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Messages - niftyprose

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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

2
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

3
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.
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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

4
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

5
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

6
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.

7
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.

8
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.

9
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.


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