Roland Super Cube 60 Squeal Help

[misterc57]

Hey Folks

I picked up one of the 80s gray Super Cube 60 with two inputs and 7 pots. There is a normal and gain input jack. The normal input works fine. As soon as I insert a cable into the gain jack the amp emits a loud high pitch squeal.

This is not just a schematic request but I am having a hard time finding the proper schematic and will need that to continue. Once I have a schematic I can see what the two inputs do not share.

Thank you! MarkO

[Jon Snell]

I expect the ground has parted from the high gain socket.

[g1]

Or the grounding switch of the normal jack is not closing. These are what I think is called the 'SCL' model, try this schematic: https://music-electronics-forum.com/...etch?id=922334

[misterc57]

Yes SCL. Thank you for the schematic!

So, I find that if I move the plug inserted into the gain jack, I can change the intensity of the squeal or make it gone completely.

I guess I need to remove the jack from its board and see if I can manipulate the tabs. It is the jack with the 6 tabs connected to the board.

[g1]

I guess I need to remove the jack from its board and see if I can manipulate the tabs. It is the jack with the 6 tabs connected to the board.

Before you do that, measure the resistance from tip to ground of the normal jack, with nothing plugged in. It should be zero ohms.
If not, the switch contact of the normal jack is either dirty or bent. Try cleaning it.

[misterc57]

Just got back to this. Tip to ground on normal jack was good, under 1 ohm. I removed the drive jack from the board. Could not see anything wrong, nor could I bend anything due to it being in its enclosure.

I installed a switching jack; switch and ground lug joined and connected to the ground wire of the normal jack, tip lug connected to the board which connects to R3. I am getting a loud ground buzz when I insert a guitar cable. The switch is working properly on this jack. Wondering what I am doing wrong. Is there supposed to be a resistor included?

Thank you!

[misterc57]

What is the dash line in the schematic connected to this input jack? Looks like it goes to a channel switch but this model does not have a channel switch jack..

SCL-40_60_100.pdf

[g1]

Those are all parts of the 'Drive' jack, J2. You can't just replace it with a switching jack, it has to be an exact replacement. Like you said, it has 6 tabs. Part of the jack is the channel switch.

[misterc57]

Any suggestions on where to order a replacement jack? Thank you

[misterc57]

Not sure I am going to find a replacement jack for this.

How about a redesign? One jack and one normal/drive toggle switch in position of the second jack.

Looks like we have 5 connections on the jack board.

#1 to ground
#2 to switch
#3 to switch
#4 to normal input
#5 to drive input

Switch position DRIVE sends #4 "normal" to ground
Switch position NORMAL sends #5 "drive" to ground

Not sure about # 2 and #3, which should go to ground based on the switch position.

Doable? Bad idea?

Thank you

[Helmholtz]

Not sure, but this one looks similar: https://www.musikding.de/63mm-Stereo...ith-2-switches

[g1]

Yes that looks similar, I wonder if they are only using one set of switch contacts in the Roland.
I think even a TRS jack with one normally closed switch (on sleeve?) might work. Plugging into it would lift one contact, and ring to sleeve connection due to mono plug would act as closing another switch contact.

How about a redesign? One jack and one normal/drive toggle switch in position of the second jack.

I think you would still want to use 2 jacks, there is also some attenuation and voltage divider action due to R2,R3, and the switch in the normal jack when it is not in use.

As to the JK-1 parts around U2A, when using the 'normal' jack, the switch #3 contact is grounded and the #2 is open. That kills the signal to pin2 of U2A and pin3 gets the normal signal.
When using the 'drive' jack, the switch #2 contact is grounded and the #3 contact is open. That kills the signal to pin3 of U2A, and pin2 gets the drive signal.

[misterc57]

The Roland jack has only one physical switch.

[misterc57]

Not sure, but this one looks similar: https://www.musikding.de/63mm-Stereo...ith-2-switches

Pin orientation does not look the same..

[Helmholtz]

A single switch version is available from the same supplier, search the website.