Roland GP-100 Rack Effects Processor

Roland GP-100 Guitar Preamp Effects Processor
Roland GP-100 Guitar Preamp / Processor

Today I took a drive out to a used music shop that I hadn’t visited in a few weeks. I didn’t expect to find anything, but there they did happen to have this little gem sitting on the shelf that I almost missed. The Roland GP-100 was in mint condition with no visible scratches or marks on it at all. The manual was all torn up so it looked like the person who previously owned the Roland GP-100 spent more time with the manual than using the processor…laugh. In any event, the store had a price tag of $125 on the unit and after a little bit of thinking I decided to pick it up. After bringing it home and going through some of the effects with the guitar, I’m so glad I bought it. It’s much nicer than I thought and the reviews are quite good on the GP-100.

I was excited to pick up the Roland GP-100 because I was in need of a rack effects processor mainly for keyboards and synths. I also heard that the GP-100 was used a lot with guitar synths as well, so I figured it should work out well with keyboards. I have yet to try it out with anything other than a guitar, but for guitar it’s really fantastic. All of the effects are really good and I was hard pressed to find anything really wrong with the unit or sound. I was nervous about the knobs being “jittery” but they work just fine. My Boss SX-700 had some finicky knobs which I replaced and now work fine. I also didn’t have any bad hissing or humming noises with the Roland GP-100 either. It’s really quiet and works very well.

Very much like the Yamaha FX500 unit I picked up a few months ago, the Roland GP-100 has some really interesting effect patches. I’m sure one can reproduce them on more current models, but I honestly hadn’t heard some of the effect combinations before and I thought that was really cool. I flipped through the first 100 patches with the guitar and I’d say all but maybe one or two were completely usable. In fact with many I wanted to whip out my Boss RC-50 and do some looping because I thought many of the effects would worked well with ambient or chill type of music. It was very easy to find 2 or 3 effects to layer with which would create some really interesting gooves. The GP-100 instantly was a breath of fresh air despite it being an older processor and I was constantly being inspired to create something unique with the sound effects.

Some of the more cool effects that I found to be totally usable were Slow Gear, most of the Reverse effects, chorus stuff, and many of the glistening tremelo and vibrato patches. Even the synth emulations were excellent. Without a doubt, if I was into creating ambient and atmospheric sounds or layers with the guitar the Roland GP-100 would be a goldmine of inspiration…absolutely! I can hardly wait to try it out on some synth and keyboard stuff.

For more info about the Roland GP-100 you can check out this site here:

The site gives a great Comparison between GP-100 and GX-700 which ultimately influenced me to get the GP-100.

If anyone has any comments about the Roland GP-100 Guitar Preamp / Processor, please leave a note below and I’ll do my best to answer any questions. I’ll update more about experience with the Roland GP-100 as I work more with it over the next couple of weeks. Stay tune!

10 thoughts on “Roland GP-100 Rack Effects Processor

  1. The following info was found on a blog at . The original blog is very slow loading and in fact for me it doesn’t load at all, so I copied some of the important info from Google Cache below. Perhaps this will help others regarding the jittery knobs for the Roland GP-100.


    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.


    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.


    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.


    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.


    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


    Attached are some of the photos that were missing in the original blog post which were snagged from Google image gallery. Sorry, it’s the largest size I could get too.

    Roland GP-100 Jittery Knob Fix 1

    Roland GP-100 Rotary Knob Fix

    Roland GP-100 Skipping Bad Knob Replacement

    Roland GP-100 Battery Replacement Photo

  2. I also forgot to mention that the Roland FC-200 Pedal Board works great with the Roland GP-100. They were kind of made for each other and the FC-200 is covered quite well in the GP-100 manual. I happen to have bought a Roland FC-200 about eight years ago and am glad I always kept it. It’s been a quite useful board for some of my gear.

    Roland GP-100 Rack Effect Processor

    Roland FC-200 MIDI Pedal Board for Roland GP-100

  3. Jeff

    I have been using the GP-100 since 1995. Through all my different gear tangents over the years the GP-100 has always had ‘something’ it could continue offering to my sound, no matter how obsolete it supposedly is. I’m pretty much an amp and pedals kind of guy these days. But recently I have been using the Roland for shimmer reverb effects using the harmonizer. In Oct (2010) I did a 3 day music festival with my SG and the GP-100 as my only gear. It sounded awesome and I got several compliments on my ‘tone'(haha it’s digital!).

    Mine does suffer from the data-knob jitter these days. I may get motivated and fix it, or not. I use an ADA MPC foot controller and my sounds are pretty much done, so I don’t edit as much as I used too.

    16 year old digital technology still going strong. I’m glad someone else is enjoying theirs too.

  4. Thanks for the comments Jeff!

    In addition to the quality and functionality of vintage gear, I find it’s the nostalgia that often drives me to buying and trying out such gear. When I was growing up in the 80’s I didn’t have the cash to buy what I needed. When I entered college in the 90’s I had to take my eye off the ball a bit and along with being strapped for cash couldn’t always purchase the gear I wanted as well. Nowadays with so much vintage gear going for cheap on the used market, it’s fun to finally have an opportunity to pick up such gear.

    A lot of old gear was “Good Enough” for Pros back in the day. I still believe much of it is still useful today although I know there are obviously more options available although some not always better.

    Enjoy and thanks again!


    1. I put up a blog about my GP-100 last week, which is how I found your blog 🙂

      I am still impressed with the harmonizer on these things. It’s not an Eventide H8000, but I still get nice POG-like synth and organ textures from the GP-100. It fills the space if several effects that I will probably never purchase individually: Feedbacker, Pitch bender, Harmonizer, Vibrato, and Slow Gear.

      As I like to say, “Good Enough” is, by definition, good enough!

  5. Alex

    HI! Glad I stumbled across your site. I bought a Roland GP-8 in 1985. I think it was brand new. It was about $700. (I think). It took all my lawn mowing money to purchase but my GOD did that think sound like heaven. especially to an extreme beginner. yes, crazy that a beginner would invest that much. yet, I had to have it. I had played violin since the age of 5 and at 16, I finally was able to convince my parents that guitar was for me (that or I just started playing guitar on my own and that was that lol) they would not pay for lessons or equipment despite paying huge amounts of $$ for violin teachers who were members of the national symphony orchestra. fair enough. they did give me three lessons for my birthday. But even the first time I saw an electric guitar my juices were flowing and I may have drooled a bit :p So, it was almost a foregone conclusion that I would buy the GP-8 when I first heard it. I had a $99 Bradly strat copy. A Fender sidekick 65 reverb SS amp and the GP-8. I joined a band in college and used the GP-8 for 3 years or so before moving to a Digitech dsp 2101. and then a few other things etc. So, here I am – many moons later, having sold all of my old equipment years ago, stumbling across your blog. I did a search for the GP-8 just out of curiosity and was suprised to find some on Ebay. I then stumbled across the GP-16 and the GP-100 and your site. For the prices that these are going for, I am inclined to pick one up. My question, if anyone would mind chiming in, is this: GP-8? GP-16? or GP-100? I play guitar only through a Reverend Hellhound head into a 2×12 cabinet. sounds great but the lack of flexibility with pedals is beginning to annoy me. I long for the days of a pedal board that was unrivaled in its flexibility. screw these pedal boards with 4 buttons. wtf is that good for? Never understood that. I dont want to be playing whack-a-mole with my feet onstage. The FC-100 had two banks so I couuld essentially access 20 sounds within 2 clicks max. The only thing I didnt like about the GP-8 was lack of reverb, noise and the lag when switching between sounds. So, I would greatly appreciate some advice. I dont have a lot of dough (what? a poor musician-type? I know, shocking). Thank you all in advance!

    Peace and great sounds


  6. MIchele

    I have 2 units GP100 in order to get one in music room and another for stage.
    I am vary satisfy of them, till the point to thinking about selling all other amps (tube fender “the Twins”) and many effects that at the moment I don’t use any more (also for the easiest way to play of the GP100).
    Enjoy your GP100, and forget the age.
    The GP0100 sound will surprise your friends for years in the future!

  7. MIchele

    Hi boys,
    anybody knows how to backup the patches data in a pc?
    Using the 2 software GP100 explorer and Patches Editor, the trasmitted data was wrong or not compatible with the GP!
    Please help me…

  8. Michele

    Update: the problem was fixed with an update to the drive of my software and a new USB to midi hardware… So everything goes well now!

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