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

[dmeek]

Can you post another photo of the foil side under the input jack and gain pot? Maybe clean off the old flux, it's a little blurry there.
One thing I notice is that there is no resistor between the input jack and the + input of the op-amp. The chip could have taken a hit of static.

[olucafont6]

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.

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.

Yeah, you were right g1 - it looks like those two holes with the empty / shallow solder are just extra and not used. That's kind of disappointing...

Can you post another photo of the foil side under the input jack and gain pot? Maybe clean off the old flux, it's a little blurry there.

Yeah - I think I ran out of space for uploading photos on this thread, but I made an Imgur album with the previous photos and some new ones:
https://imgur.com/a/w3bJg2c

And yeah, I'll clean off the flux (not sure if that mattered for the picture). Thanks!

[DrGonz78]

Looking at all your pictures, which are excellent, it looks like a case where the unleaded solder on the board is deteriorating. So when we say shotgun soldering there is good troubleshooting in that step. The unleaded solder sucks in so many ways.

[dmeek]

Your photo of the jack is the phones jack - wrong end of the board. However I believe this schematic is correct. I'm guessing the transistor is a FET.

[olucafont6]

Looking at all your pictures, which are excellent, it looks like a case where the unleaded solder on the board is deteriorating. So when we say shotgun soldering there is good troubleshooting in that step. The unleaded solder sucks in so many ways.

Yep, I'm hoping to start resoldering some of it tomorrow.

Your photo of the jack is the phones jack - wrong end of the board.

Ooops, yeah you're right, I got turned around. I added an image below the actual input jack and gain potentiometer to the Imgur album in case that's helpful:
https://imgur.com/a/w3bJg2c

The schematic is cool - I looked for one of those before I made the original post but couldn't find one.

[olucafont6]

So I finally got to resoldering today - I took out the U2 component (I think that's an op-amp or something like that?), put everything back together and there was no hiss. There was a low-volume crackle if I turned up the volume, gain, and overdrive a lot, but I'm guessing that would have been there when the amp was working fine as well (and I don't usually turn it up that loud anyway).

I will try replacing the op-amp re Jon Snell's comment - hopefully that's the problem, because I had a lot of trouble just removing the solder from those 8 pins (though I think the solder sucker I was using wasn't the best).

[DrGonz78]

Research signal tracer on this site. There are several different ways you could go about tracing signal through amp. You can try just using a multimeter to measure AC signal but cheap meters are very unreliable. You can build your own diy signal probe that can be very inexpensive. Do you have DC voltage on the output? Now everything is resoldered what voltage checks might have changed?

Edit: I think I missed the bus here. I had it in my head that the amp wasn’t passing signal or something. But really just chasing down the hissing IC’s. Still cool to build a tracing tool and learn how it works though.

[Mick Bailey]

My preference is to install a socket for the new opamp now the old one is removed to make future replacement or troubleshooting easier. A DIY 'audio probe' is really useful for tracing faults in solid-state amps and effects pedals. Despite having a scope and half a dozen meters, I find using one really quick and useful for this kind of problem.

[olucafont6]

My preference is to install a socket for the new opamp now the old one is removed to make future replacement or troubleshooting easier.

Oh cool, didn't know that was a thing. I already ordered a couple op amps without the sockets, so I might just solder it directly to the board on this time, but I'll keep that in mind.

Yeah, I saw someone talking about building an audio probe on a different post - seems cool, maybe I'll try that if replacing the op-amp doesn't work.

[olucafont6]

So I ordered a replacement op amp, but it ended up being too small and I guess not the same kind (see comparison: https://imgur.com/ynk7hH7). I thought as long as it said 4558 on it it would be basically the same, but I guess not.

Could someone help me identify a valid replacement op amp (preferably one that comes with a socket, re Mick Bailey's suggestion)? The original looks like it says:

ST (Manufacturer) CHN
4558C
KV6015

I've tried searching the last two identifiers together, but I couldn't seem to find the exact same model anywhere.

[DrGonz78]

Yeah you got what is referred to as surface mount type. It is much smaller tech. Try this out. Click access denied to see the link.

[g1]

You need a 8 pin DIP package. Any 4558 with a D or P suffix will do.

[olucafont6]

Ah okay, I see - yeah didn't notice the difference on the listing when I purchased it.

Just bought a couple of the RC4558P ones DrGonz78 linked to, as well as some sockets. Thanks!

[olucafont6]

It worked! I soldered the socket on and then plugged the new opamp into that, and the hiss is gone.

It feels like it sounds a little different than how I remembered it - the overdrive and gain don't seem like they make it sound as crunchy as before or something. It might be cleaner overall - which is maybe a good thing

Thanks so much again to everyone for the helpful responses - really appreciate all the insight and guidance!