New DIY Build - "Sparta" Semi Modular Analogue Synth

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Broadwave
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New DIY Build - "Sparta" Semi Modular Analogue Synth

Post by Broadwave » Sun Nov 27, 2016 8:51 am

After the recent upset with both the Minilogue and KARP - I just wasn't happy with either - I've decided to get my soldering iron out, dust it down and plug it in :wink:

Welcome to the SPARTA project - based on the Oddy but with a few extras: rotary controls (easier to do, and cheaper), Normalized Patch Points, Plug-in analogue VCFs (ARP/Roland/Moog), 3rd VCO, aftertouch and a few other bits. I've cheated slightly by using the CME Xkey 37 It's an easy option with pressure sensitive Mod, Pitch Bend and aftertouch - No point in making life hard by tearing down and rebuilding a battered MIDI controller :wink:

The panel is on order from Front Panel Express, as they now do digital UV printing directly to the aluminum. All the modules (VCO/LFO/VCF etc) plug directly onto a main carrier board. Most of the PCBs are ready for etching, I've just got the keyboard side of things to do - The MIDI to CV is handled by my old Doepfer MCV4 (I knew it'd come in useful one day)

Initial Design
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Side View
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PCB Layouts
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Panel has arrived from FPE ;)
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PCBs for 3 VCO's, LFO/Noise/S&H, VCF, ADSR, AR/VCA, Aftertouch VCA's, Glide board (modules that plug onto the main control PCB)
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Last edited by Broadwave on Tue Jan 31, 2017 12:01 pm, edited 1 time in total.

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Re: New DIY Build - Semi Modular Analogue Synth

Post by Yekuku » Sun Nov 27, 2016 12:30 pm

Absolutely jaw dropping ! :shock:
How much did the panel from schaeffer cost ?
Keep us updated with the progress !
It is all about sharing...

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Re: New DIY Build - Semi Modular Analogue Synth

Post by Rokk » Sun Nov 27, 2016 1:51 pm

Whoa! Keep us posted!

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Re: New DIY Build - Semi Modular Analogue Synth

Post by Hubaswift » Mon Nov 28, 2016 3:23 am

Looks great! Will it be duophonic, or in this case paraphonic, similar to the Odyssey?

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Re: New DIY Build - Semi Modular Analogue Synth

Post by commodorejohn » Mon Nov 28, 2016 3:36 am

Super cool! I'm assuming by the fact that you made PCBs that you've already got the design worked out? Post some demos as soon as you can, I'm curious to hear how it sounds!

(Hmm...I've been pondering getting into modular lately, but a fully-patchable semi-modular such as this is just as appealing...once you get it all debugged, I might be interested in building one of my own...)
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Re: New DIY Build - Semi Modular Analogue Synth

Post by Broadwave » Tue Nov 29, 2016 7:40 am

@Commodorejohn - I'm using the standard ARP VCOs/VCF/VCAs etc. that I always use, so I know they (usually) work off the bat - Unfortunately, I have to build a bigger UV source for the 3 larger PCBs that carry the pots and switches, as my current UV box is too small, so I'll have to get on with that as a side project :roll:

@Hubaswift - At the moment the synth is designed as purely mono, but I have considered using my Hexinverter MIDI to CV as it's up to 4 note poly. I'll give it a try once everything's up and running - it could be worth putting one in for the extra functions. :twisted:

@Yekuku - The panel cost £193/$239/€226 inc.taxes and delivery from Germany to the UK. I always make sure I design and have the panel made before building - It's not exactly cheap, so it's an incentive to make sure I finish the project ;)

VCO/VCF/VCA Carrier PCBs - I'm using stripboard to distribute the internal in/outs to each module (basically the same idea as the original Odyssey, there's no point in changing something that works well) - I just hope I don't get too much crosstalk.

The middle contact of the switches go to 3.5mm jack sockets that turn off the internal CV/FM sources - so all external CVs pass through the level pot - I've done this mod on several Odysseys, it's a PITA but worth it.
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Re: New DIY Build - Semi Modular Analogue Synth

Post by Broadwave » Tue Nov 29, 2016 8:55 am

VCOs are stuffed and ready for testing. Fully discrete versions of the Odyssey MKIII VCO - No Op-Amps here thank you. Easy to build, reliable and very stable :wink:

The CMOS 4011's clean up and boost the squarewave to 0-10v for the ARP Ring Mod (on the larger board), also based around a 4011. The little board at the end is the Portamento circuit, which I almost completely forgot about :shock:

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Out of interest - The size of my complete Odyssey VCO compared to the 2600 4027-1 VCO Saw Core submodule
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Re: New DIY Build - Semi Modular Analogue Synth

Post by Broadwave » Thu Dec 15, 2016 4:16 pm

It's almost completed ;) - All the circuits work but I've just got to sort out a small problem with the MOD/Aftertouch routing. The chassis arrived this morning, so I'm currently busy with the end caps. Should all be done by the end of the month.

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Re: New DIY Build - Semi Modular Analogue Synth

Post by cornutt » Thu Dec 15, 2016 8:35 pm

How do you plan to implement the plug-in VCAs? I recall that one of the Studio Electronics boxes had that, and it was a planned feature for the Waldorf Stromberg.
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Broadwave
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Re: New DIY Build - Semi Modular Analogue Synth

Post by Broadwave » Fri Dec 16, 2016 5:15 pm

I'll be able to access the VCF module via a small panel on the back - Switch off... swap the VCF... switch on ;)

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Re: New DIY Build - Semi Modular Analogue Synth

Post by jxalex » Fri Dec 16, 2016 5:28 pm

Broadwave wrote:I'll be able to access the VCF module via a small panel on the back - Switch off... swap the VCF... switch on ;)

what about schematics? Can it be something open source with publicly available schematics? You do not have to be alone with experimenting and designing with that.
Interested about that someone like me will develop it on too, like rack version?

You could save time this way and get improvement hacks this way better.
I were already derailing another thread into DIY synth project.

People are improving JX10 becouse there are schematics about it.

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Broadwave
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Re: New DIY Build - Semi Modular Analogue Synth

Post by Broadwave » Wed Jan 04, 2017 12:37 pm

It's all done and tested - It took a bit of time to sort some daft things out (LFO not triggering S&H properly, then I found out I was using the wrong trigger signal! DOH!), and the 5v gate signal wasn't enough for the AR envelope, so that's been boosted to 10V.

I've just got some cosmetic things to do - Finish the leather side panels and attach the back I/O board, tidy up the internal patch point birds nest... Oh, and change the knobs for the correct size (they sent 21mm not 16mm - I might swap them out for satin aluminum ones, the black looks too heavy).

I'll get a video up ASAP.

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Re: New DIY Build - Semi Modular Analogue Synth

Post by commodorejohn » Wed Jan 04, 2017 4:07 pm

Sweet :D Now we just need a kit option...
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Re: New DIY Build - Semi Modular Analogue Synth

Post by Stab Frenzy » Wed Jan 04, 2017 11:23 pm

Looks really nice, good work.

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Re: New DIY Build - Semi Modular Analogue Synth

Post by sw_hunt » Thu Jan 05, 2017 11:04 am

Very professional design work :)
Can you please tell me what PCBCAD software you're using and what you use for designing the front panel?
Many thanks

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