concert lead noise

[Johann]

I just got a concert lead from a friend of mine, and while it's a great amp mine seems to be very noisy.

when I turn it on I get a loud pop through the speakers, and when I play certain things through it(it seems to be some notes more than others) I can hear crackling through the speakers, and sometimes there is just general popping and other unusual noises.


I planned on taking this to a tech because I have some other stuff I need to get worked on as well, but I was just wondering perhaps if this is something that a good cleaning couldn't fix, or if there is a more serious problem here.

[JoeArthur]

The pop through the speakers is normal for most solid state amps - transistors do not require warmup and most of them do not have a standby switch so you don't hear the noise while powering on. Powering off can also produce a pop. It can be somewhat minimized by setting the volume controls to zero and unplugging any instrument.

Is this an older two channel or one of the newer single channels?

On the older two channel models, general crackling sounds on certain notes usually means one or more of the interconnecting pins/lugs between the circuit boards has become loose or otherwise faulty.

Dirt is usually the worst enemy of these amps. Unlike tubes, transistors usually work or they don't. Since you ain't complaining about things not working that is a good sign.

A good cleaning of the controls would probably make a world of difference. I don't know about the newer single channel models, but on the older ones the preamp circuit boards needed to be slightly removed for a good control cleaning - the pot opening is facing downward toward the circuit board. The pins and connecting lugs for the input jacks and bright switch need to be removed for clearance, then the control knobs and the nuts/washers on the controls since that is the only way of mounting used by the circuit board.

Trying to clean controls without doing this is only going to guarantee the cleaner is going to soak the board, very little of the cleaner will make it into the control body and in general is a futile effort at best.

I guess that is a long about way of saying make sure that your tech has worked on concerts before turning yours over to him. If he hasn't he can unintentionally cause other problems - like forgetting where pins need to be connected to having your amp start picking up local radio stations.

Let me clarify what the noise sounds like. If you unplug your instrument, turn the volume controls completely to zero, does your amp still make noises? If it does, does it sound like random low level crackles and popping along with hiss that comes and goes - like the sound you might hear from being by the ocean as the waves come in?

[Johann]

it's the older two channel model.


I suspected it might be wiring and just general filth, I'll have a look at the inside later and see what I can't fix up



and generally whenever I turn it on or off regardless of what's plugged in there is a pop, it just varies in loudness from time to time.



and really aside from the general hum of the amplifier, the crackling only occurs when I'm playing through it, and gets exponentially worse as I increase the volume. bass guitar is more of a culprit than normal guitar playing though, I've found.

[Johann]

I seemed to have somehow "fixed" the problem, probably just creating more in my ignorance 



I opened it up to have a look at it, and I didn't notice any loose wires or any remarkable dirt, for being a 72 this thing is spotless. then I had a look at the on/off switch and noticed this what appears to be a large resistor or cap hanging off of it, one side unconnected to anything, the other side to the switch. I touched it, and the lead was so brittle and old it broke off 



I feared this was going to cause some trouble, so I booted her up to see if it made things worse, and aside from the on/off click, it seems to play perfectly now, no more scratchiness at volume.


I've possibly just ruined it in my neophyte amp-tech role, but it seems to have improved now.

[Johann]

and now after putting the case on it it's back to the way it was.


it seems that when I really dig into it it makes more noise, I'm not entirely sure what the cause is now, other than a bad wire or something, as all the wires appear to be connected, the only immediate visual clue was that loose capacitor


edit: I've been thinking this had something to do with it for a while, so I took it off of my cabinet and laid it somewhere away from it where it wouldn't be vibrated by anything while playing, and it seemed to have stopped making noise. so it only produces the scratching noise when it's shook, so I just need to find the loose component or components that are causing the problems now

[JoeArthur]

Yes, it does seem like you have isolated the problem down to a physical intermittent.

There is a .047 cap between both sides of the AC line. Seems funny for it to be on the power switch, but heck I've seen funnier things. There should be another one on the common terminal of the polarity switch. Normally, the one across the powerline is also on the polarity switch, bridging both switched terminals.

If your controls are scratchy sounding, that could cause the problem. That would be my first guess.

My second guess would be the input jack connections to the preamp circuit boards, especially if it seems to happen, for example only when using the normal input but the brite input is fine.

What sometimes happens is someone decides to clean the controls, realizes the circuit board needs to be removed, and attempts to do so without removing the pin connections for the input jacks and treble boost switch. The input jack to board connections are the shortest, usually the yellow wire to the normal input jack and during the struggle to remove the board the female connector that slips over the pins gets bent out of shape or winds up with a split down it's side. Once that happens, they'll never make good contact again and they usually wind up having to be soldered.