Static / hiss from Orange Crush 12L with nothing plugged in

[olucafont6]

I have an Orange Crush 12L that recently started making a hum / hiss / white-noise sound that gets worse when I turn up the volume, overdrive, gain, etc. It does this with or without a guitar / 1/4 inch cable plugged into it.

I'm assuming something got loose when the amp has been in my car - the problem went away randomly, but then came back when I took it in the car again.

I was able to take apart the amp and get the circuit board out, but I can't see any visible problems. I have a multimeter but not really sure what to check for.

I realize it's a very cheap amp, just wanted to see if it would be relatively easy to fix Thanks!

[Jon Snell]

Nice little practice amp.
Not a lot to go wrong here.
Without test gear, oscilloscope and the like, all I can suggest you do is firstly remove U2 and check for a clean no hiss in your speaker.
If it is no longer hissing, replace the Tl072/4558/4660 etc whichever it is using.

[Mick Bailey]

A fault that comes and goes when the unit is moved suggests a mechanical problem and it looks like some re-soldering has been done on the board.

There are a couple of areas that need looking at; on the picture of the copper side of the PCB, go to the 2nd pot from the left and the 3rd solder pad up from the centre of the pot has a hole where it looks like a component leg should be soldered. Also just a little lower to the left of this is a dry looking joint - the component leg has a gap around it and it may need re-soldering. Take a good look at the rest of the board to see if there are any other areas that are suspect.

[Mars Amp Repair]

Hello Olucafont6,
On some of the amps that are supported on one end by the pots, the rivet connections on the pot itself can become loose. To verify if this might be an issue for you, you can obviously (if you haven't already, wiggle the pots and twist them slightly to determine if the rivets have become loose. Note: the center/wiper rivet typically does not need re-tensioning. It is also the most difficult one to re-tension w/o damaging the phenolic wafer.
If this is the case you can very gingerly pinch the rivets to tighten them while being very careful to not break the brown phenolic wafer in the pot.
Other than that all the suggestions that the other dudes have suggested all sound good, too.
See attached pic.

[Mars Amp Repair]

Oops, here's the pic...

[DrGonz78]

A fault that comes and goes when the unit is moved suggests a mechanical problem and it looks like some re-soldering has been done on the board.

There are a couple of areas that need looking at; on the picture of the copper side of the PCB, go to the 2nd pot from the left and the 3rd solder pad up from the centre of the pot has a hole where it looks like a component leg should be soldered. Also just a little lower to the left of this is a dry looking joint - the component leg has a gap around it and it may need re-soldering. Take a good look at the rest of the board to see if there are any other areas that are suspect.

Yeah that area of the board looks like it needs some attention to a few solder joints and that missing solder joint.

[g1]

There is not a lot of connections on that board. Pots, jacks, and power supply related stuff and you are already 2/3 the way there. 'Shotgun' resolder of the whole thing might be quicker than trying to isolate a defective joint.

[The Dude]

There is not a lot of connections on that board. Pots, jacks, and power supply related stuff and you are already 2/3 the way there. 'Shotgun' resolder of the whole thing might be quicker than trying to isolate a defective joint.

^^^^^^^^ That!. You could spend more time looking for a cold solder joint than you would just resoldering the entire board.

[olucafont6]

Hey everyone, thanks so much for the helpful suggestions - wasn't expecting so many responses so quickly

Without test gear, oscilloscope and the like, all I can suggest you do is firstly remove U2 and check for a clean no hiss in your speaker.
If it is no longer hissing, replace the Tl072/4558/4660 etc whichever it is using.

Yeah, I saw some other people talking about that particular component - I'll try that, doesn't seem like it will be too difficult.

There are a couple of areas that need looking at; on the picture of the copper side of the PCB, go to the 2nd pot from the left and the 3rd solder pad up from the centre of the pot has a hole where it looks like a component leg should be soldered. Also just a little lower to the left of this is a dry looking joint - the component leg has a gap around it and it may need re-soldering. Take a good look at the rest of the board to see if there are any other areas that are suspect.

Yeah, I noticed the hole as well - I tried measuring the resistance with a multimeter, cause I saw someone else do that in a video, but there didn't seem to be a difference in the connection between it and the one right next to it. I don't know if that actually makes sense though I'll try resoldering those two connections first.

On some of the amps that are supported on one end by the pots, the rivet connections on the pot itself can become loose. To verify if this might be an issue for you, you can obviously (if you haven't already, wiggle the pots and twist them slightly to determine if the rivets have become loose. Note: the center/wiper rivet typically does not need re-tensioning. It is also the most difficult one to re-tension w/o damaging the phenolic wafer.
If this is the case you can very gingerly pinch the rivets to tighten them while being very careful to not break the brown phenolic wafer in the pot.

Interesting - yeah I checked them out and they seemed okay to me, but I'm not exactly sure what a bad connection would feel like.

There is not a lot of connections on that board. Pots, jacks, and power supply related stuff and you are already 2/3 the way there. 'Shotgun' resolder of the whole thing might be quicker than trying to isolate a defective joint.

Haha - I don't think I'm that confident in my soldering skills to do the whole board. I'll try the other suggestions first - we'll see if it comes to that though

[Mick Bailey]

Don't just resolder the hole - check if a component leg is protruding or not. What's supposed to be soldered in there? It looks like a capacitor or maybe resistor from the pictures. Establish what the problem is before taking action.

[DrGonz78]

Haha - I don't think I'm that confident in my soldering skills to do the whole board. I'll try the other suggestions first - we'll see if it comes to that though

10 years ago when I dove head first into buying and fixing old amps, I would make it a point to solder a bunch for practice. So anytime I got a smaller practice amp to clean up I would usually solder many if not all the joints on the board. I did this in a very cavalier fashion for a while until I was much better at soldering. The key to a good solder joint is a good hot iron and not applying the tip for too short or long of a duration. Too short of time and lack of sufficient heat while soldering leads to bad solder joints. Also, too short of time applying the tip to the work can lead to multiple attempts at re-flowing the solder joint. That right there is what I think weakens pads on a circuit board all too often. Then again if you apply a nice hot tip to the solder joint for too long that is a recipe for disaster.

I would go out and find some old circuit board that is basically garbage and start practicing re-flowing the solder on that first. Or just dive into that little circuit board to the orange amp and make your mother proud!

[Mars Amp Repair]

Re: Pot rivets:
You'd have to check the pot rivets while it was still in the case (or in a state where you can operate it) by just loosening the mounting nut & attaining some play in the pot so you could wiggle it while the amp was on with a signal applied & just listen for pops, volume/tone changes, etc. Sorry I did not mention that part!
In a static condition like you have w/board out of unit, you'd have to connect the ohm meter & watch for the reading to bounce around when you stress the pot. A bit more difficult to do and not a definite a test.
I would suggest really only doing this test w/the amp is a functioning mode.

[olucafont6]

Don't just resolder the hole - check if a component leg is protruding or not. What's supposed to be soldered in there? It looks like a capacitor or maybe resistor from the pictures. Establish what the problem is before taking action.

It's whatever the green squarish things are C11 and C12 on the middle right of the board It does seem like those components are kind of angled so one leg is much shallower in the hole than the other one.

10 years ago when I dove head first into buying and fixing old amps, I would make it a point to solder a bunch for practice. So anytime I got a smaller practice amp to clean up I would usually solder many if not all the joints on the board. I did this in a very cavalier fashion for a while until I was much better at soldering. The key to a good solder joint is a good hot iron and not applying the tip for too short or long of a duration. Too short of time and lack of sufficient heat while soldering leads to bad solder joints. Also, too short of time applying the tip to the work can lead to multiple attempts at re-flowing the solder joint. That right there is what I think weakens pads on a circuit board all too often. Then again if you apply a nice hot tip to the solder joint for too long that is a recipe for disaster.

I would go out and find some old circuit board that is basically garbage and start practicing re-flowing the solder on that first. Or just dive into that little circuit board to the orange amp and make your mother proud!

Okay haha - thanks for the tips. I probably won't get to the soldering until the weekend, but I'll try the things you mentioned.

Re: Pot rivets:
You'd have to check the pot rivets while it was still in the case (or in a state where you can operate it) by just loosening the mounting nut & attaining some play in the pot so you could wiggle it while the amp was on with a signal applied & just listen for pops, volume/tone changes, etc. Sorry I did not mention that part!
In a static condition like you have w/board out of unit, you'd have to connect the ohm meter & watch for the reading to bounce around when you stress the pot. A bit more difficult to do and not a definite a test.
I would suggest really only doing this test w/the amp is a functioning mode.

Oh okay, gotcha. Yeah once I've put the amp back together I'll give that a shot if it's still making the hissing sound.

[g1]

I think that is an extra unused hole under C11. Looks like there is also one under C12 but it has solder on it. I think the extra holes are for if different size C11 and C12 are used (alternate supplier).
The spot circled in red probably does not have a component lead in it, like the other open hole.

[DrGonz78]

I think we all would appreciate a few more pics of the board. Top and bottom.

oops I didn’t notice the first post has pictures of both. Sorry I am medicated today and now I have the munchies too. But really we need some confirmation from the OP about either extra pads or if a component might be missing. G1 already nailed that part. But some of the solder joints look horrible.