crOwBX 8-voice

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jimfowler
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Post by jimfowler » Mon Jan 07, 2019 10:56 pm

well, now i'm kinda glad scott sent me the older boards despite my having ordered the newer version. at least i know it'll work when i do get around to finishing it.

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mOBiTh
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Post by mOBiTh » Tue Jan 08, 2019 6:24 am

jimfowler wrote:well, now i'm kinda glad scott sent me the older boards despite my having ordered the newer version. at least i know it'll work when i do get around to finishing it.
all seems pretty random as to who got what.

has anyone outside of the USA received any boards from Scott in the last year?

mcbinc
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Post by mcbinc » Wed Jan 09, 2019 1:34 am

Has anyone heard from Scott recently? A month or two ago, I emailed asking about boms/schematics for old boards that are no longer available on the cs80 site. Haven't heard back and haven't seen any activity recently...

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whomper
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Post by whomper » Wed Jan 09, 2019 3:10 am

mOBiTh wrote:
jimfowler wrote:well, now i'm kinda glad scott sent me the older boards despite my having ordered the newer version. at least i know it'll work when i do get around to finishing it.
all seems pretty random as to who got what.

has anyone outside of the USA received any boards from Scott in the last year?
I have received my 4 boards set mid 2018 in Israel.

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whomper
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Post by whomper » Wed Jan 09, 2019 3:13 am

BTW, does anyone know if I need to have jacks connected to the main board when testing sound? All my tests are only with CV and gate in for 1st board.

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Chrutil
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Post by Chrutil » Wed Jan 23, 2019 8:19 pm

Hi all,
Now that the holidays are over I finally was able to start looking at debugging my board. I built one 2.4 voice card so far and I'm trying to get it to work.
I rigged a set of switches and pots giving 0-5V to serve as input to the voice card since I'm not planning on using the crowbx backplanes or host boards.

I see no output, but starting to probe I was able to find a saw wave on pin 2 of the A6 and A8 TL072's in the vco part, that's somewhat encouraging.
I only have the schematics from http://www.cs80.com/crowbx/schempdf/ which is not the same as the 2.4 voice cards, but hopefully there are enough similarities to get some clues.
Unfortunately I only know enough to get in trouble, so I'm not sure what I should measure next but I'll keep poking to see what I can find.
Anyone have anything to suggest? Otherwise I was going to probe the 3310's next to see that I have output.

By the way, does anyone have a description of the voice card pins and the signal expected? I think I have most, but there are a few I am unclear about.

Here's my hobo test rig 8-)

Image

Image

Thanks,
C

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Chrutil
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Post by Chrutil » Thu Jan 24, 2019 12:26 am

Just an addition, so on pin 12 on A10, which is an LM13700 in the filter I see the saw wave and can see the effect of twisting resonance (full on at 0v and off at 5v) and cutoff frequency knobs, so things seems to be working up and including the VCF.

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mOBiTh
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Post by mOBiTh » Thu Jan 24, 2019 5:28 am

If you're not aware it's easy to destroy an LM13700 by probing the amp bias inputs - I did on one of mine.

Correct way to measure the bias current is via the voltage across the series resistor feeding this pin iirc

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mOBiTh
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Post by mOBiTh » Thu Jan 24, 2019 5:29 am

whomper wrote:BTW, does anyone know if I need to have jacks connected to the main board when testing sound? All my tests are only with CV and gate in for 1st board.
Which jacks are you referring to exactly?

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Chrutil
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Post by Chrutil » Thu Jan 24, 2019 11:19 am

mOBiTh wrote:If you're not aware it's easy to destroy an LM13700 by probing the amp bias inputs - I did on one of mine.

Correct way to measure the bias current is via the voltage across the series resistor feeding this pin iirc
I was not aware of that - thanks for the tip!
Getting odd readings off the envelopes. I think I'll build me another voice card next week to have something to compare against.

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Chrutil
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Post by Chrutil » Fri Jan 25, 2019 1:29 am

Chrutil wrote:
mOBiTh wrote:If you're not aware it's easy to destroy an LM13700 by probing the amp bias inputs - I did on one of mine.

Correct way to measure the bias current is via the voltage across the series resistor feeding this pin iirc
I was not aware of that - thanks for the tip!
Getting odd readings off the envelopes. I think I'll build me another voice card next week to have something to compare against.
After poking for a minute tonight I realized that I have no output because I am an idiot.
Not only had I left R202/R204 open, sending the output to the OBX output header, not to the new inline port below the 15V voltage regulators, but I also measured with the 10x probe on my scope :deadbanana:

Now that I looked proper, I do indeed have a good output. I think there's something odd with the envelopes, but with AD and R set to 0 and full Sustain it all seems good and I see a nice saw wave and filter and CV and VCO1F and VCO2F seems to be working just fine.
This is just probing with a scope so no actual test yet. And no calibration either, so yeah..
I might just have to build up either a 4 or an 8 voice carrier/host board combo so I can try it out.

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whomper
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Post by whomper » Fri Jan 25, 2019 1:55 am

Chrutil wrote: After poking for a minute tonight I realized that I have no output because I am an idiot.
Not only had I left R202/R204 open, sending the output to the OBX output header, not to the new inline port below the 15V voltage regulators, but I also measured with the 10x probe on my scope :deadbanana:

Now that I looked proper, I do indeed have a good output. I think there's something odd with the envelopes, but with AD and R set to 0 and full Sustain it all seems good and I see a nice saw wave and filter and CV and VCO1F and VCO2F seems to be working just fine.
This is just probing with a scope so no actual test yet. And no calibration either, so yeah..
I might just have to build up either a 4 or an 8 voice carrier/host board combo so I can try it out.
Hi, that's great. I'm also getting back to debugging mine and would really appreciate if you perhaps specify what voltage you get along key points so that I can check my build, perhaps even which path should I trace saw wave.

Could you also perhaps send over a high Rez image of your voice card build?

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Chrutil
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Post by Chrutil » Fri Jan 25, 2019 9:29 pm

Hi Whomper,
I am away for the weekend but will try to take some readings and make a hires photo on Sunday night.
Cheers,
C

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whomper
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Post by whomper » Sat Feb 02, 2019 2:12 am

mOBiTh wrote:
whomper wrote:BTW, does anyone know if I need to have jacks connected to the main board when testing sound? All my tests are only with CV and gate in for 1st board.
Which jacks are you referring to exactly?
Well, any ones that might require to have GND connected to the TIP so as to not leave input open.

jvq
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Post by jvq » Sat Feb 02, 2019 4:19 pm

Chrutil wrote:
I think there's something odd with the envelopes, but with AD and R set to 0 and full Sustain it all seems good and I see a nice saw wave and filter and CV and VCO1F and VCO2F seems to be working just fine.
Note that A/D/R use an inverted scale of 0V (minimum) to about -230mV (maximum). Search for "attack" on http://www.muffwiggler.com/forum/viewto ... ?p=1489765 for more info.

Some more info: if you look at the CEM3310 data sheet they say "Zero to -5V varies the times from 2ms to 20s". However, if you look more closely you see that the example schematic in the data sheet has 10K/470R voltage dividers on the A/D/R inputs. In the case of the OB-X, the voltage dividers are missing. If you do the math of what removing the voltage dividers does to the input levels, that leads to the range of 0V to -230mV mentioned above.

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The Real MC
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Post by The Real MC » Mon Feb 04, 2019 1:54 am

jvq wrote:In the case of the OB-X, the voltage dividers are missing.
They are not missing. Oberheim put them on the processor board in the demux S&H section instead of on the voice cards. Since the OBX is a monotimbral instrument it only needs one set of voltage dividers to feed all the cards.
I haz a wrench, to fix da synth.
http://www.analoguediehard.com/

jvq
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Post by jvq » Mon Feb 04, 2019 3:53 am

Yeah sorry about that I'm trying to be helpful but I end up being vague.

What I meant to explain, to myself anyway, is that even though the CEM3310 datasheet talks about a "-5V to 0V" CV range, that actual voltage range is used nowhere in the CrowBX / OB-X. In the OB-X, for each A/D/R CV, there is an inverting op-amp with a 4K87 / 100K ratio on the processor board, which converts 0V-5V to -240mV-0V. The same thing happens on the CrowBX host board.

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Post by randel » Mon Feb 04, 2019 1:10 pm

Chrutil wrote:
By the way, does anyone have a description of the voice card pins and the signal expected? I think I have most, but there are a few I am unclear about.
Image

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whomper
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Post by whomper » Mon Feb 04, 2019 2:41 pm

randel wrote:
Chrutil wrote:
By the way, does anyone have a description of the voice card pins and the signal expected? I think I have most, but there are a few I am unclear about.
Image
So helpful! Thanks for the table and voltage mappings. Should come in handy in debugging.

BTW, my envelopes measure -0.25 to -0.5 on IC pins and the attack/decay/release do not work. Not sure where's the problem.

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whomper
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Post by whomper » Mon Feb 04, 2019 3:41 pm

whomper wrote: BTW, my envelopes measure -0.25 to -0.5 on IC pins and the attack/decay/release do not work. Not sure where's the problem.
When carrier board is connected to main board and there is no sound card installed, I get -0.23v to -0.45V out of Attack/Decay/Release.

When the main board is not connected to anything, I get proper 0 to -0.23v.

As the carrier board in that section is just wire that runs through all 4 card slots, what could possible alter voltage in such a way?

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Chrutil
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Post by Chrutil » Mon Feb 04, 2019 4:40 pm

This is all super helpful.
Thank you guys!! :hail:

C

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whomper
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Post by whomper » Wed Feb 20, 2019 4:29 pm

A quick update on my build (4 voice complete), yeah, I know this is an 8 voice thread but I reckon most here have V2.4 as I and the main thread is awfully quite....

I have managed to get all 4 voices working, meaning tuning according to procedure (all but VCA level in the end, not sure its needed but we'll see once all voices are connected...)

Front and carrier boards are all working but one last, hopefully, issue:

When front board is not connected with the carrier one, I get proper 0 - -0.25v for Attack, Decay and Release. Once carrier board is connected, the range change to -0.25v to -0.48v, i.e. an offset of -0.25v.
As carrier board only adds 4 board connectors and a 1n cap to ground, I am puzzled as to what can cause that.

Any thoughts greatly appreciated!

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whomper
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Post by whomper » Thu Feb 21, 2019 11:43 am

whomper wrote:A quick update on my build (4 voice complete), yeah, I
Front and carrier boards are all working but one last, hopefully, issue:

When front board is not connected with the carrier one, I get proper 0 - -0.25v for Attack, Decay and Release. Once carrier board is connected, the range change to -0.25v to -0.48v, i.e. an offset of -0.25v.
As carrier board only adds 4 board connectors and a 1n cap to ground, I am puzzled as to what can cause that.

Any thoughts greatly appreciated!
Have managed to solve the envelop issues. Removing 1nF SMD caps on the carrier board across all pins solves the issue.

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Post by Nuclues » Thu Feb 21, 2019 6:01 pm

Hi Whomper
Just to understand, is it vers 2,4 voiceboards you have in your working Fourvoice?

I have 8 voiceboards (vers 2,4) with no sound, so i'm very interested :)

best from Nick

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Chrutil
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Post by Chrutil » Thu Feb 21, 2019 6:52 pm

Nuclues wrote:Hi Whomper
Just to understand, is it vers 2,4 voiceboards you have in your working Fourvoice?

I have 8 voiceboards (vers 2,4) with no sound, so i'm very interested :)

best from Nick
Hi Nick,
Whomper and I have been comparing notes offline and yes he has the 2.4 voice cards.
What's your setup, do you have the host board, the 8 voice carrier board and 8 voice cards built?
Do you have Gate working (as far as the gate LED) on each voice card?

Thanks,
C

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