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ChromaTalk Archives: September 2010

New display

Heinz Weierhorst [21010276]

See The Chroma Now Supports an External Alphanumeric Display, August 2010.

Congratulations to Dave and Sandro.

The alphanumeric display is a must for all Chroma users! So easy to work with. Now one can see all that hidden things with just one view. Absolutely great.

Thanks a lot!

Re: Advice on keeping Chroma

Go to first message in thread, August 2010

Philippe [21010227]

The Chroma generates sound like no other and is really the reason we are all here discussing this (with Chris' help of course!). As far as any sonic upgrade to the Chroma, I want to try that OPAMP upgrade. I thought the demos really opened up the sound. If I were to get a P5, it would have to be a Rev 2 with the SSM audio Integrated Circuits and maybe Luca's mod's. The P5 3.x and Chroma both contain Curtis parts. A couple issues with the P5 Rev 2 and 3x is MIDI upgrades can be hard to find or not very flexible (No program dump/save, really? wtf?) I have seen a 2 with a good MIDI port. So, I think the instability of the 2 gives it's character...

Hi Chris,

Just read this email of yours and was wondering where I could find more infos about this OPAMP upgrade you are talking about. Would you have a link to share?

Re: CPS - An experience

Go to first message in thread, June 2010

Chris Borman [21030194+]

I got a couple PS upgrade boards quite awhile back. I had my own switchers. My Chroma never booted @ first power up, always took a couple tries. Never actually looked but thought it was either the reset circuit or my switchers current capability. Lately, this boot issue has become worse. While testing the 25th+ CPS Kit, the right half was hosed, left half worked fine then my keyboard went somewhat south - Now the Chroma boots @ first power up every time and the audio boards tune as well (at least as well as they can...) I hear the tuning jingle so the audio path is still there? I think the h/w somewhere in the keyboard scanner circuitry path took a dump. I see no display flashing (int) effect at all while hammering on the keys. So maybe the keyboard was loading the PS the whole time? Thoughts?

As far as further CPS testing, I just need to check that each sensor is addresed, functions and not shorted or open. Other than maybe Arun helping out here with a spare Chroma... (Of course after I verify that I did'nt blow up my KYB scanner!)

Since it is in my plans, I will use my PICDEM FS USB board to interface to and write a simple scanner to check CPS operation.

Chris Borman [21030194+]

Forgot to add - No sound from keyboard hits.

Heinz Weierhorst [21010276]

Hi Chris.

With a scope look at !KINT while pressing some keys. It should go "low". Next is !K Mask, should also go" low". There is a (transparent) latch build around Z49-B; C. It's ok? Are strobes !RDNOTE and !RDVEL present? Another thought is, when autotuning the main processor disables the keyboard. Is that routine "hanging"?

CC+ Chroma Mackie C4 Editor

James Coplin [16330036+]

I've made a set of templates for the Mackie C4 controller for the CC+ interface. It might also work with the ChromaCult interface but I can't test it since I no longer have one. If it does work (or if it doesn't) with the ChromaCult interface let me know. The page has screen shots of the 5 pages in the editor and some more information. I think it should be fairly straight-forward. There are 2 files you need. The c4i file is the sysex specification and parameters for the Chroma. The c4l file is the template layout file. It contains the labels, pages, etc. If you prefer a different layout on the C4 then the one I have made, you easily can make a new layout without having to edit anything in the c4i. Let me know if you find any errors, have questions, or requests for changes/additions.

Considering the C4 can be had readily for $300-$400 it's a heck of a value in my opinion. If you are considering getting one, keep in mind that Mackie support for the product is not officially but realistically at an end. While it is a great sysex and cc controller, it does not support checksums - something to keep in mind if you are planning to make editors for your equip. Enjoy!

James R. Coplin

Re: Front Panel on eBay

Go to first message in thread, August 2010, which includes pictures from the auction

Chris Ryan [21030691]

On 2010-08-24, at 4:25 PM, Chris Ryan wrote:

Item #250687444386, "buy it now" price of US$799.00, ends August 31. Edited description: "Auction includes one fully populated Chroma front panel with all circuit boards (EQ board, I/O board, computer board) and display. These are spare parts that were sold to me several years ago (2004ish) as working by someone I trust, but I never installed them to test so they are untested by me but believed to be functional. They have sat bubblewrapped and unmolested on a shelf since then and now I'm cleaning out the parts bench. I did swap out my Chroma's I/O board a few years ago when it was starting to have issues but the problem turned out to be with the power supply. My original I/O board is the one installed on this panel and is believed to be working since it was just fine before the power supply started going south. The CPU board is missing some ICs so that will obviously not work as-is. There are a few mounting screws (for mounting the PC boards to the standoffs) that are missing as they have been donated to my Chroma."

This has been re-listed as item #250692914059 for USD$599.00, ends September 15.

See eBay Updates below.

Phantom Chord

Chris Ryan [21030691]

I've been talking off-list to the owner of 21010129 and he is having the "phantom chord" problem—occasionally a bunch of notes will sound (without player input) on the Chroma. I had this issue years ago. I seem to remember a list discussion on the topic at some point but I can't find it. Am I correct in remembering that the occasional triggering of a bunch of notes on the Chroma is the result of a power supply issue?

Bypassing the EQ

Tom Moravansky [21030431]

I had some time this evening and wanted to bypass the EQ controls. I only use the balanced XLR mono output and I never use the EQ to shape the sound. Looking at the schematics, it seemed like a simple operation and it was. I cut the trace leading from pin 7 of Z5 to the non-polar cap (C20) and added a jumper from pin 1 of Z5 to C20 instead.

Luca Sasdelli [21010226]

Hi Tom,

just to integrate your suggestion with the recommendation to replace 4558s with more "musical" ICs like the OPA2134 (quite cheap on eBay); the overall sound quality is improved, with deeper basses and more definition throughout the mid and treble ones. Possibly, even Z18 and Z19 on Channel Motherboard should be replaced as well.

Just my 2 cents

Joe Porter [21030058]


Sounds good, I'm not a fan of the EQ on the Chroma either. Is there a document on the Chroma site that outlines this and the ICs replacement you mention Luca?

Luca Sasdelli [21010226]

Hi Joe,

indeed those dual OAs are broadly interchangeable, i.e. the package pins are the same. Therefore you can unsolder the four 4558s from EQ board, install four 2x4 DIL quality sockets (recommended) and then simply fit the OPA2134s. As per Heinz kind suggestion, replace the C1 and C2 cap (near to power connector J4) with 22uF tantalum ones.

During some OAs experiments I had to solder four 68nF ceramic caps across pin 4 and pin 8 of each OA to avoid self-oscillation; although the OPA2134 doesn't present this issue, those capacitors provide a further power filtering, so I've left them in place.

About the Channel Motherboard there is a bit more work to do:

  • remove all Dual Voice Boards
  • unscrew the CMB from its basement
  • if you need/prefer to work on CMB on separate bench, you have to disconnect the power, audio, digital and ground cables from it
  • unsolder Z18 and Z19
  • install two 2x4 DIL quality sockets
  • insert the new OAs
  • suggested to replace even C1, C2, C3 and C4 with news ones, because of their age
  • reassemble as previous

Please observe the usual antistatic procedures, e.g. don't wear isolated shoes during the work and touch the Chroma chassis often to lower your body charge. Of course the soldering iron must be connected to ground.

Here you'll find an image of an EQ board with such "upgrade" :)

Randel Osborne [21030467]

I, too, did this to the EQ board and the Channel Mother Board, and was pleased with the results.

On The Bench: Rhodes Chroma 3

Request for the Chroma site

Tom Moravansky [21030431]

Would it be possible to install some type of simple search capability for the user group messages?

Until Luca re-posted his op-amp info, I was going crazy digging through messages month by month looking for it.

The rest of the site is well indexed and it is pretty easy to get to anything else quickly, but digging up old info from the user group messages is very difficult.


(apologies if this has come up before, but I couldn't find any reference to it…)

Dave Bradley [16330135]

Google searches any website better than their own built in engines. Just use the following format in a google search box: op amp

Tom Moravansky [21030431]

I thought about the Google engine (actually spent a few days in class doing 'google hacking' as part of a penetration testing course), but I didn't know if that had already been decided.

thanks for the reminder though; Google is pretty efficient.

Chris Ryan [21030691]

There has been a Google site search box on the home page of the Chroma site since January 2005. I maintain a Google Sitemap and the site is very well indexed.

Last time I checked, though, the search was rarely used. Of course, this could be partly because it's only on the home page. The site was designed to work at 800x600; now that monitor resolutions have increased, I could bump this up which would make it easier to include a search box on all pages.

Tom Moravansky [21030431]

Before I sent the message I did check around the User Group page and a couple other sub pages looking for a 'Search' prompt. I rarely spend much time on the home page and missed that one.

The main reason I asked for a Chroma Talk archive specific search is because of how things are indexed. For example, enter: luca op amps into the search box on the main page. The hits returned are for an entire month, not specific messages. If there was a lot of activity, it's still a scrolling exercise. Sure you can use "Find on this page…", but it would be kind of nice if the applicable messages only came up with links to the thread.

As I type this I'm realizing that would probably necessitate a change to the way the messages are archived which would necessitate a change to the interface handling the mailing list, which would…

never mind – back to a more worthwhile endeavor – debugging a voice card.

Chris Ryan [21030691]

I'll look at extending the search box across the entire site.

By-message indexing is of course a good idea, but as you point out would necessitate a wholesale change in the way things work (and getting eleven years of messages into the same database). Something else for me to investigate, though, as currently I'm putting together the archives manually—which, especially as the list has been busier than usual this year, can be a fair amount of work. Computers are supposed to make things easier. :)

Chroma Pressure Sensor

Chris Borman [21030194+]

Chroma Club,

I have enough of the major cost parts (FSR & PCB) left over for 10 more CPS Kits. Build #3! If anyone else is interested in their Chroma having PolyPhonic Key Pressure, send me a note and I will invoice you.

For you guys currently waiting, the few remaining CPS Kits from build #2 will be shipped tomorrow!


P.S. Don't fret if you can't get in on this now. I will ensure the PCB & FSR guys save their manufacturing data.


Do we have any practical audio/video examples yet on how this kit works btw ? Would be greatly appreciated.

Dave Bradley [16330135]

Yes, I was just thinking this. Can somebody with the sensor already installed post some suitably Vangelis-esque demos of poly pressure?

Chris Borman [21030194+]

btw - Fellow member Arun [21030348] stopped by to pick up his CPS Kit. That was neat actually meeting in person a fellow RhodesChromaite! Another interesting tidbit - Phil Dodds [See Philip Dodds/Tony Williams Interview] lived just 5 miles from me and my two Chromas and I never knew it until just recently. I contacted his wife Susan to give our thanks.

Arun Majumdar [21030348]


It was really great to meet Chris in person! What superb experience and all around inventive, creative and nice guy he is :)

I was very grateful that he took the time to share some of his other ideas and I hope he will bring them to fruition - it's a rare and wonderful experience to be with someone filled with wonderment and technical prowess in building these great kits.

I just back from some work and, late this Sunday night, catching up on my emails.

My plans for this coming weekend are to start on the Chroma kit and I will be happy to post videos of my progress.


Motherboard woes. a follow-up

See Motherboard woes? and related threads, June-July 2010

RJ Krohn [21030455]

hello all, i figured i'd follow up about the problem that i seem to be sharing with at least 2 other list members (to recap, my chroma fails to enter the autotune function).

i took my motherboard to another list member to test it recently, and while i only tested it with one voice card seated (time was of the essence), it exhibited the exact same problem. so, i believe i have effectively narrowed this down to the motherboard, which is good.

here's where it gets tough: i have replaced all IC's, both diodes, and all electrolytic caps. the only things left are to:

  1. re-check all of my solder joints on the IC sockets(did this at installation, but maybe i missed something?)
  2. checking passive parts; resistors and film caps.
  3. checking harness connections(again, already did this, but scraping the bottom of the barrel here).

im probably gonna be just too busy to get to this for another month or so, but wanted to weigh back in on this in case anyone else made progress, or one of you is sitting on a pile of NOS spare chroma motherboards from 30 years ago, which is of course highly probable.

Luca Sasdelli [21010226]

Hello rj,

having you replaced everything, I'd suspect some socket issues; during my board service, I've found some problems in having both PCB tracks make contact with the sockets, maybe because the metal within passing holes suffered during unsolderings. Therefore I suggest to take out all ICs from sockets and then carefully check each pin with respective schematics references, using an ohmmeter (better if beeping on contact, like mine).

I've also found the DVBs connectors being failing on several contacts, so I've de-soldered and re-soldered each one.

Anyone working with touchosc?

Thomas Story [21030352]

Before I delve into spending hours and days creating a template for the Chroma, has anyone else been working with this amazing piece of software? [See TouchOSC.]

I have it set up on my iPad and Ableton Live and it works great. I just got it working with osculator in OS X, and with a standard template sending midi CC"s it is controlling the Chroma perfectly!

I'm going to start by just creating a basic template, but was wondering if anyone has started down this road all ready.


'Sounds exciting!!, when you get your template done how about a video ?

What are you using for a midi interface on the IPAD ?

Thomas Story [21030352]

No midi interface necessary, all done through wifi or an ad hoc setup on your computer. It works fantastic, you can have up to 5 controllers going at the same time transmitting.

Need to work on a controller layout, you can have multiple pages, so I'm trying to figure out the best way to have it laid out. Just follow the panel? Move things around? So design stage...


But how do you transmit info to the Chroma then ?

Thomas Story [21030352]

Through another application called Osculator, OSX.


so you need an Ipad and another osx mac ? Thats allot of resources, no ?

Thomas Story [21030352]

Well, I all ready have my mac set up a sequencer so it's not really another resource for me. If you are strictly using the Chroma sans computer then no, this is not a viable option.

The ipad comes and goes and performs other duties when I'm not working on music, primarily when I travel, so it's not like it's tied down to the Chroma full time.

I like the fact that one is not tied down to a hard layout as with a hardware knob box. For those sequencing their chromas with a computer and happen to already have an ipad then the cost is negligible.

eBay Updates

Chris Ryan [21030691]

Item #250700492647, listed twice previously (for USD$799 and $599 [see Front Panel on eBay, August and above]), is now offered for $449. "Auction includes one fully populated Chroma front panel with all circuit boards (EQ board, I/O board, computer board) and display."

Item #270641006225, "Back Panel Power Supply Parts." From the description: "Original back panel out of a Chroma. Includes parts of the power supply attached to the panel with parts missing, most obviously the transformer. All the jacks are there with some mild corrosion showing. What you see is what you get. Sold as-is for parts."

Pictures from the auction:

Item #270641006266, "Switch Stack Assemblies." From the description: "Original switch stack assemblies out of a Chroma. All contacts are there in good condition. Sold as is for parts."

Picture from the auction:

The last two items are from the same seller, "arti," perhaps Arti Haroutunian, who posted to the list a few times in 2004 (see for instance Chroma Parts For Sale, December 2004). I've contacted the seller regarding serial numbers.

Chris Ryan [21030691]

This is in fact Arti and his Chroma, 21030388, has finally been added to the registry—just as it's being parted out.

Chroma FSR /Pressure sensor

Andrew Dalebrook [21010180]

Just a quick thank you to Chris B; my pressure sensor kit arrived down under yesterday. It looks well designed, now I just have to find some time to get everything working : )

Jesper Ödemark [21010135]

I can only second that... this weekend maybe? :)

Johnny Vintage [21010244]

Just put one in my Chroma myself, it's pretty easy, ignore the middle C mark.


If anyone with the kit installed could post some audio or video clips of it in action it would be greatly appreciated.

Rhodes Chroma on German Ebay

Matrix [21030220]

Not sure if this one hit the list yet. [Item #280567142916]

Go to next message in thread, October 2010