Interest for $20 Eurorack Modules

[cat_abyss]

At 20$ a piece it could be worth dropping the euro compatibility claim and just aim to create a closed system (which happens to play along with euro under certain conditions, use the same power specs and dimensions, etc).

[ljwall83]

...I therefore plan to use external breakout boards for the DAC (24 bit I2S), with the added bonus that the signal will be 0-5 instead of 0-3.3V. (These are the two boards standing at the lower part of the module)
As I mentioned I plan to use 0-5V and not add extra buffers to the ports. You can always complement with a TL074, but I want to avoid complexity, ground planes and cost drivers.

But you're only talking about outputs here? To be useful modular platform you're going to need inputs. Maybe I'm confused, but how will the inputs accept anything above 3.3V without damaging your MCU? Already the outputs of your modules (0->5v) are not compatible with the inputs? You'll need to put something on the inputs to handle the voltage difference --- ideally robust to +/-12v.

A small cost saving now, at the expense that as time passes the probability that I destroy the device by miss-patching tends towards 100%, is not a trade I would make personally.

[mazzyboy]

The 0-5V is not a "bonus" but still far short from the commonly agreed modular signal levels. Being "modular" is more than just fitting in the same case and using the same power supply. Don't go valueing stinginess over technical standards if you want to join into a system. It's not like that bit of extra would drive the cost beyond the imaginable. You want to sell a car that drives on open roads? Don't just give it a seat and an engine, but it also needs brakes and a steering wheel... even if it will move without those.

+1. I also see the 0-5V being quite a serious limitation. Sure people could mod the design, but I think overall it'll hamper development. People will naturally develop apps for the 'OG' model, not a multitude of 'unofficial' modifications. And theres a limed number of applications that Id want to be restricted to 0-5V for.

Otherwise, I think it sounds like an interesting idea. Im all for having a play around with homebrewed projects like this.

[starthief]

Don't go valueing stinginess over technical standards if you want to join into a system. It's not like that bit of extra would drive the cost beyond the imaginable.

Agreed, I think people would rather pay a little bit more to have proper signal levels and make sure the thing doesn't blow up if you look at it wrong.

The way I see it, for digital modules, it should either REALLY be Eurorack compatible and safe to interconnect with things, or just software in the first place.


And 3D printing is just not that easy for everyone. We're not all into DIY. I have no idea how makerspaces work and there's a big social awkwardness factor to overcome. I'd rather just buy an already made thing.

Also there's a pandemic on. IF the one makerspace I've heard of in the city is even still open, I probably don't want to go hang out there.

And I live in a suburb and still find going to that part of the city a bit of a hassle under normal circumstances... for people who live an hour or three away it's a lot worse.

[Yes Powder]

[...]the added bonus that the signal will be 0-5 instead of 0-3.3V. (These are the two boards standing at the lower part of the module)
As I mentioned I plan to use 0-5V and not add extra buffers to the ports. You can always complement with a TL074, but I want to avoid complexity, ground planes and cost drivers.

That is exactly where this thing falls short. Ground planes eat up stray HF and EM emission noise, and we don't want those inside a modular system. The 0-5V is not a "bonus" but still far short from the commonly agreed modular signal levels. Being "modular" is more than just fitting in the same case and using the same power supply. Don't go valueing stinginess over technical standards if you want to join into a system. It's not like that bit of extra would drive the cost beyond the imaginable. You want to sell a car that drives on open roads? Don't just give it a seat and an engine, but it also needs brakes and a steering wheel... even if it will move without those.

Agreed; there's cost-saving, and then there's just being cheap. A $20 module would be mindblowing but if it's going to make my system noisier just by being there or fry something if I plug a cable wrong, then even at that price it's no good to me.
You could double the price and it'd still be worth it, just to have it play nicely with others.

[sir stony]

One thing that I really like about this design is the closed case on the back, proofing it against accidental mechanical or electrical damage during handling. I'd love to see more modules designed with more emphasis on that aspect.

[Northpaw27]

$20 is the production cost for a DIYer if I understand this correctly. Which means that in a retail environment it would be ~$60 at which point you’re heading towards doepfer territory. It might flourish as a DIY system but I can’t see this working on a larger scale.

[johan]

At 20$ a piece it could be worth dropping the euro compatibility claim and just aim to create a closed system (which happens to play along with euro under certain conditions, use the same power specs and dimensions, etc).

That was the idea, it is somewhat compatible, but I understand that it wont work with all devices...

One thing is whether it is compatible or not, another is if the reduced dynamic range will prevent the usage. I dont have the experience to say if +-12v is needed in some occations?

[johan]

[...]the added bonus that the signal will be 0-5 instead of 0-3.3V. (These are the two boards standing at the lower part of the module)
As I mentioned I plan to use 0-5V and not add extra buffers to the ports. You can always complement with a TL074, but I want to avoid complexity, ground planes and cost drivers.

That is exactly where this thing falls short. Ground planes eat up stray HF and EM emission noise, and we don't want those inside a modular system. The 0-5V is not a "bonus" but still far short from the commonly agreed modular signal levels. Being "modular" is more than just fitting in the same case and using the same power supply. Don't go valueing stinginess over technical standards if you want to join into a system. It's not like that bit of extra would drive the cost beyond the imaginable. You want to sell a car that drives on open roads? Don't just give it a seat and an engine, but it also needs brakes and a steering wheel... even if it will move without those.

Excellent feedback, I really appreciate it. The EMI is definitely something to consider. You can say that there are ground planes on the modules, but the interconnections and especially the I2S signal needs to be investigated. Maybe it works, maybe you need copper tape, maybe it has to be a PCB instead of wires...

[XODES]

The AE format from Tangible Waves might be a better fit for such a module idea, as it runs on 5V only, so you wouldn't need extra level adaptations.

Plus, a lot of (assembled) modules are in this price range, and it looks like users would be very happy to see more developers adopt it.

https://www.tangiblewaves.com/

[johan]

The 0-5V is not a "bonus" but still far short from the commonly agreed modular signal levels. Being "modular" is more than just fitting in the same case and using the same power supply. Don't go valueing stinginess over technical standards if you want to join into a system. It's not like that bit of extra would drive the cost beyond the imaginable. You want to sell a car that drives on open roads? Don't just give it a seat and an engine, but it also needs brakes and a steering wheel... even if it will move without those.

+1. I also see the 0-5V being quite a serious limitation. Sure people could mod the design, but I think overall it'll hamper development. People will naturally develop apps for the 'OG' model, not a multitude of 'unofficial' modifications. And theres a limed number of applications that Id want to be restricted to 0-5V for.

Otherwise, I think it sounds like an interesting idea. Im all for having a play around with homebrewed projects like this.

Thank you, this is exactly the feedback I value. For inputs I planned on using simple voltage dividers (two resistors, hoping that most outputs won’t be that capacitive anyway). It is definitely possible to add some op-amps to handle the voltage levels for in and outputs and it will not break the bank. But the component count and complexity of assembly increases significantly and quite soon you end up with a module that uses a custom PCB and looks like everything else…
I have no problem accepting that this approach doesn’t work for Eurorack, this is the whole reason for testing the idea with all you experts (fail fast).

Are there some modules where a limited output range would work better than others?
Is it ok for a VCO, or a delay/reverb unit for example?

[johan]

The AE format from Tangible Waves might be a better fit for such a module idea, as it runs on 5V only, so you wouldn't need extra level adaptations.

Plus, a lot of (assembled) modules are in this price range, and it looks like users would be very happy to see more developers adopt it.

https://www.tangiblewaves.com/

This is excellent, I was not aware of this system. It is definitely in line with many of the ideas I was considering. (and the price is in the same ball park too
Thanks!

[sir stony]

Are there some modules where a limited output range would work better than others?
Is it ok for a VCO, or a delay/reverb unit for example?

Most functional modules are fine with that, as commonly gate and clock signals are 5V, and sequencers with a limited octave range can do very well, too (like the division6 dual mini, a module I really love and use often). For logic functions, your design would again need more inputs to become interesting. Triggers are a bit more critical - usually they will work at 5V, but they are meant to use 10V. It's really the audio signals that are not fine with 5V. A single audio signal is 5V p-p nominal, but with a 5V supply, you sacrifice all the headroom, and quite a lot of analog (vco, lfo, filter) modules spit out 10V p-p or even beyond. CV can use the full 20V p-p range.
All this sums up to why I said first "not as a tool of sound creation".

[johan]

Are there some modules where a limited output range would work better than others?
Is it ok for a VCO, or a delay/reverb unit for example?

Most functional modules are fine with that, as commonly gate and clock signals are 5V, and sequencers with a limited octave range can do very well, too (like the division6 dual mini, a module I really love and use often). For logic functions, your design would again need more inputs to become interesting. Triggers are a bit more critical - usually they will work at 5V, but they are meant to use 10V. It's really the audio signals that are not fine with 5V. A single audio signal is 5V p-p nominal, but with a 5V supply, you sacrifice all the headroom, and quite a lot of analog (vco, lfo, filter) modules spit out 10V p-p or even beyond. CV can use the full 20V p-p range.
All this sums up to why I said first "not as a tool of sound creation".

Got it. After some thought - its not that difficult to add an LDO, op-amp and a few resistors to expand the voltage. Ill do some simulations and see how it can be solved.
Thanks again for the feedback!

[johan]

I did a quick simulation using half of a tl072 to output 10Vp-p. Four or five resistors and some decoupling caps should be ok!


Any feedback on the circuit is appreciated!

[sir stony]

Usually, input impedance is 100k in eurorack land. Sometimes 50k. And very rarely less than that. Remember you can't use AC coupling for the inputs if you want to process cv, too.

[nexgen23]

I am definitely very interested in this!

[nexgen23]

I did a quick simulation using half of a tl072 to output 10Vp-p. Four or five resistors and some decoupling caps should be ok!


Any feedback on the circuit is appreciated!

Nice work, if you don't mind me asking, what are you using to run the simulations? I'd love to play around with building some circuits in a non-destructive way (via software I assume). Thank you for your hard work BTW!

[osten]

Nice work, if you don't mind me asking, what are you using to run the simulations? I'd love to play around with building some circuits in a non-destructive way (via software I assume). Thank you for your hard work BTW!

This looks like old school pSpice to me

[johan]

You are absolutely right, I used LT spice that is reliable, has lots of libraries (had to import tl072) and quite easy to work with (once you learn how it works)
https://www.analog.com/en/design-center ... lator.html
There are several online tools with similar performance too

[chaosium]

Agreed; there's cost-saving, and then there's just being cheap. A $20 module would be mindblowing but if it's going to make my system noisier just by being there or fry something if I plug a cable wrong, then even at that price it's no good to me.
You could double the price and it'd still be worth it, just to have it play nicely with others.

Yes, if someone has access to a 3d printer and eurorack, lowest possible cost is not the issue mm\';;;;;;-0o"
/6666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666666-*]90o/;

Edit: My cat has opinions.

[ATW]

Shapeways is a contract 3d printer and 3d printing, fabrication, prototyping marketplace worth exploring.
https://www.shapeways.com/

I am sure there are others like this, as an alternative to maker spaces and 3d printer access in the meantime.

[nexgen23]

You are absolutely right, I used LT spice that is reliable, has lots of libraries (had to import tl072) and quite easy to work with (once you learn how it works)
https://www.analog.com/en/design-center ... lator.html
There are several online tools with similar performance too

Thank you, I’m going to play around with it a bit when I get the chance.

[minatorymodular]

Driving the cost as low as possible doesn't make a ton of sense to me if the result is worse than an O_c. I'd rather have an O_c 2.0 that was easier to flash and load with different apps. If there was a software app that let the user add any combination of apps in a standard format, I'd be interested. If the hardware sacrifices too much to get the cost lower, nobody might be inspired to write software for it.