Hi all, I recently got a Roland Bolt 60 that a friend found on the side of the road. It was a bit beat up but not too bad.the power switch had failed, some cosmetic stuff. It sounds pretty good really.
I'm having problems with the reverb though. If I turn the reverb up and smack the cabinet I get a nice splashy reverb sound so that means the output part of the circuit works. As I'm writing this I think I'm answering my question, but here I am anyway.
There's a dual opamp, a 4558, that is used in the reverb circuit, one side before the tank and one after. I used an audio probe and the guitar sound gets to the opamp, but I get no output to the tank. I was concerned about the voltage as the schematic made it look like it should be 30v and I only have about 8v. But the output works, so that can't be right.
I assume the opamp is the issue, but if anyone who remembers how zener diodes work wanted to look at the schematic id appreciate it. Here's a link. https://el34world.com/charts/Schematics/files/Roland/Roland_bolt_60.pdf
Thanks!
These might help you a little bit in figuring it out, or at least help you in the right direction.
https://sound-au.com/project34.htm
https://sound-au.com/project211.htm
Thanks, those are helpful. I think my zener is bad, unless something else in the circuit could be dragging the voltage down somehow, but not sure what that could be. That the output still works points away from that, but not sure. Maybe it still works well enough for the output but doesn't have enough juice to feed the two transistors?
Anyway, I'll have another look this evening.
Check you have continuity through the Driver transducer as well as the cable going to the tank.
Check you have +7volt & -7volt rails at the 2 boost transistors
BTW, D11 & D12 are plain diodes not Zeners.
Phil
It looks like D10 is a 30V 500mW zener, RD-30EB
Where did you measure the 8V? The 30V should go to pin8 of the op amp. As you mentioned, if the op amp was only getting 8V I don't think you would hear the tank output but I guess it's possible.
Like Phatt said, check the resistance at the input jack of the reverb tank. Broken wires inside the tank are the most common cause of reverb issues, especially when the amp gets tossed around/abuse.
I meant to follow up on this but got busy and forgot. I ended up changing the opamp out and it all worked perfectly. The input section had failed and the output worked.
It's a really nice sounding spring reverb. Really a nice amp all around. There were further issues, the weird effect loop selector switch was flaky. Every time I played a low note the vibration would cause that switch to make noise. I thought it might be a tube at first, but I had spares enough to prove that incorrect. It looks like a pain to change out or even jumper, so I'm just not touching it for now.
Thanks to everyone for the help. This forum is great, nice community of helpful people.