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ChromaTalk Archives: April 2000

New Articles

Chris Ryan [21030691] · Sat, 1 Apr 2000 09:14:54 -0800

I've posted two new articles to the site. Fender's Triad Interface, from the August 1983 Polyphony magazine, is a brief description of the Chroma's computer interface.

Actually, as Erik Vellinga [21010286] points out in an August 2004 post, the Chroma (25-pin) and Triad interfaces were distinct; the latter was not on the original Chroma and its presence on the Polaris is unconfirmed.

An excerpt from The A-Z of Analogue is a short history and review of the instrument.

The latter article is interesting in that it claims that "CBS marketed a 60-minute video featuring Peter Vetesse using the Chroma." Has anyone ever seen this?

Chris

TIFF Scans of Programming, Service Manuals

Chris Ryan [21030691] · Sat, 1 Apr 2000 19:51:05 -0800

I noticed that the Music Machines site has added downloadable scanned TIFF versions of the Chroma Service and Programming manuals.

I'm in touch with someone who is working on producing these manuals in PDF format, which I hope to be able to make available on the site, but these might be useful in the meantime (they're fairly poor quality black and white).

Both manuals are now available at this site in HTML (Programming Manual, Service Manual) and as PDFs (see Manuals).

Dave Bradley [16330135] · Mon, 3 Apr 2000 10:06:09 -0500

I have all the manuals - including the interface manual and the service manual. I've got to say that reproducing the service manual will be a heroic job - it's huge, and has lots of large format schemo pages.

I salute you for your efforts, sir, and will drink a Three Stooges beer in your honor tonight!

Dave Bradley Principal Software Engineer
Engineering Animation, Inc.

The Service Manual was added to the site in August 2006.

Philip Dodds Interview

Chris Ryan [21030691] · Wed, 5 Apr 2000 21:14:46 -0700

Philip Dodds was VP of Engineering at ARP, 1972-81, Director of R&D at CBS, 1981-83, and the man responsible for the Chroma--see "The Rise and Fall of ARP" and "The Synth That Survived ARP's Fall."

I contacted him to ask if he would do a "virtual interview" for the site. I think there are a number of issues not covered in the published articles and interviews on the Chroma, and some interesting topics that have arisen on this mailing list, technical and otherwise. Anyway, he said he'd love to do it, and suggested that the story after the ARP sale hasn't been told.

So I'd like to ask for some input from you. This is a chance to ask some questions of the "father" of the Chroma. Send me your ideas, and I'll conduct the interview and post the results to the site.

Chris

Kurt Otto [21030572] · Thu, 6 Apr 2000 00:06:13 -0500

fantastic!!!

Larry C [21030864] · Thu, 6 Apr 2000 06:35:43 EDT

I can't Wait.....Hmmmmmmmmm I wonder who designed that "Tapper" ? (just kidding)

Best Regards,
Larry

Jimmy Moyer [21030184] · Thu, 6 Apr 2000 03:21:30 EDT

I personally find much of what Philip writes of a technical nature to be suspect. For example, below is one of his quotes from Keyboard.

Anyone who's ever looked, however, knows the heart of the Chroma is a Motorola 6809 processor, somewhere between a 6800 and a 68000 in the evolution of chips and completely at odds with Intel chips of the time. The keyboard is scanned by second processor, an Intel 8039 a slow (and rather strange to program) chip intended as a microcontroller and also unrelated to the general purpose X86 chips. It would indeed be interesting to really know about these and other design decisions, but the quote suggests a fanciful memory, at best.

-> Jim

The heart of the Chroma was an Intel 80186. We were a beta site for Intel. We helped Intel debug the 186, which preceded the now-famous 286. We were ahead of the PC, which had an 8086. If you flip up the Chroma's front panel, on the right side you will see an 80186, a stack of RAM, and various other silicon glue: It's a CPU card. Take that card out, put in a SCSI controller and a hard disk drive, and you've got a desktop PC. It was a full-fledged programmable computer in a very proper sense. Paul DeRocco, the chief hardware architect, designed this system and wrote all the Chroma's assembly code. Paul selected the 186 because it had a very good I/O [input/output] structure that allowed a lot of simultaneous data to come in on a lot of data lines. The 80186 was designed as a peripheral controller, whereas the 80286, 386, 486, and so on are really designed more for desktop PC usage. But it's the same family and same instruction set.

Don Tillman · Sat, 8 Apr 2000 14:09:05 -0700 (PDT)

I personally find much of what Philip writes of a technical nature to be suspect. For example, below is one of his quotes from Keyboard. Anyone who's ever looked, however, knows the heart of the Chroma is a Motorola 6809 processor, somewhere between a 6800 and a 68000 in the evolution of chips and completely at odds with Intel chips of the time.

I wouldn't necessarily blame that on Phil; perhaps the original circuit did use a 186. Or maybe something got lost in translation at Keyboard Magazine. It would be a very good question to ask him.

Also note that Phil's name is on two ARP patents for the design of the ARP Electronic Piano keyboard, so I really doubt he's clueless about these things.

And I guess this is a good time to advertise my web page of ARP patent reviews and resources. Check it out:

http://www.till.com/articles/arp

-- Don

Don Tillman
Palo Alto, California, USA

Chris Ryan [21030691] · Sun, 23 Apr 2000 12:24:13 -0700

Need Input: Philip Dodds Interview

I haven't received much input for this; I want to put together a final list of questions in the next week.

Philip Dodds was VP of Engineering at ARP, 1972-81, Director of R&D at CBS, 1981-83, and the man responsible for the Chroma--see "The Rise and Fall of ARP" and "The Synth That Survived ARP's Fall."

I contacted him to ask if he would do a "virtual interview" for the site. I think there are a number of issues not covered in the published articles and interviews on the Chroma, and some interesting topics that have arisen on this mailing list, technical and otherwise. Anyway, he said he'd love to do it, and suggested that the story after the ARP sale hasn't been told.

So I'd like to ask for some input from you. This is a chance to ask some questions of the "father" of the Chroma. Send me your ideas, and I'll conduct the interview and post the results to the site.

Chris

Jimmy Moyer [21030184] · Sun, 23 Apr 2000 17:52:02 EDT

Hi Chris.

One thing that might make some difference in 2000 for me has to do with the pressure sensor option.

Were any of these ever shipped? I'm guessing there were issues with mass production that made it impractical or uneconomic. I'm wondering if the specs are available anywhere? Would it be possible (if not necessarily easy or cheap) to hand build one today?

One other issue I'd raise is why the design ended up with only a single noise generator shared by all the voices. This seriously limits the utility of the Chroma for percussive sounds. Building more noise generators is a mod I'm considering.

-> Jimmy

Dave Bradley [16330135] · Mon, 24 Apr 2000 13:41:56 -0500

What plans did they have for future Chroma designs? I heard rumors of a longer keyboard, for one thing. Were there any plans to change or enhance the voice architecture?

What about hotrodding our Chromas? Does Phil have any insight on how we could speed up software envelopes, make LFOs go faster, make a working polypressure interface, etc?

What about (hopefully commented) source code for the ROMs? Any way to allow hackers to implement their own OS, or maybe play with some of the keyboard algorithm behaviors?

Erik Vellinga [21010286] · 25 Apr 2000 00:34:09 +0100

Let's ask Phill some questions, thanx Chris for this opportunity !!! Sorry about my Engiliesch... J

  1. I think Dave Bradley really has got a point ! Ten years ago I tried to build a MIDI interface, finally ending up buying the Kenton MIDI kit. But still I want to be able to output the velocity right, and do things like programming the sounds by my PC etc. I have tried to decompile the Chroma EPROM's but did not sucseed. But I do have them in a ZIP file (for those of us who want them, mail me) I would ask Phill to give us the source code, we ( ? and I ) could try to build a simple and cheap MIDI interface, reprogramming the EPROM's, to replace the Chroma Interface on the Chroma. And one that can do it all !!! 16 channels in Cubase ! Writing in the display's !
  2. Did Phill and his team do anything for the Polaris? The 80186 he (did he really say it?) said to be the hart of the Chroma was not used in the Chroma ( 6068 ), but....right !!! in the Polaris !! ?????? If you want the Polaris Service Manual, mail me.
  3. What is the story about "Close encounters of the third kind" ?
  4. The ARP piano has the same look as the Chroma, how are they related?
  5. How does Phill feel about the keyboard? I think it's a too simple design to be proud of...sorry Phill...The Chroma is really enormous!! No bad words about it. ;)
  6. Do there really are special serial numbers? Who built the Chroma? Fender? Rhodes? CBS? Some organ company? You? And what about the Polaris? And which Chroma's are the best and why?
  7. MIDI and Chroma Interface, TRIAD.. what is it? The Polaris has a TRIAD interface because it has a high speed serial port besides MIDI ? The Chroma Interfa ce is parallel, but what is it? Did MIDI evolve from it? Did Phill have anything to do with the MIDI assossiation? I found that the Chroma code used in the parallel interface does share some codes and algorithms whith the MIDI protocol, that is no coincedence, is it?
  8. Can Phill give some tips and tricks and/or funny stuff about the Chroma?
  9. I think it was stupid to change the name ARP to Rhodes !! Would it not have been better to keep the brandname ARP alive? Why?
  10. I have a working Apple II , is the original Chroma program plus hardware still available by Phill or his friends?

Greetz,

Erik Vellinga
Netherlands

Eirikur Hallgrimsson [21030467+] · Mon, 24 Apr 2000 18:37:13 -0400

  1. The ARP piano has the same look as the Chroma, how are they related?

Extending Erik's question, are any parts interchangeable? It would be good to know if the basic keys and switch assemblies are the same. I've often thought of picking up a junk Arp Piano just to see if I could scavenge parts. I've never heard anyone say that that was an instrument worth having it its own right.

I second the motion on source code. I fear that Phil probably doesn't have it. It may be in archives somewhere at Fender.

Eirikur

Bill Lacey · Mon, 24 Apr 2000 21:45:12 EDT

Chris,

I second Jimmy's request to know more about the pressure sensitive option. A few more (disregard if info is available elsewhere):

  • How did Phil get involved with Arp in the first place?
  • Besides the Chroma, what other instruments was he involved with at Arp?
  • What has he done with himself since then? What's up for the future?
  • What does he have to say about 'modern' virtual analog synths like the Korg Z1, etc. Anything out there that he gets excited about?
  • Like Erik, I would like to know more about the Polaris, and if he had anything to do with it, and what were his impressions of it (may help me to decided whether or not to spend money fixing it).
  • Does he have anything to say about the power supply (suggestions, excuses, apologies, snickering laughter....)?

That's all for now.

Thanks.

Bill Lacey
Digital Sound & Picture, Inc.

See Christopher Now's post Aftertouch and Velocity below for more suggested questions. Go to next 'Philip Dodds Interview' thread (May 2000). The interview took a couple of years to complete, for various reasons; see Philip Dodds/Tony Williams Interview for the final result.

Don Tillman · Mon, 24 Apr 2000 23:45:02 -0700 (PDT)

The ARP piano has the same look as the Chroma, how are they related?

They just look alike.

I have the service manual for the ARP Piano in front of me; inside it bears no resemblance to the Chroma. The keyboard is physically very different, there are four top-octave generator chips instead of VCOs, the envelope generators are different, the Piano has resonator banks, the list goes on.

Folks interested in ARP stuff might want to check out my ARP Resources web page.

And my reviews of all the ARP patents I could find.

(Including Phil Dodds patents for the ARP Piano keyboard mechanism!)

-- Don

Requests for source code ...

David Clarke [21030085++] · Mon, 24 Apr 2000 22:22:46 -0400

In the recent thread about questions for Philip Dodd, several people have expressed a desire in getting source code. Just out of curiosity, what would people do with it (if they had it)?

Regards,

David Clarke

Don Tillman · Mon, 24 Apr 2000 23:56:36 -0700 (PDT)

I'd fix the damn bug in the code where you have, every once in a while, a note playing much much louder than it ought to. I can't help but think this is some 16-bit wrapping of a timing value, but I have no idea.

Seriously, there's all sorts of hotrodding you could do. The problem is, where do you stop? I mean, if you're going to start adding features you might as well replace both power-hogging microprocessors with a modern chip that's 100 times faster and a tiny fraction of the power. Then you can swap the monster power supply for a tiny one, and use smartcards for patch storage, and things could easily get out of control.

-- Don

Dave Bradley [16330135] · Tue, 25 Apr 2000 10:12:02 -0500

Heh heh <evil laugh>! Faster processors, snappier envelopes, audio rate LFOs...

As long as we're wishing...

  • Add a true low note priority kbd algorithm with note stack memory. Multiple banks of presets.
  • Increase the resolution of some parameters (more than 7 levels of resonance!)
  • Add a special input port to our new processor and build a knobby control panel with lcd which calls out parameters by name as you edit modulation sources.
  • Add ability to store multitimbral patches and play from multiple split points or multiple layers without using the Apple (OK, I don't know how you would represent that on the front panel!)

I haven't slung assembly code in years, but hotrodding a Chroma would be a powerful incentive to do so!

Eirikur Hallgrimsson [21030467+] · Tue, 25 Apr 2000 14:20:59 -0400

The lack of low/high note priority in mono mode is a big priority for me. I go to play a solo and my slightest brush against another key cuts off a note that I expect to keep playing. I often find myself looking down to see that, yes, I AM holding down a key and hearing nothing. This makes my keyboard skills sound worse than they are, which takes some doing. I'm a low-note priority guy at heart, coming from PAIA and the Roland SH-1000 (which was internally a V/Octave machine).

The second major issue would be to take out the velocity curve changes in the 1.4 (14?) final version of the firmware. You need to have that version in order to get the Chroma Cult MIDI box to work completely right (with earlier firmware you lose access to sounds 45-50). I agree with Ken Y. that the original velocity curve was better. This is probably a very small fix that wouldn't increase the code size (because it just replaces a table). It also doesn't require real development work--just finding out the old values (which could probably be read out of the EPROMS, if the old source code is lost). This last version of the firmware probably also has bugfixes, and it would be good to get those out to everyone.

See Aftertouch and Velocity below.

The last time I had my Chroma serviced I was told that there are availability issues for the EPROMs used in the Chroma. Was I to want to have the OS updated, they would re-use my existing EPROMS (Erasable ROMS) and if one or two had died and were not erasable they would replace from their small existing stock. Is this true?

Thanks to Don Tillman, I guess I won't go buying an ARP piano for parts!

I've been doing some PC-hacking recently, dropping a 400 Mhz AMD CPU into a Pentium 100 box, etc. What say we overclock the Chroma? I'm kidding, unless we made source changes. We'd lose the low end of LFO range, and the maximum time for attack/decay would be reduced. Might be worth it for a lark, though. Fast LFO and punchy envelopes might be achievable with a minor hardware change (replace CPU, maybe replace a clock crystal). I believe that all the I/O and communications stuff is latched and strobed, but there still could be a lot of things that would prevent this from working.

Eirikur

Erik Vellinga [21010286] · Tue, 25 Apr 2000 22:09:21 +0200

Yes Eirikur! I Have the same trouble playing in MONO mode. I used to play a Pro-One for my famous solo's but since it's uP is dead (does any-one know how to get a new uP? Wine Country has put a lot of effort but cannot help me..)I try to play them on my Chroma. The sound is fabulous but it's hard to play. Coming to THE note in the solo there is no note at all that is playing ! Terrible. That could be fixed in the new CHROMA 2000 EPROM's.

I would be willing to try to build a MIDI output directly in the CHROMA. I have experiance in programming 8051 assembly so it can take some time finding and learning other software.

The codes generated by the uP in the Chroma are really a lot like MIDI. Key nr. velocity etc. In stead of a kind of translator that reads the parrallel output of the Chroma interface, looking up every Chroma word and translating it into MIDI language like all MIDI interfaces for the Chroma do, I could make a small circuit to replace the parallel port by a serial MIDI port. That's simple I think. Then modifying the original output and input codes in the EPROM could make MIDI full up to date multitimbral. That's not hard to do also. And it would be relative cheap!

Any suggestions?

David Clarke [21030085++] · Tue, 25 Apr 2000 19:20:49 -0400

The lack of low/high note priority in mono mode is a big priority for me.

For that, would you be willing to loose/change the operation of one of the current algorithms - or would you want/need it to be in addition to the existing ones?

The second major issue would be to take out the velocity curve changes in the 1.4 (14?) final version of the firmware.

Does anybody have an older (non-rev 14) version of the firmware? I know the location/contents of r14 velocity table in ROM (and shouldn't have any problem locating it in an early rev of firmware). If there's interest, and if anyone has a revision of firmware with a 'better' velocity curve, I can certainly provide instructions on what to patch and where (or simply provide an updated EPROM image for the affected EPROM).

The last time I had my Chroma serviced I was told that there are availability issues for the EPROMs used in the Chroma. Was I to want to have the OS updated, they would re-use my existing EPROMS (Erasable ROMS) and if one or two had died and were not erasable they would replace from their small existing stock. Is this true?

The Chroma uses 2716's, which aren't exactly new technology - but quite a few places still carry them. If you're stuck and can't find them locally, Jameco (www.jameco.com) is always a good first stop to find 'mature' parts. You can also get by by using a 2732 (if you have to).

Jimmy Moyer [21030184] · Tue, 25 Apr 2000 21:02:30 EDT

I'm pretty sure I recall that unpleasant velocity curve change on the 1.4 upgrade. (I did just double check and that is what is in there now.) I returned the 8039 chip from the previous version (which they'd been nice enough to return to me) and that restored what at least felt like the old curve. I've never noticed any downside from doing that. (I am running Syntech midi interface just fine.)

-> Jimmy

David Clarke [21030085++] · Tue, 25 Apr 2000 22:25:24 -0400

Chroma wish list

As long as we're wishing...

  • Add a special input port to our new processor and build a knobby control panel with lcd which calls out parameters by name as you edit modulation sources.

Actually - I've already done this! :->

I haven't got around to scanning picture of it yet (to upload to the site) - but it has 95 individual knobs (one for each param), and it does have an LCD display to actually tell you what you're modifying! The whole thing connects via the Chroma port, so no internal Chroma mods required at all.

David Clarke

David later took some pictures and wrote a short article about his controller: see ChromaKnob (Chroma Knob Box).

Eirikur Hallgrimsson [21030467+] · Wed, 26 Apr 2000 00:26:42 -0400

On Tue, 25 Apr 2000, A. Gordon Clarke wrote:

For that, would you be willing to loose/change the operation of one of the current algorithms - or would you want/need it to be in addition to the existing ones?

Yes, I would very cheerfully lose the current behavior in mono mode for low-note priority. Other soloists (like Erik) will probably agree.

Does anybody have an older (non-rev 14) version of the firmware?

Yes. I have the version with the "better" velocity curve and the bug that disables patches 45-50 when the Chroma Cult MIDI interface is attached. I had a Chroma once before that I had upgraded to rev 14, and found that I agreed with Ken Y. (of Chroma Cult) that the velocity curve wasn't as agreeable.

I'm willing to pull 'em and ship 'em to you if that would help. I don't have anything to read them with. 2716s....now I remember. This is so funny. That's the last generation of hardware that I was intimately familiar with debugging. Early DEC terminals had 2716s, and some 1970's emusic projects had them.

You have to be kidding about the 95-knob box, right? How do 95 knobs map to only 50 parameters?

Dave Bradley [16330135] · Wed, 26 Apr 2000 08:51:18 -0500

You have to be kidding about the 95-knob box, right? How do 95 knobs map to only 50 parameters?

There are 95 editable parameters on the right panel - params 1 thru 5 are global to the patch, while there are 2 sets of params 6 - 50, one for A and one for B.

Dave Bradley [16330135] · Wed, 26 Apr 2000 08:54:00 -0500

Re: Chroma wish list

Actually - I've already done this! :->

I haven't got around to scanning picture of it yet (to upload to the site) - but it has 95 individual knobs (one for each param), and it does have an LCD display to actually tell you what you're modifying! The whole thing connects via the Chroma port, so no internal Chroma mods required at all.

You have GOT to scan this and get it up on the site! What has your experience been programming with it? Is it very much more intuitive, so that it causes you to program a lot more, or was it not worth the effort?

Could a person talk you out of schemos and or code?

David Clarke [21030085++] · Wed, 26 Apr 2000 18:34:23 -0400

Re: Chroma wish list

You have GOT to scan this and get it up on the site!

It's on my 'to do' list - but other things always seem to grab my attention first...

What has your experience been programming with it? Is it very much more intuitive, so that it causes you to program a lot more,

The biggest difference I find is that I don't get as tired of programming now. Before I would change a few things, push a few buttons, and then just stop trying to get the sound I wanted and find another preset closer to what I wanted to use. For 'quick' things before it was always too much bother to get the sound 'right' on the Chroma (if I needed to get something quick, I'd maybe use the P-5 instead).

Now that I don't have to worry about hitting the 'Param' button, or the Edit A or Edit B or try to remember what foot switch mode "4" means, I find I can whip up something quite quickly.

or was it not worth the effort?

I think it was worth the effort - I'm glad that I did it. It was conceptually a simple project ... the only real pain in the butt was the sheer 'multiplicity' of parts (95 pots, 3 wires each, then you've got the Chroma interface, with 20 or so wires - then all the address and data lines, etc.)

Could a person talk you out of schemos and or code?

Actually, both are very simple and straight foward (nothing fancy was required ...) After I get the pictures and info to the site I'll see if anyone is still interested in finding out more.

Regards,

Dave

David Clarke [21030085++] · Wed, 26 Apr 2000 18:21:37 -0400

Yes. I have the version with the "better" velocity curve and the bug that disables patches 45-50 when the Chroma Cult MIDI interface is attached... I'm willing to pull 'em and ship 'em to you if that would help.

If you'd like to do this, I should have no problem producing a set of rev 14 EPROMs with an updated (read to mean 'the old') velocity curve. I'll send you my mailing address in a different e-mail note.

Once completed I'd be happy to upload the particulars of the change to this list ...

You have to be kidding about the 95-knob box, right?

No kidding, it's real :-> (Cherry end-blocks too!)

How do 95 knobs map to only 50 parameters?

Dave Bradley correctly provided the answer to that one (there actually are 95 modifiable parameters which are stored in memory).

Dave.

David Clarke [21030085++] · Wed, 26 Apr 2000 19:26:17 -0400

Mono Mode

I'm going to take a quick look to see what would be involved in modifying Kybd Alg #8 (Bottom Note, Mono) to be a 'proper low-note priority mono mode.'

Now, to do that, I'd need your input as to how a 'proper' low-note priority mono mode should work.

My basic understanding is "if I press a high key, continue to hold it and then press a lower key - the lower key should steal away from the higher key and sound. If I continue to hold the high key but release the low key - the high key should sound once again."

Now - if we agree to that point, how should envelopes be handled (both the envelopes on the filter and on the amplifier)? Specifically, consider the case where the note does not have infinite sustain (i.e., it will decay away). When the low note is pressed, should the envelope be retriggered? If so, should this 'new' envelope be used when we go back to the high note, or should we expect that the envelope for that note will have continued to decay at it's original rate?

A similar question about velocity - should the velocity of the second key (low note) be ignored in preference to the 'original' high key velocity or should the low note's velocity be played as struck? When the low note is released, should we revert back to the high note's velocity - or use the 'most recently played' one?

(These questions are much easier to answer on a 'real' monosynth, since there the gate is asserted and held asserted as long as one key is down - and the 'low note priority' really just changes the outgoing CV value.)

Regards,

Dave

Eirikur Hallgrimsson [21030467+] · Wed, 26 Apr 2000 23:06:02 -0400

De-bouncing the Chroma....

I just had to run power to the Chroma's new location to check this out. Wow....it can't be just my machine. Mode 8 doesn't work well at all! Just try to play some rapid upward runs. At least with my playing, I get some dead notes every time. I think this is because this mode is trying to be low-note priority and if I don't cleanly release the lower key before striking the higher, the higher doesn't sound (of course). Methinks the action may not return quickly enough for rapid runs in this mode. It could be software, but it could be hardware, (action return) too.

The mode that I really want is mode 4. Mode 4's behavior is pretty close to what I want except: any stray keypress steals the held note and stops sounding if it is released. What I need is for the note to revert to the held key. I assume that my momentary miss-keys are actually played on a true monosynth, but revert before they are noticed.

I would NOT like the revert to held note function to cause a new attack. That would seem counterintuitive to me and I would get annoying new attacks instead of an instantaneous slur back to my intended note.

I think what I'm looking for is actually LAST note priority with one additional rule. When the current note is released (key up), if there are any keys held down, slur to the lowest. I write it that way because more than one key could be down. I would call this "last note priority with respect for held keys." What we are actually doing here is a form of de-bouncing. Thinking that way, I am quite sure that I want to discard the velocity of the mis-key. Keeping the velocity of the mis-key could still extinguish the desired note (the mis-key had a low velocity) or produce a seeming re-attack by suddenly raising the volume on the intended key.

Boy, does what I'm asking sound icky to implement. I essentially want the voice board (or all 8) to revert to the held note's pitch, and envelope stage and envelope level. Sounds VERY hard, because you aren't just facing a re-trigger or not question. Maybe it would be better to just not re-trigger.

Eirikur

Dave Bradley [16330135] · Thu, 27 Apr 2000 09:46:29 -0500

Re: Mono Mode

My basic understanding is "if I press a high key, continue to hold it and then press a lower key - the lower key should steal away from the higher key and sound. If I continue to hold the high key but release the low key - the high key should sound once again."

Yes, that's the essence. The important thing is, a note should always sound as long as I have a key down (assuming the envelope hasn't decayed away, natch).

Now - if we agree to that point, how should envelopes be handled (both the envelopes on the filter and on the amplifier)?

Well, this is a single trigger vs. multi trigger issue. I don't remember my Chroma kbd algorithms very well. Was there mono single triggered AND mono multi triggered algorithms? If so, they should both be modified to handle low note priority correctly. The single triggered case should ignore the new velocity and envelope info, but the multi triggered case should use the new velocity and envelope. IMO, of course.

Mike · Wed, 26 Apr 2000 16:55:32 -0700

Re: Chroma wish list

I missed this thread guys, has someone built an external programmer with knobs for the chroma? If so, your a god and could you please build me one! ;) peace
xpando

Jimmy Moyer [21030184] · Wed, 26 Apr 2000 23:20:25 EDT

IMHO the pain with the Chroma UI has not to do with the single slider, but rather with single numeric parameter *display*. Back in the early days I wrote a librarian / display program so you can see all the parameters at once in a format a human can comprehend. That was on a S-100 Z-80 machine but I later ported it to DOS. (and the Syntech interface - it was more functional pre-midi.) I still use an old 386 for this function alone. This makes it much more pleasant to actually program the Chroma.

These days I'm out of the (computer) programming loop, but it seems to me that the tables that do the display translation are the hard part of a Windows XX version. Anyone interested in the code (or the DOS app!) can let me know.

-> Jimmy

Fredrik Beckmann · Thu, 27 Apr 2000 09:04:56 +0200

Hi Everybody!...

OK, C if i got this straight!... The controlpanel is not built-in, it's external and U program the parameters using the "Chroma-port"?!...

Dave Bradley [16330135] · Thu, 27 Apr 2000 09:17:31 -0500

RE: amazing external programmer

I think it was worth the effort - I'm glad that I did it. It was conceptually a simple project ... the only real pain in the butt was the sheer 'multiplicity' of parts (95 pots, 3 wires each, then you've got the Chroma interface, with 20 or so wires - then all the address and data lines, etc.)

I have a few followup questions, if you don't mind:

  1. I assume you used regular pots - did you go to the trouble of making the pot cross the threshold of the current value before it started editing, or does the value jump to the current pot position as soon as movement is detected?
  2. What processor or microcontroller did you use?
  3. How long ago did you build it, and what would you do differently today?
  4. Did you actually attempt graphics on the display, to illustrate the patch diagrams, for instance? If so, you are a madman!

Actually, both are very simple and straight foward (nothing fancy was required ...) After I get the pictures and info to the site I'll see if anyone is still interested in finding out more.

Oh, yeah baby! I'm building a big MOTM modular now with some diy modules thrown in (I use my Chroma for the controller kbd), but I'll definitely get sidetracked and build one of these as well!

Aftertouch and Velocity

Christopher Now · Wed, 26 Apr 2000 16:36:17 -0700

Regarding the keyboard velocity and pressure sensor issues:

When I worked as a tech at a service center from 1982-1986, we routinely installed a factory-modified version of rev 14 firmware that improved the feel of the keyboard, (read: changed the velocity curve). Most Chroma owners really liked it, but to me it was a very subtle improvement as I never compared it to the older firmware - (since I've owned my Chroma, it never had the previous firmware, or even a stock rev 14) The "tweaked" version of the rev 14 firmware was 14a and only the last EPROM in the set got updated. I gave a copy of this to our fearless ChromaTalk moderator, Chris Ryan shortly before he moved back to Canada. I think that he perceived a difference, but I'm not sure if he had much time to spend using the keyboard. How's it going Chris?

See response in next month's archive: Re: Aftertouch and Velocity. See also David Clarke's subsequent article comparing the velocity responses of rev 12, 14, and 14a firmware in Chroma Keyboard Velocity Curves.

We also installed 4 or 5 pressure-sensitive kits that were bought from Fender, as far as I recall. They were about $300-$400 including the labor and about half of the owners brought their Chromas back to have it removed! It caused the normally quick and positive action to become spongy - it was about what you'd expect the action to feel like if you placed 1/4" of rubber foam under the keys (though the sensor strip was mounted to the keystop such that the keyweights pressed on the sensor). I thought it was great functionally, but ruined the feel of the action too much for my taste, especially since the aftertouch on many Yamaha boards at the time felt good to me. Even the Prophet T-8 was less sponge-like!

As for the Dodds interview, I'l like to know if there was any awareness at CBS about the Sequential Propet T-8 development when the Chroma was first shipping. I've talked with former Sequential employees who recalled having one of the first Chromas disassembled in their lab. To some people, the T-8 was a Sequential's answer to the Chroma. Ex-Sequential techs and engineers told me they were impressed with the action, but felt the leaf switch key contacts would be problematic, hence their decision to use optical sensor contacts in the T-8. From my experience, the Chroma contacts, which are self-cleaning, rarely fail and if they do, it's very simple to remedy with compressed air or a piece of kraft paper. The optical sensors on the T-8 seemed to require far more replacement, plus they were a hassle to work on - when you removed the lid, all the voices would sound from the ambient light hitting the optical sensors! We had to cover up sensors when we worked on them.

Another question I would ask Phil would be how many more Chromas and Polaris could they have built had CBS not sold off the Rhodes division? There seemed to be a lot of major Chroma parts available in the late '80s/early '90s (wood, chassis components,keyboards and dual-channel boards).

Cheers,
Chris

David Clarke [21030085++] · Wed, 26 Apr 2000 23:49:46 -0400

...The "tweaked" version of the rev 14 firmware was 14a and only the last EPROM in the set got updated. I gave a copy of this to our fearless ChromaTalk moderator, Chris Ryan shortly before he moved back to Canada. I think that he perceived a difference, but I'm not sure if he had much time to spend using the keyboard. How's it going Chris?

Can someone out there with Rev 14a installed please try the following:

  1. Do a "Set Split 18" (Chroma Interface Panel Disable)
  2. In "Program Select" mode, select any patch.

Does the Chroma do it without complaint, or does it hang? (I know this works fine in Rev 14)

Regards (and thanks),

Dave

See Rev 14a with Set Split 18 below for responses to Dave's request.

Christopher Now · Tue, 25 Apr 2000 20:10:46 EDT

In a message dated 4/25/00 5:01:11 PM, I wrote:

...brought their Chromas back to have it removed! It caused the normally quick and positive action to become spongy - it was about what you'd expect the action to feel like if you placed 1/4" of rubber foam under the keys....

I wanted to clairfy this comment - the sensor was not mounted under the keys, though it felt like it was. It actually attached to the underside of the keystop piece, so the keyweights actually pressed against it.

Chris

Go to next message in thread (May 2000)

Rev 14a with Set Split 18

Christopher Now · Thu, 27 Apr 2000 11:25:57 -0700

Someone requested trying Set Split 18 with rev 14a firmware, then selecting a patch.

Doing this does lockup the Chroma (at least mine).

Add one more bug to the fix list :-)

Chris

Erik Vellinga [21010286] · Thu, 27 Apr 2000 23:50:27 +0200

How do I know the version? Is it the number written on the EPROM's ? Set Split 18 works fine, no lock-up !

Christopher Now · Thu, 27 Apr 2000 15:03:44 -0700

The paper label for Z35 would indicate "14a" or "rev 14a" The rest of the EPROMS would be labeled with "14" or "rev 14"

David Clarke [21030085++] · Thu, 27 Apr 2000 18:13:23 -0400

Rev. 14/14a differences

Someone requested trying Set Split 18 with rev 14a firmware, then selecting a patch.

Doing this does lockup the Chroma (at least mine).

Add one more bug to the fix list :-)

Chris, thanks for trying this - I wanted to make sure it wasn't just my copy.

For those of you keen to change your own EPROMs, the single 14a EPROM is identical to the last Rev 14 EPROM, except for two things:

  • A change in the velocity lookup table
  • An error in the address for the "Set Split 18" handler address.

Regarding #2:

Rev 14a has an error right at the very beginning of the EPROM. The first two bytes of that EPROM image are:

$C306 (This data would appear at $F800 in the Chroma's memory space).

That data should actually be "$F906" if the 14a EPROM is to be used in conjunction with Rev. 14 software. Making this change will ensure that the "Set Split 18" command will work as intended (i.e., not hang the machine).

Regards,

David Clarke

Christopher Now · Thu, 27 Apr 2000 16:51:17 -0700

Nice sleuthing, David! I guess you've just given out the source for rev "14b" :-)

BTW, the lockup condition is enhanced by a lovely buzzing of the tapper solenoid - what a scary symptom!

Go to next message in thread (May 2000)

FYI: More Chromas for sale

Bill Lacey · Fri, 28 Apr 2000 00:24:51 EDT

If anyone is looking to pick up another Chroma, I found two more for sale on Harmony Central this week. Personally, I'd love to find a Chroma Expander, but have never seen one for sale on the net.

Bill Lacey
Digital Sound & Picture

ARP RHODES CHROMA!!

Asking Price: US$1350
Condition: Excellent
Age: N/A
Description:

Original Arp Rhodes Chroma. 3000 units made. This is a true analog machine: weighted keys, midi. Comes with Anvil case and foot pedals. Unit is in excellent shape. Email for pics.

Seller: Greg Mullenax, [contact info removed]
Location: BEAUMONT, TX
Post Date: 4/26/2000

FS: Rhodes Chroma

Asking Price: US$1000
Condition: Good
Age: N/A
Description:

Terrific analog monster. Plays like new. Electronics, keyboard and mechanics in mint condition. Some dings on wood paneling. Fantastic sound, modulation flexibility and weighted keyboard feel.

Seller: Keith Hendricks, [contact info removed]
Location: LIBERTYVILLE, IL
Post Date: 4/23/2000

Chroma: What kind of batteries should I put in my Chroma?

Eirikur Hallgrimsson [21030467+] · Sat, 29 Apr 2000 21:37:38 -0400

Hoo, boy! No wonder I had sporadic memory losses. Both of the alkaline AA batteries I put in a year ago had leaked. I'm surprized it held the patch memory at all!

Can't find my service manual. These were originally NiCads, right? Possibly I'm making the non-rechargeables leak by letting the Chroma try to charge them.

I was going to replace them with the new lithium AAs, but now I think I should ask first.

Eirikur

Erik Vellinga [21010286] · 30 Apr 2000 12:30:56 +0100

NO NiCads !!!!! Use alkaline AA batteries like Duracell, the are leak free and will last for years.