mixer output problems

[adam5365]

Bit of a newbie so excuse me if this a bad question

 

I work at a venue which has been having trouble with a matrix 1300 amp tripping off

We bought a new amp and during testing all seemed ok, but on Saturday night the output from the mixer stopped, when the spare mixer was fitted the needles on the meters on the new amp were hardly moving but there was ample sound from the speakers .

When we had the old mixer connected, for the same sound level from the speakers the needles on the meter were touching the red every now and then.

We cant stand the volume up high enough with the spare mixer to get the needles to swing as high as the old mixer.

Why would level meters show so high with only a relitively small sound output?

Was there something wrong with the old mixer or were we doing something wrong that killed the old mixer off?

 

 

Thanks Adam

[paulears]

sorry - but I'm really confused. You had an amp that tripped off? Meaning it died, or the power supply tripped off?

 

Then you talk about a meter on the mixer?

 

So the question is you have an amp (the new one) that doesn't produce much sound, but the mixer meters hardly move - suggesting the mixer has little or no output, but the amp is ok? So something is going on. If the other amp still functions, then you can prove the fault is in the mixer. We don't really have enough info to go much further.

[jayselway]

Hmm - I think I got the wrong end of the stick on this one....

 

I thought the OP was saying there was one amp, and two mixers, where one mixer was performing OK, but the amp went into protection, and then the second mixer was giving a healthy output but the meters weren't showing this, even though the amp was, quite audibly I gather!

[adam5365]

jay

youve got it!

Apart from the old mixer stopped outputting altogether. its almost as if the old mixer was driving hard into the new amp but not producing much sound but the new mixer is ticking over to produce the same volume.

Adam

[paulglave]

So your old mixer had a low output, meaning you had to run it hard to get any level into your power amp. and your new mixer has a higher output, meaning you don't have to push the levels so hard to get a good output to the amp. That's good. Maybe the output on the old mixer was unbalanced line level (-10db) and the new mixer has a balanced output at (4db). 14db is a lot, however you measure it.

[Simon Lewis]

Maybe the output on the old mixer was unbalanced line level (-10db) and the new mixer has a balanced output at (4db). 14db is a lot, however you measure it.

 

Actually, the difference between -10dBV ("consumer" line level) and +4dBu is 11.78 dB. However, it may still be a potential explanation to the OP's woes....

[niclights]

Adding to that, some amplifiers (and possibly the mixer) will have a senistivity switch on the back to match input/output levels (often -10/0/+4) - if so you can use these to get everything balanced properly again.

[jayselway]

OK, but lets say the mixer was "driving hard in to the amp, with low level output", it must have been driving something into the amp for the amp to register the high readings on its own meters....

 

Was the old mixer a balanced output? I'm wondering; if it was electronically balanced, and this stage started to fail, whether it could have a semi-cancellation effect, where the amp would register these higher levels without the resultant output being at all strong. In that case, I guess it would be possible for the amp to read the level from the desk, but the adverse balancing would affect the output.

 

Hmm - one to think about I think - cause surely if the output was low - say to -10dB, then the level would be lower, in it's entirety. That alone wouldn't make the meters of the amp show a high level, whilst keeping the output at a low level. DO you see where I'm coming from with that one?

 

Actually - an afterthought - could it be a situation similar to that of a bridged amp, where both sides of the amp are turned up - one side is inverted, so turning channel B up would actually reduce the output level, even though the meters would show the same level going into the amp. I've seen that happen a few times.....

 

Is the amp in question running in mono or parallel mode? I'm thinking if one output on the mixer became inverted due to a fault, it could possibly produce this effect....

 

Hmm!

[paulglave]

Maybe the output on the old mixer was unbalanced line level (-10db) and the new mixer has a balanced output at (4db). 14db is a lot, however you measure it.

 

Actually, the difference between -10dBV ("consumer" line level) and +4dBu is 11.78 dB. However, it may still be a potential explanation to the OP's woes....

 

I'd had a long day. I was just, like, explaining it in simple terms innit. As soon as you start saying the difference between -10 and +4 is 11.78, it turns into a physics lesson. :unsure:

[Simon Lewis]

I'd had a long day. I was just, like, explaining it in simple terms innit. As soon as you start saying the difference between -10 and +4 is 11.78, it turns into a physics lesson.

 

Fair enough.... but a decibel is not an absolute measurement, it is the log of a power ratio. Therefore, to quote actual audio levels it's necessary to state the reference. As soon as you do that, it's apparent that "-10" and "+4" do not use the same reference. This is pretty important when discussing amplifier input sensitivities.

 

I wouldn't call that a physics lesson, rather it is just being correct in one's terminology ;-) You could say it's the audio equivalent of spell checking !

[adam5365]

the old mixer out is balanced and is marked 0db.

 

the replacement mixer is line level out on phono

 

Quote:

 

"OK, but lets say the mixer was "driving hard in to the amp, with low level output", it must have been driving something into the amp for the amp to register the high readings on its own meters"

 

exactly the question I was trying to ask

 

the amp was definately set to stereo ( had probs with that on the old amp )

 

Adam

[notheruser]

the old mixer out is balanced and is marked 0db.

 

the replacement mixer is line level out on phono

 

Quote:

 

"OK, but lets say the mixer was "driving hard in to the amp, with low level output", it must have been driving something into the amp for the amp to register the high readings on its own meters"

 

exactly the question I was trying to ask

 

the amp was definately set to stereo ( had probs with that on the old amp )

 

Adam

Adam

anything out on phono connectors is likely to be "consumer", and will be -10dB

I'm not surprised to hear you had problems with that amp - we had a few which gave bother - opened them to find long uncut wire tails on PCB's, solder splash fragments and wire clippings kicking about inside, and very bad solder joints. Sent pictures to the manufacturer who didn't want to know, so we changed to Ecler amps and havn't looked back since.