Sync JamMan loop pedals to Eurorack tempo with Arduino

From circuitbending to homebrew stompboxes & synths, keep the DIY spirit alive!

Moderators: Kent, luketeaford, lisa, Joe.

Post Reply
User avatar
joeSeggiola
Common Wiggler
Posts: 189
Joined: Wed Jul 04, 2018 3:59 am
Location: Italy
Contact:

Sync JamMan loop pedals to Eurorack tempo with Arduino

Post by joeSeggiola » Sat Sep 08, 2018 10:00 am

My JamMan Solo XT pedal have an input jack that is used to sync the tempo of multiple units used together. Searching on the web, I found that people have reverse-engineered the signal protocol, so I made an Arduino project for syncing mine to a clock/pulse input, for using it with modular synths and general analog gear. It should also work with any of the other compatible models (Express XT, Vocal XT, SDRUM).

Arduino code

https://github.com/joeSeggiola/jamman-a ... n/main.ino

Features
  • Syncs JamMan looper pedals to Eurorack-like clock signals.
  • Main LED lights up when clock input is present.
  • Two additional LEDs blinks following tempo (quarters and measures).
  • The main LED blinks fast when incoming tempo is incompatible with JamMan (too fast or too slow).
  • Optional switch for selecting pulses-per-quarter (disabled by default).
  • Optional BPM display using a LTC-2727G (disabled by default).
Configuration

Parameters and pins configuration can be changed using the constants at the beginning of the code. Each one is commented.

Circuit

To detect clock pulses with the highest reliability possible, Arduino's interrupts are used. The input signal is taken from an Eurorack-like clock output using a mono 3.5" jack, with the tip connected directly into the Arduino's interrupt pin and ground to GND. The output is a MIDI-like signal on a stereo jack into the JamMan sync input, connected this way:
  • TX out (pin 1) -> 220ohm -> jack tip
  • 3.3V -> 220ohm -> jack ring
  • GND -> jack ground
The rest of the circuit is basic, just the usual resistors on LEDs pins and an on/off switch directly connected to the Arduino power source.

If the optional pulses-per-quarter switch is enabled, it must be connected to an analog pin in a way that it feeds 0V or 5V depending on the switch position. If the BPM display is enabled, check the LTC-2727G datasheet or adapt the code to a 3+ digits 7-segments display of choice.

Thanks
Pics of my build

I built it to fit on my pedalboard, but it could be easily made in Eurorack format, I guess.

Image

Image
Last edited by joeSeggiola on Mon Sep 14, 2020 4:51 pm, edited 2 times in total.

User avatar
jam457
Common Wiggler
Posts: 165
Joined: Sun Jun 16, 2013 9:37 pm
Location: Halifax, N.S.

Post by jam457 » Mon Sep 10, 2018 8:37 am

Cool! I always wondered about this! I sold my old jamman but often thought it would be cool if it could be clocked by something else. One question: can saved loops be recalled and externally clocked or can u only clock a loop u are currently recording?
Dark Beep

User avatar
joeSeggiola
Common Wiggler
Posts: 189
Joined: Wed Jul 04, 2018 3:59 am
Location: Italy
Contact:

Post by joeSeggiola » Mon Sep 10, 2018 10:12 am

jam457 wrote:One question: can saved loops be recalled and externally clocked or can u only clock a loop u are currently recording?
Yes, they will be clocked "somehow"... Depending on the length of the loop, the result may be different. The pedal cuts the loop and restart it when the measure beat "hits", to keep the given tempo; but I'm not 100% sure how the pedal "decide" when exactly cut. Anyway, that's for sure that it does not alter the loop speed to fit the desired tempo.

The same applies in case you record a synced loop from your synth, and then, while the pedal is playing it back, you slightly change the tempo of the input clock signal.

Also, this behavior is inherent the the pedal and JamSync technology itself, it does not depend on my code. It'll be the same if you clock the pedal with another unit, as intended by Digitech.

Long story short, if the saved loop is really similar in length to given tempo, the result is fine and barely noticeable, and it will not drift.

effiks
Learning to Wiggle
Posts: 4
Joined: Sat Mar 09, 2019 3:10 am

Post by effiks » Tue Sep 24, 2019 7:49 am

Works for me great with a Express XT as well.

Image

Thanks for the code and schematics.

effiks
Learning to Wiggle
Posts: 4
Joined: Sat Mar 09, 2019 3:10 am

Re: Sync JamMan loop pedals to Eurorack tempo with Arduino

Post by effiks » Sun Dec 29, 2019 4:41 am

I made a little Sync Box for my JamMan sync circuit. I also integrate the toggle switch to change pulses-per-quarter between Eurorack clock and Korg Volca input.

Image

User avatar
joeSeggiola
Common Wiggler
Posts: 189
Joined: Wed Jul 04, 2018 3:59 am
Location: Italy
Contact:

Re: Sync JamMan loop pedals to Eurorack tempo with Arduino

Post by joeSeggiola » Sun Dec 29, 2019 12:30 pm

effiks wrote:
Sun Dec 29, 2019 4:41 am
I made a little Sync Box for my JamMan sync circuit. I also integrate the toggle switch to change pulses-per-quarter between Eurorack clock and Korg Volca input.
Wow, it's cool. Great to see the project was helpful. Are you using an USB port to power it (I think I see it on the right)? I used a 9V plug directly into Arduino VIN (it can handle that just fine), daisy-chained with the pedal itself. You only need to be careful about polarity, since pedals power supply is center-negative.

PS: did you edit your post? I thought I have seen a question about the switch usage this morning, but was unable to reply. Did you find the solution yourself?

effiks
Learning to Wiggle
Posts: 4
Joined: Sat Mar 09, 2019 3:10 am

Re: Sync JamMan loop pedals to Eurorack tempo with Arduino

Post by effiks » Mon Dec 30, 2019 9:05 am

It's a very helpful and easy to build project. I use USB to power the Arduino directly. This will work great for most of my setups I thing. If I use it mobile, I can use a Powerbank (a nice llama shaped for example) or a RK-403 (9V TO 5V CONVERTER) from retrokits.com and at home I can just plug it into USB power unter the table.
Image
joeSeggiola wrote:
Sun Dec 29, 2019 12:30 pm
PS: did you edit your post? I thought I have seen a question about the switch usage this morning, but was unable to reply. Did you find the solution yourself?
Yes, I did edited the post. Could not delete it, so I changed it after finding the information myself. The Solution was not hard to find and I learned more about electronics.

effiks
Learning to Wiggle
Posts: 4
Joined: Sat Mar 09, 2019 3:10 am

Re: Sync JamMan loop pedals to Eurorack tempo with Arduino

Post by effiks » Tue Jun 16, 2020 2:39 am

Has anyone tried the reverse, sync a JamMan to Midi? Would this be possible?

User avatar
kakovich
Learning to Wiggle
Posts: 5
Joined: Sat Sep 12, 2020 2:45 pm
Location: Spain

Re: Sync JamMan loop pedals to Eurorack tempo with Arduino

Post by kakovich » Mon Sep 14, 2020 1:29 pm

Hello. Which changes are needed for adapt this project to make it compatible with Volca units?

User avatar
joeSeggiola
Common Wiggler
Posts: 189
Joined: Wed Jul 04, 2018 3:59 am
Location: Italy
Contact:

Re: Sync JamMan loop pedals to Eurorack tempo with Arduino

Post by joeSeggiola » Mon Sep 14, 2020 1:34 pm

kakovich wrote:
Mon Sep 14, 2020 1:29 pm
Hello. Which changes are needed for adapt this project to make it compatible with Volca units?
I don't know, what are the characteristics of the Volca's clock signal? If it's a simple square signal that is capable of trigger Arduino's digital input (at least 3V I'd say), it should work as it is. Keep in mind you can adjust the pulse-per-quarter constant before compiling the code.

User avatar
kakovich
Learning to Wiggle
Posts: 5
Joined: Sat Sep 12, 2020 2:45 pm
Location: Spain

Re: Sync JamMan loop pedals to Eurorack tempo with Arduino

Post by kakovich » Mon Sep 14, 2020 1:51 pm

joeSeggiola wrote:
Mon Sep 14, 2020 1:34 pm
kakovich wrote:
Mon Sep 14, 2020 1:29 pm
Hello. Which changes are needed for adapt this project to make it compatible with Volca units?
I don't know, what are the characteristics of the Volca's clock signal? If it's a simple square signal that is capable of trigger Arduino's digital input (at least 3V I'd say), it should work as it is. Keep in mind you can adjust the pulse-per-quarter constant before compiling the code.
As I read in other post "The sync in/out on the Volca works directly with euro, but for some reason, it's at half the speed you would expect, i.e. it sends one clock pulse every two steps. Or it moves two steps for each clock pulse it receives, one step at the start of the pulse, one step at the end of the pulse. Having a clock multiplier or divider becomes very useful."

So if as you say it can be fixed just from the code, I will try to build your project. I'm not an expert but I know the basics + motivation.

Source post: viewtopic.php?t=129241

User avatar
joeSeggiola
Common Wiggler
Posts: 189
Joined: Wed Jul 04, 2018 3:59 am
Location: Italy
Contact:

Re: Sync JamMan loop pedals to Eurorack tempo with Arduino

Post by joeSeggiola » Mon Sep 14, 2020 2:56 pm

kakovich wrote:
Mon Sep 14, 2020 1:51 pm
The sync in/out on the Volca works directly with euro, but for some reason, it's at half the speed you would expect, i.e. it sends one clock pulse every two steps.
Well, I didn't expect that. The code does NOT multiply incoming clock, it only divides it. In other works, you can only set an integer pulse-per-quarter value, so you can't set one pulse to advance two quarters. You could implement that, but probably it won't be necessary, the pedal will just be two times slower, but it will be synced. I suggest you to try as it is and check how it behaves, before putting time and effort into adapting the code for clock multiplication.

User avatar
kakovich
Learning to Wiggle
Posts: 5
Joined: Sat Sep 12, 2020 2:45 pm
Location: Spain

Re: Sync JamMan loop pedals to Eurorack tempo with Arduino

Post by kakovich » Mon Sep 14, 2020 3:37 pm

joeSeggiola wrote:
Mon Sep 14, 2020 2:56 pm
kakovich wrote:
Mon Sep 14, 2020 1:51 pm
The sync in/out on the Volca works directly with euro, but for some reason, it's at half the speed you would expect, i.e. it sends one clock pulse every two steps.
Well, I didn't expect that. The code does NOT multiply incoming clock, it only divides it. In other works, you can only set an integer pulse-per-quarter value, so you can't set one pulse to advance two quarters. You could implement that, but probably it won't be necessary, the pedal will just be two times slower, but it will be synced. I suggest you to try as it is and check how it behaves, before putting time and effort into adapting the code for clock multiplication.
Understood, I will try that. Maybe @effiks can bring some light here.
I will update you as soon as I have something done.

Thanks!

User avatar
kakovich
Learning to Wiggle
Posts: 5
Joined: Sat Sep 12, 2020 2:45 pm
Location: Spain

Re: Sync JamMan loop pedals to Eurorack tempo with Arduino

Post by kakovich » Sun Sep 27, 2020 3:50 am

It works! It behaves perfectly fine, but with the main LED blinking every two steps of the Volca, and with secondary LED blinking per quarter (8 total steps of the Volca). So I just press "play" in my Volca Sample in time with the quarter LED, so my loop will start with the sequence of the Volca. This is enoguh for making it work nice, but I guess the expected behaviour is the main LED blinking on every step of the Volca.

I'm also powering it with a powerbank via USB. Right now works for me like that, let's see if I go with the 9V input.
Also: this is very interesting because with your code it's possible to take the signal and sync it with some visuals using Processing. I will try that.

Thank you for your time and your help! This is great.

IMG_20200927_102541.jpg
You do not have the required permissions to view the files attached to this post.

User avatar
joeSeggiola
Common Wiggler
Posts: 189
Joined: Wed Jul 04, 2018 3:59 am
Location: Italy
Contact:

Re: Sync JamMan loop pedals to Eurorack tempo with Arduino

Post by joeSeggiola » Sun Sep 27, 2020 8:29 am

Great!

kakovich wrote:
Sun Sep 27, 2020 3:50 am
the main LED blinking every two steps of the Volca, and with secondary LED blinking per quarter (8 total steps of the Volca) [...] I guess the expected behaviour is the main LED blinking on every step of the Volca.
If it's true that the Volca sends one pulse every two step, this is the consequence. The only way to "fix" this, is to use some code in the loop() function to guess the correct timing to run pulseFlagSet() in between two input pulses: that way you are artificially multiplying the input clock.

kakovich wrote:
Sun Sep 27, 2020 3:50 am
let's see if I go with the 9V input.
It will work, the Arduino should run fine with up to 12V on the Vin pin. Just remember that the polarity of the pedalboard power bus (daisy-chain or whatnot) is center-negative!

User avatar
kakovich
Learning to Wiggle
Posts: 5
Joined: Sat Sep 12, 2020 2:45 pm
Location: Spain

Re: Sync JamMan loop pedals to Eurorack tempo with Arduino

Post by kakovich » Sun Sep 27, 2020 9:40 am

joeSeggiola wrote:
Sun Sep 27, 2020 8:29 am
If it's true that the Volca sends one pulse every two step, this is the consequence. The only way to "fix" this, is to use some code in the loop() function to guess the correct timing to run pulseFlagSet() in between two input pulses: that way you are artificially multiplying the input clock.
Okay, this is embarazing but I discovered in the advanced settings of the Volca that we can choose between send one pulse per one step or one pulse every two steps. By default is one pulse per two steps,

So yes, problem solved!

Post Reply

Return to “Music Tech DIY”