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ChromaTalk Archives: April 2013

click noise on envelope

Philippe [21010227] · Mon, 1 Apr 2013 01:25:11 +0200

Hello list,

I am getting a short click noise at the very beginning of every note played by my voice #6 oscillator A. It sounds like some synths that have such fast envelopes that when attack is at 0 a click like this can be heard. Only here I get it only with voice #6.

Could that be a trimmer to adjust ? If yes, which one. Or could that be a dying component not doing the proper job as it weakens ?

Any suggestion strongly appreciated.

Regards,
Phil

Dave Bradley [16330135] · Sun, 31 Mar 2013 18:29:39 -0500

Probably a cap going bad.

Philippe [21010227] · Mon, 1 Apr 2013 01:34:20 +0200

Thanks Dave,

That was more or less one of the things I was suspecting. Would anyone have any suggestion as which ones to change first ? as I don't know how to understand a schematic to locate which caps could regulate the enveloppe attack...

Paul DeRocco [21030230] · Sun, 31 Mar 2013 21:27:31 -0700

From: Phil a

I am getting a short click noise at the very beginning of every note played by my voice #6 oscillator A. It sounds like some synths that have such fast envelopes that when attack is at 0 a click like this can be heard. Only here I get it only with voice #6.

Could that be a trimmer to adjust ? If yes, which one. Or could that be a dying component not doing the proper job as it weakens ?

Any suggestion strongly appreciated.

It's not a trimmer.

You can help narrow it down by trying seeing if it's a VCF or a VCA issue. Most sounds that have a sharp attack apply that attack to both circuits. You could try setting all filter mod depths to zero, and manually tuning the filter so you hear a fairly heavily filtered sound. If you get no click, then it's probably a bad 3350 VCF chip. If you still get a click, then it's either a bad 3360 VCA chip, or more likely, the VCF is putting out a signal with a strong DC bias on it. The latter could be caused by a bad Z14 op-amp, or a shorted C13 or C14 capacitor, although that's not their usual failure mode.

It's not hard to see if there's a spurious DC voltage on the filter outputs: you can do that with a voltmeter. Z14 pins 1 and 7 should both be less than a few tens of millivolts.

Luca Sasdelli [21010226] · Mon, 01 Apr 2013 10:59:34 +0200

Hi Phil,

the mentioned caps are likely the S&H ones. The Chroma uses four control voltages per-synth on DVBs:

  • VCO pitch
  • Pulse width
  • VCF cutoff
  • VCA volume

all envelopes, modulations etc are calculated by the CPU and only the instantaneous sum of all of them is fed to the DAC, to be converted in one of the CVs; this greatly reduces sum offsets and ensures high reliability on desidered final values. So, because the DAC works in multiplex way (the digital value is presented on data inputs, and the converted voltage is captured and stored for separated functions, this 50 times per second), all generated CVs are temporarily stored in a sample-and-hold memory, to be supplied to relevant control sections in a continuous and hopefully stable fashion.

There are two S&H types: slow and fast, allowing either long or quick voltage changes.

Should one of those S&H memories fail, its CV would be wrong, thus causing an unwanted variation on the related CV. The relevant high-impedance OAs are also responsible for the correct timing.

In detail:

  • Pitch A: C24, C32, Z21
  • Width A: C25, C33, Z21
  • Cutoff A: C26, C34, Z22
  • Volume A: C27,C35, Z22
  • Pitch B: C28, C36, Z23
  • Width B: C29, C37, Z23
  • Cutoff B: C30, C38, Z24
  • Volume B: C31, C39, Z24
  • Volume B: C31,C39

Ref. Dual Channel Board Schematic 2

P.S.: apart from the above circuit description, once you begin to work on S&H, I suggest to replace all S&H caps in a time instead of stress the board with repeated solder/unsolder etc. Moreover, because all capacitors are of about same age and worked in the same environmental condition, they are subject to fail in similar way. The new caps should be polypropylene (PLYP) type: you can easily find some 5% or better tolerance with low prices.

Cheers
Luca

Marais · Mon, 1 Apr 2013 06:54:13 -0400

for future reference and our records, could we please have mouser parts numbers for these.

Thank you, m

Paul DeRocco [21030230] · Mon, 1 Apr 2013 10:40:15 -0700

From: Luca Sasdelli

the mentioned caps are likely the S&H ones. The Chroma uses four control voltages per-synth on DVBs:

  • VCO pitch
  • Pulse width
  • VCF cutoff
  • VCA volume

You could be right, but I don't really see how a bad S&H would cause a click on a fast attack. It can cause droop, or 50Hz modulation, or total failure, but a click? I'm thinking DC at the output of the VCF. But again, it's best to diagnose these things with a scope, or at least a meter, than to start changing parts willy-nilly, in the hope that you guess right.

Luca Sasdelli [21010226] · Mon, 01 Apr 2013 19:50:04 +0200

Ciao Paul,

indeed last year I worked on a DVB that presented a unwanted peak on VCF cutoff at key press: it was the S&H failing due to a capacitor that had its value less than 1/10 of the printed one. I agree with you that the DAC/mux, without a proper S&H, should keep the voltage around a given level, with or without 50Hz noise, but that's it :-)

And I strongly agree with you about checking the circuits with proper instrumentation before beginning to replace parts, but I feel that Phil doesn't has any.

Cheers
Luca

Luca Sasdelli [21010226] · Mon, 01 Apr 2013 19:51:40 +0200

for future reference and our records, could we please have mouser parts numbers for these.

Well, next time I need some of them, if Mouser prices are lower than those at my usual suppliers, I'll take note of them and I'll post them here.

Philippe [21010227] · Tue, 2 Apr 2013 00:15:03 +0200

Hi Paul and Luca,

It happens that all the components listed by Luca have been recently replaced so I guess the problem is elsewhere. I followed Paul's indications and I still hear the click unchanged with filter fully closed. I looked at Z14 which has also been changed recently and instead of reading 082 as I read in the partlist I read TL072CN Is this an acceptable equivalent ? or could this different component be the source of the problem ?

Paul DeRocco [21030230] · Mon, 1 Apr 2013 15:20:59 -0700

That's just a low-noise version of the 082.

Philippe [21010227] · Tue, 2 Apr 2013 19:31:21 +0200

OK. I swapped Z16 and Z14 and the problem is identical. Should I probe pins 1 and 7 of Z14 with my multimeter playing that voice or not playing it ?

Paul DeRocco [21030230] · Tue, 2 Apr 2013 11:07:56 -0700

From: Phil a

OK. I swapped Z16 and Z14 and the problem is identical.

Swapped them with what? Chips from a different board?

Should I probe pins 1 and 7 of Z14 with my multimeter playing that voice or not playing it ?

You might try selecting a pulse shape, and setting the width to zero so that you don't hear any tone. Also, turn off all filter modulation. Then, measure the voltages as you manually vary the filter cutoff from min to max, and see what happens. It shouldn't matter whether notes are held or released, because that would only affect the amplifier downstream.

A related test would be to do the above, apply an envelope with a sharp attack to the volume, and play some notes. Do you hear a click when you play a note, or nothing at all? See if manually adjusting the filter cutoff changes that.

Philippe [21010227] · Tue, 2 Apr 2013 21:02:38 +0200

Swapped them with chips from another board yes. I did the test you suggest with my multimeter at 200mV (lowest position I have) and get :

  • Pin 1 : 02.2 to 02.5
  • Pin 7 : 05.3 to 05.5

I found some new 1uF 50V caps. Do you think they can be placed at C13 & C14 ? And if yes, should I swap them already ?

Philippe [21010227] · Wed, 3 Apr 2013 02:11:40 +0200

I am not so sure what you mean exactly by sharp attack, you mean attack at 0 ? of envelope 1 or 2 or both or it doesn't matter ? I am asking as I am not getting any significant result editing those. However investigating further I noticed the click noise comes from the resonance. If I set the resonance to 0 I get no click at all anywhere. As soon as I increment it the click is heard when pressing down AND releasing the key playing that voice board but only with Patch# 0, 1, 2, 3, 13, 14 ,15. When in Patch# 0 the click is heard on channel B only.

Paul DeRocco [21030230] · Tue, 2 Apr 2013 17:33:47 -0700

If it happens when you release the key, then I expect you've got the release time set to zero as well.

Have you set all three modulation depths on the filter to zero when you hear the click? What happens when you do that, and set the resonance to some nonzero value (but not 7), and manually vary the filter tuning? Do you still hear the clicks as you play? Or do you only hear them when the envelopes are modulating the filter? Patch 0 is the best thing to test with, because you're only listening to one channel.

Philippe [21010227] · Wed, 3 Apr 2013 13:05:36 +0200

Yes it happens with attack and release at 0. I am working wit the scratch patch (set split 39) so all modulations are at 0. It appears the problem only happens at resonance set at 7 and filter tune from 0 to 32. At any other value the problem is gone. Strange thing is although set split 37 shows the click happens only with channel B (that is when the bottom portion of the digit is lit) the sound only reacts when I touch parameters of channel A...

Paul DeRocco [21030230] · Wed, 3 Apr 2013 09:13:08 -0700

From: Phil a

Yes it happens with attack and release at 0. I am working wit the scratch patch (set split 39) so all modulations are at 0. It appears the problem only happens at resonance set at 7 and filter tune from 0 to 32. At any other value the problem is gone.

If the resonance is at 7, then the filter is self-oscillating, which is a rarely used feature. Did the sound you originally noticed the problem on have the resonance at 7?

Strange thing is although set split 37 shows the click happens only with channel B (that is when the bottom portion of the digit is lit) the sound only reacts when I touch parameters of channel A...

That's not strange. When you use patch 0, you split the voice board into two independent channels. It's like having two single-oscillator boards. They are both controlled by the A parameters, because you wouldn't want every other note to be controlled by a different set of parameters.

Philippe [21010227] · Wed, 3 Apr 2013 18:18:42 +0200

Did the sound you originally noticed the problem on have the resonance at 7?

yes

Paul DeRocco [21030230] · Wed, 3 Apr 2013 09:36:28 -0700

In that case, it might be worth changing C14 (and might as well do C13 too). These capacitors tend to increase in resistance over time, eventually completely preventing the channel from self-oscillating, which causes the board to fail auto-tune. Yours isn't at that point yet, but what you might be hearing is the filter thumping as it tries to start oscillating. I don't know for sure that that will help, but caps are cheap and easy to change, and those caps are definitely implicated when self-oscillation is involved.

Philippe [21010227] · Wed, 3 Apr 2013 18:41:32 +0200

OK, I have some new 1uF 50V caps here. Do you think they can be placed at C13 & C14 ? Or do you recommend to specifically get some 1uF 35V 20% as the partslist specifies ?

Paul DeRocco [21030230] · Wed, 3 Apr 2013 11:14:33 -0700

Any 1uF cap will work. They have essentially zero volts across them in that circuit.

Philippe [21010227] · Wed, 3 Apr 2013 23:45:27 +0200

I changed C13 & C14 but unfortunately the clicks are still there...

For Sale: Chroma Enabler Programmer

Marais · Thu, 4 Apr 2013 09:06:06 -0400

Chroma Enabler Programmer for sale. US/Canada only please. 95 knobs of Chroma Programming Bliss. This is ser # 002 hand made and wired by Randel. Life changes and other needs force me to have to sell. This is one of ten units in the world! Great condition. like new. If you have dreamed of owning and Enabler and looking to save on the cost and wait of a new unit Please email ASAP for more details, photo's, etc.: [email address removed]

Marais · Wed, 10 Apr 2013 08:01:37 -0400

Sale Pending: Chroma Enabler Programmer

Sale is now pending for Chroma Enabler, thank you for all the interest. It will be going to a good home.

My Chroma will go to my grave with me one day, but for right now film composing is more important than 95 knobs : ( But the iPad Editor is fun too.

Polaris replacement battery

Dryden Chambers · Sun, 7 Apr 2013 20:25:47 -0400

Can someone please share the specs for the Polaris battery ? Appreciate the help. DC

Chris Ryan [21030691] · Sun, 7 Apr 2013 17:39:09 -0700

Short answer: "Alkaline 'D' cells should be used." See "Replacing Batteries" in the Disassembly section of the Polaris Service Manual at the site.

Spheremusic - Chroma poly aftertouch sensor new

Chris Ryan [21030691] · Mon, 8 Apr 2013 19:46:01 -0700

Auction for "a mint unused example of Chris Borman's brilliant pressure sensor, which unleashed the potential of the great Rhodes Chroma to have polyphonic aftertouch - the way towards the most expressive performance that can be obtained from a keyboard." Start price is £190.

vemia10525a

vemia10525b

2 Chromas sold on Vemia - record prices?

Doug Terrebonne [21030114] · Mon, 15 Apr 2013 19:04:49 -0700

Looks like the 2 Chromas for sale on the Vemia auction last week have sold and might have set new records for prices -

  • Chroma w/CC+, flight case - 4000 GPB / $6,110
  • Chroma w/CC+, LCD, BCR-2000 - 5092 GBP / $7,778

Chris Ryan [21030691] · Mon, 15 Apr 2013 19:08:36 -0700

I'm hoping to get prices and serial numbers from Peter [21010096].

Marais · Mon, 15 Apr 2013 22:26:24 -0400

I'm glad I own a German Shepherd & Doberman lol m

Syntech Interface on eBay

Chris Ryan [21030691] · Tue, 16 Apr 2013 21:56:09 -0700

Item #330907938540, USD$489.00, no bids, ends tomorrow. "As seen in another listing for this item, it is the original MIDI interface specifically made for the Rhodes Chroma, and it is a rarity to find them available [see Syntech/Chroma Cult MIDI Retrofit]. Mine has the original hard copy of the owners manual, printed in 1985, as seen in pics. It is guaranteed to work with a working Chroma, so long as the Chroma has the interface connector and circuitry inside (nearly ALL have this). The other seller that listed it, didn't mention this possibility, though."

eBay330907938540

Chroma 21030864 For Sale on eBay

David Clarke [21030085++] · Sun, 21 Apr 2013 11:22:26 -0300

I usually keep an eye out for on-sale Chroma items - but my searches missed this one. It wasn't until a friend pointed it out that I saw it:

[eBay item #161008145118; see 21030864 in the registry]

Not much time left in the bidding - and it is strictly 'for pickup only' - but a starting bid of USD $1,500.00 makes it one of less expensive Chromas seen in a while.

Picture from the auction showing the installed Chroma Cult memory expander:

eBay161008145118

Who uses the Syntech interface?

Paul DeRocco [21030230] · Tue, 23 Apr 2013 11:43:22 -0700

I'm wondering how many people here use the Syntech MIDI converter with their Chroma. That would of course be a subset of the people who don't have the CC+ upgrade. And I'm curious whether it's primarily used for interfacing to a different keyboard, or for interfacing to a computer. I'm toying with the idea for a quickie project, a Chroma to USB converter that's Syntech compatible, but that would only work when talking to a computer.

Peter-Jan Kleevens [21010014] · Wed, 24 Apr 2013 00:04:55 +0200

Hello Paul,

I use it with my non CC+ Chroma. I hook it up with either Cubase on my Atari Mega St4 ( still works perfectly) or with Cubase on my MacBook Pro.

cheers

Brian McCully [21030361] · Tue, 23 Apr 2013 15:47:52 -0700

I use the syntech less than the cc+, but I have both a syntech and cc+ in a Chroma. It was typically MIDI I/O interfaced to a MIDI interface that's hooked to a Mac. What's the concept for?

Paul DeRocco [21030230] · Tue, 23 Apr 2013 16:09:19 -0700

For just that sort of thing. It would fit into a D-sub shell with a 25-pin connector on one side and a USB mini-B connector on the other, and would connect directly to a computer. But it would only be a USB device, not a host, so it wouldn't be useful with another USB device like a keyboard or sound module.

It would be a pretty easy project, but I don't know that I'm actually going to do it. I'm just weighing potential interest. I figure people who have a CC+ or a Syntech wouldn't need it, although it would certainly be faster than old-fashioned MIDI and more compact than a Syntech. But for other people I'm mostly wondering if the inability to connect to another USB device is a deal breaker.

Matt Hillier [21010094+] · Wed, 24 Apr 2013 00:07:42 +0100

i use one for triggering midi from cubase and editing using sounddiver both from a pc.

Chroma Dust Cover

Nicholas Vining [21030777] · Tue, 23 Apr 2013 13:06:16 -0700

I noticed that LeCover sell a Rhodes "Khroma" dust cover. It looks like it has the right dimensions, but for all I know it could be for a Polaris or something.

Has anybody on the list bought one of these? I have one for my Minimoog (which came with it when I bought it) and I'm very happy with it, and it would be nice to have some anti-dust protection.

Howie Shen [21030552] · Tue, 23 Apr 2013 16:05:06 -0700

If you are willing to invest a little money for a really nice cover, check out: DigitalDeckCovers Custom Dust Covers.

I had them make a custom cover for my Yamaha DX1 using their highest quality materials (you select the grade) and it fits perfectly. Now, I think I spent $70 for it, so I wouldn't be willing to pay this to cover just any synthesizer, but it was certainly worth it to protect my cherished DX.

No, I haven't yet ordered one for my Chroma, but seriously considering it now that I know their product is worth it.

MIDI Interface on eBay Germany

Chris Ryan [21030691] · Sat, 27 Apr 2013 17:40:28 -0700

Item #181096400670, €299,00. Looks like a white-painted Syntech.

eBay181096400670

Chroma and Expander

Nicholas Vining [21030777] · Sat, 27 Apr 2013 20:11:50 -0700

Go to previous messages in thread, March 2013

As an epilogue to this, via some thread necromancy:

Brian [21030361] e-mailed me earlier this week letting me know that he was thinking of parting with the 0120 Expander, and offered it to me at a very fair price (after I desperately tried to trade a lot of things for it earlier this year.) Naturally, I jumped on it - one jaunt down to Seattle later, it is now living on top of Chroma 21030777. I have to make the little tip->ring cable thing, and find a DB25 cable to get it talking directly to the Chroma, but these are projects for tomorrow.

They look... surprisingly dorky on top of each other. :) I will also try to record some audio or video of everything going at full tilt; while there are videos out there with a Chroma Expander in them, they are either the Vintage Keyboard Studio ones where the Expander is non-operational, or, uh, Herbie Hancock...

(The Polaris from Trading Musician is still sitting at my friend's in Seattle, waiting for me to collect it (I didn't get a chance to do so today.) I originally bought it for spares for my Oberheim Matrix-12, but the recent tuning failures on that particular beast were not due to bad CEM3372 chips and so I may see if I can figure out what's wrong with voice 1 and if it can live to fight another day.)

Chroma 21030247 For Sale on eBay

Chris Ryan [21030691] · Mon, 29 Apr 2013 08:07:23 -0700

Item #161017281863, starting bid US$3,000.00, no bids yet, or price of AU$4,500.00. "Fitted with the new power supply and new CC+ which updates many aspects of its operation and makes it easier to incorperate into a 2013 workflow but most of all makes it reliable ... in beautiful condition ... all voices tune and it sounds and plays incredibly."

Not a lot of info on this unit in the registry, but it's changed hands a couple of times in recent years: see 21030247.

eBay161017281863

knob box design and display sets?

Jesper Ödemark [21010135] · Tue, 30 Apr 2013 12:25:33 +0200

Hi list,

I haven't kept up to date on the display subject, but I've tried to catch up since I'm planning to go through with the drehbank modification of mine.

I've found nice and retro-looking knobs in green and blue (+orange) that I plan to use. I'll make a blackfaced panel in the same size as the original panel, but with new cherry end cheeks so that it can sit on top of the Chroma with the old panel still visible. I haven't decided on the angle yet since that depends on what feels best in my studio setup.

When drawing the front panel I came up with the concept of arranging the knobs just like the buttons are on the Chroma. Akward maybe, but stylish and easier if you're used to the chroma design and way of thinking. I opened up the drehbank today and modification of that seems easy indeed. Unless I want to be really anal about arranging the knobs in groups of five they're already mounted 2 by 4 on small boards inside and hooked up by flat cable to the controlling board.

The snap, and bank buttons of the drehbank (also on a solo board) can be placed where the bank edit and store buttons would be expected to be (making it logical too). The eight CV input sockets of the Drehbank (that can be assigned to whichever function) I plan to bring out where the EQ pots are on the Chroma. All this drawing made me think of the display again and placing a red and black on the same spot as the original is would look great. It would also save on a lot of graphics design on the knob panel that I first planned.

This leads to the questions I was about to ask (much writing leading up to this)...

Was there ever a display set offered or did everyone make up there own since there weren't much costs involved?

And if no sets, can any of the europeans point me in the direction of the best supplier here? :)

Also, I'm no zeroes-and-ones-wiz though I know some who are. Is sending the commands to the sparkfun controller easy?

Adrian [21040017] · Tue, 30 Apr 2013 15:48:48 -0700

On 2013-04-30 03:25, jesper wrote:

Was there ever a display set offered or did everyone make up there own since there weren't much costs involved?

Don't buy the Parallex display from Parallex direct - over a year ago I ordered one on their web site, paid by credit card and have heard nothing since. I've sent a half a dozen follow-up emails both direct and via their web form and the response has been a solid NOTHING. Their company should be avoided at all costs (i.e. $42.99!)

The Sparkfun option looks a lot better to me but I haven't been following progress to know where it's at... too much to do!

David Clarke [21030085++] · Tue, 30 Apr 2013 23:27:42 -0300

...Was there ever a display set offered or did everyone make up there own since there weren't much costs involved?

There was originally some discussion about having a display + box put together by one of the list members - but there was very little interest - plus no one really seemed to like the same box/mounting solutions.

On top of that, of the users who opted to use the display, many used their own preferred approaches for cabling - some wanting to use the DB-15 interface on the rear panel that comes with the CC+ - while others wanted to directly connect to the AMP connectors on the CC+ board itself.

In short - no display 'kit' is currently available. It is very much a "choose which display you like, the cable solution you like and our desired mounting" and go from there situation.

A few of the different approaches are shown here: The Chroma CPU Plus (CC+): Alphanumeric Display - User Implementations

And if no sets, can any of the europeans point me in the direction of the best supplier here? :)...

I don't know how they are overseas, but for any dealings I've had with them, Digikey can't be beat for service. I would check out www.digikey.se (Parallax P/N = 27979-ND).

Also, I'm no zeroes-and-ones-wiz though I know some who are. Is sending the commands to the sparkfun controller easy?

The one drawback with the SparkFun is that it does have to be set up before it can be used with the CC+. There are several ways to do this with a few small components (inverter, battery, etc.) to allow the controller to be programmed from the serial port of your PC) - but if you don't want the hassle, the Parallax unit does not any of that sort of 'software' setup.

I expect that if there were a few people interested in the SparkFun solution - that there are probably a few folks in Europe who would be willing to get the controller, attach it to a display and perform the programming - so it would be 'ready to go' (but of course, that would undoubledly increase the price beyond what it would otherwise be for 'do it youself').

Go to next message in thread, May 2013