Remote rehearsal gizmo: the Phone Jam

mayfly

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ok, so I'm trying to find a way to conduct rehearsals with the band.  Typical video conference software (zoom, facetime, skype) do not work because of the latency - you just can't play together.  I did hear of a project called LOLA that is supposed to offer real-time networked rehearsal, but for that you need special hardware and, get this, a 1Ge network connecting everyone.  Yea we just don't have that.  In addition, my band-mates are not at all technical and would not be able to make that work (especially since I'm not there to help).

So I took a step back and thought "ok, what communication thing has zero latency, is simple, and everyone has it".  The answer is the telephone.  Land lines to be precise.  I'm thinking if we can get instruments and vocal mics into it, and if everyone can hear it, we should be able to practice.  Now, it will sound like crap (only 3kHz audio bandwidth), but if I did it right at least YOU would sound great.  :)  More than two people will need a conference all, but that's do-able.

Enter the Phone Jam.  At least that's what I'm calling it.  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.
 
Very cool.

The more things change and the more hitech solutions the world gives you, sometimes you realise that the old stuff always worked best. After all ...
 
Phone Jam. What a fine idea. :sign13: I hope it works out well for you.
 
ok this is what I got so far: a sh*t pile of schematics:

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Fortunately most this I have built before when I designed a live sound mixer for my band.  The new stuff includes the telephone hybrid interface and the headphone driver.  Both of these I prototyped and got them working.

The telephone hybrid interface, and telephone stuff in general, is a funny thing.  It's 100 year old analog technology that manages to put input and output onto the same 2-wire cable.  It does this with a clever mix of current and voltage waveforms that are decoded in your (old school) phone with a transformer.  I managed to get my hands on an old application note for digital modems from National Semi which had a solid-state implementation.  I prototyped it and it actually works:  I can receive audio, and send audio independently.  I'm still pretty nervious about the 90VAC ring tone mind you.  Here's the prototype:

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I prototyped the hybrid phone interface and the headphone amp; everything else I had built before.  I can't take credit for the headphone amp: It's a complete lift from Douglas Self.

More to come.





 

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Gee, I wonder why I'm suddenly feeling very electronically inferior right now. I have to follow a schematic just to hook up one pickup a volume pot and an input jack.
I stand in wonder before the Master... :headbang:
 
Moving fast with this.  I've started laying out the PCB.  I'm making it larger than normal just so I can place everything and get it routed with minimal effort.  Even so, here's what I have to deal with:

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The board is on the right, and everything that I need to put on it is on the left.  Each line represents a connection that I need to make.  The pots, switches, diodes, and chips are placed already; the pot/switch/diode positions are dictated by the mechanical design, and the chip locations are dictated by the pot positions.

Here we go.
 

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I'm with Phil and Magnus. I kind of feel like a deer in the headlights. Blink, blink. :icon_biggrin: :icon_thumright:
 
Sorry guys.  I'm moving a bit quickly to explain stuff like I usually do.  That and I'm home-schooling the kids while I'm trying to develop this thing.

Speaking of that, here's where the board is at now:

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worked most of the night and part of today on it.  Now I need another PCB for the connectors...
 

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Blink. Blink.

:laughing11:

I respect your impressive understanding of this stuff. I can think of numerous amps, pedals and whatnot I'd get to making.
 
Working fast on this.  Here is the connector PCB:

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I threw caution to the wind and ordered both PCBs from good old Seeed Studios.  I selected fast shipping - let's see how fast I can get them!

Now on to mechanical design...
 

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With the boards on order and the parts on order, I put my mind towards mechanical design.  I immediately found mistakes that I made on the board design  :).  The main one is the power LED should be 10mm to the right.  Turns out I also forgot to order sockets for the chips on the board.  Will sort that later.

Anyway, I designed the mechanicals using an off-the-shelf hammond box with a custom cover plate.  The box is too big for the electronics (it's 7x7x2 inches), but it's the smallest one that fits.  A smaller custom box will be a priority once I make sure the protos work.  Here's the cover plate:

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I think that maybe - just maybe - the sones have more resources than the rest of us. :)  (See the bandwidth requirements of the LOLA project above)
 
Update:  I got the boards back from the board shop:

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These and a big bag of parts from Mouser.  Let's go!

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