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Roland GP-100 Jitter Repair

This is a thread I borrowed off a mailing list for the Roland GP-100. The GP-100 is one of the first digital amp modeling effects units. I have two of them, and was getting an annoying hum in one of them, so I spent some time this evening taking the "Broken" unit apart.

This thread is from the Roland GP-100 mailing list dated March 2003 between Rex and Kevin. I have no idea who Rex and/or Kevin are. The pictures are Kevin's, though.

Who knows but I'm glad I had it tonight.

Rex Started:

Did you ever wrestle with a GP-100 that had a jittery PARAMETER or NUMBER/VALUE knob? You know -- where you turn the knob in one direction and the display jumps two or three steps in the other direction? It's the most annoying "feature" of many Geeps, and those who must live with it curse it loudly. If this sounds like you, relax...your problems are solved. Most likely, the culprit is the knob itself. I've experienced this problem on both of my Geeps, and in each case, the problem was a small crack in the core of the knob (the central part that grips the encoder shaft). This flaw is hidden from view unless you remove the knob and look at its backside. There is one fairly wide, very uniform split that's supposed to be there. If you find two cracks or splits, that's one too many. The split causes slop in the knob-to-shaft coupling, which causes switch bounce, which causes...well, you know the rest. So do yourself a favor: go to the and get Roland's US tech support number (unless you live outside the USA, in which case you can go to and find the number that's closest to you). Then call that number and order up a couple of new knobs at US$ 2.00 each. Then install the knobs, sit back, and enjoy Geeping as it was meant to be. That's what I did, and now my Geep never jitters at all.

Rex //Computer Guide

At this point, I have no idea if those knobs are still available. My unit was in fact having the jitters. I took it apart to try to diagnose a huge humming noise making it unusable, but while I had it opened I went ahead and took a look at the jitter problem.

Just a quick how-to (this may be old news, disregard if it is and a couple pics of how to fix the encoder problem the best you can without replacing them..

Blowing air or contact cleaner will most likely make the problem worse then it is. These are not optical encoders, what happens to these usually is the grease they use to lubricate the little ratchet thingy gets all over, contact cleaner and compressed air makes it a bigger mess usually. Also what happens is the ratchet teeth get worn and it doesn't 'center' properly on the clicks. Anyhow, a phillips screwdriver, small jewelers screwdriver and a pair of needle nose pliers are all you need. I used some contact cleaner sprayed on a q-tip to clean everything, used a pencil eraser to 'burnish' the wheel and contacts, one more cleaning with the cleaner and a dab of silicone grease on the teeth - a very small dab with a toothpick.

Also, the reason I even bought a GP100 (paid 100.00 for it), is the previous owner was quoted 150.00 to replace the backup battery - its a common $3.00 CR2032 battery available at radio shack in a slip in holder as you can see by the pic. This one had the 'replace battery' screen up and the owner freaked out. If you replace it powered up you probably wont lose your presets (I don't have a schematic so I say probably), just be careful not to drop the battery on the main PCB or on the 110v mains wires/terminals that are exposed on the PS board - or you could just back up your presets on a computer and change it with it unplugged/power off I guess. Be careful when working with this plugged in, the AC wires are exposed and easy to lay your arm on by accident - trust me on that

This is probably old news but I was bored tonight and got sick of the 'jitters.' Back to the way it should be now, took ~15 minutes to do.. If you want these pics for a web page or whatever grab them now - they wont be up for long..


Thanks Kevin, I did snag those photos and have reposted them here, 6 years later give or take a few days. Unlike Kevin's prowess, it took me about 2 hours to get the GP open; and then additional time to figure out how to get the knobs off and stuff. Before searching out the original e-mail; I used quite a bit of compressed air blowing. But, nevertheless that seems to have fixed my problem; at least for the moment. My hum went away once I had the whole thing apart; no idea why. It stayed away while when I got the thing back apart.

Comments (Comment Moderation is enabled. Your comment will not appear until approved.)
Glenn's Gravatar I've been putting up with the jittery knob for a while, but your blog entry encouraged me to take it apart and fix it. And, it's my mailing list :-). Thanks.
# Posted By Glenn | 5/22/09 11:55 PM
Jeffry Houser's Gravatar Glenn,

I greatly enjoyed the list as I was on it. Thanks for being the host.

My input hum came back once I got the unit back in the rack. However, it is sporadic; as opposed to all the time.

I assume some type of loose connection is being made, but I couldn't figure it out. Everything looked right to me. Of course, I'm not an electrician or anything like that. ;)
# Posted By Jeffry Houser | 5/23/09 1:46 PM
Pete's Gravatar I gold hold of a GP 100 recently, after wanting one for years. There's been a bit of a gloomy cloud on the horizon though, because I knew that one day issues with the battery would arise. This is the only info I've managed to find on the web about the subject, but It's all I hoped to find. I can't thank you enough! Cheers.
# Posted By Pete | 2/4/10 5:09 PM
Rex Robitschek's Gravatar Hi Jeffry,

I'm the "Rex" you quoted in this thread. I was searching the web for GP-100 info and came across your blog. Both issues — the one I posted and Kevin's follow-up — can cause the jittery behavior of the control knobs. I'm glad folks are still getting good use from the information in the GP-100 mailing list. Pity it fizzled out; a lot of good information was passed around.

Regarding replacement of the battery, the word from folks who have done it is that if you (carefully) replace the batter while the unit is powered up, all will be well. I've also heard it said that if you don't keep it powered up during the procedure, the Geep may not only forget its presets, but forget how to be a GP-100 entirely. However, I can't speak from experience. I've yet to need to replace a battery in one.
# Posted By Rex Robitschek | 6/27/10 7:10 AM
Jeffry Houser's Gravatar Rex,

Thanks for the follow up. ;)

I have not yet needed to replace the battery either. Something which I'm thankful for!

I haven't been able to successfully remove the jitters entirely either; but I haven't spent much time on it.

My taking apart, and putting back together, the unit helped to fix the weird hum; but I have no idea why. It still comes back on occasion.
# Posted By Jeffry Houser | 6/28/10 1:20 PM
Chris's Gravatar I have an old Roland GP-100 and decided to try to find the rotary encoder replacement, because I'm having the same jitter problem myself. It's an Alps rotary encoder, and I believe it is part number EC11B15242AE. It has 30 detents (15 pulses) per rotation and push-on switch (0.5 mm travel). I haven't been able to find part ending in 'AE' that's in stock, but at Mouser, they do have the AF (EC11B15242AF) in stock, which is practically the same as the 'AE', but with a push-on switch with a bit more travel (1.5 mm vs 0.5 mm). I don't think it'll make much difference - the knobs will stick out 1 mm further, but I doubt it'll be a major problem. The pin out is the same, although the switch body is a bit thicker (7.75 mm vs 6.7 mm). I'm ordering a few of these, will install them in my GP-100 - if I can remember to return to this site, I'll let you know how it goes.
# Posted By Chris | 7/10/10 4:45 PM
Jeffry Houser's Gravatar Chris,

Cool; I'd love to hear your final analysis. Thanks for the post.
# Posted By Jeffry Houser | 7/10/10 11:19 PM
Rex Robitschek's Gravatar Chris,

In case the almost-matching encoders don't work out, give Roland a try. I bought one from them a few years back. I don't remember the price, but I do remember that I thought they were quite reasonalbe.
# Posted By Rex Robitschek | 7/11/10 2:18 AM
bordeau didier's Gravatar Hi

I Can't switch the channel of my amp with the "EXT CONTROL" function of my GP100 ...the parameter is "ON" !!!

couls anyone help me ?

Thank you from france
# Posted By bordeau didier | 7/12/10 8:14 PM
Chris's Gravatar I installed the new Alps rotary encoders (EC11B15242AF from Mouser) and they work! The knobs only stick out a little bit more than before (it's hardly noticeable) and the extra 1.0 mm of travel necessary to push the button isn't a problem at all. My old encoders (the original Alps EC11B15242AE) were totally shot, and I couldn't edit patches, etc.

I'm not the original owner of the GP-100, so I don't know how well the original encoders worked when new, but even these new encoders will skip every once in a while. So they don't work absolutely perfectly, but my GP-100 is totally usable again.

I may look around at rotary encoders from different manufacturers to see if there are some that are more robust, i.e., don't skip at all. Encoders with less detents/pulses per revolution might work better, because these Alps encoders have such small spacing between detents, they are bound to skip occasionally, and the overall design of these Alps encoders seems a bit suspect. I got an extra two to replace the ones I just installed when they wear out. They were $5.61 a piece, so not too expensive.

I hope this helps someone fix their old Roland GP-100. It's a great unit! I use it mainly for effects, which are excellent.
# Posted By Chris | 7/17/10 3:08 PM
Jason Robertson's Gravatar I also suffered from this jitter problem until I found this link. Just carried out all the instructions and my parameter knob now works flawlessly. Thanks!
# Posted By Jason Robertson | 7/24/10 6:23 PM
red fender's Gravatar How do I get the preset settings for a GP100. I just need a few to try on my GTPro as I sold my GP 100.
# Posted By red fender | 8/10/10 4:02 PM
Chris's Gravatar Thanks for the info- - gonna see if i can get rid of the jitters asap! By the way, i recently downloaded a patch editor for the jeep for my pc. I bought a $3 usb/midi cable online and now there is no problem with losing presets, because you can just save them on your computer. Also, there are a number of user-made presets that you can download and use at Editing is really easy this way too. Highly recommended. it's at
# Posted By Chris | 10/5/10 6:40 PM
Roland's Gravatar Update: For those still using this preamp/processor Mouser DOES stock EC11B15242AE ALPS encoders. The only physical differences are the length of the threaded shaft and the D-shaped knob shaft. Filing off the square locating nub on the base of the threads and installing your old nut takes up the difference. I cut down the D-shaped shaft with a Dremel and shaped and cleaned it up with a file (not really recommended or required).
# Posted By Roland | 11/22/13 3:23 PM
tpz's Gravatar I've also replaced both encoder bought ,in Europe, from a big Electronic shop (art. Nr. 729-5555). Also Here I had to cut the shaft a Little bit with a dremel. Now Unit is working is battery ;)...cheers
# Posted By tpz | 6/1/14 5:11 AM
doormouse's Gravatar This is a great guide for cleaning rotary encoders and a big thanks to the OPs and for the re-posting over the years. Although my experience lies in drum machines and synths, I can tell you this will save you much time and money. Roland uses some of the cheapest button switches you can find and they will fail. Anyhoo, as to the original hum problem, it sounds like the encoder is not properly grounded itself or that you have a bad capacitor that is bridged and causing that seepage. If possible ON BATTERY POWER NOT AC, you can sometimes detect a bad cap by touching the plate on top and listening for the hum to go up in volume to isolate which cap is bad. Worked for me. Caps are frustrating because they are hard to test and bulging comes at end of life/catastrophic failure. Another test I do is the sniff test. Smell around the board until you find ozone and that is usually the offending part. I have also seen a factory reset work wonders on pedals that were "broken" but that merely had very badly mucked with user presets. May also have some sort of calibration setting in there that will help. I find this is usually present on "one channel only works" kinda fixes. Thanks gain for the guide and keep on jamming!
# Posted By doormouse | 3/22/15 10:35 AM
Patrick's Gravatar I did a job on one of these recently. Fitted a couple of new power transformers so it can run from 240V here in Australia. I sorted out the unreliable encoders while I was in there. My question is does the push button switch on the parameter control do anything? I scrolled through loads of different menu pages and couldn't find anywhere that it did anything. They both change values smoothely as required now and the switch on the value dial works fine. I'm just not sure if the parameter switch ever did anything or theres something up with it now that I've had it apart.
# Posted By Patrick | 9/2/15 12:17 AM
Scientizt's Gravatar Dear Jeffrey,

Thanks for this nice info. I bought a GP-100 for 25 bucks because the pots were not working well. The unit was in good shape, and i fixed it in about an hour using your "tutorial". Both pots work well now and i really love this unit, it's big but tight sound is perfect for the music that i make.

Best regards from Holland!

# Posted By Scientizt | 1/21/16 10:03 AM
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