Skip Navigation.
Section 0

ChromaTalk Archives: October 2008

Re: Resurrecting a Chroma

Go to first message in thread, September 2008

Michael Grossman [21030350] · Wed, 1 Oct 2008 12:54:11 -0700

Upon further investigation I have discovered that autotune does not consistently tune the all VCOs precisely every time. After warming up if I repeatedly press autotune (or set split 50), random VCOs will be somewhat off. If I autotune a few times I can get all the VCOs pretty close. Then over time they all stay in tune. Has anyone encountered this type of anomaly?

Luca Sasdelli [21010226] · Thu, 02 Oct 2008 00:06:48 +0200

Hi Mike,

did you set the zero-point with the I/O board trimmer? It s responsible for the DAC linearity. A randomly working autotune is generally due to a bad reading from the ADC/DAC when sampling the pitch. Moreover, I recommend to check single VCO tuning: you can do it either via a scope to the test points, or by ear by seeking for the "hollow" timbre of 50% duty-cycle waveform (wave shape must be set @ 32). Please hit a [SET SPLIT][31] just before adjustment.

A last detail: when tuning the Chroma, the instrument is open and the voice boards can run at a lower temperature in respect when the case is closed; just keep it in mind, so you can put the cover on after a first tuning, leave it some time to settle the temperature at normal value, and then do a final retouch afterwards.

Chris Smalt [21010280+] · Thu, 2 Oct 2008 03:55:00 +0200

Moreover, I recommend to check single VCO tuning: you can do it either via a scope to the test points, or by ear by seeking for the "hollow" timbre of 50% duty-cycle waveform (wave shape must be set @ 32). Please hit a [SET SPLIT][31] just before adjustment.

Yes, this is key advice: I did it once (by ear), and both of my Chromas remain nicely in tune, and oscilator beating is even across the 8 (or 16) voices.

New Audio

Chris Ryan [21030691] · Thu, 2 Oct 2008 18:49:42 -0700

I've posted a couple of recordings contributed by Chris Smalt [21010280+], who recently rejoined us after an absence of many years. An original composition, "Silent Rage," is "13 tracks of Chroma, all mono, no chorus, just reverb and some delay added. Some rhythm provided by rubbing hands, snapping fingers and tapping the mic stand with my foot. The sounds are a mix of factory presets and custom patches. The track was originally published in 1999 on a 7-CD compilation called 'Bohemian R.A.P. CD', that included tracks recorded by various contributors to the rec.audio.pro usenet group."

Also an audience recording, possibly of Peter Vettese, from the 1984 Musicom trade show. Chris writes, "almost 20 minutes of non-stop live playing two Chromas and a Polaris (and briefly a Rhodes), straight into the PA, no effects, no sequencing. ... At a time when everyone was looking to sound digital and sequenced, here was someone improvising live, just hopping through some presets, retuning the instrument by ear, using a musical idiom and sounds that weren't hip at all. What he showed off in particular was the flexibility of the Chroma when played live."

Thanks Chris!

Sysex load on Chroma

Richard Willoughby [21030348] · Thu, 9 Oct 2008 19:45:54 -0700

I've tried loading a bank via Sysex into the Chroma for the first time, and although I'm getting the green light on the Midi box, I haven't been successful at loading anything.....the Chroma doesnt even react. Previously to getting the CC+ I had been loading via tape. Do you need to change any settings on the Chroma to allow a bank load (besides setting the unlock switch on the back)? Usually I don't have any problems with Midi Ox loading sysex in my other gear.

David Clarke [21030085++] · Sat, 11 Oct 2008 17:46:45 -0400

Richard - nothing 'special' should be required.

In general terms, for the sysex to be received/used. As long as the file is a valid sysex file, the patches should be updated.

The data at The Chroma CPU Plus (CC+) User's Guide: MIDI System Exclusive (SysEx) identifies the type of messages expected/received.

For a full bank you'd have: 

    F0 08 00 4B 59 7F 33 pp 0h 0l .... pp 0h 0l ....

    pp 1 to 50 (dec)

The program dump is parsed as it is received so if something has become bad about the sysex - the system should still try to store as many complete programs as it can.

A full sysex bank should be 5958 bytes in size.

If the file is good, then the flashing MIDI activity LED should be a good indication that the data is being successfully send to the Chroma.

A test to see what is occurring would be to replace the first few patches of the current bank with the scratch patch (so it is easy to identify if they do/don't get updated).

e.g.:

  • Push the program select button
  • Push Set Split 39 ("0" will appear in the large display)
  • Push "store" "1"
  • Push "store" "2"
  • Push "store" "3"

You should now be able to confirm that patches 1, 2 and 3 have the scratch patch inside.

Get a known-good sysex file - e.g., perhaps one from the factory sets.

Send the sysex file to the keyboard.

The MIDI activity indicator should be active during the complete transfer.

Once the transfer has completed, the "program modified" flag should appear in the large display.

You should now be able to select programs 1, 2 and 3 and confirm that the scratch patch sound has been updated/changed to whatever was in the sysex file.

Richard Willoughby [21030348] · Sat, 11 Oct 2008 16:27:21 -0700

yes, it is strange as I thought that if the Midi In was getting the data then the Chroma would respond in some manner..... I'll have to try it again....perhaps I'm just sending corrupt data, or the wrong data entirely.

Battery Reminder 2008

David Clarke [21030085++] · Sat, 11 Oct 2008 17:57:22 -0400

If you haven't done so in a while, it might be a good time to check the condition of the batteries in your Chroma.

Issue a "Set Split-6" ("Special Funct-6" on your Expander) and view the voltage in the small display window.

If the displayed value is notably under 3V, probably time for a battery change (the service manual says anything under 2.5V is bad).

Notes:

  1. if you wanted to check your Polaris at the same time - that would be LF-D-1. Two or more LEDs in the assignable Control section indicates things are OK.
  2. If you have a CC+, then there's no need to check the battery voltage as batteries are no longer used.

Another satisfied SPSU kit customer

Malte Rogacki [21010091] · Mon, 13 Oct 2008 12:30:46 +0200

So I took the plunge and instead of rebuilding the original PSU got Luca's kit.

Very, very nice. Many "issues" that were prevalent even before the Chroma sat for several years at a service tech (of course without being fixed in the end) completely vanished. No buzzing anymore.

This is definitely recommended to anyone experiencing any issues with the original power supply.

Now I can tackle the other problems, like missing voices and the broken data entry slider.

Chroma refurb query

Joe Porter [21030058] · Fri, 17 Oct 2008 12:11:10 +0000

Hi all,

Very recently bought a Chroma, it is quite an early one I think (will put the serial number up shortly), as it has a lot of the Arp boards in it.

Anyway, I am just putting Luca's SPSU in to replace the current monster PSU in there. I've noticed on Luca's images on the site that the grey cables are fed round the voiceboards. On mine they are fed under them. Was thinking I should move these from under the boards. Is there any point to doing this? Have taken them out yet so want to only do it if I need to. When I powered it up board "1" failed the autotune, so I guess I will need to take this one out to check the connections soon.

Any advice would be great. Many thanks.

David Clarke [21030085++] · Sat, 18 Oct 2008 20:04:54 -0400

... I am just putting Luca's SPSU in to replace the current monster PSU in there. I've noticed on Luca's images on the site that the grey cables are fed round the voiceboards. On mine they are fed under them. Was thinking I should move these from under the boards. Is there any point to doing this? ...

Joe - I'd say there's no specific need to move them. Most Chroma's I've come across have their cables routed line the one shown in Fwd: Chroma "Carcass" For Sale (February 2002).

Specifically - the 'round' grey cables go under the voice boards, with the flat ribbon cable being wrapped around the end of the wooden support block.

Joe Porter [21030058] · Fri, 24 Oct 2008 15:21:02 +0000

Thanks for that info.

I did take the boards out to check, and the 'round' grey cables were actually on top of each other causing tension on the cables. Anyway sorted that now, and nearly completed the SPSU replacement.

I have though had some problems with the rocker switch. It seems to be an old design which doesn't allow the cables to be removed and resoldered, so I have two questions:

  1. What is the draw in amps of the Chroma? I was thinking of putting a 5 Amp Terminal Block in to allow me to use the rocker switch and get the Chroma working now. Just want to check it doesn't draw more than 5 amps.
  2. Ultimately I'd like to change the rocker switch to a newer one. Does anyone know where you can get replacement rocker switches from? All the ones I have found in UK are a different size.

David Clarke [21030085++] · Sun, 26 Oct 2008 12:03:07 -0400

  1. What is the draw in amps of the Chroma?...

The performance manual notes a total draw of 90 watts, so you should be looking at less than an amp.

  1. ... Ultimately I'd like to change the rocker switch to a newer one. Does anyone know where you can get replacement rocker switches from?

The one fitted in the Chroma closest to me right now is marked "Arrow 2600 11 E B".

I think if you do a web search for "2600 rocker switch" (or similar) that you should be able to find some locally available replacements.

e.g.,:

http://store.globalcomponent.com/s1008.html [invalid URL as of 2009.07]

If you find one that is spec'd as 22mm x 30mm, then I think that would fit, e.g.:

Good luck.

Joe Porter [21030058] · Mon, 27 Oct 2008 21:56:35 +0000

Thanks to everyone in the community for their help so far in getting my Chroma back to life.

The website is super comprehensive, and the community very helpful (and quick to respond as well). Without it I wouldn't have got this far.

So thanks to Luca Sasdelli and his kit, I have now powered up. And in the process learnt how to solder (I know my technical skills are minimal), and more about the Chroma.

It sounds great, what a keyboard. A real instrument, that is a joy to play, despite the problems that mine still has.

Any advice on some of the remaining issues would be much appreciated. Thanks.

  1. The LED displays dim or brighten when I play chords. It seems to be more obvious when I play more notes, with a higher velocity. Is this a sign of a power consumption issue or something?
  2. I have also noticed that when I play chords with minor 2nds in (2 notes next to each other), one of these notes often doesn't play. This often seems to coincide with the point above. Does the Chroma not cope with this well, or is there something I can do to sort this (hope so)? It is almost like the CPU can't keep up sometimes.
  3. When I powered up 1st time, Autotuned fine, 1 non-functioning card. I'd like to sort that at some point. Anyway, when I started playing I had 7 keys not working, but noticed that by playing them very quickly some seemed to "wake up". I checked for dirt or something but there seemed to be no problem with that. Only 3 are now not working with a few more coming and going. There are spread across the keyboard. Any ideas what I could do to sort this out, if they don't wake up like the others?
  4. I'm getting quite a bit of background noise from the Chroma. It sounds like an oscillator that is stuck on or something, since the noise changes from Patch to Patch (in fact the pitch changes from patch to patch as well). I have checked and the voice card that didn't pass the test is definitely off. Anyone else had this problem?

Thanks again,
J

Jesper Ödemark [21010135] · Mon, 27 Oct 2008 23:55:51 +0100

Joe Porter skrev:

So thanks to Luca Sasdelli and his kit, I have now powered up. And in the process learnt how to solder (I know my technical skills are minimal), and more about the Chroma.

We've all been there. Some of us, like me, isn't far from it either. :D

It sounds great, what a keyboard. A real instrument, that is a joy to play, despite the problems that mine still has.

Great that you're in love already - it's a good start.

Any advice on some of the remaining issues would be much appreciated. Thanks.

  1. The LED displays dim or brighten when I play chords. It seems to be more obvious when I play more notes, with a higher velocity. Is this a sign of a power consumption issue or something?

Do you mean the displays or the LEDs? The displays often flicker and annoys if you do a lot. Call it a retro feature. ;)

  1. I have also noticed that when I play chords with minor 2nds in (2 notes next to each other), one of these notes often doesn't play. This often seems to coincide with the point above. Does the Chroma not cope with this well, or is there something I can do to sort this (hope so)? It is almost like the CPU can't keep up sometimes.

Sounds weird. If I understand you correct it's not normal.

  1. When I powered up 1st time, Autotuned fine, 1 non-functioning card. I'd like to sort that at some point. Anyway, when I started playing I had 7 keys not working, but noticed that by playing them very quickly some seemed to "wake up". I checked for dirt or something but there seemed to be no problem with that. Only 3 are now not working with a few more coming and going. There are spread across the keyboard. Any ideas what I could do to sort this out, if they don't wake up like the others?

If they're random I'd say it's dirt. Even though you can't see any. If it's grouped it might be some scanning issue, but I'm not tech enough to give advice there. The latter often happens to my OSCar - very obvious when it drops out eight keys at a time. :)

  1. I'm getting quite a bit of background noise from the Chroma. It sounds like an oscillator that is stuck on or something, since the noise changes from Patch to Patch (in fact the pitch changes from patch to patch as well). I have checked and the voice card that didn't pass the test is definitely off. Anyone else had this problem?

Can't that be the VCA leaking? THe voice can be OK but the VCA-part not closing as it should.

Not much help maybe, but better than nothing I guess. Maybe the rest of the list wakes up soon...

Chris Smalt [21010280+] · Tue, 28 Oct 2008 00:20:45 +0100

  1. I have also noticed that when I play chords with minor 2nds in (2 notes next to each other), one of these notes often doesn't play.

I may be stating the obvious here, but when playing two-handed piano voicings, it's easy to max out the 8 voices.

  1. When I powered up 1st time, Autotuned fine, 1 non-functioning card.

What if you take out the board, then put it back in?

I had 7 keys not working, but noticed that by playing them very quickly some seemed to "wake up". I checked for dirt or something but there seemed to be no problem with that.

I used to wake them up by gently pushing the metal "leaf" of the key contact down so it makes contact with the bottom one again (with the Chroma powered up), or in some cases, both the upper and lower contact. Just a touch seemed to be enough, as if that reset the scanning system. If a key kept dropping out, I solved that once or twice by bending the leaf ever so slightly.

Luca Sasdelli [21010226] · Tue, 28 Oct 2008 00:27:11 +0100

Hi Joe and all,

Joe Porter ha scritto:

  1. The LED displays dim or brighten when I play chords. It seems to be more obvious when I play more notes, with a higher velocity. Is this a sign of a power consumption issue or something?

Yes, as stated by Jesper, it's normal; and it doesn't change that much even with CC+.

  1. I have also noticed that when I play chords with minor 2nds in (2 notes next to each other), one of these notes often doesn't play. This often seems to coincide with the point above. Does the Chroma not cope with this well, or is there something I can do to sort this (hope so)? It is almost like the CPU can't keep up sometimes.

A missing note should be related to failed boards and/or autotune. Have a check with some voice board troubleshooting as per Service Manual: Service Diagnostics; try to disable voice boards one at a time, to see if you can isolate the problem.

  1. When I powered up 1st time, Autotuned fine, 1 non-functioning card. I'd like to sort that at some point. Anyway, when I started playing I had 7 keys not working, but noticed that by playing them very quickly some seemed to "wake up". I checked for dirt or something but there seemed to be no problem with that. Only 3 are now not working with a few more coming and going. There are spread across the keyboard. Any ideas what I could do to sort this out, if they don't wake up like the others?

Did you clean all key contacts? You can do it first with some clean blown air, and then by spraying them with some contact fluid.

Should you have some intermittent voice board self-exclusions, keep in mind that voices are assigned on a round-robin schedule, so be aware that - in this case - you are pursuing ... ghosts :-)

  1. I'm getting quite a bit of background noise from the Chroma. It sounds like an oscillator that is stuck on or something, since the noise changes from Patch to Patch (in fact the pitch changes from patch to patch as well). I have checked and the voice card that didn't pass the test is definitely off. Anyone else had this problem?

It could be a faulty VCA, as well as an incorrect analog value due to misadjusted ADC/DAC; try to follow Service Manual: Calibration and Checkout, of course skipping the PSU section.

Paul Tillotson [21030218] · Mon, 27 Oct 2008 16:52:54 -0700

Any advice on some of the remaining issues would be much appreciated. Thanks.

  1. The LED displays dim or brighten when I play chords. It seems to be more obvious when I play more notes, with a higher velocity. Is this a sign of a power consumption issue or something?"

Flickering LED display when playing the keyboard is normal on a Chroma.

  1. I have also noticed that when I play chords with minor 2nds in (2 notes next to each other), one of these notes often doesn't play. This often seems to coincide with the point above. Does the Chroma not cope with this well, or is there something I can do to sort this (hope so)? It is almost like the CPU can't keep up sometimes."

I also don't quite know what you mean here. Could it be your intermittent key contacts?

  1. When I powered up 1st time, Autotuned fine, 1 non-functioning card. I'd like to sort that at some point. Anyway, when I started playing I had 7 keys not working, but noticed that by playing them very quickly some seemed to "wake up". I checked for dirt or something but there seemed to be no problem with that. Only 3 are now not working with a few more coming and going. There are spread across the keyboard. Any ideas what I could do to sort this out, if they don't wake up like the others?

I've found that gently pulling the top bar of the key contact and letting it spring onto the bottom bar does a good cleaning and restores connectivity. This is pretty much the opposite of what Christian recommended. Mind you, his method sounds safer.

David Clarke [21030085++] · Mon, 27 Oct 2008 20:50:15 -0400

  1. The LED displays dim or brighten when I play chords. It seems to be more obvious when I play more notes, with a higher velocity. Is this a sign of a power consumption issue or something?

It is part of how the Chroma works and isn't an indication of anything being wrong.

The behaviour comes from how/when the display is updated in terms of other events in the system.

... Only 3 are now not working with a few more coming and going. There are spread across the keyboard. Any ideas what I could do to sort this out, if they don't wake up like the others?

The suggestions by others have been good. In a pinch, dampen a corner of a business card (or piece of paper) with isopropyl alcohol and pull it between the contacts associated with that key. This will help clean the contact without scraping the coating off the contacts.

  1. I'm getting quite a bit of background noise from the Chroma. It sounds like an oscillator that is stuck on or something, since the noise changes from Patch to Patch (in fact the pitch changes from patch to patch as well).

I wouldn't (in general) expect this. Via selective removal of voice cards it would be good to see if you can determine if the noise is coming from a voice card which is bleeding through.

Enrico Dibennardo [21030494] · Tue, 28 Oct 2008 09:01:27 +0100

  1. I have also noticed that when I play chords with minor 2nds in (2 notes next to each other), one of these notes often doesn't play. This often seems to coincide with the point above. Does the Chroma not cope with this well, or is there something I can do to sort this (hope so)? It is almost like the CPU can't keep up sometimes."

He's saying that when playing chords were adjacent semitones are included i.e. C E F A, E or F doesn't play, or Bb D Eb G, D or Eb doesn't play. That's what he's saying. Enrico

Is there any legato setting in our beloved instrument that might give this sort of behaviour? Although this kind of things are generally related to mono settings.

Bruce Sklar [21030660] · Tue, 28 Oct 2008 13:08:48 -0400

  1. I have also noticed that when I play chords with minor 2nds in (2 notes next to each other), one of these notes often doesn't play. This often seems to coincide with the point above. Does the Chroma not cope with this well, or is there something I can do to sort this (hope so)? It is almost like the CPU can't keep up sometimes."

In a patch that is layered, if one board was not tuning, and you had top note priority, you may have a dropout. also, the lack of dissonance in the missing minor 2nd may be more audible than a missing 5th etc. Bruce Sklar

Autotune Question

Michael Grossman [21030350] · Fri, 24 Oct 2008 13:17:42 -0700

I am still curious about the behavior of the Chroma autotune. On my Chroma autotune does not consistently tune the all VCOs precisely every time. After warming up, if I repeatedly press autotune (or set split 50), random VCOs will be a few cents off. If I autotune over and over I can get all the VCOs pretty close on occasion. Then over time they all stay in tune. Has anyone encountered this type of anomaly? On my Prophet 5 its autotune routine gets the VCOs dead on though the VCOs seem to drift over time more than the Chroma. I am using the standard patch and my Chroma is stock (original PSU and CPU). I have very carefully calibrated it.

David Clarke [21030085++] · Sun, 26 Oct 2008 12:11:24 -0400

... On my Chroma autotune does not consistently tune the all VCOs precisely every time...

In my experience, a slight difference with each auto-tune is 'normal' for the Chroma.

C2

Åke Danielson [21010068] · Mon, 27 Oct 2008 10:06:15 +0100

Hi David,

Any news on the C2-project?