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ChromaTalk Archives: August 2012

Re: Comparing Chroma to CS80...

Go to first message in thread, July 2012 (also see parent thread, Chroma vs. other polyphonic analog synths)

Tobias Menguser

Hi Tim,

Thanks for the great summary of your CS80 & Chroma experiences!



Arun Majumdar [21030348]


I have both the Chroma, the amazing Chroma Enabler (by Randel [21030467]) and the CS80. On you-tube you can find my CS80 videos by searching galaxiesmerge CS80.

I would say that the CS80 has a very distinctive, but rather wide, palette of sounds (which you can hear in the first and second of my videos [embedded below]). When I get back my refurbished CS80 (with the Kenton Midi Kit installed) I intend to show some more as well as a comparison between the two synths. The Chroma, with the Enabler, is NOT the same old Chroma!!! It is an entirely different sounding machine since I can tweak in real-time, adjust, play and do things that would be impossible without the Enabler --- the end effect is that the Chroma (which always sounded great) now has *performance* within the sound timbres.

The difference between the Chroma and the CS80 is large because the two architectures, filter design, and components are different: the CS80 is a ripping synth for massive strings and majestic sweeps while the Chroma is precision synth for percussive, pianesque, and silky strings. It is like comparing a Steinway with a Bosendorfer --- both fine pianos, but, different. The Chroma and the CS80 are, now, individually very strong as individual synths - the Chroma/Enabler is a high performance machine and the CS80 is a high performance machine: the Chroma can be tweaked in real time and so can the CS80. I find that time spent on both for sound design is well worth it and in that sense I see less limitations in either the CS80 or Chroma. If you can, get both!

The reason I am getting the CS80 outfitted with Midi is that I can control and blend the Chroma *with* the CS80 using my Kurzweil Midiboard (or my Haken Continuum). I will be releasing an album next year so you'll get to hear plenty of that :)

I hope this helps.




This may be the best description of the Chroma I have ever read, although I would add that I can can get quite close to the organic nature of the CS like something is alive inside, but in a different color.

Tobias Menguser

I agree this is an amazing description, thanks!

Re: Touch Osc Editor template Modified

Go to first message in thread, July 2012 (also see parent thread, TouchOSC iPad Template Modifications)


Is there a way we could have Oscillator control in steps so it's easier to find octaves, 5th's etc ?

I think it's pretty cool to have both the Enabler and iPad to edit at once. Very inspiring.

Leon van der Sangen [21010301]

That is verre good possible to control in steps. THE only thing is that i have to reprogram most parameters which is verry, verry time consuming. At THE moment i am at vacation and i when i get home i Will think About it.

M wrote:

A few notes, you will not need OSCulator now, and TouchOSC for Ipad is 4.99 now, the Mac editor is free.

THE free editor is also in à Windows version (workshop even under Windows 7, 64 bit.

Thanks for THE comments.


Thank you Leon, maybe a button or ? for Ocatves (0-8-16-32) and a stepped control for interval tuning would be helpful. Enjoy your holiday.


Also, If anyone is planning a iPad Editor from scratch take a look at Lemur for iPad, a little more luxurious on the interface, etc.

David Clarke [21030085++]

iPad Template Modifications

As a general question - has anyone yet set an iPad up for bi-direction MIDI with the Chroma (so the template can automatically reflect the Chroma's current parameter state?)

Rhodes Chroma w/ CC+ Midi on eBay

Chris Ryan [21030691]

Item #271028103653, USD$8,499.00. From the description: "This one is in beautiful cosmetic condition and working 100%. It has just come back from being serviced and with some restoration. It's likely the nicest Rhodes Chroma for sale anywhere. It is ready to be played and needs nothing. As the title says, this one has the CPU Plus (CC+ Midi upgrade.) In addition, it also has the newer, better power supply (SPSU kit) by Luca Sfregola [sic]. It will come with two pedals, two manuals [Performance and Programming], the Midi box, and a newly foamed road case made for this unit when it was originally purchased.

"Nothing is ever mint in my opinion and this one is no exception. This one does look absolutely beautiful so please check out the photos and judge the condition for yourself. The original cherry cabinet has been restored as well as some of the metal. This was not done with a can of spray paint, but texture coated by a professional. Many of the black oxide screws have been replaced and it has new Switchcraft washers & nuts.

"Apart from any repairs, it's been disassembled and cleaned, all sliders cleaned, all electrolytic capacitors replaced, It had the new CPU Plus board installed, a new SPSU power supply kit installed, and everything calibrated. I may be forgetting a few things so check back to see if this has been updated."

I've asked the seller for the serial number.

A couple of pictures from the auction:



Dave Blees [21030552]

"It is ready to be played and needs nothing." well, except maybe a pressure sensor kit! Looking at the photos, I wonder what's the deal with the bad fit of the top cover - definitely not as original, I'm sure.

(If he gets $8500 I'm gonna be pissed! ;^)

Dave may have been looking at this (detail from one of the auction pictures):


Front Panel Issues...

James Coplin [16330036]

I'm starting a long restoration project on a Chroma I recently acquired [21030850]. I have it squawking after a fashion but there are a host of voice card issues. One immediate thing I discovered after running through all the front panel buttons and controls is that everything is working fine except buttons 51-55. This seems like a cable/chip type issue to me considering they are such a contiguous group. Any thoughts on where to start digging in with these? Thanks!

Chris Borman [21030194+]

Well, I have an alternative to replace all 50 prog/param bits with a push button optical pot. Anybody interested? Push for Prog. Spin for Param. Real time control of your Chroma.

David Clarke [21030085++]

... everything is working fine except buttons 51-55...

James - the parameter buttons go from 1-50. Might there have been a typo in the ones you noted?

James Coplin [16330036]

Ooops! I meant 31 to 35.

David Clarke [21030085++]

Buttons 31-35 area all controlled via the -STB3 signal.

This same strobe comes into play for the following 3 other functions (from the left panel):

  • Save All
  • Link Transpose Up
  • Link Upper

If all 8 elements (31-35 + the 3 above) are affected, then suspect that the signal itself is affected, and perhaps consider looking at what appears on pin 4 of Z13 on the I/O board (74LS145).

If only the 31-35 from the right panel are affected - but the other 3 functions on the left panel are fine - then the basic signal is fine, it just seems to have a problem on the right panel. That being the case, it would be good to trace the signal from Z13 through pin 8 of J15 on the I/O board.

Good luck with your debug, and let us know how you make out.

Dave Bradley [16330135]

Chris, have you actually done this already? Is there a picture anywhere if so?

Paul DeRocco [21030230]

My first guess would be a contact problem in the tail connector. Snap it open, remove the tail, and lightly burnish the silver ink with a clean pencil eraser. That might fix it. Even just wiggling it back and forth might bring it back to life.

It's possible that there is a failure inside the membrane switch, but that's not a common problem with the Chroma, the way it is with the Polaris.

Chris Borman [21030194+]

Chris, have you actually done this already? Is there a picture anywhere if so?

I was talking with some other members about it and they suggested I put up an example. I have a three position mock I made awhile back to check spacing. I'll see if I can mock up a bezel for that so folks can see the end result and how it would look mounted on the Chroma.

Michael Di Francesco [21040001]

Yes please!!

James Coplin [16330036]

I pulled the flat conductive cable for the panel and burnished the ends as well as hit the connectors with a little TF to remove any corrosion on them and now all is well again with buttons 31-35! Thanks!

I have gotten the CC+ interface installed so now I just have the new power supply, a handful of voice card issues, and a big refinish job and everything should be perfect! ;)

MIDI Interface on eBay Germany

Chris Ryan [21030691]

Item #170887290681 (see also eBay Classifieds item #64699131), ends August 5, starting price €150,00. It's not clear to me what this is: a Syntech/Chroma Cult clone? EES?

I Google-translated the description; corrections welcome. Excerpts: "Parallel port cable for connection to the RC is internally mounted on the board; connecting cable to the RC is fixed inside. ... Functioning only with sysex transfer converted CC + chroma-tested. SysEx works but only tested by chroma-CC + upgrade." It also lists some of the chips used; see the listing.






David Clarke [21030085++]

The places that the MIDI wires attach to the board are the sort of holes that would be used for honest-to-goodness PCB-mount MIDI DIN connectors.

I strongly believe that this is either a direct Syntech/Chroma Cult clone - or an original Syntech/Chroma Cult board that has simply be placed in an aftermarket case.

That being the case, €150,00 seems expensive given that an original can presumably still be gotten for about half of that (see Classified Ads).

two cps kits available now

Chris Borman [21030194+]

btw, I have two remaining CPS Kits completed from the last run...

James Coplin [16330036]

How much with shipping to 55410?

Chris Borman [21030194+]

Fixed cost $18 US, $36 International. Sensor cost is $265. Let me know if you want one and I will send you a paypal invoice.

Go to next message in thread, September 2012

Re: What do people actually like about the Chroma?

Go to first message in thread, July 2012 (also see parent thread, Chroma vs. other polyphonic analog synths)

Paul DeRocco [21030230]

I want to thank everyone for the interesting feedback. I think for now I'll keep doing what I've been doing, which is to replace my Chroma's guts with an off-the-shelf mobo doing soft synthesis under Linux, with lots of new features. Maybe down the road, I'll do a sound module in a box, or a VST plug-in. And who knows, a digital Polaris is also feasible.

Footpedal and Footswitch on eBay

Chris Ryan [21030691]

Item #300761522424, USD$225.00, ends September 11. From the description: "The items are in very good cosmetic condition and fully functional. These are the original accessories."


Voice card plays noise...

James Coplin [16330036]

I have two voice card issues, one I'm working through the other I wanted some guidance on. My voice card 5 passes tuning but will start outputting noise as if it were the selected waveform after some time. Hitting autotune will get it working again correctly but it will go back to outputting noise after 10 minutes or so. Thoughts?

Luca Sasdelli [21010226]

Hi James,

the cause could rely on the CMOS switches (Z17, Z18): due to their high impedance, those switches could capture environmental noise and feed it to audio path. I recommend to check the respective control logic signals too.

James Coplin [16330036]

By noise, I mean it sounds like the oscillator waveform has been switched to white or pink noise as a waveform, not just hiss or background noise. Thoughts?

Luca Sasdelli [21010226]

Should the noise be similar to the generated one, another thing I would check are the CMOS switches for waveform select (Z8, Z9), including their control logic.

If you own a scope, you can install the failing card in slot #7 for easy access to solderings, and try to follow the signal before and after the noise "switching".

Paul DeRocco [21030230]

I would expect that there is a break in the WAVE A1 or WAVE B1 line, either on the board or inside a chip, or that the output driving one or the other is blown out. It is probably being driven low during autotune by capacitive coupling from a nearby line, but after a while, leakage from some nearby source causes the voltage to drift upward until it turns on the noise.

In any case, the culprit is almost certainly Z8, Z9, Z27 or Z28. You can narrow it down to two of those if you can deduce whether it is the A or B channel.

Voice Cards not selecting correct waveform

James Coplin [16330036]

Trying to run down two voice card issues has turned up something I think is even more worrisome. I created the default scratch program and checked pin 7 on Z10 just to make sure I was seeing signal. Saw wave so all was fine. I switched the waveshape to square and went back to check pin 7 on Z10. Still saw. I started checking the other boards, all of them but one were still outputting saws when it should have been squares. I hit autotune and *most* not all of the boards starting outputting the correct waveform. I hit autotune a couple more times and I was able to get all the boards but one on the correct waveform. What is going on here? It can’t be all the voice cards are bad. What could be off that would still be somewhat corrected by the autotune algorithm?


Paul DeRocco [21030230]

That sounds like a problem with the data bus on the Channel Motherboard. Make sure all six bits going into and coming out of Z3 are 5V signals. When looking at the input, it's best to trigger off the WRSYND line, so that you can limit your examination to what happens on the rising edge of the clock. You could have two shorted lines, resulting in some 2.5V levels, or something like that.

Voice Card A at high frequency, B dead and Z19, Z20, Z25 *super* hot

James Coplin [16330036]

I’m kicking up too many issues at once so I think for my sanity and all the extremely helpful people here, I’ll just focus on one at a time and work through. What I started troubleshooting was a bad voice card that failed on power up, wouldn’t come back after a set split 50. I replaced Z19, Z20, and Z25. Looking at pin 1 and 7 of Z5 and Z6, both the A & B sections are not outputting correctly. The A section appears to be oscillating at extremely high frequency and B appears to be completely dead. Z19, Z20, and Z25 are extremely hot almost as soon as I turn on the Chroma. I checked for shorts on them but they check out good with no bridging. Next steps?

Paul DeRocco [21030230]

Those chips should never even get warm. Check both supply voltages on them, and look at all the signal pins to make sure that none of them exceed the supply voltage. Since they're all hot, I'd guess something wrong with a supply voltage, or a broken ground.

James Coplin [16330036]

I think I found the problem. It looks like I ordered the wrong type of 4051 chip. I ended up with a part number that is a high speed multiplexer version that is expecting a -v on pin 7 as well as the +v on pin 16. I see other datasheets for other related part numbers have pins 7 and 8 as grounds. Now I have to wait until next week for parts to come again. I hate not being able to go buy basic parts any more...

Paul DeRocco [21030230]

Pin 7 is the negative supply for the analog switches, as opposed to the digital input. The digital input voltage range is GND to V+, while the analog voltage range is V- to V+. If pin 7 were grounded, then the analog voltage range would be the same as the digital input range, but in the Chroma, V- is tied to -12V, so the analog voltage range is -12V to +5V.

For this application, you need the old fashioned CD4051 chips, not the modern 74HC4051 or 74HCT4051 chips, because the latter only allow the V- to go down to -5V. There are also HEF series parts made by NXP that will work.

Voice Card Edge Connectors?

James Coplin [16330036]

I've noticed now that I've been having to remove and shuffle around voice cards in my Chroma in an attempt to get it up and running again that the edge connectors for where the voice cards attach to the motherboard are extremely weak. I have a couple that basically move around fairly freely. I'm having some odd system wide intermittent issues so I was wondering if a poor connection between the cards and the motherboard might not be at least part of the problem. While probing around trying to diagnosis voice card issues, I also noticed that there must be a good bit of tarnishing or corrosion in the synth. Nothing looks rusted or damaged, but I have to "scratch" up the IC legs a bit with the probe to get a reading typically so I am concerned about things like the card connectors. Should I go ahead and just proactively replace them (assuming a suitable replacement is still available)? I'm also replacing all the electrolytics throughout the synth as I work through it - anything else I should just go ahead and swap out while I'm messing with voice cards? Thanks to everyone out there, I'm going to have a bunch of questions for this project and I appreciate all the guidance the group provides.

Luca Sasdelli [21010226]

Hi James,

I agree with you about connectors fairness, therefore if you've enough patience <g> you could replace all with Digi-Key part# WM2817-ND

About electrolytics, I'd concentrate on motherboard ones (you can easily install greater capacity components as power filters) and C13-C14 on DVBs, that quite often get dry; for C13-C14 I use audio-grade capacitors. Of course, audio path capacitors (even on EQ Board) could be replaced as well with audio-grade ones.

You can also recap the DVBs S&Hs (from C24 to C39) with Polypropylene capacitors (there are 5% or less tolerance low-cost available) to regain full CV stability, as well as 5% Polypropylene for C1-C3, C2-C4, C9-C11, C10-C12 for VCO and VCF.

Paul DeRocco [21030230]

In my two units, the electrolytics I had the most problem with were C13 and C14 on the voice boards. When these dry out, they reduce the gain in the filters until they no longer self-oscillate, at which point they fail the auto-tune. I had maybe four or five out of 16 boards fail in this manner.

Paul DeRocco [21030230]

I've not seen crud on the connectors that couldn't be dislodged just by jiggling them, and you're doing more than that when you remove and replace the boards.

It is easy to fold the receptacles over 90 degrees when plugging a board in, if you're not careful, which can break contacts if you do it multiple times. It's also easy to bend the pins on the motherboard, if one of them doesn't line up with the hole in the receptacle. But if you're always careful about proper seating of the connectors, you shouldn't have to replace them. I've never had one fail.

Screws for casing

Matt Hillier [21010094+]

Hi guys

does anyone know where i can locate a set of screws for the back of a Chroma? or have any details on size needed? basically it's the 9 which old the back plate / inputs etc top the case.

Johnny Vintage [21010244]

Not sure what you mean, but the black phillips head screws in the Chroma (rear) are 6-32

83' Garth Hudson Interview Mentioning the Chroma


[Legendary Organist with '60s Supergroup The Band by Bob Doerschuk] .....a few times enjoy. Wish his rig photo was larger. Does anyone have a larger version of the photo btw ?

Chris Ryan [21030691]

Does anyone have a larger version of the photo btw ?

I have the original magazine; here's a scan.

Garth Hudson

Troubleshooting and maintenance questions

John S. Allen

Hello -- I'm new to the list and have some questions about maintenance and repair of a couple of Chroma Expanders.

  • These are being controlled by a device which has no Set Split button I can push to (for example) check the battery voltage. Is there another way to access the Set Split functions? (Possibly the data format is given in the programming manual...but then I'd need to create a controller to send the data. I suppose I could check the battery voltage with a voltmeter, but that requires removing the cover.)
  • Can the batteries be removed and replaced when the instrument is powered on, without losing the programs? I think so, but just want to check.
  • I think that the heat problem could be fixed by increasing ventilation. One solution would be to install a fan. Has anyone tried this with a Chroma? I've had good results in other applications powering a 12V computer fan on 5V so it runs slowly and is near-silent. Two possibilities I see are to make a hole in the rear of the cover for the fan, or to use a very small fan under the ventilating slots at the left of the top of the cover, so air would be drawn in the other vent.
  • One Expander that does not boot appears to have no voltage clamp on the large power capacitor., or on the power supply board. Where could I get the needed part?


James Coplin [16330036]

On the Expander, the "Set Split" button is labeled as "Special Funct." It works the same way.

I would replace the power supply with a new one entirely. I did this on my Expander and Chroma and while they were working with the old supply, the new supply fixed several intermittent strange behaviors and made the instruments more stable overall. Plus, it won't go south on you and damage the Chomra.

Paul DeRocco [21030230]

  • Can the batteries be removed and replaced when the instrument is powered on, without losing the programs? I think so, but just want to check.

Yes. Of course, while working on a live circuit, be very careful not to short anything out. You'll probably need to pry the batteries out with a screwdriver or something, but if you've got something plastic handy, that would be a tad safer.

  • I think that the heat problem could be fixed by increasing ventilation. One solution would be to install a fan. Has anyone tried this with a Chroma? I've had good results in other applications powering a 12V computer fan on 5V so it runs slowly and is near-silent. Two possibilities I see are to make a hole in the rear of the cover for the fan, or to use a very small fan under the ventilating slots at the left of the top of the cover, so air would be drawn in the other vent.
  • One Expander that does not boot appears to have no voltage clamp on the large power capacitor., or on the power supply board. Where could I get the needed part?

I'll bet there are people on this list who've replaced their PS, and would send you their old OVP for the cost of postage. I haven't, so I can't. But I agree that replacing the PS is the best idea.


Update to the CC+ processor board for among 20 other reasons the heat generated is less.

Chromas on eBay

Chris Ryan [21030691]

Item #290766364778, USD$4,499.00. From the description: "The unit is 100% functional and in excellent cosmetic condition as well. I just had it fully serviced. The boards for the keyboard assembly (contact array) was replaced, the RAM was replaced, the back up battery was switched to a lithium battery, and the voices were tuned/cablibrated. [...] This piece has been tested and is guaranteed to be in proper working order or your money back." This is Chroma 21030311, previously in the registry only via the warranty card information obtained a few years back.


Item #190718631506, starting bid USD$4,000.00, no bids yet, ends September 1. Nothing about condition. I've asked for more information.


Chris Ryan [21030691]

This is Chroma 21030860, new to the registry.

Fwd: Chroma Case

Chris Ryan [21030691]

From: Frank Grande [former Chroma owner; email address removed]

I have a Chroma case in located West Hills CA USA if anyone wants it. The case has the usual rot on the inside. The outside is just ok works.

Chroma icontrolmididesign iPad editor project terminated


FYI, per their iTunes store page. [See iPad Editors: iChromaCC+]

Doug Wellington [21030300]

Wowsers, I just checked their apps on iTunes. Looks like they have terminated development on all of their synth editors. I've got to say though, $30 for such a simple looking app seems a bit much. For a thirty buck app, I'd expect to see graphical displays of envelopes, etc., not just the same widget repeated 32 times per screen...

If I ever get over my new found hatred for Apple (because of their stupid patent lawsuits over things they didn't even invent), I'll get back to iOS development. (Obscure reference: "Can you say 'SCO'?") In the meantime, how many of you have Android tablets?

Matrix [21030220]

Here are a couple:

You can find a video with my original templates here: