Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Solid State Amplifiers => The Newcomer's Forum => Topic started by: niftyprose on May 16, 2020, 03:27:19 AM

Title: Roland Supercube 100 -- input jack advice needed (probably)
Post by: niftyprose on May 16, 2020, 03:27:19 AM
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.

Title: Re: Roland Supercube 100 -- input jack advice needed (probably)
Post by: phatt 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.
Title: Re: Roland Supercube 100 -- input jack advice needed (probably)
Post by: niftyprose 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.
Title: Re: Roland Supercube 100 -- input jack advice needed (probably)
Post by: joecool85 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.
Title: Re: Roland Supercube 100 -- input jack advice needed (probably)
Post by: joecool85 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.
Title: Re: Roland Supercube 100 -- input jack advice needed (probably)
Post by: phatt 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.
Title: Re: Roland Supercube 100 -- input jack advice needed (probably)
Post by: Enzo 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.
Title: Re: Roland Supercube 100 -- input jack advice needed (probably)
Post by: joecool85 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.
Title: Re: Roland Supercube 100 -- input jack advice needed (probably)
Post by: niftyprose 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.
Title: Re: Roland Supercube 100 -- input jack advice needed (probably)
Post by: joecool85 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.
Title: Re: Roland Supercube 100 -- input jack advice needed (probably)
Post by: niftyprose 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.
Title: Re: Roland Supercube 100 -- input jack advice needed (probably)
Post by: Enzo 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.
Title: Re: Roland Supercube 100 -- input jack advice needed (probably)
Post by: joecool85 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.
Title: Re: Roland Supercube 100 -- input jack advice needed (probably)
Post by: phatt 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.
 
Title: Re: Roland Supercube 100 -- input jack advice needed (probably)
Post by: niftyprose 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
Title: Re: Roland Supercube 100 -- input jack advice needed (probably)
Post by: Enzo on May 20, 2020, 02:02:44 PM
I think you misunderstood me.  I have zero problem with the suggested ways to fix it.  I was concerned about this line:

Quote
avoid the recurrence of problems like this.

We should do whatever it takes to FIX it, but it doesn't need reengineering, because recurrence is not really an issue.   Too many times an OP will see any failure as a design flaw.  "My 12AX7 got noisy, how can I prevent that in the future?"
Title: Re: Roland Supercube 100 -- input jack advice needed (probably)
Post by: niftyprose on May 20, 2020, 03:23:21 PM
I will try contact cleaner before I go in with the wirecutters, Enzo, honest. But what I'm hearing suggests that contact cleaner won't be enough. Could someone review my previous ;post and see if I'm talking rubbish? Best, NP
Title: Re: Roland Supercube 100 -- input jack advice needed (probably)
Post by: phatt on May 20, 2020, 10:22:21 PM

Best I can make out is R101 was never installed hence the unused pads between the inputs can be seen in the pic. the amp will work without it and may even add a little more signal to pass.

I've edited the input schematic of the Cube 60 for reference.
sw1-sw4 are the internal switches.

How it works, maybe?
With no plug in either input sw1 grounds out R101 270k which mutes the normal input while sw2 grounds the output of Q1 at (point X)
with *Normal input* in use sw4 opens and signal passes through R10 with R9 running to (point X) which is still grounded via sw2.

With *OD input* in use, sw1 and sw2 open.
sw1 lifts R101 off ground which adds to the value of R10 forming a voltage divider at the input of C6.

sw2 removes the mute at point X allowing signal to pass throuh R9.
As sw4 is then closed it forms a voltage divider out of r10 and R101.

I'm not sure about the extra internal tab (the red ? mark)
I can only assume it contacts the sleve of the plug ,, which seems pointless as the sleeve is already grounded by the threaded metal socket???
unless maybe the metal thread uses a plastic isolation washer???

Hey nifty a Q, are you saying that the Od input and the Boost Switch are on that PCB? If so then my wire numbers I mentioned earlier are wrong.
 
I'm still trying to decipher Joe's idea but thought a drawing and explanation might help.
Phil.
Title: Re: Roland Supercube 100 -- input jack advice needed (probably)
Post by: Enzo on May 21, 2020, 01:00:07 AM
I think your description works.  As to the ???, The metal bushing on a TRS jack does not short the ring.  That is a grounded ring contact, so if you plug a TRS into the jack, it grounds the ring.  Say a balanced signal.  If you plug a common TS plug in, then of course the ring contact is redundant.

The jack is poorly drawn.  Usually we expect the tip to be farther from the bushing than ring, but here the positions seem reversed.
Title: Re: Roland Supercube 100 -- input jack advice needed (probably)
Post by: niftyprose on May 21, 2020, 12:29:15 PM
Enzo and particularly Phil, thank you so much! I had figured that something like Phil's analysis would apply, but I never actually had to anatomize such a circuit before and needed some guidance. Right...

I applied contact cleaner to a 1/4" plug and worked it in and out of both inputs, then did a partial reassembly on the workbench. Amp to speaker, amp to reverb tank, jacks back in speaker chassis. I kind of hoped that would sort things out, but actually the problem is worse than before. The jacks are really noisy, and wiggling the plug creates lots of full-volume speaker abuse. I think this is because the sub-board on which they're mounted has been shaken up so much over the last few days.
=>
I think I have to go ahead and disconnect the sub-board from the main amp board, install a new input jack, and make Joe's switch-mounted-in-spare-jack-hole thing work.

It will take me 24hrs to fully digest Phil's breakdown (like a python swallowing a goat). But it sounds to me like I can put a DPDT switch into the unused jack drilling, and use it to route the signal from the guitar to either 1&4 or 2&3 on Phil's diagram (which may or may not be labelled that way in real life, but we'll cross that bridge when we come to it). I'm concerned that I may be omitting to earth something somewhere!

In answer to Phil's question: "Hey nifty a Q, are you saying that the Od input and the Boost Switch are on that PCB? If so then my wire numbers I mentioned earlier are wrong." -- I'll do my best to give a straight answer. The 1*3" PCB sub-board that appears on my first gutshots carries both input jacks, a five-cable ribbon, and separate black and white leads to the overdrive footswitch. The five cables in the ribbon *must* correspond to the inputs in your diagram, surely, and they're numbered 1,2,3,4,5 where they join the main board. The time I spent with the multimeter and trying to work out the PCB gave me the distinct impression that those number assignments are different from those in the schematic (remember this is a Supercube 100, not the Cube 60 from the schemo). I think they're just reversed. I can presumably confirm that by tracking where the connections go to on the main board. Give me time.

One small point from my previous note that didn't get answered. If I'm joining the cables from that five-way ribbon connector to the new DPDT, I will need either to pare them apart with a craft knife (messy) or lug them into some kind of breakout board. Any recommendations?

Best NP
Title: Re: Roland Supercube 100 -- input jack advice needed (probably)
Post by: joecool85 on May 21, 2020, 01:41:29 PM
In looking at the schematic again, it is either wrong, or very poorly drawn.  It shows on the Normal circuit that the tip goes to ground (tip goes to pin 2, pin 2 is tied with 1, 2, 3, 4, and 5, and sent to ground right next to pin 3.  There are some dashes in this line connecting them, which may indicate that under curtain circumstance (unplugged lead etc) they are not all connected.  Regardless, as drawn I don't see how the Normal channel could pass signal at all since it is sent straight to ground.  I think that this may look more complicated than it is.

Here is my proposed solution:

Use a mono jack.  Send sleeve to ground.  Send tip to DPDT switch.  On this switch it will either send it to R1 for Overdrive or pin 2 (I think) for the Normal channel.  On the other side of the DPDT you can ground out the opposing channel.  IE: If switched to Overdrive, send Normal channel's input to ground via 270k resistor (R101 on schematic).  If switched to Normal, send Overdrive channel input to ground (R1).
Title: Re: Roland Supercube 100 -- input jack advice needed (probably)
Post by: niftyprose on May 21, 2020, 01:52:03 PM
Wow! Joe, I think you did a bunch of my 'digestive' work for me. I have to wait until the DPDT switch and replacement jack get here, so I wlll consider carefully and may come back with further queries. Thanks again, guys. NP
Title: Re: Roland Supercube 100 -- input jack advice needed (probably)
Post by: Enzo on May 21, 2020, 05:30:19 PM
Joe, step back and look again.  That line "connecting" 1,2,3,4,5 and has the dashes in it is not a trace, it is the border of the board.  It is not a conductor.

Ignore the dotted line, and reread phatt's description.

If you follow the dotted line around it would also"short" all three legs of Q11, or whatever transistor is at pins 6,7,8.  Clearly it is not a circuit trace.
Title: Re: Roland Supercube 100 -- input jack advice needed (probably)
Post by: joecool85 on May 21, 2020, 08:20:28 PM
Joe, step back and look again.  That line "connecting" 1,2,3,4,5 and has the dashes in it is not a trace, it is the border of the board.  It is not a conductor.

Ignore the dotted line, and reread phatt's description.

If you follow the dotted line around it would also"short" all three legs of Q11, or whatever transistor is at pins 6,7,8.  Clearly it is not a circuit trace.

Wow, very poorly drawn indeed.  But you are right, definitely a PCB edge.  Confusing since each pin label has a circle, typically representative of a node/connection.

The good news, my plan still works exactly as described in my previous post  :dbtu:
Title: Re: Roland Supercube 100 -- input jack advice needed (probably)
Post by: Enzo on May 21, 2020, 11:37:15 PM
Those are open circles unlike the solid dots of joints within the schematic.  Reminds me of the drawings for FX pedals, considering it is a Roland and so are Boss pedals, I guess that makes sense.
Title: Re: Roland Supercube 100 -- input jack advice needed (probably)
Post by: phatt on May 22, 2020, 01:41:13 AM
Obviously the top OD input SKT has failed and ideally you need to replace that socket but as it might be hard to source the exact part then here is an option using only one input socket,, probably similar to what *Joe* mentioned.
Now as it's possible the input for Supercube 100 might be different to the cube 60 schem I'm working from I can't be sure this would work so you will have to tread careful and double check.
This requires an N/C switched Socket and a DPDT switch to work.
N/C means Normally Closed,, opens when you insert.

As to your Q re those ribbon wires, you can just gently use your fingernails to split them, might have to nic between them to get it started but they should seperate fairly easy.
If you need more length then use a piece of strip board and then add more wires.
With out a pic of how the ribbon connects to PCB it's hard to give advice.
Hope it helps, Phil.
Title: Re: Roland Supercube 100 -- input jack advice needed (probably)
Post by: joecool85 on May 22, 2020, 01:45:56 PM
Obviously the top OD input SKT has failed and ideally you need to replace that socket but as it might be hard to source the exact part then here is an option using only one input socket,, probably similar to what *Joe* mentioned.
Now as it's possible the input for Supercube 100 might be different to the cube 60 schem I'm working from I can't be sure this would work so you will have to tread careful and double check.
This requires an N/C switched Socket and a DPDT switch to work.
N/C means Normally Closed,, opens when you insert.

As to your Q re those ribbon wires, you can just gently use your fingernails to split them, might have to nic between them to get it started but they should seperate fairly easy.
If you need more length then use a piece of strip board and then add more wires.
With out a pic of how the ribbon connects to PCB it's hard to give advice.
Hope it helps, Phil.

Looks good to me, Phil.  Your drawing adds in the switched jack so that when nothing at all is plugged in, both inputs are grounded.  Nice touch.

To niftyprose, the DPDT Phil shows does *not* need any connections between the top pins on left and right.  What he is showing is the switch in the overdrive position.  Also remember that wires traces that cross don't connect unless there is a filled black circle connecting them where they meet.

Good luck!
Title: Re: Roland Supercube 100 -- input jack advice needed (probably)
Post by: niftyprose on May 25, 2020, 07:14:43 AM
Guys, can't thank you enough. My DPDT switch arrived two days ago but I'm still waiting for the jack, and I have to go and take care of my mum for a few days. Look for an update in about 10 days. Best, NP