crOwBX 8-voice

[ultravox]

Thanks for the update Chrutil.

I hope to start building my 8-voice system, but I guess I should try building the voice cards first and then design a rig to test them. This would at least give me a reason to dive into CircuitStudio.

[Chrutil]

Thanks for the update Chrutil.

I hope to start building my 8-voice system, but I guess I should try building the voice cards first and then design a rig to test them. This would at least give me a reason to dive into CircuitStudio.

Thanks Ultravox -
I replaced the remaining FMB3904 and now both voice cards seems to be good.

I have a little bit more work to understand if everything is working - in particular I still can't see any action from NFCV input on my home made rig, which I believe is the CV for the Notch Filter. I am feeding it 0-5V, perhaps that's not right. Most controls are 0-5V, but in particular the ADR controls are different at I think 0v - -0.25v and resonance is reversed (5v-0v).
Not sure exactly what the FMODE1 and FMODE2 switches do, other than switch to HP and maybe BP filter, I will try to compare to my Two Voice Pro so see if I can figure it out.

My end goal has been to build a digitally controlled multi-timbral poly synth from these voice cards, and have so far not built the 4 voice or 8 voice backplanes. Now that VS-1 has been announced I guess that feature set is something to aim for, normally I'd jump on that in a heartbeat, but being already in so deep on crOwBX boards I'd rather just keep going with these.

Also, I have to ask - your profile pic - I swear I have seen that photo on some album.
Maybe on the back of an Rage In Eden era single? Or earlier? I tried image searching, but nothing came up and now I just need to know

Cheers,
C

[ultravox]

Also, I have to ask - your profile pic - I swear I have seen that photo on some album.
Maybe on the back of an Rage In Eden era single? Or earlier? I tried image searching, but nothing came up and now I just need to know

Cheers,
C

It's the inner sleeve of Ultravox - Vienna CD single

[Chrutil]

It's the inner sleeve of Ultravox - Vienna CD single

I knew it! That meant something to me...

[jvq]

The only issues I've had with the FMB3904 so far are bad solder joints. It seems to lead to a fault where you can fry the buffer J112, where the VCO just stops working (because you really need that buffer ). (Edit 2020-08-08: see viewtopic.php?f=17&t=193422&start=225#p3309925 , in retrospect I don't think I ever had a problem with the FMB3904 or the J112.)

I keep finding host board bugs due to lack of CV buffering, just made a hack to buffer the VCFM and RES CV outs. I think I found all of them now. Tuning is pretty solid, after the whole thing warms up. Except one VCO failed on me again so I got to check more FMB3904 solderwork.

[Chrutil]

The only issues I've had with the FMB3904 so far are bad solder joints.

Oh interesting. No artifacts between 130-180Hz?

With your setup up and running, if you have a chance, could you measure the voltage range that is sent to the NFCV pin, and does it have any effect when twiddling it?
I'm assuming this is a notch filter CV for the band pass filter, but I hear no effect of the NFCV control, even if filter mode 1 or 2 is on (feeding it 0-5volt).
Thanks,
Christer

[jvq]

I'm not sure how to do that. I left out the parts that are not on the old crowbx voice cards (extra filters, pitch EG). I did that because I have 4 old and 4 new voices in my system.

For the third time in a row, one of my VCO's stopped working. It's the same VCO every time. The last two times I got it working again by replacing the input-J112 (Q8). I thought I fixed it for good after the second time by touching up all the FMB3904 solder joints but that was not enough apparently.

I wonder if I should try replacing the FMB3904, maybe I damaged it by soldering too long? It doesn't really make sense to me and I don't like randomly replacing parts.

My best guess why Q8 would break would be current flowing across the junction in the wrong direction (gate to drain/source). Maybe there is a situation where Q6 is in saturation and the 19V rail has dropped below 15V: in that case Q6 could pump current through Q8 to the (slouched) 19V rail. But why would that happen at all, and why only for that one VCO?

[jvq]

Regarding notch CV: I got a new host board as part of my 4-to-8 kit that I'm not using. That host board has pots / switches for the extra features, including notch CV. Looking at that board I think notch CV goes from 0-5V but it's a little confusing. There is a header "NOTCH CV" JP19 which has three pins, G, TS and T. G is connected to 0V. TS is connected to 5V. T snakes across the board to the notch CV pot and acts as the maximum value there. If I got that right (from just looking at the bare PCB and following the traces), it means that the notch CV pot won't do anything unless you connect T and TS of JP19. My guess is that there is supposed to be a jack socket there with a normaled connection (TS connected to T when nothing is plugged in).

[jvq]

Well, I got my one broken VCO back, by replacing the FMB3904. Did some damage to the board in the process but luckily I am good enough at fixing that up with wire wrap wire. Ended up soldering wires to 2 of the legs of the new FMB3904. :( But, VCO back, my 7 voice is an 8 voice again.

[jvq]

At this point I think I can say I did it: I built an 8-voice CrowBX.

- find an enclosure (picked Schroff 24571-790)
- create Schaeffer panels to mount host board, backplane, power supply etc in the new enclosure
- convert old voice cards from "CEM3310 equivalent circuits" to use AS3310 envelope generators for uniform envelope curves across all voices
- modify power supply (Oakley RPSU) with larger capacitors to handle larger current draw
- upgrade MIDI-CV converter from 4 to 8 channels
- fix various host board issues due to lack of CV buffering

Some information is available at https://crowbx-6d48f4aa5932532a5cd4216f ... index.html

Coming from the 4 voice, the 8 voice feels like a wonderful luxury (less note stealing).

Thank you Old Crow for creating and sharing all this stuff!

[ultravox]

Congratulation jvq, nice job.

[jvq]

Thanks!

So it turned out I cheered to soon because that one VCO kept failing on me. I think I finally got it now. The integrating capacitor (C8) was failing open, meaning there was a current going through it. This current was stronger than that generated by the exponential converter so the sawtooth was stuck at its highest value. It took a lot of work for me to pin that one down.

I think the failure was partly mechanical; sometimes after working on the VCO I probably moved the capacitor, temporarily fixing the fault. The expo converter worked all along. Nothing wrong with that FMB3904. While working on this I ended up creating a breakout board with the LT1013 on it and an LS318 I had lying around. But that was all a dead end, it was the capacitor.

By building the CrowBX into a 4U case I lost the 1/4" patch points of Crow's 5U panel. I had space left over in my case so I made a little expander panel that brings out some of the patch points (OSC1, OSC2, VCF, PW1, PW2, LFO CV, LFO OUT) and which can hold 20HP worth of Eurorack modules. I put a Maths in it. Now I can use the Maths as a second + third LFO, or function generator, or mangle the main LFO, etc.

[jimfowler]

selling my 8-voice backplane, voice cards, etc. pm for details.

- jim

[JanneI]

Hi all! What's the current status of 8-voice projects? Some have finished their builds with the 8-voice backplane? Has anyone done a proper programmer with patch memory yet? Since there's the VS-1 project going on I guess there's not much hope that Scott would finish the programmer himself?

I was thinking of making my own version, but if there are other options, it would be nice to hear what you guys have accomplished!

[jvq]

As I posted above, I have a functioning 8-voice build with the original 4-voice control panel (with various fixes) built into a beefy 4U rack case with a built-in 20HP Eurorack bay. I am happy with the analog control, I don't see myself building a programmer.

[JanneI]

As I posted above, I have a functioning 8-voice build with the original 4-voice control panel (with various fixes) built into a beefy 4U rack case with a built-in 20HP Eurorack bay. I am happy with the analog control, I don't see myself building a programmer.

Ok, thanks for the reply! I found your docs and I'll check them out, thank you! So, just to clarify, you simply used the oldcrow 8-voice backplane with the modded 4-voice control PCB?

Does someone still have a 8-voice backplane board for sale? PM me.

[jvq]

So, just to clarify, you simply used the oldcrow 8-voice backplane with the modded 4-voice control PCB?

Yes. I mounted the old control PCB to a new aluminum front panel; I updated my site with a photo where you can see the basic layout of the case.

There were some issues with that because not all CV outputs on the 4-voice control panel are buffered. Their impedances were OK for 4 voices but not for 8. You can see my workaround for this at https://crowbx-6d48f4aa5932532a5cd4216f ... plane.html as "host board bugs". In one case I tweaked resistor values to get impedance that works with 8 voices, in another I managed to add opamp buffers.

In short I had to mod the control panel a bit.

To connect the motherboard and the control panel I used made board-to-board cables with Molex KK 396 connectors. Lots of crimping.

The later CrowBX voice cards have extra features that are not on the original: more filters types, pitch EG. If I had had 8 such voice cards I would probably have built up a new control panel. But because 4 of my voices are "old" and don't have the extra features it made no sense to me to build a new control panel.

[jpeterman]

Hey Chrutil, did you get your issue straightened out? I should be getting a bigger case and I am re-entertaining making a single voice version of this for eurorack. Modular Addict has the boards in stock: https://modularaddict.com/oldcrowmodula ... o-pcbpanel

Two things are stopping me though. I have the feeling that 1 voice simply won't cut and also not sure all these issues have even been resolved.

[Chrutil]

Hey Chrutil, did you get your issue straightened out?

Hey, the voice mards mainly work, but I still don't have the FilterType and Notch filter sorted.
Lowpass works beautifully, highpass seems to work too, but I have no control of the Notch CV and I'm not sure what the problem is.
The vactrol/LED part of the voice card is still somewhat of a mystery for me.
I'd love to hear if anyone that's been building the 3310/2.4 voice cards what they did with the LED3 and LED4 (next to the vactrols)
Should the LED be populated? What type of LED? Polarity? Does this make the Notch CV work?

Anyhow, I'm on a DIY break at the moment, got a bit burned out last year so now I'm mainly just jamming and working on an old car, but I'll get back to soldering at some point.

I am surprised that the crOw BX is still being sold and I wonder if they have a current BOM for what they sell? I have still never seen a 2.4 voice card BOM, and gad to make my own from earlier versions and silkscreen.
I consider crOwBX abandonware and would advice anyone against investing into it, unless they know what they are doing and are confident they can do it with little to no documentation.
That said, I have every intention of finishing my 16 voice one day (or two 8 voices, or a bunch of SEM-like single voices or a combination).

Thanks,
C

[jvq]

Just wanted to share that I built a working auto-tune function into my 8-voice. https://crowbx-6d48f4aa5932532a5cd4216f ... otune.html

It's as automatic as can be expected given the analog control panel: the user needs to configure an appropriate sound for VCO1, tell the machine to tune VCO1, flip the sound to VCO2, tell the machine to tune VCO2. But it works.

[ultravox]

Nicely done!