What's taking out the input stage(s) of my power amps?

[cpizey]

I have 2 Peavey 2600 power amps. No problems whatsoever for the last 6 or 7 years.

Now, within a week of each other they have each developed what I assume are input faults, each on one channel only.

 

On the faulty channel I can hear output (speaker hiss, and also some noise when I turn/up down the volume controls on the amp).

When I switch the amp's built-in crossover out all is fine. But with the crossover switched in its as though there is no input.

There's also nothing coming from either of the through outputs (for feeding other amps), regardless of whether the crossover is switched in/out.

 

Set up is like this: desk (with various inputs and effects on sends/returns or inserts) to 2 separate graphics; then the outputs of these to inputs A nd B on the Peavey 2600.

The 150Hz crossover is switched in on the Peavey 2600 (as is a low cut, to get rid of the lowest frequencies).

 

Two questions.

1) What could be taking out the crossover? Where best to look first?

2) Would something like this isolator protect the amp and stop this happening again (once I get the amps repaired).

 

Thanks!

[vlfaudio]

Looking at the manual, the x-over is a low pass ie it cuts off frequencies ABOVE 150Hz as opposed to the low cut switch which attenuates frequencies below 40Hz: The through/out jacks also carry the low pass signal with the switch in. Likely nothing wrong with your amps at all.

 

Cut/Pasted from manual:- "With the switch IN, the input signals are routed through the crossover, and the low frequencies are

automatically sent to the corresponding channel. At the same time, the high frequencies are sent

to the HIGH OUT (18) jack and must then be patched to INPUT of the other channel of this amplifier

or to another amplifier input to complete the bi-amped system. Additionally, the low frequencies are

sent to the THRU/LOW OUT (17) jack, and can be patched to other amplifier inputs to permit even

larger systems"

 

I have 2 Peavey 2600 power amps. No problems whatsoever for the last 6 or 7 years.

Now, within a week of each other they have each developed what I assume are input faults, each on one channel only.

 

On the faulty channel I can hear output (speaker hiss, and also some noise when I turn/up down the volume controls on the amp).

When I switch the amp's built-in crossover out all is fine. But with the crossover switched in its as though there is no input.

There's also nothing coming from either of the through outputs (for feeding other amps), regardless of whether the crossover is switched in/out.

 

Set up is like this: desk (with various inputs and effects on sends/returns or inserts) to 2 separate graphics; then the outputs of these to inputs A nd B on the Peavey 2600.

The 150Hz crossover is switched in on the Peavey 2600 (as is a low cut, to get rid of the lowest frequencies).

 

Two questions.

1) What could be taking out the crossover? Where best to look first?

2) Would something like this isolator protect the amp and stop this happening again (once I get the amps repaired).

 

Thanks!

[cpizey]

Thanks for the reply. I am aware how the crossover (and low-cut) functions. There is no sound at all coming out when the crossover is switched in (not even 40-150Hz), so the amp is definitely faulty. After some advice from folk more knowledgeable than me, it turns out there is a chip that controls the crossover and low-cut, that has probably failed. The question is why. Cheers.

[KevinE]

Input circuits on amps often fail because something nasty has gone up the input XLRs. That could be static discharge, (unlikely in this damp weather) or an earth fault elsewhere in the system that has used the amps inputs as a route to earth. A popular way of doing it is a laptop where someone's cut the earth off in the mains plug or a mains cable where someone tripped over it and yanked the conductors or trapped a flex.

[Gareth Connor]

In the past 6 months I have had one Peavey 2600 amp as well as another manufacturer's amp come in for repair with this exact fault - one input stage failed. In both cases there were no obvious reasons for the failure and there were no other problems or faults with the amps. Replacing the failed parts cured the faults.