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Author Topic: Roland Supercube 100 -- input jack advice needed (probably)  (Read 904 times)

niftyprose

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Hello guys esp. Joseph, my first post on this forum. I'm a total n00b on amp repairs but have some electronics knowledge and experience gathered elsewhere. I have a pretty basic problem with a Roland Supercube. If that makes you yawn, the payoff is an amusing photo.

OK, here goes. The amp is a Supercube 100. It's a solidly-built 1 x 12 combo, the bigger brother of the original orange Cube. It will have been built between '78 and '82, likely late '70s because it has the stock speaker used in the Japanese units (later EU ones were assembled here in the UK with Celestions). Build quality is excellent throughout and the sound is good, if not quite my thing.

There are two input jacks, one for a footswitchable drive channel and one for a clean channel.

When I plug into the drive jack, there's a series of cracks and thumps that goes on for several seconds, that is, some time after the jack has gone into place. It's loud enough to make me worry about speaker damage. There's often a brief high-pitched squeal which sounds like microphonic feedback in a cheap pickup. The clean channnel jack is a little noisy but bearable.

I took the amp sub-chassis out of the main box yesterday. Here's the label on the reverb tank, which has nothing to do with my query but might give you a laugh:

http://unblotted.com/extmedia/FoldedLine.jpg

I'm inclined to think that the problem is with the input jacks, which are the only part of the circuit subject to mechanical stress. What I fiound was a neat PCB sub-board with both jacks soldered to it. There's a five-cable connector to the main board, presumably a shared earth plus connections to the two jacks. There are also two cables to the drive footswitch.

http://unblotted.com/extmedia/_0014934.JPG

The PCB looks pretty simple, and I can't see any problems:

http://unblotted.com/extmedia/_0014933.JPG

The obvious suspects are the earth wire from the outside of the jacks to the PCB, and the very tiny soldered lumps that you can see at the top of the PCB photo, which are involved in the footswitch. To my shame, I'm not sure how the footswitch to the drive channel works. I mean, it's obviously closing a connection on the sub-board to route the signal, but how is the connection made without a power supply? Is it the case that the signal is routed off the sub-board, goes through the footswitch and back to the sub-board? Sheesh!

It may be the case that someone reading this says, "Aha, the famous Roland jackboard problem!" and tells me a two-minute fix to identify and replace the notoriously weak link in the chain. If not, I'd like a 'best practice' type solution. It wouldn't break my heart to replace the jacks and the sub-board completely, although I don't think I'd relish having to connect to that five-way ribbon. Also I don't want to disable that footswitch...

TIA, NP.

« Last Edit: May 16, 2020, 03:31:51 AM by niftyprose »

phatt

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Re: Roland Supercube 100 -- input jack advice needed (probably)
« Reply #1 on: May 17, 2020, 07:29:58 AM »
Does wiggling the plug in any of the 3 sockets create any noise?
It could be as you mentioned, a mechanical issue as those sockets have internal switching which do have a habit of failing and as they are enclosed it's hard to work out if anything is failing.
As to the 5 wires, my guess from left in pic of the back of the pcb.
1&2 are signal hot from the 2 inputs.
3&4 is part of the switching setup
5 is circuit common.

It's likely the foot switch just re-configures the input,, similar to the old style hi/lo inputs on many old fenders. I'd guess one of those sockets has a failing internal switch.
Sorry can't be more help. Phil.

niftyprose

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Re: Roland Supercube 100 -- input jack advice needed (probably)
« Reply #2 on: May 18, 2020, 04:43:48 AM »
Hi Phatt, that's a great start -- many thanks. I actually hadn't considered that the five wires might be anything other than signals from the two jacks but now you mention it...

Practically speaking, my options are i. to source exact replacement jacks and solder them to the sub-board and ii. to use standard jacks and  build my own sub-board from perf. Neither route is particularly easy. Any reason to choose one over the other apart from the non-issue of collectability/original condition?

Best, W.

joecool85

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Re: Roland Supercube 100 -- input jack advice needed (probably)
« Reply #3 on: May 18, 2020, 09:34:47 AM »
Hi Phatt, that's a great start -- many thanks. I actually hadn't considered that the five wires might be anything other than signals from the two jacks but now you mention it...

Practically speaking, my options are i. to source exact replacement jacks and solder them to the sub-board and ii. to use standard jacks and  build my own sub-board from perf. Neither route is particularly easy. Any reason to choose one over the other apart from the non-issue of collectability/original condition?

Best, W.

Option 0, which should be tried first, is to clean the existing jacks.  Use some deoxit or similar, apply liberally to a 1/4" plug and work it in and out of the jacks for a dozen or more times.  Now try the amp.  If this doesn't fix it, you might need to replace the jacks.  They look like fairly standard PCB mounted jacks though.
« Last Edit: May 18, 2020, 09:55:35 AM by joecool85 »
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joecool85

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Re: Roland Supercube 100 -- input jack advice needed (probably)
« Reply #4 on: May 18, 2020, 09:56:06 AM »
Maybe something like this: https://www.mouser.com/ProductDetail/Amphenol-Audio/ACJM-PVB-2S?qs=t8VhaDIDl4uv4ueacfq3DQ%3D%3D

Alternatively, you could always do it without pcb or perfboard at all and simply point to point wire it.
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phatt

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Re: Roland Supercube 100 -- input jack advice needed (probably)
« Reply #5 on: May 18, 2020, 08:12:56 PM »
Probably not that simple Joe. :-\
Using the pic of back panel,
It looks like the top socket has at least 5 terminals while the bottom socket only has 2 terminals.
That tells me the top is an odd ball socket that is likely hard to replace.

Those encapsulated sockets come in many types so hard to work out how the switching works.
The internals are often quite delicate and maybe not working to spec.

Q for Nifty,

1/ Again I ask is the issue only present when you plug in?
OR
2/ Can it be evoked later by wiggling the plug After you plug in?
If it only happens at plug in then the issue could be a failing circuit.

If both 1&2 then yep failing sockets.

Here is the input setup from a Cube 60 which shows what I think you have, note the top OD input socket is drawn with the 5 terminals while the Normal  and Footsw units are 2 terminal.

Phil.

Enzo

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Re: Roland Supercube 100 -- input jack advice needed (probably)
« Reply #6 on: May 18, 2020, 11:18:47 PM »
Looks to me like a common TRS with cutouts.  Tip with cutout, ring with cutout, ground?sleeve.  Five terminals.

joecool85

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Re: Roland Supercube 100 -- input jack advice needed (probably)
« Reply #7 on: May 19, 2020, 09:33:33 AM »
Looks to me like a common TRS with cutouts.  Tip with cutout, ring with cutout, ground?sleeve.  Five terminals.

This was my thought as well.  I do agree with Phil though that matching it on the old PCB could be difficult as the pinout seems odd.  But point to point wiring on it should be straight forward enough.  Between a multimeter and spending some time tracing where the PCB connects which pin to what, you should be able to figure it out.

Does anyone have a schematic for this amp?  That could help as well.
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niftyprose

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Re: Roland Supercube 100 -- input jack advice needed (probably)
« Reply #8 on: May 19, 2020, 12:55:03 PM »
Hello guys, thank you to everyone for support and careful suggestions. You can tell that I'm a n00b because of the inter-post gaps while I source items that I don't have on the shelf. The latest is Joe's recommendation of contact cleaner, due in 48hrs.

I will attempt to make sense of what's in front of me. Phil, as far as I can remember the noise only happened right after plugging in, thus I will take the hint that it's likely to be a board rather than a jack fault. And I suspect that your Cube schematic applies to my device, too. I'm noticing how the oddly configured switchable input in the diagram corresponds to the multiple terminals of jack #1 in the Supercube.

Meanwhile, a cautionary tale. SInce this is an old and slightly exotic amp I didn't pay much attention to the weird-looking mains plug. Today I found that what I had assumed was an old-fashioned Japanese export number was actually a European two-pin shoved into a very large two-to-three pin adapter. Although a large earth cable leaves the chassis via the mains cable, it doesn't actually connect to earth. I doubt this has anything to do with the symptoms I've described, but I shall certainly sort it out before I power up again.

More anon...

Best, W.
« Last Edit: May 19, 2020, 12:59:02 PM by niftyprose »

joecool85

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Re: Roland Supercube 100 -- input jack advice needed (probably)
« Reply #9 on: May 19, 2020, 01:16:06 PM »
Looks to me like a common TRS with cutouts.  Tip with cutout, ring with cutout, ground?sleeve.  Five terminals.

This was my thought as well.  I do agree with Phil though that matching it on the old PCB could be difficult as the pinout seems odd.  But point to point wiring on it should be straight forward enough.  Between a multimeter and spending some time tracing where the PCB connects which pin to what, you should be able to figure it out.

Does anyone have a schematic for this amp?  That could help as well.

Not sure how I missed Phil's clipout of the model 60 schematic.  Assuming this is similar to the 100, I think point to point would be super easy.  Basically on the switched jack it simply grounds itself out when unplugged.  Also, I would change it and just use one jack.  The only difference is that one jack goes straight in and one goes through a 270k resistor.  Simply use a single jack that goes through a 270k resistor.  Then use a spst switch to bypass the resistor.  Put the switch in the hole for one of the inputs.  Done.  More robust, no stupid switching jacks to deal with, and an easily switchable boost circuit instead of swapping your cable to a different jack.
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niftyprose

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Re: Roland Supercube 100 -- input jack advice needed (probably)
« Reply #10 on: May 20, 2020, 05:05:39 AM »
Joe, that sounds like excellent advice. I'm likely to sell the amp (too big for me, and I like the sound of my Gibson Skylark) so will need to consider carefully, but it would be great to avoid the recurrence of problems like this. Thanks to everyone for helping me figure out what I thought would be much simpler than it actually is... Best, W.

Enzo

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Re: Roland Supercube 100 -- input jack advice needed (probably)
« Reply #11 on: May 20, 2020, 06:54:00 AM »
Simple jack failure.  It doesn't need to be modified, it isn't like the jack breaks once a month.  Just fix it and it will continue on.

joecool85

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Re: Roland Supercube 100 -- input jack advice needed (probably)
« Reply #12 on: May 20, 2020, 07:41:34 AM »
Simple jack failure.  It doesn't need to be modified, it isn't like the jack breaks once a month.  Just fix it and it will continue on.

True, but fixing it as per OEM would be a lot more (unnecessary) work as compared to my suggestion.
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phatt

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Re: Roland Supercube 100 -- input jack advice needed (probably)
« Reply #13 on: May 20, 2020, 10:11:03 AM »
I'm with Joe,, For an experienced repair shop they would know *EXactly* were to source parts,, but for the once a year home fixup guy,, well I've been caught a few times. :-\
Yep looks the same ,, oh bugga this one is slightly longer and won't fit or worse the sw is NO not NC.
At least with open frame like switchcraft you can visually see how it works.
Oh and they are easy to clean and the metal tabs are much *Thicker* and hence last for years longer that those plastic encapsulated units. I've pulled many of those type out and they just crumble.  :grr
Phil.
 

niftyprose

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Re: Roland Supercube 100 -- input jack advice needed (probably)
« Reply #14 on: May 20, 2020, 01:36:20 PM »
Hello guys, small update. I just ordered some components on eBay and get a few days to think while they're coming in.

I spent a first hour with the amp this afternoon. If I were to put Joe's plan into action, what would I have to do? The advice about using an SPST switch to bypass the 270k resistor and so engage or disengage drive turned out too difficult to action, only because I couldn't find R101. By my reckoning it must be on the main board somewhere, but it totally resisted my efforts to find it.

Joe's fix of putting the switch inside the unused jack drilling was just too good to pass up, however, so I started looking for second best. I've kind of settled on the following course of action.

I will remove the five-way connector from the input jack sub-board, leaving the sub-board attached to the footswitch jack but otherwise disconnected. I will tape it ouf the way to the back of the chassis with a label in case anyone wants to reverse my changes.

I've bought a Switchcraft-type input jack and a small DPDT switch that will mount into the jack drillings.

I will connect the jack to the centre two terminals of the DPDT.

I will connect the two end terminal pairs of the DPDT to lines 1&4 and 2&3 on the five-way connector as per Phil's diagram. If I've understood correctly, this should mean that I can route the signal to either drive or normal.

Assuming I haven't gone hopelessly astray, this leaves two issues to deal with:

1. Is there a way of connecting to the five lines of the ribbon cable so that I can attach them as needed? I guess I can just razor the wires apart but would prefer something neater and more permanent.
2. I spent some time with the multimeter and looking at the sub-board and I can't square what I see with the numbering given on Phil's circuit diagram. Could this be an engineer's error, or the SCL-100 was different from the 60, or should I stick to the numbering scheme on the diagram whatever?

TIA, NP