Remote rehearsal gizmo: the Phone Jam

"May the music passing
through this device give
joy to all that hear it"

ok, after a bunch of testing and tweaking, I've got two prototypes that don't sound too bad:


The idea is you plug a mic and an instrument into the jacks on the left, your phone in the center, and headphones on the right.  The knobs are for various levels.  There is one switch for taking the device on and off-hook.  Yep, it works like a phone!  Ran into a snag though:  I thought that gaming headset mics would work just like regular mics.  Wrong-o, brainiac 5. They are a bizarre little interface that needs a small bias voltage applied (we're talking 3.3 to 5 volts here) and a whack of gain otherwise they don't work.  I had to make a quick prototype of my soon to be patented "crappy headset mic to balanced XLR" conversion device, which is the green thing in the middle. 

Early tests showcase the limited bandwidth on phone lines, and some kind of 60Hz hum on the phone line that I need to figure out.  Otherwise, they actually work!



  • PhoneJamProto.jpg
    487.1 KB · Views: 361
This is such a good idea. I can see them being useful even after this virus business blows over. You may have something that could be a marketable item.
Needs more R+D... And cowbell. 

Fantastic job so far Sir. I am in Awe. :headbang: :headbang:
Mayfly said:
I'm imagining a box where you plug a mic, your instrument, and a set of headphones into it, then connect it to a household phone jack.  You make a call using your phone, get connected, then start using the Phone Jam box to play music together.  You hear yourself well, and the other people well-enough.

I'm at the prototyping stage and have some initial schematics.  More to come.

Back around 1988 or '89 I worked for the late audio engineer Eric Small, and I was once talking to him about a hypothetical device that was similar to what you've described...Eric goes "oh, you mean a telco hybrid!" and jumps up from his chair, runs out of the room, and 60 seconds later comes back holding a DIY Bud box with an 1/8" TRS jack on one side and a pigtail terminated in an RJ-11 plug on the other side. It worked great for recording phone conversations and/or playing rough mixes over the phone for clients. Not sure what was inside it, but I'm guessing very little (maybe just a transformer?) because it was completely passive.

Not sure whether I still have it, but I kept that widget for years. Thanks, Eric!
Yup!  Mine has a transformer in it as well :)

Update:  my violinist and I tried the boxes over a phone call and they functioned just fine. 

BUT!  Even though we live within blocks of each other, there was juuuust enough delay to ensure we could not play in time.  Pissed me off.  So the project is dead sadly.

Isn't that always the case ... not enough bandwidth.

At least you're close to each other so you could run a wire between the houses ....  Nah, on second thought, probably not worth the bother of getting a permit from the town. 

Currently we're just rehearsing on the porch.  works great now, but won't be so cool when winter comes...
Mayfly said:
Currently we're just rehearsing on the porch.  works great now, but won't be so cool when winter comes...

I'm curious how this worked out for you? There was a time when most long distance landline connections were routed via satellite with a minimum lag of 1/4 second. It might be that in some areas local calls are no still not packet-switched and packet switching has improved a lot, still I don't know what LL latency is like today). I do know physical signal latency is an important aspect of backbone high speed links.

Anyway, was your use-case all relatively local? How's it worked out?

Hey Sadie,

I gave it a couple of tries with my violin player.  There was still noticeable delay, too much to play together unfortunately.  And my (lack of) line telephony knowledge meant that the sound was not that good.  If I were to do it again I'd use better bandwidth filtering and companding to improve the signal and better sneak it though the local exchange unmolested.  But, it did function.  Still have the prototypes.

Our final solution was to rehearse on the porches and back yards of various band members, and to use jamulus in the winter time with me hosting the server.  Jamulus was ok, but still not really great.  The women in the band were getting pretty frustrated with the thing dropping out and connections lost etc.  And their kids were getting frustrated with the moms stealing all the equipment!  :)

But ... it's summer!  And we had our first gig in a long time last month with more on the way!
That's awesome, so good that live gigs can happen again, we're not out of this yet, at least there's progress to something more like normal.

Jamulus sounds pretty great, a few months back I'd looked at ninjam and didn't find it was easy to build on current Linux versions. I'll install a jamulus client and give it a go.