checking if you DO have attenuation controls on the rear or a button that redirects the signal away from the amp.

if you could work out how to upload pictures of both the control surface and the rear we could eliminate anything obvious.

 

 

[MarkPAman]

…… so, following on from what James said, what happens if you put a link lead between the mixer out & power amp input sockets?

[Richard P-W]

Can't find a detailed enough picture online... Is there perhaps a button that makes the onboard amps into monitor amps rather than main output ?

[jimbo123]

Can't find a detailed enough picture online... Is there perhaps a button that makes the onboard amps into monitor amps rather than main output ?

 

there is no switch or button that would redirect output signal from mixer. all the graphic led's flash as normal. its as if the mixer is giving lower output to the amp

is there anything that maybe faulty that would drop the signal

and as you say conect leads from line out L & R to inserts L & R this I presume would overide the graphics control board & so I would be using just the channel I have cd line input conected to.

this would not cause any damage to the mixeramp it self would it?

 

Can't find a detailed enough picture online... Is there perhaps a button that makes the onboard amps into monitor amps rather than main output ?

 

there is no switch or button that would redirect output signal from mixer. all the graphic led's flash as normal. its as if the mixer is giving lower output to the amp

is there anything that maybe faulty that would drop the signal

and as you say conect leads from line out L & R to inserts L & R this I presume would overide the graphics control board & so I would be using just the channel I have cd line input conected to.

this would not cause any damage to the mixeramp it self would it?

 

I have taken some pictures of the amp Also have taken the mixer section screws out and lifted the mixer up so I could take some photo's

But I dont know how to upload them into this forum?

 

Will try linking line out to line on rear of mixeramp to see if I get full output

will let you know the outcome in the morning ( thursday )

[MarkPAman]

I have taken some pictures of the amp Also have taken the mixer section screws out and lifted the mixer up so I could take some photo's

But I dont know how to upload them into this forum?

 

See here :)

[jimbo123]

SORRY GUYS just done another test cd into behringer mixer into amp inserts & guess what? the volume is still low

I dont know why I thought they were ok..

So....it looks like the problem is with the amps, there are 2 x amp modules. these are fed from mixer down to insert board then into power supply with ribbon type cable connectors

from the power supply board there is a small ribbon cable that connects to each amp module. I dont know if the audio section is anything to do with the power supply

will do a bit of inspection, I can trace back from the inserts to the ribbon cable to locate Lt & Rt pins on the ribbon

cant think its the amps, because its very rare you would have the same fault on both LT & RT channels?

But next thing I am going to do is check again line out into another amp, if thats ok then it will say the mixer section is fine....

be back soon

[Doug Siddons]

Jimbo123 where abouts in the UK are you?

[DrV]

SORRY GUYS just done another test cd into behringer mixer into amp inserts & guess what? the volume is still low

I dont know why I thought they were ok..

So....it looks like the problem is with the amps, there are 2 x amp modules. these are fed from mixer down to insert board then into power supply with ribbon type cable connectors

from the power supply board there is a small ribbon cable that connects to each amp module. I dont know if the audio section is anything to do with the power supply

will do a bit of inspection, I can trace back from the inserts to the ribbon cable to locate Lt & Rt pins on the ribbon

cant think its the amps, because its very rare you would have the same fault on both LT & RT channels?

But next thing I am going to do is check again line out into another amp, if thats ok then it will say the mixer section is fine....

be back soon

There is a circuit element which can affect both amps. There is a timer which monitors the incoming AC and acts as a quick reaction to a mains failure. The way it cuts the power to the amps is via a pair of signals called "control L" and "control R" which drastically reduce the gain of the input long-tailed pair. The only part of this circuit which is common to both amps is IC 5 and, more importantly, the electrolytics C34 (2.2uF) and C35 (10uF). If either of these has drifted low then it will keep dropping out between mains cycles. If you want the schematics PM me. If you want someone in Surrey to fix it for you PM me also!

 

Cheers

Dave

[jimbo123]

SORRY GUYS just done another test cd into behringer mixer into amp inserts & guess what? the volume is still low

I dont know why I thought they were ok..

So....it looks like the problem is with the amps, there are 2 x amp modules. these are fed from mixer down to insert board then into power supply with ribbon type cable connectors

from the power supply board there is a small ribbon cable that connects to each amp module. I dont know if the audio section is anything to do with the power supply

will do a bit of inspection, I can trace back from the inserts to the ribbon cable to locate Lt & Rt pins on the ribbon

cant think its the amps, because its very rare you would have the same fault on both LT & RT channels?

But next thing I am going to do is check again line out into another amp, if thats ok then it will say the mixer section is fine....

be back soon

There is a circuit element which can affect both amps. There is a timer which monitors the incoming AC and acts as a quick reaction to a mains failure. The way it cuts the power to the amps is via a pair of signals called "control L" and "control R" which drastically reduce the gain of the input long-tailed pair. The only part of this circuit which is common to both amps is IC 5 and, more importantly, the electrolytics C34 (2.2uF) and C35 (10uF). If either of these has drifted low then it will keep dropping out between mains cycles. If you want the schematics PM me. If you want someone in Surrey to fix it for you PM me also!

 

Cheers

Dave

 

Thanks for that Dave, I would be intrested in the shematics, jimbo11757@yahoo.co.uk

I,m a little too far away to get it fixed, thanks anyhow, I have located these caps & ic they are on the power supply board. I will replace these. is there anything that would make these parts fail

[DrV]

Thanks for that Dave, I would be intrested in the shematics, jimbo11757@yahoo.co.uk

I,m a little too far away to get it fixed, thanks anyhow, I have located these caps & ic they are on the power supply board. I will replace these. is there anything that would make these parts fail

 

They suffer from old age just like the rest of us. In fact what happens to electrolytics is that the electrolyte very gradually leaks out of the can and they dry out. Their capacitance falls and the internal resistance increases (the latter effect is not so important in this instance but the reduction in capacitance is, as it shortens the time-constant). Operating at elevated temperatures exacerbates the problem as it increases the internal pressure and they leak more quickly. This is why cap manufacturers quote a lifetime at a certain temperature.

 

Dave

[Electrolytic]

 

 

They suffer from old age just like the rest of us. In fact what happens to electrolytics is that the electrolyte very gradually leaks out of the can and they dry out. Their capacitance falls and the internal resistance increases (the latter effect is not so important in this instance but the reduction in capacitance is, as it shortens the time-constant). Operating at elevated temperatures exacerbates the problem as it increases the internal pressure and they leak more quickly. This is why cap manufacturers quote a lifetime at a certain temperature.

 

Dave

 

I can confirm this has happened to me...

[jimbo123]

Hi dave changed the ic for a new one & also changed the caps, just having a coffee then I will test it out....just tested the caps & if I have done it right the reads 10.4 & the other reds 2,8 uf ( got the tools but its me being unsure how to use them) but I try..

will let you know the out come?...

 

OK put it all back together & the problem is still there...BUT...I have put the amp modules in a different way..the one that was at the rear of amp I have put it at the front

Now there is only output from one side. but the sound is still low..why then if I reverse the amps I get both working but the other way only one amp works...?

This has to be a simple problem but I cant get my head round it.. is one of the amps faulty & causing problems..is there a component that feeds both amps with signal thats faulty more left than right. can only think of a ic preamp 4560

there is one on the power supply???

[DrV]

The 4560 on the PSU board is just part of the temperature sensing circuit. If you want to check the amps out separately you should be able to remove the fuses and ribbon cable for one half at a time and check the other half.

 

Dave