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ChromaTalk Archives: September 2011

Chroma Cult Patch Credits

Chris Ryan [21030691]

New on the site this month is a list of the author credits for the Chroma Cult patch banks (which are available on the Patch Downloads page). I've been looking for this list ever since the site started, over a dozen years ago; many thanks to Brian McCully [21030361] for providing a copy.

I've "de-anonymized" three registry entries, originally sourced from the warranty list (see "Registry Approaches 500 Instruments," March 2008), as a result: Damase Giguere [21030284]; Rick Manasa [21030520], who apparently played on Bob Seger's classic "Seven;" and Mikail Graham [21030159]. I found Rick and Mikail on the web and I've contacted them to see if they have any more information, and whether they still have their Chromas.

I heard back from Rick Manasa; see the entry for 21030520 for more info.

I heard back from Mikail Graham; see 21030159 for a minor update on hist instrument, which he still owns. [January 2013]

Several current and former list members contributed patches, as noted. If you have any further information about other contributors, please let me know.

Re: re-glueing the CPS etc.

Chris Borman [21030194+]

Go to first message in thread, August 2011

I don't know what Jesper used, but in light of the 3M 77 Spray adhesive failures, I am going to give Liquid Nails Home Project adhesive a try tomorrow. It is formulated to adhere wood to impervious surfaces such as plastic and fiberglass. I suspect the adhesive failure is occurring at the PCB FRP surface.

I will post my results tomorrow eve.

This works fine. I will use this product for all future builds and is ideal for field repairs. Liquid Nails 'Perfect Glue', PG-00. Apply a bead, spread out on the opposing surfaces. Lightly clamp for 1 hr. Done. Good from -60F to +300F, flexible, shock absorbing, gap filling to 1/4".

For field repairs, remove the Damper Bar/CPS assembly. Use a small brush or wood mixing stick to apply a thin layer of glue in between delaminated surfaces. Lightly clamp for 1hr. Keep the glue away from the ends of the array where the FSR vents!

Don't try for force adhered areas of the sensor PCB off the wood spacer. This glue has tremendous holding power so sparce applications will suffice for field repairs. I would suggest also adding screws to mechanically fix the the vertical mux bd to the Damper bar. This will in turn secure the central region of the sensor array.

Sorry for the design flub!


Dave Manley [21030547]

Hi Chris,

Thanks for the quick follow through and 'ECO' :-) - I'll try it out this weekend.

I'm curious though about the FSR venting - any more info on that? I don't see anything on the Sensitronics website.

Chris Borman [21030194+]

ECO Paperwork... Nooooo!

Venting allows the flexible Mylar with the FSR patch, which stands off the opposing circuits via some type of spacer, to be pressed down onto the circuit, increasing the FSR to Circuit contact area, lowering the resistance causing an increase in current flow through the circuit the harder you press. Without venting, you would have a bubble preventing contact. Interlink has a document that should explain it.

Dave Manley [21030547]

Weekend results: the wood spacer was at least half off from each pcb, so I took a thin piece of plastic and gently walked it through the remaining glue and separated the rest of the spacer from the pcb. It came over easily with little force required. Before re-gluing I checked the resistance at each FSR by clipping an ohm meter between the +5 common and each FSR return signal. On the left hand side when squeezing between thumb and index finger, the resistance drops down to about 5K, while on the right hand side it drops to about 1K. The 'B' below middle C on the other hand only drops to ~100Kohm. To make sure it wasn't a soldering problem (measurements were taken at the headers by the mux board), I probed at the via on the backside of the pcb nearest the FSR and saw the same ~100K. I'm thinking I shouldn't glue this up and install it.

Chris Borman [21030194+]

Hi Dave,

Why don't you pack it up and return it to me so I can take a look. I will start building a replacement CPS Kit for you.

See follow-on thread CPS re-glueing re-visited, again, October 2011

Re: chroma for sale

Go to first message in thread, August 2011

Chris Ryan [21030691]

On 25/08/2011, at 7:26 AM, Keith Hedger wrote:

I recently bought a Chroma on eBay but find I need to turn around and sell it. Some unexpected financial problems have reared their ugly heads. I'll include the original eBay description below. I haven't had a chance to do a lot with the Chroma, but everything seems to work fine on it.

I'm not really setup to ship it so this will have to be to 'local' buyers only - pickup in Cambridge, MA. I'm going to wait a few days before placing this on the local Craigslist. If anybody's interested, get back to me. I just need to break even on it... $4500.00 takes it.

Now on craigslist Boston: see posting ID 2567239420. "The Chroma is a big beast so I'm only interested in local buyers. Pick up in Porter Sq., Cambridge." This is Chroma 21030607.

note triggering (threshold?) difficulty

Brian McCully [21030361]

Just got the replacement CPS re-installed and this time around it seems to function properly - yay! With tech time, my time, Chris Borman's [21030194+] time and extra materials, it hasn't been a piece of cake by any means. Hopefully no more problems...thanks to Chris for remaining civil with my pestering (off-line) questions during this de-lamination and reliability set of issues.

Anyhow, playing the Chroma is like driving an old sports car. I'm almost afraid it's going to go careening off the stand because I'm having too much fun. Don't want to hurt either of us too badly now... ;>)

One new thing I just noticed since playing the keyboard for an extended period yesterday, was that light playing (which will trigger low velocity values elsewhere) will not trigger some of the upper keyboard notes - specifically the high B, C and mostly the D. I cleaned under the contacts (lightly with a rubbing alcohol soaked strip of paper) and examined the action of the key contacts while playing and they act like all of the other key contacts - same distance and movement like the other leaf(s). These notes will trigger, but it seems like I have to play over a certain velocity threshold - like hard. Playing fast licks yields intermittent skipped notes but anywhere else on the keyboard playing in the same manner will trigger all notes just fine, as expected.

More thorough cleaning required? Scanning chip starting to lose bits? Any input is appreciated. thanks, -Brian

John Leimseider [21030434++]

I suspect that you can fix this by moving up the stop-bar (with the pressure sensors) a very small amount. I have one of the original pressure kits in my Chroma and the set up is EXTREMELY critical... Too low and the notes won't trigger softly, too high and the pressure isn't sensitive enough. When it's set correctly, it's awesome!

Paul DeRocco [21030230]

It becomes less sensitive to position if you remove the felts under the fronts of the keys, and rely entirely on the pressure sensor for stopping the key travel.

Brian McCully [21030361]

note triggering (threshold?) > fixed !

Thanks for the quick response(s). I added back in the front felt first and it didn't correct the problem, although the action is pretty much the same, regardless so I'm going to leave the felts in. In retrospect I'd think leaving them out may correct for this situation, due to the need for some 'extra throw', but I guess the (vertical) cross-bar position is the ultimate determination.

Then I very slightly raised the top end of the cross bar (~1/2mm) and it totally corrected the problem. I can see now that the top leaf contact wasn't making it all the way unless I was pressing hard(er) (which wouldn't matter if the sound hadn't triggered), or I had to play with enough force to make the top contact occur. Wow - just that very small amount is absolutely necessary.

I also re-read the on-line installation notes in regards to the 'vertical positioning'. I guess I didn't quite connect this problem with 'There is a fine line between limiting operation of the second velocity leaf switch and not getting enough travel for full deflection of the CPS Sensor' because it's possibly more focused towards the CPS sensor operation, but maybe if there is a next update to the online notes, something for troubleshooting to the effect of 'if notes play intermittently or a velocity threshold above a certain amount is required (i.e. notes won't play unless hard velocity is required), then try (slightly) adjusting the vertical height of the bar, so that the 2nd leaf contact occurs even with the softest playing force'. (just a suggestion...)

Thanks again! -Brian

Found in the Service Manual

Donald Tillman

Hey folks,

While debugging a VCF problem on a voice board, I noticed this adorable little paragraph in the "Dual Channel Board Circuit Description" section [specifically, Filters] of the Service Manual:

"Op-amp Z29A isn't really part of the filter at all, and should have been drawn someplace else. It's a current inverter. Op-amp Z29B is connected in the rather unconventional 'left-facing ground buffer' configuration. Unfortunately, the theory behind this circuit is beyond the scope of this document. Suffice to say that it works perfectly."

Heh-heh. Yeah, it's a simple inverter.

But why is it there? It doesn't say.

I believe that it's there for patch topologies where oscillator A syncs oscillator B, and the two oscillators are mixed together, and it makes up for an inversion in between, so the sync'd oscillators are in phase. Wouldn't want the sync'd oscillators to subtract.

Paul DeRocco [21030230]

Since I wrote that, I'll try to remember what it was about.

You may be right about the sync polarity, but I think there was another issue, too. The summing junction of Z10A isn't perfect, and actually has a little bit of the oscillator signal on it, high-passed, due to the fact that the loop gain of the op-amp goes down as the frequency goes up. So you don't want to connect this noisy node directly to Z18, because you'll get a little bit of bleed-through into the output through the inter-switch capacitance of Z18.

When I wrote "it works perfectly", I was actually joking about Z29B. Of course, its only purpose is to tie off the unused section so that it doesn't do anything. We could have used a single op-amp, but we always tried to keep the number of different parts to a minimum, and a dual didn't really cost any more.

Jeffrey D. McEachin [21030073+]

We could have used a single op-amp, but we always tried to keep the number of different parts to a minimum,

No wonder the Chroma is such a magnificent instrument - it was designed by REAL engineers. :)

Heinz Weierhorst [21010276]

Hi all.

It's true Z29-A has nothing to do with the filter but with VCA B. The VCA is a current out device and is routed through Z18 to different destinations.When Z18 is in position 0 and 1 it's connected to VCF A frequency control node, if in position 2 it's connected to VCA A out thus summing both currents together. If in position 3 Z29-A comes in! It is a simple current to voltage converter and inverting but it's connected to channel A audio summing amp Z8 which is inverting too. At the output of Z8 the signal is in phase. It's simply to get the right level balance and phase if VCA B is used as a mixer for VCO B. See parameter chart -> patches.

Chroma on eBay UK

Chris Ryan [21030691]

Item #150659027697, starting bid £1,500.00, no bids yet, ends September 12. From the description: "This instrument has been fitted with Sandro's [21010294]'s CC+ replacement motherboard which besides extra stability, gives an extra 3 banks of program storage (now 200 total), MIDI in/out, and other benefits. The power supply has also been replaced. The Chroma has just returned from a complete check-up & service by Roy Paynter, one of the original Chroma trained engineers, so technically it is working fine. Cosmetically: the keyboard and facia are excellent, the metal parts like the top are very good, the wooden parts like the rails and sides are just average with plenty of marks and scrapes. The flight case supplied is not the original Bulldog [Anvil?] case with the melting foam. It is functional but not pretty with marks and dents, and one corner protector is missing.

"This is what is included in the sale: Chroma keyboard; Flight case; original Chroma double hold/sustain pedal; Yamaha swell pedal; 3 original Chroma footswitches - 2 are labelled Rhodes (one unused) & 1 is labelled Chroma; MIDI in/out box [CC+]; Mains lead; Ring binder containing: CC+ Users Guide, Programming Manual (copy), Performance Manual (copy), Service Manual (copy)."

I've asked the seller for the serial number.

Chris Ryan [21030691]

This is Chroma 21030095.

Rob Belcher [16330123]

That one came from a good home :)

Chris Ryan [21030691]

Sold for £2,051.00.

Native Instrument's Retro Machines mk2

Brian McCully [21030361]

Just received the update for Komplete 8 and they actually include a 'Chroma' folder, in with a bunch of other classics (moogs, oberheims, etc.) in the Kontakt Retro Machine sets. It's pretty good, albeit a very limited set (about 10 'instruments') and nowhere near as capably creative, but some of the sample patches are quite recognizable, and have some decent variability to them with filtering and such.

I'm sure this has probably been discussed, but it'd be great if someone could use N.I's Reaktor engine (or the like) to re-create a Chroma. It's one of the few classics I haven't seen a soft synth 'model' of. Not sure that I'd ever have the time (or the chops!) to tackle such a project...

Paul DeRocco [21030230]

I've been tinkering with writing a VST plugin that does Chroma sounds. I don't have a lot of time to put into it, so it's slow going, but the basic synthesis algorithm is done but not fully debugged. What takes time is all the peripheral stuff, like the user interface. If I get anywhere with it, I'll certainly let everyone know.

Chris Smalt [21010280+]

oh yessssss! How about using a real Chroma as a dongle for copy protection? :-)

Re: CEM3350

Go to first message in thread, August 2011

Doug Terrebonne [21030114]

Hi, the 3350s are in. Anyone else who hasn't emailed me I should still have a few left over so let me know.

Help: looking for connectors

Riccardo Grotto [21010249+]

Hi everybody,

"doctor analog" is restoring a Chroma which unfortunately has been damaged by the batteries acid (the original owner kept it in storage for all these years since early nineties).

After replacing the CPU board and the power supply unit with brand new "Chromatalk devices" and cleaned and restored the ruined tracks, it has become clear we need to change some of the connectors on the main and the channel (voice) boards.

If available they should come in pairs (male, female).

Please let me know if they're still available somewhere.

Thanks a lot for the help.

Paul DeRocco [21030230]

Unless you've completely broken off a pin, it's hard to imagine needing to replace the connectors on the channel motherboard. They're just 0.1" headers anyway, and lots of people make them. The edge connectors on the voice boards can get bent over due to careless insertion, but can usually just be bent back. It helps to reseat them properly if there isn't another board in the way, and you can get your fingers on them. But if you need to replace them, they're Molex 22-15-2086, which you can buy from Digikey.

Luca Sasdelli [21010226]

Ciao Riccardo,

io li ho presi da Digi-Key:

  • femmine WM2817-ND su suggerimento di David Clarke [21030085++]
  • maschi WM2352-ND

Riccardo Grotto [21010249+]

Thanks Luca and Paul for the precious infos.

Re: Chroma 21030828 on eBay

Go to first message in thread, July 2011

Chris Ryan [21030691]

On 22/07/2011, at 9:46 PM, Chris Ryan wrote:

Item #260822534712, starting bid USD$3,995.00 with no bids yet; or price of USD$4,550.00; ends August 1.

Back as item #260861138264, starting bid USD$3,495.00 with no bids yet, ends October 2.

From the description:

"I’m the single original owner of this amazing Vintage Rhodes Chroma (Serial Number 21030828). This refurbished Chroma works as flawlessly as it did on the day I bought it. It has a new, completely upgraded, power supply. All voices register and autotune properly. The original factory pre-set sounds have been loaded from the original cassette. You won't find a better Chroma than this one. This is one of only 1400 ever produced. It's still one of the purest and most unique sounding polyphonic synths ever made.

"A copy of the manual is included (they never gave me an original… just a copy!). The original cassette tape of voices from the factory is also included. [...] I hate to let it go (unexpected expenses). It belongs with a high end studio or in the collection of someone who will use it often.

"No Sustain or Volume Pedal is available. Anvil Case available per your request for additional cost."