Build for acoustic guitars

[Erajer]

Hello guys, i'm considering putting a pi stomp with speakers into an acoustic guitar and I want to share it with you, i'm still thinking about how it's makable
Don't run i'm not crazy, the idea is making something like the Lag Hyvibe system
Ola Englund demo https://www.youtube.com/watch?v=BRGEMSlkzHg

Long story short, it's a digital preamp with on board effects amplifying 2 little speakers glued on the table. Turning the guitar itself into a speaker, allowing effects and backtrack usage without pluging the guitar.

Thought we can make event better with a pi Stomp my guess is:

• glueing 2 speakers to the table, connected to a mini amplifer board, less than 10 bucks for that.
• Make a build of the pi stomp with screen and pots deported from the board, maybe no screen at all
• Connect 2 mics in inputs (piezo and ambiant), with a mixer and an EQ begining every PB, we can replace a real acoustic preamp right ?
• Send output 1 to the mini amp and the outpuk jack OR split them betwin output 1 and 2
• Use input 3 for backtrack possibilities, ideally from a bluetooth module connected to a phone(no idea what or how) or with an output Jack at least
• add a battery slot with enought power for everyone

I event thought about arcade buttons on the table instead of footswitches, or on the side in the curve of the body for don't drill the table.

So what do you think ? Doable ?
Can we make build with battery, wich one and how many ? Can we connect the bluetooth module and the amplifier to the Pi power supply ? What about the tuner on the lcd screen ?

Early thanks

[Crosenau]

Hi there, my name is Chris. I made one of these using a pi 0W and put it into my acoustic guitar. I’d like to send you some pictures to show you how I did it.

My acoustic did not use the tree fall sound core. I only used a audio injector zero sound card and a pie zero w, a 5 3.5 watt stereo amp and 2 x5 watt vibration speakers (contact speakers).

Initially I used a pi3, but using 6 AA batteries; it only lasted around 8 mins! (It also melted my battery tray) Switching to the pie zero w resulted in a more “typical” feeling battery usage. (Around an hour a day, for 1-2 weeks)

Drawbacks to using a pie zero w:
Boot takes around 60 seconds.
More latency

But overall I like it.
I can post more details shortly, also I want to swap in a sound card with a built in amp (mino)

-chris rosenau

[Crosenau]

Here are some images of my first attempt
Takamine/ jasmine with battery holder installed
https://drive.google.com/file/d/1v7oc784m4PI7cNLRH3vwT5TKEhdVs9Oi/view?usp=drivesdk

https://drive.google.com/file/d/1shUa3tXhMY3jm4ntjKmUrwgv2R0hdDqv/view?usp=drivesdk

Pi zero w and audio injector zero mounted
https://drive.google.com/file/d/14XgNSuqwVEOzFpIs_c5DcR3p-yAZtl_Y/view?usp=drivesdk

Mini amp and voltage regulators (1 for amp 1 for pi)
https://drive.google.com/file/d/1wUSMa2aXgU2-tm9zMiDQ8bBDq0R50_tH/view?usp=drivesdk

I am not an engineer or electrician, so most of my work was guessing.
I imagine powering it through the gpio would have been a better idea, and now in hindsight, the stereo amp is overkill. I think 1 mono speaker and amp are enough. But, this was an experiment; and I did learn that the best speaker mount is on the back/inside of the body.

I would not suggest a piezo, as it would be more likely to feedback. I used a clip on mag, mounted semi-permanently.

The noticeable lag works perfcitky fine as I am adding effects only. This is similar to the pre-delay most effects offer :-)

[Randall (Admin)]

Cool ideas Erajer!

Definitely check out what Chris has done.  Really cool stuff!   

To add some pi-Stomp details...

A pi-Stomp built from the recommended RPi 3A+ typically draws about 250 to 300mA when running, and over a half amp when booting.  Most of that is drawn from the pi itself.  The extra pi-Stomp peripherals only draw a small fraction of that.  So for more than a few hours use, you'd definitely want a battery with a few thousand mAh capacity.   

I'd probably suggest a LiPo battery so you can recharge it.  It'll either need to be rated or regulated to 5.0V cuz the RPi will shut down if your voltage varies much from that magic voltage.  You might be best off just buying a purpose built solution like the following to handle charge controlling etc.:
https://www.tindie.com/products/pisugar/pisugar-s-plus-battery-for-raspberry-pi-3b3b4b/

That shop has larger and smaller modules as well.  I've seen similar solutions on other RPi shops.

Regarding your inputs... with the AudioInjector Zero and IQaudio Codec Zero cards, you have 2 inputs.  The pi-Stomp board adds buffers to accept high impedance inputs, but they are configured for unity gain.  It's meant for "Instrument level" signals.  "Mic level" signals would likely require a some gain via some kind of preamp to be usable.  But like Chris suggests, piezo's, and maybe any mic are likely to feedback so maybe consider magnetic pickup if you can.  It'll probably work fine without a preamp too.

For killing two birds with one stone, the IQaudio Codec Zero card does include a powered speaker output (1.2Watt mono) which can be independently controlled via alsamixer.

[Erajer]

Thanks and congrats Crosenau for your feedback, it ll be precious if you already build one =D

So what abouts the vibrations speaker ? Does it sound good ? According to you, a solution 1.2watt mono like Randall said will be fine ?? I already found 1w 8ohm vibrations speaker

Thanks Randall for the intel about the IQaudio Codec Zero card. If i get it i could plug in directly a magnetic mic ? Noice
Can we plug the IQaudio on other rasp pi than the zero ?

But i'm concerned about the mic, my guitar for this project is an "Ovation" Style magnet involve some hard drilling on the table on the center and i want to avoid that for now. and Lag system use piezo according to their manual, but they already
https://www.hyvibeguitar.com/wp-content/uploads/2021/05/HyVibe-Installation-Instructions-EN.pdf
I can still add a cheap preamp for the signal (and the tuner). I even found a passive one but no tuner... tought call
https://fr.aliexpress.com/item/4001095275232.htm

I rode something about powering Pi-based projects with power banks, found some with 2 USBs are 5 volt 1 or 2 a. the 2nd output (for amp first) could be for a guitar preamp instead. But they are usually powered by 9v battery and thought I got it, this one can give 5v/3a or 9v/2a via usb, even 12. I suppose it will be enought and seems to be the cheaper way to get lot of autonomy
https://www.amazon.fr/dp/B088BZW3SD?tag=powerbank20fr-21&linkCode=ogi&th=1

My last concern is about getting bluetooth as input for send backtrack from my phone, Is a way for IQaudio Codec Zero card can do it ?
Or Should I connect blutooth thing via jack input ? eventually, i guess i can power it via Pi's USB

Thanks again guys, it's really good to see this crazy idea going on and even already made ^^

[Crosenau]

The wattage depends on how loud you want to get it. My current vibration speakers are 3w
https://www.ebay.com/itm/153015439881 and
https://www.ebay.com/itm/163818582079

I have got them loud enough to hear the magnets hit the base. So 4w would be better if your going to get it really loud. -- Although, I was able to negate this by reducing bass response with an EQ.

When you say "table" i imagine you mean the acoustic guitar face?

I am working with Randall on a solution for an acoustic version.

~Chris Rosenau

[Erajer]

Yes i meant the front of the guitar, the only piece of wood on ovation's guitars ^^
Please forgive my english vocab, it's the french word for it

Thanks for links about speaker, I'm just still wondering if 3 or 4w speakers are ok with 1.2w amp

Because Randall's solution seems good for the QI and the power.
After many checks the Pisugar battery  seems to be a better solution than powerbanks and no need to power anything else with passive preamp.

I also thinking about a way to replace footswithes by little soft touch buttons on a piece of wood.
Edit: Just thought about a PS2 joystick for arduino, I suppose we wan plug it in Debounce like any sw

About the navigation knob, how do you use without a screen ? Thought the best way to use it is to switch pedalboards

[Randall (Admin)]

Regarding alternatives to a big-ish LCD and encoder for navigation.  What I've been considering for smaller builds is this:
https://www.adafruit.com/product/4393

Nice size and it includes 2 pushbuttons which could be used for navigation.  I'm pretty sure they are debounced, so even more circuitry "for free".

At one time, I did have the LCD working with pi-Stomp and the code is still in the codebase:
https://github.com/TreeFallSound/pi-stomp/blob/master/pistomp/lcd135x240.py

It just displays the Current Pedalboard, Snapshot and some dummy colored squares (as plugin proof of concept).  A few hours work to get it displaying a smaller and reduced set of objects like the standard LCD.

Never tried to get the navigation working.  It would require a new state-machine in modalapi/mod.py   Nice project for someone.  Maybe I'd spend some time on it if there is enough interest.

[Erajer]

Nice found, I keep it in mind for another build idea ^^
Though the lack screen is an energy economy we can afford, especially in the absence of visual tuner
In my vision, the best screen is an e-ink, yes want to maximize the autonomy !!

I solve some isues like bluetooth, a usb dongle with a jack output SO EASY (i'm so dumb)
Also find how to connect all that stuff and made a draw, but i forgot a power button DAMN

This should include ATM:
- Pi stomp coke kit without: Audio Injector, LCD header (and screen if possible) and do i need "MCP3008 ADC used for analog ins" ?
[edit: i need MPC3008 for joysticks]
- Pisugar S+ :https://www.tindie.com/products/pisugar/pisugar-s-plus-battery-for-raspberry-pi-3b3b4b
- Passive preamp : https://fr.aliexpress.com/item/4001095275232.html
- IQaudio Codec Zero cards : https://www.elektor.fr/iqaudio-codec-zero-sound-card-for-raspberry-pi-zero
- Dongle BT Jack USB: https://fr.aliexpress.com/item/1005003585665169.html
- Joystick 1 or more : https://fr.aliexpress.com/item/1005002740079191.html
- Resonance vibrating Speaker: https://www.ebay.com/itm/163818582079
                           or https://fr.aliexpress.com/item/1005003907347243.html

So please correct me if something wrong and thanks again for your advices

[Randall (Admin)]

You've got some cool ideas.  That BT dongle is a clever solution if it works.

"Passive Preamp" usually means just a volume pot (voltage divider) and if it has a tone control, just a low pass filter (high freq shunt).  So no impedance matching (unless it contains a transformer) and no gain (unless it's powered).  Pretty sure a piezo will need both impedance matching (piezo=high, card inputs=likely low) and some gain.  I'm not 100% sure of that, cuz I despise the sound of piezo's and thus, avoid them.  I can't seem to find much documentation on the "Electret" mic input of the IQAudio Codec Zero.  Maybe they just expect a raw electret element to be connected which "may" also work for piezo, but I believe usually an electret usually contains an FET transistor to do impedance matching before connecting to additional circuitry.  Again, not sure.  But I would not assume that just because it has a "mic" input, it'll sound good with a piezo.  I'd definitely experiment before committing any part of your design to that assumption.  Ideally, you'd know what the specs are for the mic input, so you could design accordingly.  Maybe it would only require an email to IQAudio.

Regarding what you require from a Pi-Stomp board, I'd say, "almost nothing".  The pi-Stomp PCB includes: Bypass relay, footswtich debounce, Analog control ADC (MCP3008), Audio input buffering (and power filtering for the op-amp), mounts for LCD, Encoder and volume pot.  What of that do you need?  Do you need an encoder?  What will it control if you don't have visual feedback?  I suppose you could have it select presets where each preset is mapped to a single detent of the encoder rotation.

[Erajer]

Thanks, i read about in an article during my search
IQaudio are on twitter so i asked them about piezo, wait and see
In dat case can I power the pi + a preamp with the pisugar ?

For the rest, idk if i need a screen for first config at least, but the project is about acoustic. The point is add few effect and a screen to remind whats on seems overkill when I can make more elaborates setups on phone. Maybe 1 heavy board with hi gain soud for the joke.

Joysticks are a way to get multiples ctrl in a little space and  requires MCP3008. Though encoder for pedalboard selection. I 'm a total  noob in dat matter and I take the kit as it is and already build.IDK for the rest.
Are you implying I din't even need to buy the stomp core kit ?

[Randall (Admin)]

Not saying you shouldn't use a pi-Stomp PCB, but most of what it offers, it sounds like you don't require.  In fact, Chris made a system very much like your ideas before he had a pi-Stomp.  pi-Stomp adds controllability (change of pedalboard, snapshot, effect enable, debounce, parameter tweaking, system control, etc.) and signal buffering & bypass.  Mostly things for electric guitar and foot controlling.

You, on the other hand, probably just need a buffer or preamp.  That doesn't necessitate pi-Stomp.  In fact, if you need more gain than a buffer (ie. a "preamp"), the pi-Stomp PCB doesn't offer that.

You're talking about having a joystick, which yeah, can control a lot, but what are you going to control without visual feedback (eg. LCD)?  When you move it up and to the right, what the heck would that do?

And it sounds like you want to control it with your phone anyway.  So how 'bout, Implement your diagram, minus the joystick, and with a preamp that'll deal well with your input.  DONE.  No real need for pi-Stomp in that case.  It'll also be way less bulky.  No pi-Stomp PCB, no hat hacker or LCD. 

[Erajer]

Sorry for the confused explications, the point of joystick is having 4 switchs (at least) in 1 allowing me using a direction like a switch. Mostly snapshots and loop control when i'm playing
Exemple: Up and down for specifics snapshots, left for record a loop ect...

I'm sure to need the MCP for sticks (according to this article, sorry it's in french but got schematics https://raspberrypi-tutorials.fr/utiliser-un-joystick-sur-le-raspberry-pi-avec-mcp3008 ), If i get it right, i need at least a PCB for the MCP and a resistance to connect the sticks (unless I don't get it, which is fairly possible).
A volume knob is conveniant such as the transcoder for switch boards.
Maybe a rotary switch or just 2 buttons for up and down could be better solution.
And it's all I need though. and yes i want it the build thin as it can to keep it convenient.

My original built idea was about an electric guitar  for traveling with a traditional speaker and a real use of the stomp core (i guess).
But since I got a broken acoustic and knowledge about the hyvibe so I'm still trying figure it out.

If plug a piezo si such difficult, I can go magnet but in dat case, it's a lot of work with permanents drills but i think  I can make it with humbucker (single coiled format) screwed on a piece of wood who is glued on the back of guitar's body. Cuz I don't think the front can hold it by itself and I suppose post sound will be better.
Can I still do that without a full stomp core kit ? In dat case what do you suggest ?

Edit: After a talk with the luthier, magnet is too invasive for my guitar and require some tests before dig it
He think the piezo is the best thing and agree with you about the need of an active preamp.

So idk if i just power it with a battery or if i should go back to the to the powerbank

[Randall (Admin)]

You only need an ADC for an Analog joystick (which uses pots).  But a joystick like what you describe, "4 switches a'la Nintindo game controller (https://www.adafruit.com/product/504) can be used as digital input and needs no ADC, just multiple (digital) GPIO's.

[Erajer]

Really NICE !!!  It will be good with plastic cap
So I can really do it with without the stomp core kit at all
Though the soundcard took all the GPIO's pin, do I need an extension or a splitter for connect all that ?
like https://thepihut.com/products/modmypi-triple-gpio-expansion-board?variant=20063137726526

In dat case, my guess for a volume and pedalboards switching is going by GPIO too
Found a rotary for gpio https://www.tme.eu/fr/details/mikroe-3299/cartes-dextension/mikroelektronika/knob-g-click/
But it seems a bit difficult to make it work, so 1 for the volume and 2 buttons will be enough for pedalboards switching
Or USB with something like that ? https://www.amazon.com/gp/product/B07GR864FV/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1
Seems we can even do it with an old optical mouse and a spinner toy https://youtu.be/9l_ijd1mSfU
If it's right, we almost did it