Old Roland GP100 rack preamp -stereo output issue

[Nick Birkby]

Hello all,
Im setting up my Roland GP100 rack preamp and am having a problem that might be obvious but is baffling me a bit. Im setting it up for stereo operation, but when I plug in both the L and R cables, one defeats the other, as I recall Right becomes the working one and Left (mono) goes silent. Both the stereo outputs ( A and B) behave in the same way. I looked through the manual but I cant seem to find any reference to this. Any advice would be welcome, as i said it might be something obvious but its eluding me right now! Thanks so much

[BigRedX]

Do you have to specify a stereo signal path in the device for the outputs to work as a stereo pair?

[Wonks]

That sounds wrong. The output jacks (well at least the right one) will have some form of switching involved, so squirting some contact cleaner in there and pushing a plug in and out several times might fix things. Like effect send and return jacks on amps, if the sockets aren't used, then the contacts can corrode.

But it might be a bad solder joint on one of the outputs.

You've got two sets of outputs. Can you set it up to use the second set and do they work OK?

[ef37a]

From the manual, https://cdn.roland.com/assets/media/pdf/GP-100_OM.pdf
it seems to me that the output jacks follow convention? That is, plugging into just the left output monos L&R outs. Plugging into both outputs gives stereo operation.

There are two input jacks, front and rear but these are both mono and the front jack takes priority.

Could be tarnished jack switches as Wonks says but I usually find you need to get in there and use a strip of thin card moistened with cleaner to remove the grime. In really bad cases you might need some very fine Emery paper, again with lubricant/cleaner. I am guessing that rack unit came from a time when everyone smoked and we had open fires!

Dave.

[Kwackman]

Red herring alert...
You ARE using leads with mono jacks?
Red Herring alert over.

[Nick Birkby]

Thank you for all the replies. I will try switch cleaner again and if that does maybe open it up and have a look. As I recall both sets of stereo outs behave in the same way.

Im working on the rack again this afternoon and will report back.

Ps the jacks are mono.

[Hugh Robjohns]

... when I plug in both the L and R cables, one defeats the other, as I recall Right becomes the working one and Left (mono) goes silent. Both the stereo outputs ( A and B) behave in the same way.

That's very odd!

The output circuitry is very simple.

The left and right outputs each come from the collector of a transistor buffer, via a 1k resistor and a 10u capacitor (with a 100k tie-down resistor on the output side). Each output connects to the tip of its respective TS output socket.

The mono-ing function is achieved by wiring the tip contact on the right socket across to the left tip.

So, if you plug into the left only you get a mix of left and right. If you plug in to both, that tip contact opens and each channel works independently.

So... from your description it would appear you're not getting any left output at all, and actually only the right channel is present when in mono mode.

While it's possible for one left output buffer to die it seems unlikely that both would fail. So I suspect it's either an internal setup or configuration problem, or the left channel of processing has failed somewhere.

Does the headphone output provide proper stereo?

Can you find an effect with identifiable left/right elements (ping-pong delay, for example) to proce which channel elements are present in mono and stereo output modes?

I highly doubt squirting noxious substances into the sockets will help.... this problem sounds more fundamental.

[Wonks]

It seems there is an internal L/R balance control. Worth checking that.

[Nick Birkby]

It seems there is an internal L/R balance control. Worth checking that.

I will have a look for this.

I opened the unit and looked, it appears clean, no repair work or strangeness.
The headphone out seems fine though I couldnt find any very obvious ping pong delay patches in the time I was with it.

The jack sockets seem fine and have been sprayed. There is a definite physical disconnect when the right jack is plugged in- the L mono dissapears. I can plug in L mono on the A set of outs and R out on the B set, though as I said I couldnt hear any obvious stereo ie ping-pong or left right panning.

Anyway I will keep trying. Its probably due to be recapped, though there are lots....Thanks again for the replies.

[Wonks]

You could try a factory reset in case it’s purely software related.

https://support.roland.com/hc/en-us/art ... y-Settings

1. Hold the PARAMETER knob while powering on.
2. Press WRITE

That’s it.

If you’ve only just got it, then fine, but if you have any patches you’ve created and want yo jeep then do a sysex backup of your patches.

[Tomás Mulcahy]

Personally I would make 100% certain I am reading the labelling correctly. With dyscalculia (and I imagine for dyslexia too) this is the kind of thing I need to be wary of. All the sockets are close together, so are easily confused if you have one of those learning differences- especially since (at least on photos of the Japanese model) The Left input is on the RHS! My solution is to actually stand behind the rack unit at eye level, rather than looking over it from the front (ie upside down) of the rack.

This issue crops up for one or two students every year as well, those learning diffs are qauite common.

[Nick Birkby]

Thanks I did a reset but no change. Ive had it for a long time but mostly used it in mono so I didnt notice.

Last thing is try and find the pan trim and see if its oxidised or something.

Yes, there are a lot ins and outs on the back. I pulled the whole rack out to make sure I could see it all properly.
I then noticed Id plugged another unit in incorrectly!

I will either use it in mono or if I feel strongly enough take it to a tech.
The chorus patches on these units are really quite classy. They have a surprisingly glossy produced sound. I was thinking of using it as an effects unit (minus amp / speaker sims) with my sansdamp psa1 which is in the same rack.
I will post a picture soon.