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ChromaTalk Archives: November 2003

Fwd: "Red Chroma's"

Chris Ryan [21030691]

Some more information on "Halloween Chromas" from the fellow who did the screen printing at ARP and Fender. The original threads:

From: "Witt, Robert"
Date: October 24, 2003 1:27:14 PM PDT
To: Chris Ryan
Subject: "Red Chroma's"

Recently stumbled across a two year old discussion regarding a Fender Chroma with "red" switch panels.

I know what this likely is.

I was the "screen-printing guy" at both Arp and Fender, and manufactured all of the switch panels used on all instruments until Fender closed the R&D facility in Woburn. After that I understood they oursourced the parts. But to the question. John Shykun had long had the idea that the Chroma color scheme should be "updated" for the Polaris project. In pursuit of this he had us mix up a rainbow of what he referred to as "earth tone" colors. What you've seen is an example. We experimented with retrofitting this schema onto the Chroma as well as using it for the original Polaris demo units.

These were never available on production units, so the one that you have seen pictures of is either;

  1. Part of a matched set of Chroma and Expander units provided to Herbie Hancock as a "special"; or
  2. My own personal unit which I build out of parts and fitted with a set of the "special" panels. This unit, which had no serial number, was sold in '91 to an enthusiast in Colorado. It was packed up and shipped... and never heard from again.

See Earth-Tone Chroma Identified? (July 2008) for news of an instrument that could well have been Robert's.

Beyond those 2 (3) units..... I don't believe we ever actually let an "earth tone" unit out the door. (Excepting the Polaris units, on which "earth tones" were the official prototype color) It's possible of course that a set of switch panels made it onto one of the lab units in Woburn... we were always doing things like that.

Interesting times, and wonderful instruments.

robb witt

I replied that, assuming Herbie Hancock didn't sell his units, it seems there was either a third red Chroma, or the one shipped to Colorado was used for parts for Andi Beit's instrument, 21030620. (Andi, where did you get your Chroma?)

Robert Witt replied:

From: "Witt, Robert"
Date: October 27, 2003 5:59:58 AM PST
To: Chris Ryan
Subject: RE: "Red Chroma's"

Chris -

Feel free to post my message. I should add that, having read Andi's message more closely, it is possible that he is exactly right and does have a demo unit of some kind. Again, there would not have been more than one or two (which is why I'm still suspicious that it's one of Hancock's units). The presence of a pressure sensor is, as your list will understand, also pretty unique. Protoypes for this were largly constructed by a fellow named Mark Smith [2103-PT-002], with some very minor fabrication help from myself. Not sure who did the circuit design.

Again, "in the day" these orange units were referred to as "Earth Tone" units, per the original request from John Shykun.

As far as other info, I was a member of the crew that survived the ARP "11/7" (bankruptcy chapters....) and transitioned to CBS curtesy of Philip Dodds tireless efforts. My efforts were limited to managing the screen shop that fabricated the membrane switch assemblies, and graphics panels.... with occaisional assistance elsewhere in terms of assembly, test, and that sort of thing.

I'd be happy to respond to any questions anyone might have.

See Panel Colour Themes: The Polaris Prototype.

Keyscan code disassembly/corrections/scan rate

David Clarke [21030085++]

Folks - while taking some measurements for the "attack/response" discussion last week, something else caught my eye.

When looking at the keyboard response, I happened to notice that keyboard scanner seemed to be running at 0.7mS per scan. I thought this to be a bit odd as that the service manual says that this value should be approx. 1mS. Further, I too had thought it was running about about 1mS, based on the really quick look that I had taken at the source for the scanner before (the output from that noted at the bottom of the EPROM Code page).

Anyway, this bugged me enough that I had to dig into a bit more.

The first thing I've done is actually look at the code in the key scanner EPROM. Attached please find scan2.asm and scan3.asm, updated, commented assembly source files for both the Rev 2 and Rev 3 keyscan code. Admittedly, the comments probably aren't perfect - but they're better than what I had previously provided to the site.

** Note to Chris R. - these two files can (and should) completely replace REV2.OUT, REV3.OUT, and REV2DCD.WPD [on the EPROM Code page].

The files have been replaced; see Chroma EPROM Code or use the above file download links.

The big change for me in this code is that I now interpret the timer data differently. I had (incorrectly) thought the timers were "count down" type, and so the timing difference between Rev 2 and Rev 3 (a timer value of 0xEF versus 0xF4) was really negligible.

Now, understanding that the timers count UP, we're looking at the difference between a count of "17" and "12" (for Rev 2 and Rev 3, respectively).

In practical terms, what this means is that the Rev 3 keyscan code can detect 'faster' key presses than the Rev 2 code. It also means, that for the exact same main firmware, the same speed of strike on Rev 3 code will 'seem' slower.

For an example of this, lets take the case where a key strike (in 'real' time) takes 13.056mS.

The Rev 2 code interprets 1 time cycle to be 1/8MHz * 512 * 17 = 1.088mS. That means a Rev 2 keyscan implementation would see 13.056mS as 12 "time units" (it is these time units which are sent to the Chroma's main CPU).

The Rev 3 code interprets 1 time cycle to be 1/8MHz * 512 * 12 = 0.768mS. That means a Rev 3 keyscan implementation would see 13.056mS as 17 "time units".

So - for the exact same key strike time, a Rev 2 keyscan board would 'see' the strike as about a 1/3rd faster than the exact same strike on a Rev 3 keyboard.

This observation will change some of the things we show in Keyboard Velocity Curves. Specifically it may mean the addition of another graph showing how the values convert into 'real' times (and not just times sent to the Chroma's main CPU), and a correction/update to the note after the graph (but before the data table at the end of the article).

Chris R. - over the next while I'll look to update this chart/text data and provide it to you.

Chroma Velocity Curves has been revised.

Rich Hilleman [21030351+]

Nice work, as always. I suspect there is more time lost in the software than any hardware mod can make up for.....

Frequency Response (was "Re: Chroma: Attack Times")

David Clarke [21030085++]

Go to first message in thread (October 2003)

"H.T. Vellinga" wrote:

As an addition to this; I am very much interested in the frequency spectrum of the Chroma. ... Can anybody confirm this? Maybe there is a defect in my Chroma's audiomixer??

I took a quick look at the schematic for the mixer, and I couldn't immediately see anything that should be frequency limiting (at least nothing below 50kHz).

That being said, I did a quick test with the scratch patch.

I used the Pitch Mod settings to push the pitch up and up. What I saw was that the amplitude started to fall off gradually, being down by about half amplitude by the time you get to 20kHz. Once you start pushing up past that the signal is heavily attenuated to where by the time you got to 30kHz+ there was no more output.

Poking a bit closer I went back and looked at the raw output of the VCO (pin 3 of the 4151). What I saw here was that I could get to 30kHz or so, but not beyond.

So, the absolute 30k limit seems to come from the root VCO itself. That limit could probably be changed by swapping out some components, but you'd probably have to go beyond the VCO to make sure you saw any benefit from that (as other things further down the audio chain will also start to limit frequency response. For instance the buffer amplifer at the output of the VCO (Z10) also serves as low-pass filter, with a corner freq. approx. 31kHz (meaning by that time the output will already be attenuated by 0.7x.)

All that is to say, depending on the patch and the audio path, you may not be able to reach 50kHz or anything like that - but I would expect that you should be able to get healthily above the 7kHz or so limit that was observed.

Dave

P.S. Here's what you can do to duplicate the frequency test (which will also confirm how high you can hear :->)

  1. Set up a scratch patch (e.g., in Param Select mode, select Edit A and Edit B, and then press each of the 50 buttons in on the right-hand panel, while holding down the Param Select button).
  2. Set Pitch Mod 1 Select (Param 27) to "2" (Env 1A)
  3. Set Pitch Mod 2 Select (Param 29) to "2" (Env 1A)
  4. Set Pitch Mod 3 Select (Param 31) to "2" (Env 1A)
  5. Set Pitch Mod 1 Depth (Param 28) to "63" (Deep)
  6. Set Pitch Mod 2 Depth (Param 30) to "63" (Deep)
  7. While holding down the key of your choice, adjust Pitch Mod 3 Depth (Param 32) from -64 (Shallow) to 63 (Deep). This should sweep the frequency from low to past cutoff/audiblility.

Power Supply Replacement?

Paul Tillotson [21030218]

How many folks have gone the whole route and replaced their Chromas' power supplies? Can you estimate the amount of bench time it took, or might take a skilled tech? If my 5 volt supply is "bad" is full on replacement the best option or am I looking to spend as much on this procedure as I spent on the Chroma, when the old 5 volt supply can be fixed or replaced kinda cheaply? Do lots of folks get along just fine with completely stock power supplies?

And what's the deal with my serial number? [see First Chroma Serial/Model Number Overlap?, October 2003] We'll find out soon, I think.

See Fw: Your Chroma.... Serial Numbers below.

My impression is that I really do not want to replace the whole power supply if I can get by with a easier, cheaper fix that will leave my Chroma as dependable as it was right up until it failed completely.

Blah!

Henry Salvia [21030307]

The conventional wisdom is that the stock Chroma power supply is a hack, mainly the cheapo homebrew +5 digital switching power supply. My memory is that it switches at 60 or 120 Hz, and this isn't so hot for a switching power supply.

I bought my Chroma from Gus Zoppi Music in Detroit in either late 1981 or early 1982. It had *lots* of problems (the PC boards had the Arp logo on them) and it spent a lot of time in their shop. I came in once when the tech was on the phone with whoever was doing phone support for the Chroma while he reamed them out on the design of the power supply... I eventually had it replaced by CAE in San Mateo CA, who came to the same conclusion.

Paul Tillotson [21030218]

Message Thanks for the reply, do you remember how many hours on the bench this took?

Henry Salvia [21030307]

Don't know. Peter did mine as a kind of prototype, so he had it for a few weeks. Basically he bought a few off-the-shelf power supplys, bolted them in, and re-worked the wiring harness to hook them up. The power requirements are pretty stock: +5 digital +/-15, +5 analog, something like that. You just need to make sure the power supplies have enough current to drive everything, find room in the box to hold them all, and re-work all the power wiring harnesses. They may have fixed the power supply in later runs of the Chroma for all I know, and it may not buy you much to replace the one you have.

Any estimate I give on bench time won't matter, really. No matter where you live you probably have at best a few options of where to take in a Chroma for some work. Whatever they quote is what it will cost. But its not a complex job. My guess would be 4 hours.

David Clarke [21030085++]

My impression is that I really do not want to replace the whole power supply if I can get by with a easier, cheaper fix that will leave my Chroma as dependable as it was right up until it failed completely.

I am running 'original' power supplies in each of my Chromas, and while the design is admittedly not the best, those supplies have been able to do what I have wanted from the keyboards.

In terms of $, it should cost considerably less to get the original supply up and running versus doing the PSU upgrade (especially if you're going to have to pay for someone else's labour costs).

I personally intended to stay with the original supplies.

Paul Tillotson [21030218]

Fw: Your Chroma.... Serial Numbers

I can't find any of the emails about duplicate serial numbers on different revision Chromas [see First Chroma Serial/Model Number Overlap?, October 2003], but here's my serial number along with a prognosis on the power supply. I think I'll replace it.

Thanks

From: [email protected]Backline
To: Paul Tillotson
Sent: Monday, November 10, 2003 9:46 AM
Subject: Re: Your Chroma....

Hi Paul,

First off your Chroma is ser# 21030218

As for the PSU...I've subbed in a working 5v supply line and the chroma seems to work. The patches are a little useless sounding, but all the functions seem to work. Did you have any saved patches that actually sounded like something? It's possible that the memory battery is dead.

If it were my chroma I'd do the PSU mod...having said that I also think you can get away with a repair. The psu pcb shows no signs of overheating, burning, etc. The only problem with doing a repair is that the failed component is an over-voltage protector on the 5volt line. This part is NLA. Removing it would mean that some degree of protection would be lost, so I can't guarantee what would happen if (when) you have another psu failure.

Repair would be about CAN$120 The PSU mod described on the net would be about CAN$500-$600

Let me know...

Richard.

David Clarke [21030085++]

I can't find any of the emails about duplicate serial numbers on different revision Chromas, but here's my serial number...

Paul - if possible (on your next e-mail exchange) would it be possible for Richard to confirm:

  1. If the serial number came from the tag on the PSU and if so
  2. can check the serial number written on the inside wood base (near the voice cards).

(The currently presumed 'duplicate' S/N may only be present on the wood, with no sticker on the PSU - if yours is only on the PSU, or if the PSU and wood don't jive, then it could be that the Power Supplies - and serial number tags - got swapped over the history of the keyboard's travels).

The auction for the Syntech Midi Interface

David Clarke [21030085++]

Wow - the Midi Interface that was up for auction on Ebay (that closed yesterday) ended up selling for $223.50.

The new ones avail. from MIDI Retrofits (Ken Y.) would only be $210 (if shipped in the US)...

Wayne Griffin [16330111]

I am the pathetic sod that bought it at said price. I happened to forget at the time that that was still around... (xxx) happens...

[w] MYSTERON

PS- Now all I need is a Chroma to go with it!

David Clarke [21030085++]

I am the pathetic sod that bought it at said price. I happened to forget at the time that that was still around... (xxx) happens...

On the bright side, there wasn't a huge difference between the Ebay price, and the direct purchase price :->

PS- Now all I need is a Chroma to go with it!

There's always a couple on the 'Ads' page looking for a good home.

Welcome,

Dave

Books of Patch Presets? (on ebay)

David Clarke [21030085++]

There's currently a listing on Ebay with a title of "Rhodes Chroma program printouts vol 1-5" and a description of "2 original manuals covering setting for all the presets."

Anybody know what this might actually be?

Chris Ryan [21030691]

Yeah, I have these. Two spiral-bound books with parameter listings for all five factory sets, printed out I think using the Apple II software.

See Manuals: Program Printouts.

David Clarke [21030085++]

Any nice pictures or graphics, or just raw text with things like P1 = 2, P2 = 3, etc?

Chris Ryan [21030691]

Just text.

Chris Ryan [21030691]

Here is a scan of the patch books ...

Chris Ryan [21030691]

... and here is a scan of one of the patch listings.

David Clarke [21030085++]

Just for comparison, here's what you'll get if you use the Patch Conversion Tools to generate a text listing for the same Program (Program 1 of Factory Set 4 - Cowbell):

  • SYX2TAPE.EXE FS4.syx
  • TAPE2TXT.EXE FS4.SND
Dump for Program 1
Control - Patch       (Param 1)  11   Series Filter Mode - Ring Mod
Control - FSW Mode    (Param 2)   0   Left: Latch       Right: Sustain
Control - Kybd Alg    (Param 3)   6   Mono - Last Note, Multi-Trigger
Control - Detune      (Param 4)   6   0 = No Detune, 1 = Sharp, 31 =
More Sharp
Control - Out. Sel    (Param 5)   0   Output 0
A - Glide Rate        (Param 6)   0   0 = None, 1 = Fast, 31 = Slow
A - Glide Shape       (Param 7)   0   Portamento
A - Sweep Mode        (Param 8)   0   Asynchronous Free-Run
A - Sweep Rate        (Param 9)   0   0 = Slow, 63 = Fast
A - Sweep Rate Mod   (Param 10)   0   None
A - Sweep Wave Shape (Param 11)   0   Sine
A - Sweep Ampl Mod   (Param 12)   0   None
A - Env 1 Ampl Touch (Param 13)   0   None
A - Env 1 Attack     (Param 14)   0   0 = Instant, 1 = Fast, 31 = Slow
A - Env 1 Attack Mod (Param 15)   0   None
A - Env 1 Decay      (Param 16)   5   0 = Instant, 1 = Fast, 30 = Slow,
31 = Infinite
A - Env 1 Decay Mod  (Param 17)   0   None
A - Env 1 Release    (Param 18)   4   0 = Instant, 1 = Fast, 30 = Slow,
31 = Thresh
A - Env 2 Delay      (Param 19)   0   0 = None, 1 = Short, 30 = Long, 31
= Retrig on SWP A
A - Env 2 Ampl Touch (Param 20)   0   None
A - Env 2 Attack     (Param 21)   0   0 = Instant, 1 = Fast, 31 = Slow
A - Env 2 Attack Mod (Param 22)   0   None
A - Env 2 Decay      (Param 23)   2   0 = Instant, 1 = Fast, 30 = Slow,
31 = Infinite
A - Env 2 Decay  Mod (Param 24)   0   None
A - Env 2 Release    (Param 25)   2   0 = Instant, 1 = Fast, 30 = Slow,
31 = Thresh
A - Pitch Tune       (Param 26)  30   0 = Low, 12 = Concert, 63 = High
A - Pitch Mod 1 Sel. (Param 27)   0   KYBD Glide A
A - Pitch Mod 1 Depth(Param 28)   0   -64 = -Deep, 0 = None, 63 = Deep
A - Pitch Mod 2 Sel. (Param 29)   2   ENV 1A
A - Pitch Mod 2 Depth(Param 30)   1   -64 = -Deep, 0 = None, 63 = Deep
A - Pitch Mod 3 Sel. (Param 31)   0   KYBD Glide A
A - Pitch Mod 3 Depth(Param 32) -32   -64 = -Deep, 0 = None, 63 = Deep
A - Waveshape Select (Param 33)   1   0=Sawtooth, 1=Pulse, 2=Pink Noise,
3=White Noise
A - Waveshape Width  (Param 34)  32   0=Narrow Pulse, 32=Square Wave,
63=Broad Pulse
A - Waveshape Mod Sel(Param 35)   0   KYBD Glide A
A - Wveshpe Mod Depth(Param 36)   0   -64 = -Deep, 0 = None, 63 = Deep
A - Cutoff LP/HP     (Param 37)   1   0 = Low Pass, 1 = High Pass
A - Cutoff Resonance (Param 38)   5   0 = Min Res., 7 = Max Res.
A - Cutoff Tune      (Param 39)  17   0 = Low Freq., 63 = High Freq.
A - Cutoff Mod 1 Sel (Param 40)   0   KYBD Glide A
A - Cutoff Mod 1 Dpth(Param 41)   0   -64 = -Deep, 0 = None, 63 = Deep
A - Cutoff Mod 2 Sel (Param 42)   0   KYBD Glide A
A - Cutoff Mod 2 Dpth(Param 43)   0   -64 = -Deep, 0 = None, 63 = Deep
A - Cutoff Mod 3 Sel (Param 44)   0   KYBD Glide A
A - Cutoff Mod 3 Dpth(Param 45)   0   -64 = -Deep, 0 = None, 63 = Deep
A - Volume Mod 1 Sel (Param 46)   0   ENV 1A
A - Volume Mod 1 Dpth(Param 47)  15   0 = None, 15 = Deep
A - Volume Mod 2 Sel (Param 48)   1   ENV 2A
A - Volume Mod 2 Dpth(Param 49)  15   0 = None, 15 = Deep
A - Volume Mod 3 Sel (Param 50)   4   Pedal 1
B - Glide Rate        (Param 6)   0   0 = None, 1 = Fast, 31 = Slow
B - Glide Shape       (Param 7)   0   Portamento
B - Sweep Mode        (Param 8)   0   Asynchronous Free-Run
B - Sweep Rate        (Param 9)   0   0 = Slow, 63 = Fast
B - Sweep Rate Mod   (Param 10)   0   None
B - Sweep Wave Shape (Param 11)   0   Sine
B - Sweep Ampl Mod   (Param 12)   0   None
B - Env 1 Ampl Touch (Param 13)   0   None
B - Env 1 Attack     (Param 14)   0   0 = Instant, 1 = Fast, 31 = Slow
B - Env 1 Attack Mod (Param 15)   0   None
B - Env 1 Decay      (Param 16)  31   0 = Instant, 1 = Fast, 30 = Slow,
31 = Infinite
B - Env 1 Decay Mod  (Param 17)   0   None
B - Env 1 Release    (Param 18)   8   0 = Instant, 1 = Fast, 30 = Slow,
31 = Thresh
B - Env 2 Delay      (Param 19)   0   0 = None, 1 = Short, 30 = Long, 31
= Retrig on SWP A
B - Env 2 Ampl Touch (Param 20)   0   None
B - Env 2 Attack     (Param 21)   0   0 = Instant, 1 = Fast, 31 = Slow
B - Env 2 Attack Mod (Param 22)   0   None
B - Env 2 Decay      (Param 23)  31   0 = Instant, 1 = Fast, 30 = Slow,
31 = Infinite
B - Env 2 Decay  Mod (Param 24)   0   None
B - Env 2 Release    (Param 25)   0   0 = Instant, 1 = Fast, 30 = Slow,
31 = Thresh
B - Pitch Tune       (Param 26)  45   0 = Low, 12 = Concert, 63 = High
B - Pitch Mod 1 Sel. (Param 27)   0   KYBD Glide A
B - Pitch Mod 1 Depth(Param 28)   0   -64 = -Deep, 0 = None, 63 = Deep
B - Pitch Mod 2 Sel. (Param 29)   2   ENV 1A
B - Pitch Mod 2 Depth(Param 30)   1   -64 = -Deep, 0 = None, 63 = Deep
B - Pitch Mod 3 Sel. (Param 31)   0   KYBD Glide A
B - Pitch Mod 3 Depth(Param 32) -32   -64 = -Deep, 0 = None, 63 = Deep
B - Waveshape Select (Param 33)   1   0=Sawtooth, 1=Pulse, 2=Pink Noise,
3=White Noise
B - Waveshape Width  (Param 34)  32   0=Narrow Pulse, 32=Square Wave,
63=Broad Pulse
B - Waveshape Mod Sel(Param 35)   0   KYBD Glide A
B - Wveshpe Mod Depth(Param 36)   0   -64 = -Deep, 0 = None, 63 = Deep
B - Cutoff LP/HP     (Param 37)   0   0 = Low Pass, 1 = High Pass
B - Cutoff Resonance (Param 38)   0   0 = Min Res., 7 = Max Res.
B - Cutoff Tune      (Param 39)  20   0 = Low Freq., 63 = High Freq.
B - Cutoff Mod 1 Sel (Param 40)   0   KYBD Glide A
B - Cutoff Mod 1 Dpth(Param 41)   0   -64 = -Deep, 0 = None, 63 = Deep
B - Cutoff Mod 2 Sel (Param 42)   3   ENV 2A
B - Cutoff Mod 2 Dpth(Param 43)  26   -64 = -Deep, 0 = None, 63 = Deep
B - Cutoff Mod 3 Sel (Param 44)   0   KYBD Glide A
B - Cutoff Mod 3 Dpth(Param 45)   0   -64 = -Deep, 0 = None, 63 = Deep
B - Volume Mod 1 Sel (Param 46)   2   ENV 1B
B - Volume Mod 1 Dpth(Param 47)   0   0 = None, 15 = Deep
B - Volume Mod 2 Sel (Param 48)   2   ENV 1B
B - Volume Mod 2 Dpth(Param 49)  12   0 = None, 15 = Deep
B - Volume Mod 3 Sel (Param 50)   0   None
Panel - Edit Mode                 2   Edit A
Panel - Edit Program              3    
Panel - Link Balance              4    
Panel - Link Type                 0   No Link
Panel - Link Program             46    
Panel - Keyboard Split           12    
Panel - Main Transpose Type       0   No Transpose
Panel - Link Transpose Type       0   No Transpose
Panel - Sequence Program Number  18

Chroma Items on eBay

Chris Ryan [21030691]

Paul pointed out that there's a Chroma for sale on eBay. There are several other items as well.

  • Chroma, currently US$730 (reserve not met) is item number 2575107518. Arlington, Texas, U.S.A.
  • "Rhodes ARP Chroma EQ Circuit Board," currently $10, is item number 2577425513. Milwaukee, Wisconsin, U.S.A.
  • "ARP Rhodes Chroma I/O Circuit Board," currently $10, is item number 2577626707. Milwaukee, Wisconsin, U.S.A.
  • Programming manual, currently $5, is item number 2577523769. Pembroke, Massachusetts, U.S.A.