Roland jc-50 chorus/vibrato switch

[Locrian99]

Hey so I picked up an 83 jc-50 on Craigslist this morning, sounds phenomenal first experience with a jc and happy I picked it up.   The bat however is broken off the chorus vibe switch.   I ignorantly thought this would be easy to swap, and it still works fine but I'd like to get it "better".   Of course being 40 years old the switch is discontinued.   And it's weird!   I sure there's got to be some sort of work around to make a "regular" switch work but it's beyond me.   I'd prefer a slide style switch.   It's and on/off/on from what I can see.  Any thoughts. 








Err resolution on the schematic picture sucks.  I'll have to get a better resolution.   












Lastly is it possible to make any simple changes to get "more"
Reverb from the amp, make it a bit springier?   

[GGBB]

It's not on-off-on - it's on-on-on 3P3T. I think there are rotary switches that do this, and you should be able to make a tele 3-way super switch work as well which is 4P3T (https://www.premierguitar.com/pro-advice/mod-garage-meet-goldos-double-wafer-3-way-switch) - but physical fit is a problem for both unless you don't mind modding the amp. Maybe put it on the back panel and leave the front switch disconnected?

[Locrian99]

K thank you for the info.   Weird looking switch how they've got it done up. 

[antonis]

is it possible to make any simple changes to get "more" Reverb from the amp, make it a bit springier? 

Try to raise R35 value..

[Rob Strand]

is it possible to make any simple changes to get "more" Reverb from the amp, make it a bit springier? 

Try to raise R35 value..

In most cases it's better to raise R25 to drive the spring harder.   Raising R35 can increase "clang", hum and noise.

Raising by a factor of say 1.4 to 1.5 would be a good way to edge up the reverb level.   If you want a factor of 2 you start to need more details - without that perhaps increase both R25 and R35 by 1.4.

To work out the right balance of R25 and R35 you need to know the precise signal levels in the amp (and also how much more reverb you want).   Some amps drive the reverb with a low signal which promotes the problems mentioned above whereas others are already driving the spring hard in which case R35 would be more correct.

Make sure you check the Rnn designators and the part values match, or better still make sure the schematic matches your amp.   There are different versions of amps out there.

EDIT:

I checked over the levels marked on the full schematic.

The reverb drive level isn't low it is quite reasonable.  You could increase it a tad, no more than a factor of 1.4.
For simplicity you might be better off just increasing R35 to increase the recovery amp gain.

While checking the amp, to me it looks like the recovery amp gain is set to quite a reasonable level.    If you think the reverb is low then maybe there's a fault somewhere.   Is the reverb tank original?  it might have been replaced with the higher impedance drive coil which will then make the reverb level low.

[Locrian99]

I like a lot of reverb apparently.    There's a fair amount but I would like to have more, I always feel like 10 should be too much.   The hum you mentioned though might be an issue as at ten there does seem to be a bit.    Every think looks fairly original in there and from the bright switch it's the top first schematic in the service manual.  Was trying to find the tank specs without success earlier thought maybe replacing the tank might help as well perhaps with a long decay, not sure where to measure to figure out the impedance of the current tank it's also mounted in the chassis.   



Edited : due to bad typo.

[antonis]

A soft brush and a hair blower could make things better..

[Rob Strand]

I like a lot of reverb apparently.    There's a fair amount but I would like to have more, I always feel like 10 should be too much.   The hum you mentioned though might be an issue as at ten there does seem to be a bit.    Every think looks fairly original in there and from the bright switch it's the top first schematic in the service manual.  Was trying to find the tank specs without success earlier thought maybe replacing the tank might help as well perhaps with a long decay, not sure where to measure to figure out the impedance of the current tank it's also mounted in the chassis.   



Edited : due to bad typo.

Yes, the reverb tank looks original and so does the wiring.  So maybe just raise the value of R35 by a factor of 1.4 to 1.5 and see if that is enough.   

For some reason specs on that particular unit are hard to find.   From what I can see the reverb tank is different to that used on other JC amps.  The circuit is similar with few value changes.  From the circuit I'm fairly certain the drive coil is 8 or 10 ohm, the DC resistance will be around 0.8 ohm to 1 ohm.    The output coil is likely to be 2200 ohm, DC resistance about 200 ohm.  It would take me a long time to see if I had some info on that reverb tank.  The same reverb tank is used on the Roland Bolt 30 Roland Block 30; "Block" might actually be "Cube".; not sure about the Cubes, some do seem to have 8 ohm drive coils.

The hum could be a due to dried electrolytic capacitors, especially electrolytic on the power supply filters. Dried caps is common in something of that age, especially in an amplifier.   There could be dried caps in other parts of the circuit.

[Locrian99]

I like a lot of reverb apparently.    There's a fair amount but I would like to have more, I always feel like 10 should be too much.   The hum you mentioned though might be an issue as at ten there does seem to be a bit.    Every think looks fairly original in there and from the bright switch it's the top first schematic in the service manual.  Was trying to find the tank specs without success earlier thought maybe replacing the tank might help as well perhaps with a long decay, not sure where to measure to figure out the impedance of the current tank it's also mounted in the chassis.   





Edited : due to bad typo.

Yes, the reverb tank looks original and so does the wiring.  So maybe just raise the value of R35 by a factor of 1.4 to 1.5 and see if that is enough.   

For some reason specs on that particular unit are hard to find.   From what I can see the reverb tank is different to that used on other JC amps.  The circuit is similar with few value changes.  From the circuit I'm fairly certain the drive coil is 8 or 10 ohm, the DC resistance will be around 0.8 ohm to 1 ohm.    The output coil is likely to be 2200 ohm, DC resistance about 200 ohm.  It would take me a long time to see if I had some info on that reverb tank.  The same reverb tank is used on the Roland Bolt 30 Roland Block 30; "Block" might actually be "Cube".; not sure about the Cubes, they do seem to have 8 ohm drive coils.

The hum could be a due to dried electrolytic capacitors, especially electrolytic on the power supply filters. Dried caps is common in something of that age, especially in an amplifier.   There could be dried caps in other parts of the circuit.

Thank you as always a very thorough response.   I had thought about possibly replacing caps.   As yes it's 40 years old.   I think I will clean up some of the dust in there replace the caps while trying that resistor change.    Just need to order the caps my pedal stuff doesn't have anything near that big lol.