I've gone DIY again - Sparta Synthesizer

Broadwave · Post by **Broadwave** » Sun Nov 13, 2016 2:20 pm

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

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

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.

voip · Post by **voip** » Sun Nov 13, 2016 5:08 pm

This seems very well though out and designed. Has much testing or prototyping been done, or is this an established design?

Edit - OK, done a little digging and notice that there are other designs around with a Broadwave "badge".
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Broadwave · Post by **Broadwave** » Sun Nov 13, 2016 7:54 pm

voip wrote:This seems very well though out and designed. Has much testing or prototyping been done, or is this an established design?

Edit - OK, done a little digging and notice that there are other designs around with a Broadwave "badge".
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I've done quite a bit of custom work over the past 20 years... I thought it was time to build something for myself.

voip · Post by **voip** » Tue Nov 15, 2016 10:26 pm

Good luck with the project. Looking forward to seeing the result.

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Weirdofromouterspace · Fri Nov 18, 2016 12:35 pm

That looks cool - like some 'Odyssey goes 2600' concept

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Broadwave · Post by **Broadwave** » Tue Nov 22, 2016 7:13 am

The panel has just arrived. It's ok - the digital print is a bit low rez, but good enough for a home brew

Everything seems to line up, so I can finish the PCBs now - Very happy with the Xkey integration, it matches beautifully.

But... I forgot about the 3 mounting holes on each side

Akos Janca · Post by **Akos Janca** » Tue Nov 22, 2016 8:12 am

Thank you for sharing, I like this beautiful concept very much. Is it an Xkey Air?

Broadwave · Post by **Broadwave** » Tue Nov 22, 2016 9:20 am

Akos Janca wrote:Thank you for sharing, I like this beautiful concept very much. Is it an Xkey Air?

Thank you... No, it's just the standard version as I don't need wireless for this project. Getting used to the low profile key travel takes a while, but once you've got it, it's very responsive.

The only problem I have to deal with is the Pitch Bend... My MIDI to CV converts the bend to +/- 1volt and mixes it with the 1v/Oct CV - so I need to find a way of lowering the CME's Bend output... I'm hoping that it uses a standard Force Sensing Resistor, so I can use a couple of trimmers to get the output voltage down to a sensible level before the digital circuitry.

There's a few things I'd like to add (bend depth & velocity control for both the VCF & VCA) so I'll have to discreetly put them on the back panel - No doubt I'll think of a few other things too.

It's all part of the fun

Akos Janca · Post by **Akos Janca** » Tue Nov 22, 2016 10:21 am

Thanks - I haven't tried the Xkey yet but I'm interested in buying some controller keyboard. I see that you will not attach it for good to the Sparta - good name by the way - but it fits perfectly.

Broadwave · Post by **Broadwave** » Thu Dec 01, 2016 12:05 am

All the plug-in modules are done, just the main 3 carrier boards to do

The VCF modules will be accessible via the rear panel so they can be swapped out - I've currently got the ARP 4035 & 4075... Korg MS20 and Roland M121 on the way.

Broadwave · Post by **Broadwave** » Sun Dec 04, 2016 9:17 am

The 3 main carrier boards are now done... Just assembly and testing to do now. Fingers crossed the switches and pots line up to the panel.

Broadwave · Post by **Broadwave** » Sat Dec 10, 2016 4:02 pm

All the modules are fitted and working

Just waiting for a few quotes for a basic bent aluminium chassis, then I can get on and assemble everything.

Broadwave · Post by **Broadwave** » Thu Dec 15, 2016 3:36 pm

Everything is working except for the Mod/Aftertouch routing. Looks like I'll have to resort to some CMOS switching

The chassis has arrived, but the knobs are stuck at Heathrow - apart from that, it's sounding pretty good. Just a week or two and it'll be completed.

Escapegoat · Post by **Escapegoat** » Thu Dec 15, 2016 4:22 pm

Fantastic work. I'd love to build a desktop version if you decide to make boards/etc available?

Is there any crosstalk/oscillation issue when bringing so many signals to the patch panel?

Akos Janca · Post by **Akos Janca** » Fri Dec 16, 2016 10:19 am

Thank you again, it's good to see this. I will be interested in the sound.