Build at least one module, to test and confirm the design

[coryalder]

No description provided.

[coryalder]

MODULE BUILT!

Here (hear) it is in action in the Vancouver Hack Space eurorack. That panel needs to be out of something other than cardboard, the pot shafts are too short, and it's missing all but one of the 3.5mm jack nuts. Tested all four channels, headphone output, level, and pan. haven't tested line out, and haven't checked everything with a scope yet.

[KeLaiFu]

any updates on this? Looks like a great module.

[coryalder]

Hi KeLaiFu! Yup, everything works with the circuit. There are a couple tweaks to the PCB footprints that I haven't got around to circling back and doing - the only one that's really an issue is the 3.5mm jacks (#3) - they're pretty tight and the jacks sit ever so slightly cocked to one side (you can see it in the HP jack in the photo above how it's not lined up with the white silkscreen).

I also have had a hell of a time sourcing potentiometers with white indicator marks. LMK if you have any questions about building it, happy to share details - this project fell off the top if my priorities - but i'm not done with it by any means :)

[KeLaiFu]

Brilliant, I will see about getting the PCBs made up.
As for the issues, I intend to change the footprint for those jacks anyway as I have a million thonkicons and none of the ones you used in the build.
I can't source those pots with the marker on here (in China) either, but I found a few options for knobs that can be put on those ones you used, so I will go with that. I will post anything I make to my github, with links and credit to you, of course.

[coryalder]

As it’s currently laid out, there’s not much room for knob caps - so watch out for that!

Re thonkicon jacks, they’ll work for all the inputs, but the outputs are stereo - thonkicon does sell stereo jacks but i don’t have any of them which is why I used these less standard jacks. Looking forward to seeing what you come up with! :)

[KeLaiFu]

I was just pondering if i should change the pot layout, theres not much room horizontally, but vertically theres wiggle room but the block of IO has a certain style.
A question that just came to me, what's the output level from this module? I realised that I wouldnt be able to put this direcly into my erica output module without splitting back into 2x mono, so are the volume levels from this safe to plug into my amp?

[coryalder]

Depends on the jumpers J5 and J6. The gain can either be unity, so 10V in = 10V out, or it can be 2/3rds so 10V in = 6.66V. With a 10Vpp standard eurorack audio signal you’d get 6.66Vpp. Line level is in the range of 0.5Vpp to 1.75Vpp, so it’ll be a little hot - probably not enough to damage anything, so you can just keep your 4 track volumes low enough to avoid clipping if you do this.

if you want it quieter you can change the values of the gain resistors (R17+R38 and R19+R30). If you do - you may want to make R35+R36 smaller to bring the headphone volume up a bit. Alternatively you could move the stereo pot to where the gain resistors are - currently the master volume is only controlling the headphone volume. Changing that has a tradeoff - if the master volume controls both the line and hp volume you won’t be able to get usable levels out of both at the same time (either headphones will be too loud or line will be too quiet).

Trimpots would make it possible to decide your output levels, but makes calibrating the module harder.

This stuff is just stacks of tradeoffs, choose your own adventure!

[coryalder]

You could also split the L and R line outputs into two jacks if you wanted - but my intent was for this to be your output module

[KeLaiFu]

wow, it's been over 3 months! I have finally got the parts and almost finished building my version of this, but I am confused about R2 and R4, why are they THT? I don't see any reference to them in any of the online documentation.

[coryalder]

Amazing! So glad you're building one! Please post pics and feedback when you've got it running!

For R2 and R4 - they're optional, which is why they're thru-hole. If you've used a linear potentiometer (B10K and not A10K) for headphone volume, adding these two 1.5K resistors will make your linear pots into pseudo-log pots which theoretically is better for sound. You can read more about this technique here: http://geofex.com/Article_Folders/potsecrets/potscret.htm but the short answer is just leave them off unless you notice that the headphone volume is weird.

I haven't updated the pdf of the schematic since I added those, but if you open the kicad project there are a few clues that's what's going on - but I need to make it more clear

[KeLaiFu]

Nice! you really have thought of everything! I just checked my stash and I only have B10k dual gang pots, so this saves me from making an order.

I only have the PCB currently fabricated, so assuming I get it working, I will make a panel for it later on. I changed the layout on the IO, but it's basically the same.