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 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
Combining Lo-Fi MFOS designs
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Ashcroftt



Joined: Apr 28, 2014
Posts: 3
Location: Budapest, HU

PostPosted: Tue Apr 29, 2014 2:37 am    Post subject:  Combining Lo-Fi MFOS designs
Subject description: Power, grounding and CV sharing
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Hi all,

Long time lurker here, been building more stuff recently, and now that I'm about to start a bigger project I'd really appreciate some informed opinions on a couple aspects of it while my parts order arrives. Very Happy

I have recently acquired a very nice little box that housed some microscope parts originally, and it looks like it was made to become a synth at some point. A couple of pics of it with a crude paper layout plan:

Posted Image, might have been reduced in size. Click Image to view fullscreen.
Posted Image, might have been reduced in size. Click Image to view fullscreen.

The dimensions are 384 mm x 195 mm x 55 mm. It might get a little tight with all the wiring, but I'd love to fit in everything so that the knobs and switches don't protrude from the box into the lid. I have some special plans for the 14 mm deep lidspace too... Cool

My goal is to make a nice and compact portable (battery operated) drone/noise synth that has some audio and CV/gate inputs, 1V/Oct not required. Doing some youtube research I found that the MFOS WSG and Echo Rockit are both pretty nice and very much to my liking. They are relatively simple circuits with very good documentation, so I chose them as a base for the project.

The final design would consist of the following modules:

MFOS WSG
MFOS Echo Rockit
Ken Stone Digital Noise
MFOS Guitar to Gate (with gate to trigger mod.)
Dual VCA (something very simple)
Dual AR (or AD, also simple, with manual gate)
internal CV matrix mixer (passive or active)
Stereo mixer with two inputs and many more internal ins
Headphone amp (simple TDA2822 or an Objective2)
Power board (battery level, or maybe charging)

Here's a messy block diagram:

Posted Image, might have been reduced in size. Click Image to view fullscreen.

It is quite an ambitious project for me, I come from a pedal DIY background, but I'm certain I'll learn a lot while building this. I plan to build all modules separately first, debug and measure them, and finalize the design and make a faceplate when I'm happy with everything.

I'll put my questions in the next post for better readability.

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When building something, make sure you make it not only idiot-proof but cat-proof also. You'll thank me later...
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Ashcroftt



Joined: Apr 28, 2014
Posts: 3
Location: Budapest, HU

PostPosted: Tue Apr 29, 2014 3:59 am    Post subject: Questions Reply with quote  Mark this post and the followings unread

This might take some time, I'm at work ATM.. Sad

I have run ito a few problems while designing this little box of noise, and I am especially clueless what the best option would be to power this mess, how to ground certain things and how to patch CV-s between different "modules".

Power and grounding:

Power requirements for the modules are quite different (schems in the links):

MFOS WSG +9V and ground
MFOS Echo Rockit +/-4,5V from a single 9V battery with virtual ground + 5Vregulator for the PT2399
Ken Stone Digital Noise +/- 15V, should work fine with +/-9V
MFOS Guitar to Gate +9V and ground
Dual VCA usually +/- 12V, may work with +/-9V,
Dual AR usually +/- 12V, may work with +/-9V
CV matrix mixer (passive or active) passive Very Happy , generic active should be fine with +/-9V
Stereo mixer should be fine with +/-9V
Headphone amp +/-9V



Now I have +/- 15V, +/- 12V, +/- 9V, +9V and ground, some virtual grounds aaaand also a PT2399 part which needs a 5V regulator. My first idea was to use two 9V batteries connected together for +/-9V, or a couple lithium rechargable cells/phone batteries for +/-7,2V or +/-9V.

I know i want to have a separate battery indicator for each battery that flashes when they get below a certain voltage (this looks good), and a safety shutdown feature if one of the batteries dies before the other. The Objective2 charging circuit seems handy for this.

I would like some indicator LEDs, but those would be transistorized and powered from a separate supply not to put too much strain on the common supply.

Question 01: What would be the best way to power these circuits? Convert them all to accept +/-9V? That is probably a bit out of my league. Use separate supplies for some modules? How to manage the 5V regulator on a battery so it doesn't eat it up too fast.

Question 02: How to manage the grounds? Which ones can be tied together, where should the front panel be connected, and what about input/output jack grounding? This is especially problematic with the Echo rockit, and the split supply virtual ground. I know I should try to stick to star grounding or at least star of stars, but this is pretty confusing with a battery supply.

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Ashcroftt



Joined: Apr 28, 2014
Posts: 3
Location: Budapest, HU

PostPosted: Tue Apr 29, 2014 4:49 am    Post subject: CV patching Reply with quote  Mark this post and the followings unread

My other big question is how to manage the control voltages between modules. I would like to take voltages from the LFO on the Echo rocket, some Oscillators from the WSG, envelopes from the AR, etc. and connect them to certain places, like the VCA inputs, filters, Oscillators...

My plan was to make a passive 4 x 4 CV mixer, with switched in- and outputs rather than use patch cables - more compact. This way I could route a mix of 2 x 4 different CV-s to 2 x 4 separate points in the circuit, and also switch inputs and outputs without patching. I have no real estate for rotary switches, so I'd rather have 2 different CV-s on each input and two output destinations on each output switch. A 4 x 4 matrix of push-pull switched 9mm pots would be used for the routing, so I can turn any of the CV-s on and off instantly.

Now my main problem is that I only have an approximate idea what values to expect for my CV-s. The WSG ones would probably go from 0 to ~+8V, the ones from the Echo Rocket are probably ~+/-4V, and I may even want to feed some external CV-s in too, just for fun... And there is still the problem of what voltage are all these referenced to in case I use separate supplies for some modules? I may need an active buffer, or level shifting/amp? I'm kinda lost... Embarassed

I have no idea how these would behave when mixed, what are the tolerances of certain input points, and how to manage these overall. I know, build the modules, scope the outputs and inputs one by one, and see what happens if I connet this to that... I would however appreciate some if someone has already tried some of this and has some advice.

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elmegil



Joined: Mar 20, 2012
Posts: 1484
Location: Chicago
Audio files: 14

PostPosted: Tue Apr 29, 2014 5:55 am    Post subject: Reply with quote  Mark this post and the followings unread

I'm not sure about the ability to get all that to fit inside the box.... I built a MFOS Soundlab Mini-Synth Plus into a cigar box that I think looks about the same depth. Keep in mind that any jacks are going to take up a LOT of space. I did bananas, and those stick out a good 3/4" or more from the back of the lid (I put all the controls on the top surface). Depending on the type of jack you use, a 1/8" jack might only stick out 1/2" but that's still significant when working in such small spaces. Pot bodies also usually stick out at least 1/2" from the back of whatever panel they're on.

I just used bananas so that it was simple to patch. I'm not sure but I think stacking would work to mix them; I mostly was concerned about splitting though, many of the things I want to modulate have multiple inputs.

For power I used two 9V batteries, + of one wired to - of the other and that wired to ground. With a dpdt switch cutting off the two rails when not in use.

Looks like a fun project, I look forward to your results Smile
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