Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Solid State Amplifiers => The Newcomer's Forum => Topic started by: Mark N on September 21, 2021, 11:21:22 PM

Title: Orange Crush 12L (No Sound)
Post by: Mark N on September 21, 2021, 11:21:22 PM
I have an Orange Crush 12L practice amp that suddenly stopped working around the same time my Danelectro Nifty Fifty (which I made another thread about) started malfunctioning. I get no sound through speaker or headphone jack.

This one has a 4558 as IC1 so I reused the trouble shooting from the Danelectro Amp (which uses an TL072, but I believe they have the same pin out) Using Enzo's helpful advice from the other thread I tested the DC Voltage on the pins and got

Pin 1: 0
Pin 4: -14
Pin 7: 13
Pin 8: 13

So I assume this IC has gone bad, correct? My understanding is that Pin 7 should read around zero. I tested the sound using an audio probe as well, I was able to trace sound from the input jack to a capacitor but then the signal goes to IC1. Testing the other leg of the capacitor I got no sound. I pulled the capacitor and was able to run a signal through it fine.

I plan on ordering another 4558 IC chip, but is there anything else I should be checking?
Title: Re: Orange Crush 12L (No Sound)
Post by: willpirkle on September 22, 2021, 07:01:02 PM
Yep, pin 7 is an output, and should be ~0VDC so that IC is definitely toasted (yes, same pin out as the TL072). You could socket it, if you’d like to experiment with other op-amps, or make changing it simple in the future if it fails again. I couldn’t find the schematic for the 12L, but I did find the 20L which includes over-voltage protection diodes on the input. Assuming those are also there on the 12L (2 diodes connected to pin 3), then changing the op-amp should do the trick. But Enzo may have something else to check - he’s a super-boss around here!
Title: Re: Orange Crush 12L (No Sound)
Post by: Mark N on September 23, 2021, 01:55:14 AM
Thanks for giving it a look, Willpirkle. Unfortunately, the 20L schematic is a whole different design. I did try to look for a schematic, but I don't believe anyone traced it. There aren't any diodes near the input. Audio signal goes through a capacitor, then resistor to ground before going into pin 5 of the IC chip. Pin 3 appears to just go to ground.

I didn't know over-voltage protection was a thing, but now I do. So that was helpful.
Title: Re: Orange Crush 12L (No Sound)
Post by: flester on September 23, 2021, 07:41:14 AM
I had this model and got a tech to successfully repair it by changing the Opamp. If you have the skills it might be worth replacing it, using a socket so that it would be easier to repair again.

But then some pots and PCB traces failed and I made it worse while trying to fix it. I decided to gut it and made it into a hybrid head, plus a handy, bright orange,  1x6" cab for other projects. The power supply section is still useable, I think.

A pity in a way because it is probably one of the better small amps in that price range.
Title: Re: Orange Crush 12L (No Sound)
Post by: Enzo on September 23, 2021, 11:17:16 AM
You have 13v on the output pin of your op amp instead of zero.  Doesn't matter that the amp is different, that still sounds like a bad op amp, so change it out and see if progress has occurred.  For small practice amps like this I rarely get out a schematic.
Title: Re: Orange Crush 12L (No Sound)
Post by: Mark N on September 24, 2021, 10:49:11 PM
Thanks again, Enzo!

Flester, sorry to hear yours fell apart, but glad to see you reused what you could. This lil' amp does sound good. Once I get it fixed up I'm debating whether or not to keep it. I've got too many amps as is and I'd rather not have it keep breaking on me. It definitely is fun to play though.