crOwBX 8-voice

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ultravox
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Re: crOwBX 8-voice

Post by ultravox » Mon Jun 15, 2020 7:08 am

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.
This means nothing to me... Oh, Vienna!

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Chrutil
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Re: crOwBX 8-voice

Post by Chrutil » Mon Jun 15, 2020 12:34 pm

ultravox wrote:
Mon Jun 15, 2020 7:08 am
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

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ultravox
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Re: crOwBX 8-voice

Post by ultravox » Mon Jun 15, 2020 2:57 pm

Chrutil wrote:
Mon Jun 15, 2020 12:34 pm

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 ;)
This means nothing to me... Oh, Vienna!

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Chrutil
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Re: crOwBX 8-voice

Post by Chrutil » Mon Jun 15, 2020 5:46 pm

ultravox wrote:
Mon Jun 15, 2020 2:57 pm
It's the inner sleeve of Ultravox - Vienna CD single ;)
I knew it! That meant something to me... :tu:

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Re: crOwBX 8-voice

Post by jvq » Fri Jun 19, 2020 11:31 am

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 :) ).

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.

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Re: crOwBX 8-voice

Post by Chrutil » Fri Jun 19, 2020 11:31 pm

jvq wrote:
Fri Jun 19, 2020 11:31 am
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

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Re: crOwBX 8-voice

Post by jvq » Sat Jun 27, 2020 2:30 pm

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?

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Re: crOwBX 8-voice

Post by jvq » Sun Jun 28, 2020 10:16 am

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).

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Re: crOwBX 8-voice

Post by jvq » Wed Jul 01, 2020 4:32 pm

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.

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Re: crOwBX 8-voice

Post by jvq » Thu Jul 02, 2020 2:36 am

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

- 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!

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Re: crOwBX 8-voice

Post by ultravox » Thu Jul 02, 2020 9:03 pm

Congratulation jvq, nice job.
This means nothing to me... Oh, Vienna!

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