Korg X-911 Analog Guitar Synthesizer (With Demo Recording)

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chromium
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Korg X-911 Analog Guitar Synthesizer (With Demo Recording)

Post by chromium » Thu May 08, 2008 1:52 pm

I just picked up a neat little "effect" - a Korg X-911 guitar synth.

Image

These were only built for a short time (~1981), probably didn't sell too well, are kinda scarce as a result.

...and this one had seen better days!

For those who don't already know if it, this isn't like most of those stomp-box synths (Electro Harmonix Micro, Boss SYB-5, etc..) that are basically octave/fuzz boxes with filters. This one is actually a real analog synthesizer, based on some of the same circuitry used in Korg's venerable MS models. It's designed to track note-on/note-off and derive the pitch of an input signal (guitar, bass, mic, another synth, whatever...), trigger its internal oscillators, and match the pitch of the notes you are playing. It has built in distortion as well, and many of the synth functions you would expect - envelope generators, glide, adjustable touch sensitive dynamics, a resonant low-pass filter, and a couple of oscillators. You can blend in your dry or distorted signal with the synth sounds as well.

That's a lot of "stuff" stuffed into a small package!

Image

This one came to me (relatively) cheap, as it was busted. It was one of those great Ebay auctions where the guy is selling stuff like old handbags, troll dolls, Korg X-911, hair scrunchies... He didn't know if/how it worked, but guaranteed that "it would make weird noises"! :mrgreen:

And that it does! :bananaguitar:

One of the pots was broken and seized up, it wouldn't trigger properly (bad 4011 NAND gate in the trigger stage), and an LED was shattered/burned out. I found a schematic online, sorted everything out, and now it works like a champ! I still need to tweak its "intonation" a bit. There are a number of trimpots inside that have influence over this. Adjusting them to track pitch properly seems like more of an art than a science (that's what I was working on in that pic above).

That said, I'm *really* blown away by it's tracking ability! I have a late model Roland guitar synth setup too, and being that this old Korg doesn't even have a dedicated/specialized pickup or anything, it does a *very* respectable job tracking notes.

Even with bass!! :sb:

I was jamming with it a bit last weekend, and ending up recording a little improv song thing to demonstrate some of the sounds it can make. All the synth parts in this demo were made by the Korg, and "played" using an Alembic Distillate bass (and a SG Special on those "bubbly", slow-attack sounds in the middle). Those crazy blips at the beginning are from string noise made by sliding my hand gently over all four strings - causing the Korg to freak out. There's some normal bass in the middle, which is from the Distillate as well.

I used a compressor to smash the input signals a bit, to help even out the dynamics so the Korg could do its best job possible with tracking. I then ran the Korg into the Space Echo, and then thru an old Alembic F2-B preamp. Here are some shots of the setup:

Image

Image

Oh yeah- and the song:

Squelch

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Kwote
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Post by Kwote » Thu May 08, 2008 2:27 pm

that's really cool man. i'll be sure to check the demo soon.
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Post by shamann » Thu May 08, 2008 2:59 pm

One of the local shops had one in over the weekend, didn't stay in stock long enough for me to even consider it.

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Post by felix » Thu May 08, 2008 5:23 pm

Awesome, nice find (and repair job)! Those are super cool, I've wanted for a while, but as you said, they are fairly rare.

I was skeptical on the tracking too, but it sounds like it works very well.
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Post by zerosum » Thu May 08, 2008 6:30 pm

:eek: Whoa :sb:
You always have interesting posts, great demo too!
I would love to play with one of those!

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chromium
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Post by chromium » Tue May 13, 2008 11:14 am

Thanks!

I didn't try it on this recording, but I'm thinking that it will be fun to experiment with bouncing tracks thru the 911 - have it double the source track, and manipulate it in real time as it follows along (or attempts to - the sound of which might also be a desirable outcome!). Endless possibilities!

Ever the archaic guitar-synth nut, I now have an old Maestro W-2 "Sounds for Woodwinds" incoming. That's falls more into the pseudo-synth realm - fuzztone, tremolo, octave, filter multi-effects-type box. I've been looking forward to that one, though. Wonder what a drum track will sound like thru it?? :domodance:

...or I can just plug in the upright - Melvin Jackson style! :mrgreen: :eek: :help:

Image

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Post by zerosum » Tue May 13, 2008 11:28 am

I now have an old Maestro W-2 "Sounds for Woodwinds" incoming. That's falls more into the pseudo-synth realm - fuzztone, tremolo, octave, filter multi-effects-type box. I've been looking forward to that one, though. Wonder what a drum track will sound like thru it??
I wonder..................... 8)
Looking forward to hearing it!!

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Korg X911!

Post by pigsnoot » Fri Dec 12, 2008 4:18 pm

Hello
My name is Micha Volders and I'm a anolg synth enthousiast/musician
Great Job repairing that X911!
I recently acquired a x911 myself , but the pitch tracking is not working, Now I'm little technical myself and after trying everything, including feeding it CV/gate from my MS10 (with worked beautifully) It still couldnt pick up the pitch from an audio signal (Frequency to volt/hz conversion) though it does trigger the vca envolope at one pitch/note only all the time when I feed it a signal......SO I opened it up, and discovered this big brown flat capacitor wich had some nasty slimey goo underneath it, so I thought or It's glue or it's leakage from the cap...When I touched one leg with a little screwdriver it changed and filpped around the pitch....Could this simply be the problem , by just replacing the cap?
Any help would greatly be appreciated !

Grtz
Micha

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Post by Kent » Fri Dec 12, 2008 5:06 pm

Impossible to say. Do you have a photo? It is probably a good idea to go in and replace all of the electrolytic capacitors at this point and the calibrate the machine.

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Post by lewis » Mon Jan 12, 2009 10:59 pm

chromium
hey have you figured out what each of the trim pots does on the bottom of the x911.
love to find a filter resonance adjustment!! :)

just got one of these and don't want to disrupt that tracking you talked about being a fine balance!!!

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chromium
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Post by chromium » Tue Jan 13, 2009 12:23 am

lewis wrote:chromium
hey have you figured out what each of the trim pots does on the bottom of the x911.
love to find a filter resonance adjustment!! :)

just got one of these and don't want to disrupt that tracking you talked about being a fine balance!!!
Hi Lewis,

Welcome, and yes I did know my way around that thing pretty well for a while there. PM me your email address, and I'll send you some PDFs that will map everything out.

@Pigsnoot - how'd your's work out? I didn't see your post here, but we corresponded a bit offline after it - so hopefully you were able to get up and running.

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Post by dr.morton » Sat Jan 17, 2009 8:15 am

What a great find!
Sounds better then some of the new stuff available.

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Post by snufkin » Mon Jan 04, 2010 6:50 pm

Hi I have used one of these for ages but it has a problem
my synthe section does not sound and the filter pot does nothing

Im pretty good with electronics and neatly re-soldered a cold joint but its quite an intimidating circuit

could this be a dead filter chip?

does the synthe section have its own VCO?

Im tempted to sent it off to a tech rather than tracing the fault myself with an audio probe

if any one can help thanks

any chance of those PDFs :guinness:
Last edited by snufkin on Thu Jan 07, 2010 5:00 am, edited 1 time in total.

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Post by Morley » Tue Jan 05, 2010 3:17 am

I did a youtube video with mine a while back
Sold it as I needed the money but kind of miss the little bugger :bananaguitar:
[video][/video]

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Post by chromium » Wed Jan 06, 2010 5:13 pm

Snufkin- just saw your post. Shoot me an email at the link in my profile, and I'll forward you the PDFs (zipfile) of all the schematics. It details all the sub-sections. The problem with mine was the same old dead CMOS proplem I've had with lots of other gear. Best to blow thru there and replace all of that while you're in, IMO. Can't say that is causing the problem you described, but just something to keep in mind while you are in the mode of repairing it. We can talk more in email, and I'm happy to try and help you identify your problem.

@Morley - your video is partly what inspired me to pick up this unit. Thank you for taking time to share all those demos. Its a wonderful experience to see all those venerable music machines in action!

I also sold my X-911 when I bought sandyb's old 5U system, and I miss it as well. I bought an Asys RS35 hoping it might provide some of what made that old Korg fun, but still need to port it to 5U or build a small euro system (leaning towards the latter now - funny how that happens :party: ).

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