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ChromaTalk Archives: August 2005

GenEdit ST Chroma Editor

Chris Ryan [21030691]

Dave Blees [21030552] contributes an article about his editor for GenEdit ST for the Atari platform. The editor has support for continuous controllers and sports a full parameter editing interface. Screen shots are included, and the editor is available for download, along with a bank of sample patches (still working on getting these in Syntech sysex format), for anyone with an Atari!

Thanks Dave!

Jesper Ödemark [21010135]

Cool! I'll check this out when I get some time to fool around in the studio next time... The CC-thingy is great, that's what I've been missing on the Chroma Editor I use today [Der Chroma-Editor].

Chroma Photos for Upcoming Keyboard Column

Chris Ryan [21030691]

Mark Vail (Vintage Synthesizers) is writing about the Chroma for his Vintage Synths column in Keyboard magazine and asked for a photo. I had my friend Oli Gardner take some pictures of my Chroma last night for the magazine. I think the results are excellent [see the Photo Gallery]. Mark wants to use #2, though I think the close-ups show the detail and character of the instrument in a way that's rarely seen.

Malte Rogacki [21010091]

Beautiful pictures!

I can see why Mark wants a total instead of a closeup, but please somebody convince him not to take #2! The black background blurs with the bottom of the instrument; and the overall impression is almost gothic!

David Clarke [21030085++]

I'm partial to #1 - but I personally like #2 too.

Jack Colburne [21030142+]

I also prefer #2... made me go "OOOOooooo". I think the dark background looks richer and I don't have the "Bright Light! Bright Light!" reaction I get from the white in #3. I also think that you can more comfortably see detail without the high contrast.

I Really like #1 and #6. Very classy.

The drop shadow on #4 looks like someone is "dreaming" about a Chroma.

Hey Chris, you've got a good looking box there. In very nice shape.

Jesper Ödemark [21010135]

I like the close-ups - especially the panel reflection in the black keys! *mmmmm*

But my Chroma envies the not-battered wooden sides! ;)

Chroma (Nuclear) Power Supply Mod Help

Jeffrey Koepper [21030671]

HI I am having trouble with a Chroma that I modded with the "NUCLEAR POWERED CHROMA" mod by Don tillman. I modded the chroma and installed the modern replacement power supply and everything works great except the voices are now out of tune? The power up diagnostics pass all voices but they are obviously out of tune. I checked and verified that all voltages are correct. Another weird thing is that the tuning seems to be related in some way to the pulse width, patches with different pulse width settings are out of tune differently depending on the pulse width settings. Any Chroma experts out there with any ideas about this? I really think this is a nice mod and should make the chroma stable for years.. thanks analoguejeff

for ambient electronic music -visit

Stu Ervin

are you missing a ground somewhere???

Paul Tillotson [21030218]

Did you perform the modifications yourself? If so, was it difficult and are you very technically proficient? Mine's back in the shop with another bout of power supply troubles.

David Clarke [21030085++]

I'd first check to see if it is possible that there's only one board which is misbehaving (it is possible for a board to pass auto-tune, but still to have other sicknesses).

If all the voices seem out of tune, then I would double-check:

  1. The voltages as seen on the channel motherboard are OK (esp. the +/-12V supplies)
  2. That the DAC null was adjusted (the adjustment noted at the right-top of page 5-1 in the Service Manual).
  3. That the voice card trim procedure (service manual page 5-1, half-way down 2nd column) was also completed for all board.

(Any change to the power supply voltages could/will likely change the settings noted in step 2 and 3, therefore requiring readjustment).

Good luck - and let us know what you find.

Jeffrey Koepper [21030671]

HI I was just checking it and it seems like the keyboard tracking is off, I put the chroma in monomode single voice and as I play up the keyboard each C gets a little sharper. Any ideas?

Jason Creek [21030668++]

Hmmm... if you're scrolling through all 8 voices, then whichever voice is landing on c each time is sharp. are you sure you're only using one of the 8 voice cards?

Jeffrey Koepper [21030671]

HI I did some more testing today and found something kind of weird. With the new power supply in the Chroma there is a voltage fluxuation happening on the 12+.- and 5 volt lines when certain parameter values are changed. For instance the +12 volt goes from 12.38 to 12.34 when the waveshape value is changed from 0 to 63, Also the +12 goes from12.38 to 12.41 when the resonace is changed from 0 to 7, the other voltages also seem to be affected by .03 or .04 with in the range of the certain parameters like waveshape amount, tuning, resonance and filter tune. Any ideas on this ? This may be the cause of the tuning problems. Has anyone else installed the map80--4000 in their Chroma? Any help will be appreciated, cya analoguejeff

Jason Creek [21030668++]

Hmmm... sounds like you've installed a switching power supply, eh?

Did you save your old power supply, by chance? Why did you change it out- just the 60Hz humming issue? I would imagine that if you kept it "maintained" (i.e., replaced all questionable parts now), that power supply should be a once every 20 years maintenance issue... None of my beeswax, bro. I just hope your Chroma is okay, you know.

I just get the feeling that a switching power supply's voltage varies with the current that is demanded of it, which, in this application, is a horrible thing, if true.

Best of luck. I'll check out your ambient music meanwhile. Thanks for the link.

Jimmy Moyer [21030184]

I put a MAP80-4000 in my Chroma over the winter and it has been solid as a rock since.

As someone else suggested, I'd be suspicious of a grounding problem. It may not perfectly clear from Don's original photos, but all the grounds need to be tied by a high current path to the output grounds on the power supply. All the output grounds are tied together internal to the power supply.

Also for safety purposes you want the back panel, hardware, etc. tied to the ground from the wall outlet which essentially means you need to tie the power supply's input and output grounds together. They are not tied together internally to the power supply.

Jeffrey Koepper [21030671]

HI thanks for the reply. Did u have any problems with the map 80? How were your + and- 12 lines? the problem I am having is weird, for instance I turned the chroma on a measured the voltages, the -12 was at -13.3 volts the 2 5 volt lines were at 5.3,It seems like the power flucuates with this supply. Also the voltage changes when parameters are editting by like.3 volts. I have all the analog and igital grounds tied to the 2 comm points on the output of the power supply, the ground from the ac input is tied to t he back panel and to the ground input on the power supply. Does that sound right?

Jeffrey Koepper [21030671]

HI ok I see from the archives it is the over voltage protect board. I think mine is causing a problem. Has anyone tried the nte 4096 diode as a replacement? I was curious about installation of the 4096. Which side does the black band go towards the positive or negative terminal on the Over protect board?

David Clarke [21030085++]

I have all the analog and igital grounds tied to the 2 comm points on the output of the power supply, the ground from the ac input is tied to t he back panel and to the ground input on the power supply. Does that sound right?

I don't have the newer supply in a Chroma here - but an earlier poster noted " need to tie the power supply's input and output grounds together. They are not tied together internally to the power supply..."

If you haven't done this, it might be something to check. Specifically, to see if this could be an issue you can measure the voltage between the incoming AC/wall ground and the local/power supply ground. These should be at the exact same potential (which should be at the same level as the chassis ground).

... It has an LV0V6 on it. I am having a hard time finding that part. ...

A couple points/notes:

  • The original L60V6 part is likely available through one of the folks on the list (check out: Source for L60V6, August 2004)
  • With regard to the operation of the 5V supply (in general), I have yet to find an original Chroma which hasn't had developed a problem with the big 47000uF cap. While some Chromas may still run OK most of the time, they can get flakier and flakier. If your power supply still has the original baby-blue Mallory cap, I would be suspicious as to whether or not it is still actually able to do its job properly.

Check out the 3rd para. of the "Calibration and Checkout" section of the Service Manual. If you see the voltage on top of the cap normally dipping below 6.2 volts, the cap may no longer be able to hold the PSU up high enough. A drop-in replacement is the Panasonic GAA series (47000uF, 25VDC, computer grade). These run approx. $20ea and are readily avail. through digikey ( under P/N P10074-ND.

Jeffrey Koepper [21030671]

HI here is a regular chroma power supply question, What purpose does the little board on top of the large capacitor? It has an LV0V6 on it. I am having a hard time finding that part. The symptom of the chroma power supply is that it works fine, until you hear a buzzing coming from the supply when this happens the digital 5v goes down to like 2v. If I remove that little board from the cap the problem goes away. I am testing this supply outside of the Chroma. Any ideas?

Jimmy Moyer [21030184]

I have all the analog and digital grounds tied to the 2 comm points on the output of the power supply, the ground from the ac input is tied to t he back panel and to the ground input on the power supply. Does that sound right?

Sounds like you also want the back panel tied to the power supply output ground. (Or as you said in another post tie the power supply input and output grounds together.)

For some reason the ground return from the channel motherboard is through the back panel and not any of the molex connectors, even though there are unused pins that could have been used.

I've had zero trouble with stability with my map80. That you're seeing funny measurements on multiple outputs makes me suspicious of grounding as it's unlikely you have a map80 that has multiple defective regulators.

Don Tillman


As "stuervin" and "ChromaOne" have suggested, it's sounding more and more like a ground wiring problem.

You need to find another set of eyes, a buddy who knows more about electronics than you do, and have him go over all of your wiring extra carefully.

Consider yourself very lucky; in the mail archives you'll find an account of someone who simply forgot a ground wire connection and blew some stuff up. This is why I say in the article that it's important that you have a background in electronics before attempting the power supply transplant operation. In much the same way you'd want your doctor to have some experience before attempting any medical procedure, let alone something as heroic as a heart transplant.

Jeffrey Koepper [21030671]

HI everyone. First off thanks for all your help and tips. This is a great list! I do have a background in electronics and I have had alot of experience with vintage synths. I think I found the problem with the map 80 power supply mod. A wire needs to be soldered from the input ground to the output ground as soon as I did this it was stable. I thought that the power supply already had that connection built in. That part of the mod was not included in the instructions on performing the map80 mod. I followed the instructions to the letter. So just a warning to everyone be sure to perform that important mod to the map80 when installing it in a Chroma. I will let everyone know how the Chroma performs in the studio, thanks for everyone's help, especially Don Tillman for his cool mod.

Don Tillman

That part of the mod was not included in the instructions on performing the map80 mod. I followed the instructions to the letter.

Please stop misrepresenting my article; there are no "instructions". The article does not contain the words "instruction" or "step", so you could not possibly have "followed the instructions to the letter".

On the first page I state, "It should be clear that this article is a report on a project of mine and not a recommended procedure."

I mean, c'mon; how clear can I possibly be?

Jeffrey Koepper [21030671]

HI Sorry, I meant to say article, not instructions. Thanks for a very cool mod Don.

Anyone refinish their Chroma?

Jeffrey Koepper [21030671]

HI I was wondering how may people have refinished their Chroma. Any tips?

Vincent Russo [21030433]

we did, check the archives there is quite few in there.

Also note that there is a Google site search on the home page.

Chroma on eBay UK

Chris Ryan [21030691]

Item 7342255542. No bids, 9 days left. From the description:

This vintage and very rare synth was, when brought out considered the Rolls Royce of truely portable synths and is still today sought after by many. I have owned this synth for a good many years, held mostly in storage within its pack horse type flight case. this particular instrument was said to have been used by Spandau Ballet for their spot on the original Wembley live aid concert. but I cannot verify this. Unfortunately a couple of years ago I removed the keyboard to show my son and couldn t get it to load any programmes. So this instrument needs to go to someone who is, or has access to a technician who is familiar with the instrument I am told by an expert that the fault would probably be quite easily remedied .. But nevertheless is so;d as not in working order. I can promise though that no one has fiddled about or tried to fix it, so my hope that the fault is obvious. (Check out the various Chroma enthusiast websites) The body work and general condition is great as is the flight case. (No pics because lack of digi camera)

I e-mailed the seller to acquire a photo:

Jesper Ödemark [21010135]

known chroma?

Have you mailed this guy already to get him in the registry? He seemed determined enough to win the auction...

Chris Ryan [21030691]

Re: known chroma?

I have. I have also added the instrument to the registry with a picture from the previous owner (hopefully the new owner will look inside to find the serial number).

Rhodes Chroma restoration project

Rob Belcher [16330123]


Greetings to all :) I have been looking through this great website and list archives for sometime now, and have decided to finally join! I've been on AH for a few years now, and also to the Cs80 user group for a year or so, so im sure i will know some people on this site from there.

Anyway, the reason im posting is i bought a nice looking Rhodes Chroma a while ago that needs some work.

I was hoping somebody may be able to recommend a great Chroma technician or repair shop in the USA or UK that will be able to do the repair/retoration work for me, someone with lots of experience in repairing Chroma's is obviously extreemly prefferable. Alternatively, is there anyone on this list who has the spare time to take on my restoration project? It seems there are some great techs on the list who have extensive knowledge on Chroma's in general.

About my Chroma, it has a PSU problem (as many Chromas seem to) the existing PSU is not working. So ive decided, id like to swap out the existing PSU with a new switching device, to make the synth more stable. Id then like to get any other possible remaining problems fixed.

Im located in the UK, but my Chroma is presently located in the USA. As my Chroma is already in the US, ive decided it makes more sense for me to get it restored over in the USA, and then ship it to the UK. It seems also that the best techs for Chromas seem to be based in the USA. I do know Roy Paynter in the UK , (who i understand is a Chroma trained engineer) i bought a Rev2 P5 from him recently, but when we spoke last he mentioned for personal reasons he wasnt repairing any synths at that time... Roy, if your on this list and do have time to restore my Chroma please do get in touch, my email address is If there is anyone else in the UK that would like to restore a Chroma please get in touch....

But, as i mentioned before, as the Chroma is in the USA, my preference is to get it restored over in the USA and then ship it to the UK. The Chroma is in a heavy duty flightcased, so shipping wont be a problem.

Id be really pleased to hear from people that could help! I really want to get this beast restored!

Many thanks.

Paul Hackett-Evans [21010094]


I spoke to Roy a couple of weeks ago, on behalf of someone who wanted a Chroma repaired. Roy was happy to take the job on.

I'll send you Roys phone number privately, as Roy has asked me not to post it on the net.

Good luck with the restoration,

Best wishes,

Rob Vandivier [21030396]

Thanks Paul,
It's still in the garage but it would be nice to finish the friggin job. What news from mr Benchic?

only(???) 2102 for sale

Jesper Ödemark [21010135]

on swedish web site the one listed in the registry [21020003]. He wants offers...

The page, "Rhodes Chroma - helt unik analog monstersynt," (, has disappeared. Here is the text (if anyone can translate, I'd appreciate it):

Insänd av Joakim Uddling. 15 aug, 14:18. Ta bort, ändra, förnya annonsen

Endast tillverkad i ca 3000 exemplar. Inköpt för den nätta summan av 43.000 riksdaler 1982, endast en ägare. 16 röster, viktade trätangenter, fullt programmerbar. Allt fungerar, MIDI-kit installerat (Ken Ypparillas, dvs det bästa) vilket ger 8 parallella kanaler samt multitimbbralitet. Helt unikt serienummer (det enda kända hittills i 2002-serien, 21020003), möjligen en av de första 50 handbyggda. Inkl instruktionsböcker, en väldans massa ljud, en Atari 1040 ST + monitor för ljudbankerna och disketter till denna. InklOriginal Anvilcase.

Massor av info på nedanstående länk

Ring eller maila och bjud om du är seriöst intresserad.

Supply Swap

Randel Osborne [21030467]


I'm a Chroma newbie, and am currently repairing unit 21030467 for a friend, "The Packrat" creator, Dave Lovelace, who purchased the instrument in Cambridge this Spring.

Through the extremely valuable information I've received on the site, I've replaced the power supply, and built an aux board for the tapper, powerfail, and +5V analog supply.

By neglecting a ground, I, too, have burned up one of the DACs on the I/O board, and have replaced it.

At the moment, the instrument runs for about 5 minutes, at which point the display flickers, and the computer shuts down, and won't run after the power is cycled.

If I leave the instrument off for about an hour, it will run for another 5 minutes.

The powerfail seems to be working properly, although only puts out about 4.4 volts.

I will work my way through the diagnostics page of the website, but thought I'd ask a few questions:

Do these symptoms sound familiar to anyone?

What is the powerfail voltage supposed to be? Exactly 5v?

Are the LEDs supposed to flash 16 times upon auto-tune?

Is anything supposed to be connected to J22 on the I/O board?

Does the cassette interface actually need to control a cassette motor to properly load patches, or can I feed it an aiff of patch data (assuming that I can find such a file)?


Stu Ervin

sounds like maybe something is heating up, and then drawing too much current, and the power supply is currentlimiting and going into shutdown.....

you should hang a voltmeter on the +5 line and observe it during the entire cycle.

maybe you have a bad power supply?

David Clarke [21030085++]

At the moment, the instrument runs for about 5 minutes, at which point the display flickers, and the computer shuts down, and won't run after the power is cycled.

What do the voltages look like after the problem has occurred? Has one (or more) of the rails folded back, or has the 'reset' line to the main processor dropped too low?

Are the LEDs supposed to flash 16 times upon auto-tune?

Yes - one flash for each voice-card channel (8 dual-channel voice cards = 16 voices).

Is anything supposed to be connected to J22 on the I/O board?

No. Most Chromas don't have anything connected here (that's where a pressure sensor would be connected, if the keyboard was fitted with one. ref: the J22 note in The Chroma Pressure Sensor & Interface)

Does the cassette interface actually need to control a cassette motor to properly load patches or can I feed it an aiff of patch data (assuming that I can find such a file)?

Depending on the setting of Set-Split 10 (Cassette Mode), the Chroma may want to wait for a positive indication that the cassette tape motor is running.

That being said, if you change the cassette mode, you should have no problem loading patches directly from an aiff (or other sound format).

You'll find the patch data on the Patch Downloads page.

And you can use the Patch Conversion Tools to convert SYSEX into something a computer can feed back to the chroma (e.g., SND format).

(Note - there is at least one patch set already available in a computer readable format: see Factory Sets for a Factory Set 5 .wav file.

Randel Osborne [21030467]


Thanks for the response.

I spent some more time with the instrument tonight. The +5 stays rock-solid when the computer shuts down, as do the rest of the voltages, and the reset line doesn't move.

I was able to get it to run long enough to write the "scratch" patch to memory, and to play the instrument a little. It is able to recall the written patch after a power cycle.

Some of the notes hang, and some don't trigger - I think it's more of a keyboard scanning problem than a dirty contact problem.

Also, the parameter slider has stopped working, and the battery voltage displays some weird numbers, 0.0v, 3.8v, 5.8v. etc. The slider and the battery feed into op amps into the A/D converter, and the voltages into the ADC seem good. Tomorrow I'll have a further look at the output of the ADC.

I'm also thinking about replacing my +5 and ground connections from the power supply to the Molex connectors. I used a small diameter wire for this, and maybe it needs to be a lower resistance - although it is only 3 inches long.

Moog is gone

Jesper Ödemark [21010135]

Hi list... I guess most of you know but yesterday (21st of August) Robert Moog passed away at an age of 71.

Without Moog there wouldn't probably have been any ARP and without ARP no Chroma. Let's tune those oscillators to his memory...

Stu Ervin

right on man. he was a pioneer, inspired, motivated, and technically capable of making his vision a reality. i bet he had some help from his friends.... his sounds will live on long after we are all just a deleted email file in someones trash bin.....