Orange Crush 20RT - Reverb problem

[jondoe]

Greetings forum!

I have an Orange Crush 20 RT that was given to me with a blown output mosfet, It looked like the amp had some liquid ingress at some point, although if that happened before or after the mosfet blew I don't know. I stripped it down and cleaned it all, changed the blown mosfet and now the amp is working well on clean and dirty channels, the EQ works as it should, however, the reverb is very quiet and not very reverby (if that's even a word). It also has quite a noticeable hiss when the reverb is up full.

As far as I can tell the reverb function is on a separate daughter board, this was a little dirty in places so I've re-flowed all the solder joints connecting it to the board and re-flowed the crystal as it looked slightly corroded. Interestingly the board does create a very strong reverb effect if you probe it here and there, you get a nice static pop and a strong reverb effect from it, but the input is weak and barely reverbs the input signal.

I can't find a schematic, does anyone have one? I'd be grateful if anyone has one to share.

My assumption is the input signal to the reverb unit has a problem, or the board itself. Any suggestions are very welcome. I've added some pictures below.

Thanks.

https://imgur.com/R4kWNEm

https://imgur.com/Nng8HjN

[jondoe]

Just for my own notes, or anyone else that reads this, I've tested the inputs and outputs of the reverb board, of which the pin outs are;

Out1
Out2
S.Ground
Input
P.Gnd
+5v
ADJ
ADJ

This appears to be the same reverb daughter board as used in the Orange CR60 and CR120. The board is getting the 5v it needs so I've poked around with an improvised audio probe, I've found the reverb board is getting audio on it's Input pin, there is also audio output from the reverb board on Out1 and Out2. My audio probe isn't amplified so I can't quite tell if the Output is reverbed, but it's a start. The two OUT signals appear to join up to one signal and continue over to the opamp U3, pin 3, (1IN+). The reverb output is much lower than the input, but I'm not sure if that's expected or not.

That's as far as I've got

[nevetslab]

It may be that none of us have had the new generation Orange Crush series in the shop for service. I just checked the inventory list here at CenterStaging, LLC in Burbank, CA, and don't see any of them listed. I looked at the two photos you attached, and see it's a DSP module. I'd imagine Orange would have set the output level on the daughter board so it would be unity gain from input thru stereo output.

One of the test signal sources I use is pink noise (GenRad 1982), which I have passing thru a tone burst generator (GenRad 1396B) and a Krohn-Hite 3550BP filter. It allows me to excite dynamic circuits, as well as delays and reverbs, so I can listen to the tail in the off-time before pulsing it again. Many function generators provide the ability to produce gated output, which also allow you to observe the reverb/delay effect. I lieu of those, nothing like plugging in a guitar and plucking strings/chords.

As you've found where the outputs mix the 'wet' signal with the 'dry' signal, I'm guessing there is a gain stage with the Reverb level between the output(s) and the mixing stage. That should tell you if there's sufficient gain there. I haven't gone to Orange's web site to look into these amps. Looking thru my different manuals, they don't provide block diagrams to give you any clues, so you're in uncharted territory at the moment. Might be some of our members here on the forum that have been inside their Crush series to help.

[Jazz P Bass]

I would be looking at the inputs & the outputs of the Codec ic (U3)

4550VT.pdf

[jondoe]

Thanks for the feedback gentlemen. Having slept on it and run it through my mind a fair amount I decided to assume the DSP was working based on my very basic tests, which lead me to think there might be a dead cap/resistor in the circuit nearby or the Opamp it routes to is at fault. I found a couple of crappy caps with highish ESR and changed those with no affect to the reverb/quality, so I bit the bullet, pulled the Opamp at U5 and fitted a socket.

With a brand new TL027P the reverb is transformed, there is no noticeable hiss on the reverb channel when cranked up and there is considerably more reverb. I don't have an idea of how it sounded from factory, but I think this is OK now. I'll take it to a guitarist friend for a final test soon

I'll chalk this up to good luck as I'm still very new to this!