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MIDI to CV breakout panel - first time DIY
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author MIDI to CV breakout panel - first time DIY
DrReverendSeance
I am going to attempt my first DIY project starting from a schematic: the fully-buffered Encore Expressionist Breakout panel described at Dave's Hot Rod MOTM. http://www.hotrodmotm.com/expr_panel.htm

As this is my first time, I am posting my BOM and panel design for review, hoping someone with more knowledge might point out any errors I am making???

My plan is to mount 3 scratch boards onto brackets for the circuit (scratch board 1 for CV&Gate 1 to 4, board 2 for VCV&Gate 5 to 6, and board 3 for the click and start sync). I intend to secure the brackets using the jacks.

Any advice or comments very much appreciated!
DrReverendSeance
Found a source for the prototype board:
http://www.protostack.com/boards/prototyping/prototyping-board-large-s tyle-1

Updated the BOM accordingly.

Now I need to figure out how to attach the MTA-156 to this 0.1" board.
DrReverendSeance
I never did post pictures of the finished product (December 2016)



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daveholiday
Hey Doc!

I purchased an Encore a few months ago during the sale and just got it out this weekend for some testing! Needless to say I now have an 8 channel performance sequencer that drives my modular! (MC-505 + Expressionist)

But back to the point of digging up this old thread...

The back panel jacks are a pain in the ass...I would like to do a front panel double wide MU panel based on Dave Bradley's break out panel.

I basically wanted to ask how your build went, and are the any problems or weirdness that have come up since you built yours.

I also have a few questions about the buffered circuit that you may or may not be able to answer, but others might chime in!

Since the TL074 with cover 4 independent channels why not use a quad array of the TL074? 2 for 4+4 CV, 2 for 4+4 gate. I am still learning, so perhaps I am missing something, but I have made a basic 4 channel buffered CV source from a single TL074 that seems to work fine.

A quote from Dave's Site

"If you build this version, it's especially important that the opamp buffers for the CV signals provide extremely low drift and offset, so use the LT1013."

So I am curious....TL074 vs. LT1013 for CV... is this what I am missing?
daveholiday
daveholiday wrote:


So I am curious....TL074 vs. LT1013 for CV... is this what I am missing?


Just found some threads right here.......

Whew! over my head to say the least, but it does seem the the TL074 will work just fine!

But will wait for advice or further knowledge!!
DrReverendSeance
Hi daveholiday,

Aside from my own soldering sloppiness, the breakout panel developed by Dave Bradley worked well without any issues. In retrospect, I probably didn’t need to go all buffered. It was a lot of wiring though.

I used the proto boards from Phil MacPhail (Liivagera) which worked great. http://www.liivatera.com/Products/prototyping/FracProto/#1

All of the two-pin headers connect to 1/4 plugs for the back of the expressionist.

I think the T074 will work fine for the gate signals, not sure for the CV.

All the best
Robert
ixtern
DrReverendSeance wrote:
Hi daveholiday,
I think the T074 will work fine for the gate signals, not sure for the CV.
Robert

If TL074 must be used then TL074B is recommended.
But Op Amp offset is not the biggest problem in CV. You can always add offset fixing circuit to the Op Amp (although in non-inverting configuration it may be little tricky).

Offset thermal drift is the harder problem. The simplest way to fight with it is to choose better Op Amp with minimal offset and offset drift, like OPA277 or so.

The tricky way is to do it like in old days - choose Op Amp with offset compensation pins and use NTC thermistor (method described in "Nulling Input Offset Voltage of Operational Amplifiers" by Texas Instruments).
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