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ChromaTalk Archives: March 2005

Chroma Expansion Board and New Firmware

Chris Ryan [21030691]

New on the site this month is Chroma Expansion Board and New Firmware, by Sandro Sfregola with David Clarke, which documents a homebuilt hardware upgrade with expanded memory and on-board MIDI. (Sandro provided a preview on the list in January.)

Features include voice allocation display on the 8-digit LED; a shortcut for creation of a "scratch patch;" on board MIDI (a comparison with Syntech/Chroma Cult, with which it is compatible, is included) with controller mapping functionality and system exclusive dumps; and more. Schematics and firmware are available for those who would like to add the expansion board to their Chroma(s).

This is a very cool project--thanks Sandro and David!

Jesper Ödemark [21010135]

Amen!

I will build a knob box one day (ONE DAY!) and when that is finished this would be really cool too. Does anyone knows if it works fine with the EES midi too?

Werner Schöenenberger [21010114]

Hi Sandro, David and Chris,

definitely excellent work. When finding some spare time, I have to scope into this subject - definitely.

Thanks a lot.

Vincent Russo [21030433]

I guess the first question I have is, does any adventurous person have plans to make a run of boards to offer the non DIY types here ?? Im very happy with my syntech midi interface actually. But the Expanded patch memory would be nice as well as future function additions.

David Clarke [21030085++]

I'm flattered that my name appears prominently in the introductory note (and the article on the site) - but to be fair, the idea for the interface (as well as the great majority of the work) was from Sandro.

Sandro - thank you for allowing me to participate.

control voltage

Wayne Griffin [16330111]

I apologize if this has been discussed before, but I am curious about any endeavours to interface the Chroma with CV control signals from the outside world. I often send functions from my modular into other polysynths to boost the complexity of certain sounds. Has anyone ever processed audio through the Chroma? I wonder what that would sound like. How difficult would it be to create analog interface to the VC controlled portions of the Chroma? It would be really interesting to drive it from an analogue sequencer for instance...

Chris Ryan [21030691]

See "CV/Gate?" from January 2002. This is probably a good time to mention that there is now a Google site search on the home page, the new site having been pretty thoroughly indexed at this point.

Jesper Ödemark [21010135]

I think Wayne was after cv _in_ and not out. So you could control more or less everything with external LFO's, theremins, wheels, ribbon controllers and other wacko stuff...

David Clarke [21030085++]

... I apologize if this has been discussed before, but I am curious about any endeavours to interface the Chroma with CV control signals from the outside world. ... How difficult would it be to create analog interface to the VC controlled portions of the Chroma? It would be really interesting to drive it from an analogue sequencer for instance...

I think it'd be a bit tough to do.

I'd expect that most poly keyboards would suffer the same general woes - namely it would be tough to have an external signal routed on-board since the filter/amplifiers are controlled/assigned on a voice-by-voice basis and don't (necessarily) have discrete VC control over different components.

Also, just thinking about it quickly, you'd likely need to add patch points to the voice card itself, because the analog voltages for the VCO/VCF/VCA only exist once you get onboard the voice card itself.

Other poly's (like the Prophet-5) sort of 'cheat' in this area, in that patching in an external CV only goes to one of the voices, and it patches directly into the CV sections for the voice (after the sample and hold sections have already been skipped). For the Chroma, to get to 'the other side' of the sample and hold circuitry, you'd need to already be internal to the voice card.

Doug Terrebonne [21030114]

I would imagine you could make a pretty cool modular synth out of a Chroma voice board though - something I've been meaning to do with the OB-Xa voice cards I have...

Ben Vehorn [21030757]

There are CV-->midi interfaces available, they don't seem to be very common but can be found if you look. Roland made one called the OP-8m that took 8 channels of CV/Gate and 2 channels of VCF/VCA modulations and converted them to midi. I believe JL Cooper made one as well, and I have recently read that some modern modular manufacturer starting making one.

This would allow you to use analog sequencers to control the Chroma although you wouldn't be able to do things like plug an outboard LFO or envelope directly into the mod matrix (though I'm sure you could use the pedal inputs for this).

Ben Vehorn [21030757]

I would imagine you could make a pretty cool modular synth out of a Chroma voice board though - something I've been meaning to do with the OB-Xa voice cards I have...

Like the Oberheim SEMs that's more or less made for it. Here's mine for those who fancy a look;

http://www.electronic-obsession.se/studio/sem/sem.html

knob boxes for Chroma

Ben Vehorn [21030757]

I was just asking about this on The Gas Station, but figured I'd ask here since the Chroma and Voyetra 8 are the 2 main synths I want to edit...

Are there list members that are using external midi knob boxes to edit their Chroma? Of course I would like a dedicated Chroma box like the one on the Chroma site [see ChromaKnob], but I'm thinking of getting a generic midi box and making a Chroma template. I like the looks of the Mackie C4 because it has 32 knobs, displays for each knob, and lights to show relative knob values. Someone on the Gas Station suggested that certain synths (ex. MKS-80) use long Sysex string lengths that a lot of programmers can't handle. Is there anything funky about the Chroma I should know when shopping for one?

I have to admit, though, I'm not in as much of a hurry to do this since I bribed a friend who has a plotter at work to print me a 40 inch wide copy of the parameter chart...

Thanks.

David Clarke [21030085++]

Assuming you're using the Chroma Cult/KMX knob box, then as long as the midi knob box will allow you to map to a Continuous Controller, you should be OK (i.e., the most common Chroma midi interface interface doesn't use a strange SYSEX config - you can manipulate the parameters directly with CC's).

Ben Vehorn [21030757]

Great, sounds like it won't be too difficult.

Thanks!

Re: de-foaming the Chroma

Go to first message in thread (February 2005)

Olli [21010284]

hi robert

get the unit in your garden, scratch the removable rests off with a sharp knife (very small angle to not cut into the wood, take it slow until you master the technique) put on some good rubber gloves take a bottle of acetone and some kitchen paper roll and apply the product WITHOUT spilling any acetone on the keys or plastic and just wipe the foam rests off. note that you will remove the old paint that has reacted with the foam, too, but many of us agree that the wood looks even better and has a classier finish without the transparent paint. enjoy! (you can see the results of this technique on www.bluesynths.com [see Reviews for current URL]).

good luck

Robert Shanks [21030301]

Olli

Thank you, so much. I will try that. This is the first definative answer I have received. I look forward to having my favorite synth back out of the closet, defoamed and making music.

Thanks - Happy Chroma -ing

Olli [21010284]

hi robert,

thank you for the reply, i recommend doing it in the garden as acetone is pretty unhealty if breathed and in cantact with your skin. the most important thing is avoiding to cut into the wood with the knife while scratching off almost all of the foam. if you take your time, it should work well!

keep me posted

Kenton MIDI Kit

Erik Vellinga [21010286]

This message didn't get through to the list as it was too large; but I'm including it here in the archives.

Hi Chris,

Here is a pic of the Kenton MIDI kit. Mentioned on the PCB is TR808, we know is a Roland drummer. Perhaps they used the same PCB. It is definitely the Chroma Kenton, used for a couple of years in my Chroma. Now replaced by a much better Cult. Note that the Kenton had to be built inside the Chroma. I had to solder all of the small ribbon wires to the corresponding pins in the Chroma. I saw you already have the manual.

At your service,

Erik
NL

free chroma & expander

Bo Williams

Hi List,

I'm moving very soon and have a Chroma w/ expander in my storage w/ road cases. They don't work.

If someone wants them for parts, all they have to do is pick them up in Monterey CA by March 31. Otherwise I'll be forced to junk them.

Jesper Ödemark [21010135]

Damn dudes - SAVE THEM!

It's so unfair I'm in Europe...

Chris Ryan [21030691]

Yeah, I used to live in the neighbourhood (Silicon Valley) but I've told Bo that if no one else takes them, I'll pay postage, or even drive down (I'm back home in Vancouver now). Anyone want to take a road trip?

Jesper Ödemark [21010135]

Good to hear them going to a good home!

Olli [21010284]

well, would love to :-) a little far away though. even though i say to myself that it might be cool to travel to the US and meet some of the AHers.

anyway if noone wants them i'll have them picked up and send them to europe if that is OK with you Bo.

Bo Williams

free chroma claimed

Thanks for your responses! I have contacted the first respondent to claim the synths.

Paul Tillotson [21030218]

I was trying to not consider a road trip down from Seattle for the Expander...

aussie chroma on ebay again

Jesper Ödemark [21010135]

[Item 7307515602]

Jesper Ödemark [21010135]

Why doesn't those Tazmanian devils buy a splendid synth at a decent price? All the nice extras etc.

See Chroma on eBay Australia, February.

Greeting from a new Chroma owner!

Corley Brigman [21030386]

Well, thanks to the unbounded generosity of another Chroma list member [see free chroma & expander above], I now am the proud owner of an (as-yet-unworking) Chroma and Expander pair :) I know I'm going to need a lot of help on these over the next few months, but also I just wanted to add to the list of which chroma is where.

The Chroma is serial #21030386, apparently like most other USA chromas (i have spent a good deal of time in the last day reading on the Chroma site :) The Expander does not appear to have a serial number... is this a common occurence? At least there's no serial number plate, but these appear to be more rare too.

Neither of them are working yet; the Chroma hums but nobody's home, the Expander has lights and responds to input some (that tapping-back is really weird at first!) but the display is not working and after pressing 'autotune' it goes into the void too.

Now if I could just get some donated free time as well ;)

Jesper Ödemark [21010135]

So you saved those advertised on the list. Congrat's!

Doug Terrebonne [21030114]

Ah, so you're the one who beat me to them... :-/

First thing I would check on is the batteries... They're the reason mine was dead when I bought it (leaked all over CPU board)... Hopefully they were removed when the units were stored...

Corley Brigman [21030386]

Ah, so you're the one who beat me to them... :-/

Sorry :)

First thing I would check on is the batteries... They're the reason mine was dead when I bought it (leaked all over CPU board)... Hopefully they were removed when the units were stored...

I finally got to open it up tonight. And sure enough, the batteries had leaked everywhere. The chroma is pretty bad, corrosion all over the CPU board. The expander also had a blown-up battery, but somehow the corrosion doesn't appear as bad on that one. Probably explains why it is able to do something (tap at me, even though I am not doing anything...)

First, some background. Back in the mid 90s when i was in college, I had just a cz101 and a turtle beach maui (cheap ISA sampler card). In all the samples on the public sites of moogs and roland were a couple of samples just called POLARIS1 and POLARIS2. They were nothing that special, mostly open vco type drones but they sounded amazing, and I fell in love with the sound. I knew I wanted to get a polaris one day, but never saw one (and didn't know anything about the Chroma).

Eventually I found one a few years later at a music store clearance... it wasn't working. Turned out all the CEMs had been harvested (maybe for an Xpander or something), and thanks to Synthtech (plus a couple other analog logic chips that needed replaced) it started working beautifully. I've had a couple other polarises since then, always needed something fixed. And there are a few more basic samples out there from my Polaris as well.

Then I heard about the Chroma. It sounded cool, but I couldn't justify the cost for what was basically a hobby studio. So I never got one. Recently, I almost got out of music altogether (at least keyboard)... and now I have a Chroma (and an Expander to boot!). I guess it's not time to give up keyboards just yet... I'm looking forward to using this one for a long time..

Back to the Chroma problems. Well, the units were given to me, having sat in their cases for about 10 years. They were supposedly working when they went into storage. Battery leakage by itself can explain this i think, so I am hoping this is a pretty straightforward repair. The expander, it just looks (so far) like a couple of the ROM chips are busted (but I will reburn them all). The Chroma is in worse shape... it leaked in three directions. All the ROM chips are very fuzzy with corrosion. In addition, above it are some more chips which are also corroded. Traces on the board also look corroded, though I'm not sure how bad it is. And the other direction, the keyboard scanner ROM is also corroded, along with a couple other traces as well (this is on a different board). The expander needs the output jacks replaced too, as it's pretty rusty around the edges (the screws were also rusty, one was almost impossible to get out because the phillips 'fins' were rusted out). And they have the typical 'foam rot' interacting with the wood. I guess that will have to be replaced, though the cases themselves otherwise seem in good shape.

A bit of work to get started. I am hoping that these will be all the problems. But I guess you have to be a tech to own a Chroma anyways :)

This group (and the site) is a great resource... it looks like everything I need is already there. So thank you very much!

Doug Terrebonne [21030114]

I finally got to open it up tonight. And sure enough, the batteries had leaked everywhere. The chroma is pretty bad, corrosion all over the

Sigh... Such a shame so many people don't think to remove the batteries and a dollar's worth of alkalines kills a highly valuable synth. I struggled with cleaning the corrosion for a couple years with mine and finally gave up on that and found a spare CPU board and the Chroma was back to life. Luckily there was no corrosion on any of the other boards...

Stu Ervin

For all that corrosion, consider using a toothbrush, some vinegar, and some baking soda. and lots of careful scrubbing. then a final wash with plain old warm soapy water, followed by a hairdryer treatment to dry it out.

two chromas FS in Sweden

Jesper Ödemark [21010135]

Hi List!

Just received a mail from a guy wanting to sell his two Chromas. Ran across him in a search for a MiniMoog but if you're interested, mail me offlist and I'll get in touch with him...

No, no idea about prices etc. And yes, I'll try to get him to register them.

Jesper Ödemark [21010135]

Take it out and remove those batteries on the double!

electronically yours, jesper - still awaiting info on the two "Stockholm units" I mentioned...

Greetings to Chroma fans from new subscriber

Phil Jelatis

I will soon be posting information on my Chroma. I am a pro working musician in Miami,FL. At the moment it resides in a closet (out of it's case) and is so hidden by clothes that I couldn't get to it to check the serial number. I bought it new in 1983 when I lived in Boston. I lived in a house with some people that worked at ARP and I met a guy named Mark Smith who was on the Chroma team and made the transition to Fender when they moved to Woburn, MA. He gave me a design and parts list for a simple memory doubler with a toggle switch-basically a chip that piggybacked on the old one. (His personal Chroma had an orange panel with extra large program selector surfaces (!) which he said was a prototype). My Chroma worked when I mothballed it but a couple of boards were iffy. I have the Syntech midi interface. Thanks Chris and all of you other contributors. I'm inspired to take out my Chroma and get it going again.

Chroma power supply

Kevin Kelley [21030491+]

What is the chances that someone on this list has one for sale or know where I could purchase a replacement? Just wishing.

Stu Ervin

I can repair yours if you want.

David Clarke [21030085++]

Kevin - just to clarify for the benefit of the other folks on the list - are you looking for a replacement/extra (original) Chroma Power supply (e.g., as you might need if yours was missing) or do you have one now that doesn't work (and you'd either like to swap it with a working one or something else that will give the Chroma the necessary power)?

Kevin Kelley [21030491+]

I can repair yours if you want.

how much? I am not a electronics expert, I have tried what I know and am now stumped.

Stu Ervin

I can easily fix it if you want to ship to boston. they are very simple supplies, despite all the bad press about them....

Brian Silva [21030450++]

Hello,

I live in the Boston area and have 1 Chroma and 2 Chroma Expanders. Do you do tech work on them?

Brian Silva [21030450++]

Hello Again,

Thanks for the help. I just happen to live in Gloucester, MA. Who and where are you?

Chroma on eBay

Serial number 21030825, eBay item 7311739621. "Mint" condition; includes standard accessories and an unspecified MIDI kit [looking at the pictures, it's a Syntech/Chroma Cult]. No bids yet; first bid US$1000.

I was a little hurt that the seller included a reference to vintagesynth.org rather than rhodeschroma.com, until I found that it results in a "page not found" error. :)

Go to next message in thread, April 2005