Messages

1

Building pi-Stomp / Re: Pi-stomp with a mic preamp

« on: September 12, 2022, 05:33:34 PM »

Update...
Okay, I'm bringing some news...
The unit is working as a dream, and the casing is getting beautiful as I wanted.
Therefore, I used in a live situation and noticed that my wish for 5 footswitches somewhat spoiled the design.
As I will control guitar and vocal effects, I wanted as many footswitches as possible, with the one in the upper left being used to bypass and preset changes.
I thought that the upper footswitch would be difficult to press without stomping another switch together, but instead, it happens with the lower buttons.
Now I'm questioning myself if I close the center buttons, make one in the center and live with 4 footswiches or... Design a 3d printed case! I believe that I can help other that wish to use RPi4 or another similar design.

While it's not decided, I'm working with tweaking some software.

I'm providing attached some pictures, please tell me what you think.

Regards,

2

Building pi-Stomp / Re: How realistic is it to try and use the pi-Stomp as vocal/acoustic guitar fx

« on: August 10, 2022, 08:55:39 AM »

Very nice!
I had a hard time dealing with noise in my preamp, but in the end the problem was something in my raspberry pi that was injecting noise, and the noise was gone when I swapped the board.
I tried a similar bipolar psu, but it did not have common ground.
Are you satisfied with the sound quality of your design? Which chip is it based?
Regards,
Rene

3

Building pi-Stomp / Re: How realistic is it to try and use the pi-Stomp as vocal/acoustic guitar fx

« on: August 03, 2022, 08:25:46 AM »

Hello, jvphotog!

I am working on a full preamp with phantom power on stripboard.
If you have DIY Layout Creator installed, you can open the phantom power section on the attached file. (check out DIY Layout Creator on google, is a very cool open source tool for DIYers).
The XL6007 must be put in a DIP-8 adapter.
Again, I did not test it yet.

There is also project 193 from sound-au (https://sound-au.com/project193.htm), it says that it could power up to two microphones from 5V.

4

Building pi-Stomp / Re: Pi-stomp with a mic preamp

« on: July 28, 2022, 07:42:25 AM »

To anyone interested, I designed a stripboard version of the INA 217 preamp which I provide attached.
I did not test it yet, please let me know if you try it.

5

Building pi-Stomp / Re: Pi-stomp with a mic preamp

« on: July 28, 2022, 06:36:20 AM »

Hello pi-stompers!

I'm back after finishing my project and I have to tell that I am VERY satisfied with the results. It works exactly as I intended.

I'm providing a diagram of the final version to anyone interested.
The preamp pcb that I used can be found here: ebay.com/itm/114326622246, and the bipolar converter can be easily found by the name DD1718PA (yes, is that cheap, but works really well with the INA217).

About the noise issue, I discovered that it was some problem in my Raspberry pi that was injecting noise in the system, and everything worked flawlessly with a new pi.
As shown in the diagram, I installed an inductor in the 5V line from the power barrel to the DD1718PA. It helped reduce noise in the former situation with the defective pi, but I believe it should be no more required.

6

Building pi-Stomp / Re: How realistic is it to try and use the pi-Stomp as vocal/acoustic guitar fx

« on: July 18, 2022, 03:27:36 PM »

Hello, Randall,

It looks like your "universal board" is based on the sound-au design, correct?

Yep, the "universal board" is based on the sound-au project. It was actually a bad translation, and by "universal board" I was trying to say it's for a perf board.

Did you find any need to regulate the output of your boost converter or just the inductor?

I tried many things on the input and output of the boost converter, including regulating the input with the AMS1117 and the outputs with LM7812 and 7912. The only thing that made a difference was the inductor at the input. It is worth mentioning that the DD1718PA has many versions with outputs ranging from +/-5V to +/-24V, and I bought two of +/-12V and two of +/-15V. The latter is what I used with the regulators.

Have you seen any supplies that offer both a bi-polar (12 or 15v) plus an additional high voltage (30+)?

I haven't found any board that has all these output options built in, but since the requirements for a preamp and phantom power are very low in terms of current, even two cards would take up little space. In the case of an addon, I believe the best would be to make a board with everything (preamp and converters) included, I may try to do this in a perfboard in the future, after finishing my project.

Thank you!

Rene

7

Building pi-Stomp / Re: How realistic is it to try and use the pi-Stomp as vocal/acoustic guitar fx

« on: July 18, 2022, 11:37:27 AM »

Hello, jvphotog.
Glad you read my thread, I hope it was helpful for you.
I didn't have time to write my progress there yet, but I've already finished the mic preamp of my project, and I'm quite pleased with the results.
The preamp I used is based on typical applications from Burr Bown's INA217 datasheet.
It's referred to in many places as "the famous $5 preamp", and you can read more about it here: https://www.audiomasterclass.com/blog/the-famous-5-preamp-everything-you-need-to-know
I bought a PCB for it from the following link: https://www.ebay.com/itm/114326622246. I just populated with the components, as you intend to do.
For the positive/negative psu, I bought a small board called DD1718PA, you can find it in several places. It is very cheap and I was impressed with it. To take care of the noise, I just had to put a 10mH in series with the Vin, which was taken from the 5V that I used to power the pi-stomp.
I believe that the board that you linked will work similarly, as it is based on the same opamp.

This project is also worth mentioning: https://sound-au.com/project122.htm
Building it would be even cheaper, and I started designing a circuit for a universal board, which I provide attached. Please mind that I didn't build it, it is just a concept. If you try it, please let me know how it works.

Randall, I've provided some links here, please tell me if you want them removed. I only intend to help, there are no affiliate links at all.

If you need further information, I'll be glad to help.

Regards,
Rene

8

Building pi-Stomp / Re: Pi-stomp with a mic preamp

« on: June 20, 2022, 11:35:09 AM »

Hello,

Okay, I have the final result of my tests.
I bought some inductors to check if it would help, and it turns out that using a 10mH inductor in series with the 5V line eliminated the need for any other component for filtering, the noise is pretty low now.
Thank you for the guidance.

Now I have another issue.
There is a high pitched noise, apparently at a specific frequency whenever I turn the pistomp on.
It seems to come from the pistomp's preamp, as I could find by removing its connections from the audio card's input.
I've already tried some things:
- completely remove the mic preamp circuitry
- use different power supplies (included the one supplied with the kit)
- change cables and connectors

The only things that works are:
- short the 5V input to gnd briefly, then it reboots with no noise
- power it into the raspberry pi input, then disconnect and power into pistomp input (works some times)

It already presented this problem backwards, as I described here:

...Connected to the raspberry pi 4B power input, it behaves normally, without any noise, until a random moment when a whining starts.
The noise doesn't stop even if I reboot or unplug power and wait to turn it back on....
... the only solution was to power it from the pi-stomp power input....

I believe I may have broken something in the assembly or in the many tests I did, but I have no idea how to troubleshoot it. Do you have any clue?
I'll try to get an oscilloscope to find the noise frequency and I also can provide more information if needed.

Thank you,

9

Using pi-Stomp / Re: Mono plug in output jack

« on: June 20, 2022, 08:33:49 AM »

Hello, Randall,

Thanks for your detailed response.
In my case with the Pi 4B and the 1590D enclosure, I'll not solder the jack directly to the board, and so I'll install two output connectors, as I have plenty of space.
In fact, the reason of my question was to decide if I'd route the output #2 to the ring of jack #1 in case there is nothing connected to jack #2.
It would give more flexibility, but I think I'm just leaving it out for the moment, as I don't have a use case in mind. If I need it in the future, it's a quick mod to make it with a small resistor.

BTW, about using the Pi 4B, it has different power requirements than the 3B and 3A. Despite the current being 3A, I measured the consumption and it never passes 1.2A with pi-stomp (and also a mic preamp). Even though the PSU supplied has 2A, the cpu was getting throttled by low voltage.
I researched a little and discovered that the Pi 4B requires 5,1V. I tweaked a 4B psu with a compatible power jack and now the throttling is gone.
I'm just letting you know because I believe it would be good if it was noted on the hardware customization guide, in the pistomp wiki.

Regards,

10

Using pi-Stomp / Mono plug in output jack

« on: June 13, 2022, 09:14:02 AM »

Hello, Randall,

I was wondering what would happen if a mono plug is inserted in the output jack.
The output #2 will be shorted to ground, is there no risk of the audio board's output chip getting damaged?

Regards,

11

Building pi-Stomp / Re: Pi-stomp with a mic preamp

« on: May 30, 2022, 01:41:08 PM »

You are right, I'm learning a lot.

I tried using the pi-stomp's AMS1117, but I didn't want to solder a new wire to it, therefore ended up buying a little module with AMS1117.

12

Building pi-Stomp / Re: Pi-stomp with a mic preamp

« on: May 30, 2022, 12:41:18 PM »

Hello,

I'm back with more news about the preamp.

After several tests, I believe I have defined the final version of the power supply circuit.
In order to have a noise reference, I supplied power to the preamp with 9V batteries like the original design (4 batteries to get +18/0/-18V), and it is really very quiet. Then I powered the symmetric psu with the 9v battery, and got impressed as the preamp presented the same behavior of when it was powered directly by the batteries. The DD1718PA does a really good job, as it's switching frequency is very high.
Given that, I concluded that the noise I was getting was from the wall wart, and had the idea to use LDO regulators, as the DD1718PA accepts inputs as low as 3V. I bought a little module with the AMS1117-3.3V already soldered and some filtering circuit, all smd, therefore very small footprint.
The noise got better than before with the power (filtered) from the wall wart, but there was still a not acceptable noise.
The next thing I accidentally discovered was that grounding is very tricky. Running another wire from the preamp ground to the audio card ground reduced drastically the noise. I believe that there was some problem with the cable I soldered to the board, as those jumper wires are very thin.
There were still a little noise, and I was playing with RC filters on the AMS1117 inlet, then I got minimal noise with an RC filter with a large capacitor ( I believe it was 2200uF) and an 8 ohms resistor (couldn't be a large resistor because the AMS1117 has minimum required input tension of ~4.75V).
The strange thing is that I removed the capacitor and the noise didn't change, then I removed the resistor and realized that it was really it that was improving the noise, checked many times to confirm. Is it something normal/reasonable?

Anyway, I'm attached the updated schematics.

Regards,
Rene

13

Building pi-Stomp / Re: Pi-stomp with a mic preamp

« on: May 17, 2022, 06:50:30 AM »

I read this text yesterday when I was searching for this subject, very informative and fun, indeed.
I'll try it in the next iteration, but it is not a great deal. Even if it stay like this, all I have to do is mute the output prior to switching, or choose the right preamp before turning it on.
I'm providing attached a picture of the preamp.

14

Building pi-Stomp / Re: Pi-stomp with a mic preamp

« on: May 16, 2022, 10:00:55 AM »

Ps: Do you have any tips for eliminating pop noise when switching input #2 from pi-stomp preamp to the mic preamp? It happens both ways, and at the moment the mic preamp is powered all the time.

15

Building pi-Stomp / Re: Pi-stomp with a mic preamp

« on: May 16, 2022, 07:15:16 AM »

Hello,

I tested with the rc filters and it got the job done pretty well.
I also had to put an rc filter in the 5V inlet of the symmetrical power supply.
In the many tests I did, there was sometimes a very high pitch noise that I found to be from the pi-stomp preamp. It seems to be a very specific frequency.
Don't know exactly what triggered it, but to stop it I had to unplug the ac adapter and wait for a long time ~10min.
I believe that it was caused by connecting and disconnecting things on the fly, but one thing that surely caused it was when I tried to take the 5V for the symmetrical psu from the RPi GPIO. Have you ever faced it?

I'm very excited that my plans are going further.
Now there are minor things to solve:

- put the rc filters in a board.
- will the stereo/mono auxiliar output work as intended?
- will the toe switch on the expression pedal work?

After that, I'll start the work to get it into enclosure.
Thanks for the help up to now.

Regards,
-