Stompbox version of Axoloti

[Cpl_Crapper]

I am new to this and will be purchasing an Axoloti soon. I am interested in guitar effects and was thinking that it should be straight forward to re-design the Axoloti for guitar stompbox use. IE: remove the midi. mono jacks. true bybass and design a pcb to fit inside a standard Hammond enclosure. Perhaps with mounting holes for up to 4 pots or switches. Has anyone already done something like this? Is this a dumb idea? I would love some feedback on this please.

[janvantomme]

The MIDI part of the board can be removed.

The stereo jacks are not a problem. You can easily plug in a mono cable and just use the left input channel. Keeping them on the board is a plus, since you can output different effects chains on the left and right channel.

There are a lot of topics on the forum regarding guitar effects. Just do a search and you might find what you need.

Hardware configuration for guitar effects applications?

The KMI softstep is somehow the only choice if you want a usb class compliant midi pedalboard that is also USB powered, and it's reliable and roadworthy, BUT using it as ten expression pedals is very hard, and believe me I'm very much used to small pedals and foot jugglery... I was aiming myself at something like but I ended up sticking rubber buttons on the pad corners and use it mostly as switches

[Gavin]

It all depends on your goals.
Axoloti is extremely flexible, with that said the builds can be as simple or complex as you want them to be. I joined the community a little over a year ago with a similar goal for the Axo to be for guitar effects. I have looked into so many different options and along the way learnt so much from this great community, but I am only now in a possition where my build is developing into something that I am more than happy with.
If you are going to try and simplify it into a simple enclosure with a few pots, you may want to consider, how will you adjust your parameters and switches, will the setup meet the needs of all your patches, how many switches and parameters will you have in your patches, how will you view your settings, what if you want to make changes in the future.
Unless you just intend to have one effect like a delay for example loaded into the Axo and used as such, this is OK too, but the Axo is way over powered just for that.
In terms of guitar effects, the Axo can be more like a multi effects circuit board, where you get choose every part you want to add to it, except for the limitations on Audio inputs and outputs.
My live setup per patch:
16 changeable switches 2 banks = 32 switches. (Also in footswitch format)
16 changeable parameters 2 banks = 32 parameters
VGA monitor to display feedback and patch details. (optional)
2 x expression pedal inputs, (likely to be increased in the future.)
Audio split into Input / output and send / return for an effects loop.
Have seperated the midi from the main board, but it has been added to the build for future consideration and use.

As has been said in many posts, everybodies needs are different, but alot of insipiration can be found in the posts on the forum.

[thetechnobear]

straight forward to re-design the Axoloti for guitar stompbox use

I think its unlikely that the market size warrants a custom version of Axoloti for guitar/stomp box users, especially as the existing one is so easy to adapt - though there is nothing stopping someone trying to build/sell one if they believe otherwise

as others have stated, depending upon how much effort/time/skill you want to put in there are different approaches -
axo not a big board, so will easily fit in, then

• with some diy, you can add pots/switches,
• or alternatively use midi...
• bypass, you could use a wire up a true bypass, but I've also supplied an object which bypasses the adc/dac in software, that may be enough.

the only thing you need to really consider is powering, for this, you will probably want to keep the 'midi din' section, as this also contains the dc power, but you can disconnect this part of the board, and reconnect it, if the length of the axo board presents an issue for your case.

so depending on your needs, using an existing axo board in a stomp box enclosure might be no more than drilling a couple of holes for the audio io and usb host.
but with a little simple soldering you can really customise it to your needs, with pots/switches etc.

@Gavin raises interesting points, because Axoloti can do some many things, you might want lots of switches/pots to try to capture lots of different uses.
but I think its also valid to take a minimalist approach, use only (e.g) 4 pots on, and then let that drive what you can do and your 'user interface' - this will make you 'creative' in your patch creation e.g. a 'character' knob might change many different parameters in your patch, rather than having lots of knobs controlling individual parameters.
(if you look at commercial products this is pretty common, partly out of cost, but also for end user usability)

I've been struggling with this myself recently, because Axoloti is so open, its easy to get paralysised by choice (''the paradox of choice'), sometimes its just better to create restrictions/boundaries, so you can then work within them!

(nice thing about diy is, even if you choose 4 pots, nothing stopping you later adding more.. and Axoloti is relatively inexpensive, so could also build multiple pedals)

[Cpl_Crapper]

Thanks for your input guys. As I said I'm a newbie to Axoloti. My interest lies in guitar effects and the GUI interface to this makes it look so flexible and easy to create new and interesting effects. My understanding is that once the progam downloaded to the main chip the unit will then work standalone. I was concerned that the Axoloti board would be too big for a standard stompbox enclosure. I understand the flexibility of the current design, but I was thinking about a PCB that is essentially a cut-down version with things like midi removed. I guess in my mind I was thinking about a single effect say, a reverb programmed in, which would stay that way. Then build another PCB for creating a new effect. But have the flexibility of a design that would allow maybe 2 footswitches and up to 8 pots/switches to cover most requirments for control. The PCB would be designed with the pots etc in a set position so that an enclosure could be designed around it. For example if I wanted a 2 knob fuzz box I would populate and program for 2 pots and one footswitch. This is all ideas in my head at the moment as I think about what I may be able to do. After looking at the schematic I see that I would need to source the microprocessor and what looks like a custom FPGA. Would I be able to get hold of the custom chip do you think?

[thetechnobear]

the axo board is only 11cm x 5cm (without removeable midi part), is that too big for your enclosure?

My understanding is that once the progam downloaded to the main chip the unit will then work standalone

yes, loaded into flash to be executed, but the firmware can also load patches from the sdcard.
.. but your correct it can be used completely standalone, and then controlled either via gpio or midi (usb or din)

After looking at the schematic I see that I would need to source the microprocessor and what looks like a custom FPGA. Would I be able to get hold of the custom chip do you think?

Axoloti does not use an fpga, nor custom chips, as the specs says, its built around an stm32f429.

of course you could build a pcb yourself, but unless you make it compatible with Axoloti, you will also have to write your own firmware, and patching software.
(you could build around an arm chip, but still the firmware and patching software would need to be changed)

if you search on the internet you will see other options ( from pretty bare solutions, to complete solutions like Axoloti e.g. owl/bela)

Axoloti is (I think) fairly unique in that it provides a full solution, not only dsp, but hardware (audio io/dac/midi din/usb host and device, sdcard) and a patching solution.... other solutions tend to provide bits of this.

many seem to forget things like the patcher/firmware in Axoloti, are big development projects in their own right, and you get these + hardware , for 65 euro.

of course, the best solution for you depends on what you want, your skill set (in hardware/software), and time available. alongside my axolotis, I also have belas and rPIs, they all have their advantages/disadvantages

[Cpl_Crapper]

Thanks "thetechnobear" you have given me something to think about. I don't have a Axoloti yet. It would cost about £100 UK so I'm having to wait a while, but hopefully soon. I was mistaken about a custom chip. I see the other major chip is an SDRAM device. With regards to the firmware. Is this pre-loaded to the microprocessor or is it loaded at the same time as the patcher program is loaded?

[thetechnobear]

With regards to the firmware. Is this pre-loaded to the microprocessor or is it loaded at the same time as the patcher program is loaded?

They are loaded independently.

[widdly]

I'm using my Axoloti with a Roland FC200, and it is really nice guitar setup. The FC200 has a program change mode, which you can use to select a patch on the axoloti. It also has a CC mode which you can use to turn bits on and off in the current patch. There is a built in expression pedal and plugs for 6 more expression pedals. The FC200 connects via a midi cable so you can put the Axoloti on safely out of the way like on top of your amp.

There is a behringer thing like the FC200 which is ok but kind of a pain to edit.

[Gavin]

Yeah, the FC200 looks pretty cool, I almost bought one myself.
The only reason why I didn't, is because of 2 things, didn't want to have to connect it up every time I am working on a patch on the PC, and concerned would have to re-program it for different variations in the patch.
I really like how it can accommodate so many expression pedals.
As I am writing this, it is making me think about how you could easily use an Axo solely as a dedicated midi foot controller. Hmmmmm !