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The Outs - a DIY balanced 1/4" output module
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author The Outs - a DIY balanced 1/4" output module
drmarble
I've had this on the DIY list for a while - I wanted a simple dual channel output module with 1/4" balanced jacks to interface with my DAW. Since levels out from the Eurorack world are often very hot, I wanted to have an attenuator to knock down the signal if needed. And I also wanted to squeeze it into 4hp.

Here it is (rightmost module, obviously):



The signal into the 3.5mm jacks passes through a 100kA pot, and then to a small circuit board for buffering and output driving. The circuit is an impedance-balanced output I adapted from Douglas Self's Small Signal Audio Design book.

I squeezed the two channels of circuit (using an NE5532 opamp) onto an Adafruit 1/4-size Perma-Proto board. It was just big enough for the task:



The biggest challenge was fitting the height of those 3-pin output headers into a 4hp space. It took several iterations of trimming that plastic spacer on the standoff to just the right size... and even then it's a bit marginal, the way the bottom of the board scrapes against the neighbor module when installing it into the Eurorack case. I wouldn't use those headers again in a 4hp module (would just wire direct to the board). But it works!

I'd be happy to share the breadboard layout for this, but my handwritten notes are messy. I've done some layout work with the Fritzing app before, but showing vertical resistors was always kludgy with Fritzing. Any other easy layout software suggestions?

Also, this was my first project done with 24ga stranded wire. Previously I'd always used 22ga that I'd pull out of scrap pieces of balanced cable. The slightly lighter gauge made a big difference in pliability. I didn't feel like I was fighting against the wires constantly.
Jarno
Nice! That board is pretty nifty.
And yeah, do away with the connectors, if you do want to unplug the cables, there's always the soldering iron. I use pretty beefy track widths on PCB's I design myself, never lifted a trace.
Also on cabling, I use the multicolour ribbon cables, works great, not too thick, keeps connections of things like pots together (I rip off a ribbon of three wires wide).



On resizing, it seems the link to the original JPG is huge, everything else is diminutive, way to go Imgur.
KSS
drmarble wrote:
I'd be happy to share the breadboard layout for this, but my handwritten notes are messy. I've done some layout work with the Fritzing app before, but showing vertical resistors was always kludgy with Fritzing. Any other easy layout software suggestions?

DIY layout creator works well for veroboard design and sharing.

Nice work on the module! Look forward to building one once you share layout.

Right angle headers could be another way to reduce height, but agree direct wiring is good too. Especially when it goes straight to jacks as here. Another trick is to put the headers on underside and solder the pins only from on top. You'll pick up about .100 or so this way. Can use some force to pre-extend the pins to make up for the loss in length due to board thickness. Just push a single pin at a time through the plastic joining them into a header.
KSS
Jarno, can you re-size that photo so it doesn't make the thread so wide?
would be much appreciated.
drmarble
KSS wrote:
DIY layout creator works well for veroboard design and sharing.


Yeah, I like the graphics I've seen that were generated from DIYLC. I've tried to run it a few times, with different downloads, and always got those bogus Gatekeeper warnings (I'm on a Mac) that the app was damaged and couldn't be opened. Maybe I'll loop back around and work on getting it to run.

KSS wrote:
Right angle headers could be another way to reduce height, but agree direct wiring is good too. Especially when it goes straight to jacks as here. Another trick is to put the headers on underside and solder the pins only from on top. You'll pick up about .100 or so this way. Can use some force to pre-extend the pins to make up for the loss in length due to board thickness. Just push a single pin at a time through the plastic joining them into a header.


Yeah, different headers would have worked better than the ones I had. I was just trying to build it from what I had on hand already!
drmarble
Jarno wrote:
Also on cabling, I use the multicolour ribbon cables, works great, not too thick, keeps connections of things like pots together (I rip off a ribbon of three wires wide).


That's a great idea, I'll keep that in mind for the next time. I've done wiring for years in rack gear and guitar pedals, and always done flying leads everywhere. Sometimes I would take 2 or 3 wires I wanted bundled together and wind them in a twist with a hand drill, but that can get kind of bulky and stiff. Still learning the tricks for Eurorack builds to keep things compact and neat!
drmarble
drmarble wrote:
Yeah, I like the graphics I've seen that were generated from DIYLC. I've tried to run it a few times, with different downloads, and always got those bogus Gatekeeper warnings (I'm on a Mac) that the app was damaged and couldn't be opened. Maybe I'll loop back around and work on getting it to run.


Well, I tried DIYLC again today, but it's just too kludgy on a Mac. A lot of the contextual menu stuff doesn't even work - basic stuff like rotating a component, or Saving a Variant. It acts like it's doing something, no error is thrown... but just, nothing happens.

Ah well, maybe I'll look at Fritzing again. Wish there was something simple and solid that just worked.
KSS
Fritzing is a memory and graphic hog.

There is or was a German? veroboard layout program which was notfree, but seemed to have a good following. Can't remember what it was called, surely someone here will comment. something like 20-35USD AIRC.

Fewer people doing stripboard with PCBs so quick and cheap these days. Still a great way to DIY though!

Looked it up. LochMaster
came across a few that were new to me also VeeCad, And one for iOS.
Used "stripboard layout program" as search term
drmarble
KSS wrote:
Fritzing is a memory and graphic hog.


Agreed! And it hasn't been updated for over 2 years, so I assume it pretty much doesn't have a future. And, even after you slog through it's incredibly slow performance, the results are unusable for anything other than super sparse layouts. The isometric drawings of many parts (capacitors, leds, pots, etc) obscure a large sections of the breadboard.

Thanks for the other suggestions. DIYLC looks to be the best of the offerings, in terms of the feature set I'm looking for, along with active development. I'll have to try it on a Windows system instead of Mac, it seems like it's in the midst of some difficult growing pains on Mac.
plushterry
If you're into your veroboard, lochmaster is a better program than DIYLC but not as user friendly. Both decent though in their own ways.
UltraViolet
What do you think of Adafruit Perma-Protoboard? Saw it on their website and it looks like nice alternative to using a PCB for a simple circuit.
drmarble
UltraViolet wrote:
What do you think of Adafruit Perma-Protoboard? Saw it on their website and it looks like nice alternative to using a PCB for a simple circuit.


I love those boards. The holes are solidly through-plated, high quality stuff.

I wrote up some posts here about using the half-size Perma-Protoboards for Eurorack:

http://fishboytech.tumblr.com/post/155547216608/adapting-adafruit-perm a-proto-boards-for-eurorack

Although for this output module, I switched the rails around to line up with the V+ and V- pins of the IC (since the board was going to be mounted on a standoff, so I didn’t need a ground strip along an outer edge as a front panel component anchor).
drmarble
OK, I got DIYLC up and running on a Windows machine, and did a layout there. Hope this is helpful!

drmarble
And here's a pic of the actual contruction, to match the breadboard layout diagram:



The only connection made on the bottom of the board was a small wire across the 3 ground pins (the middle 3) of the power header.

For the power rails I use yellow wires for the +12 and blue wires for the -12. This follows the convention set by my benchtop power supply.

By avoiding red for either power rail, this also sidesteps the confusion that for Eurorack, the red wire carries -12, whereas most other small voltage applications use red for the + voltage. This way, with yellow as +12, when I see a red wire on a board I don't have to stop and figure out if I decided to follow Eurorack convention or the more common convention! (Red, you can see, I use for signal connections only.)
LED-man
Or just go with better line drivers from
THAT or SSM, like in this module from VDD:

https://www.diysynth.de/pcbs-panels/vdd-5002-01-dual-symetric-output-m odule-pcb-only-20.html?language=EN
drmarble
LED-man wrote:
Or just go with better line drivers from
THAT or SSM...


Could have, but it seemed like overkill. Definitely didn't need an extra 6dB of level going from Eurorack into DAW...
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