Hello, everyone!
Since I’ve been posting in other threads about what I’m trying to implement with pi-stomp, I decided to write a dedicated thread to talk about my idea.
I intend to use the pi-stomp for vocals and guitar, but also want it to be flexible to fit into other scenarios that may come up in the long run.
Below is the list of features that I plan to make different from the standard design:
1) A mic preamp inside the enclosure
I chose the “famous $5 preamp” design and bought a PCB from a UK supplier on ebay. It's a balanced preamp, and it requires a dual (positive/negative) voltage power supply, which will be a challenge. If anyone is interested, there is a lot of information about this preamp on the web by searching “famous mic $5 preamp”, which is based on the typical applications section of the INA 217 datasheet.
The preamp will be available on input #2 (Right channel), and there will be a pot for mic gain control. There will be a lever switch to choose the audiocard input from the output of the pi-stomp preamp or the mic preamp, and also turn off mic preamp when not in use.
For ease of use, the preamp power shall come from the same PSU as the pi-stomp. For this I have two options:
- An external PSU of ~18V with an internal board to step down to 5V/3A for the pi-stomp, and a divider to -15/0/+15V to the preamp.
- An external 5V PSU to pi-stomp, and a board to step-up/divide to power the preamp at -15/0/+15V.
I bought prebuilt boards for both options, but I’m still waiting deliver, then I’ll see which option is better. I prefer the second approach as there are fewer components and the conversion only takes place in the preamp, which requires very low current.
2) 5 footswitches with a led to each one
The two extra leds will come from the unused 5-pin midi ports, as explained in another thread here on the forum.
3) 3 analog control knobs. I may put more, depending on what will fit inside the enclosure.
4) Expression pedal input
The expression pedal input doesn’t really differ from the standard design but I’m thinking of hacking my cheap expression pedal to put a toe switch on it and a TRRS jack or another jack that provides 4 pins. The toe switch would be connected in parallel to footswitch #5 to enable a wah, for example.
5) Monitors out
The pi-stomp outputs will be on separate mono jacks, so that they can be routed to different places as one should carry guitar signal, and the other the vocals.
I plan to use the audio card's headphones as the monitor out, to connect to my personal monitor. It will have a stereo jack and a switch to select the output as stereo or to mix the signals into mono.
I’m using resistors to connect the signals as seen in many audio applications forums, but I haven’t tested yet to see if it will work as intended.
6) 1590D enclosure
It will take extra work to remove the central screws lugs, but I think it will worth it. Even though is a big enclosure, it will also be a challenge to fit everything inside it, and I’ll see how it fits once I have all the parts in my hands and test everything.
For now, I've built a cardboard box the same size as the 1590D, and it looks like it will fit all I need. If it doesn’t fit, I may design and print an enclosure on my 3d printer and shield it with adhesive copper, like people do to shield the cavities of the guitars.
It's a little difficult to get the necessary parts here in Brazil because most of them must be imported with long wait and taxes. Therefore, I may take a time to conclude it, but I’m already having fun with my guitar.
To better organize the design, I made a schematic of it, and I provide attached in case anyone is interested.
I’m also looking for the opinions and suggestions of the community, so please let me know if you have any questions or comments.
Thanks for your interest and time if you've read this far.
