BPPBP - Bruno Putzey's Purist Balanced Preamp (well a balanced volume control really)

I've adapted DimDim's Lascalla code for Han's 64 step board and the 4 input controller, but have spent too much time trying to be fancy using the pushbutton to select inputs and outputs. I'm thinking if I get it working for input only, I can just use a 2 way switch to select either of 2 outputs (still using the Arduino and I2S/relays).
I've kept it simple with a binary led display for the volume control, and led's for the input selection, to have a cleaner look than an LCD display and all of the issues around mounting, etc..
 
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Example Arduino sketch to control VolCB board

I put together the attached Arduino sketch. It controls Hans Polak's 64-step VolCB and 4InputSelect boards. For simplicity, it uses two rotary encoders, one to select input, the other - volume. Use it as a starting point.
 

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I put together the attached Arduino sketch. It controls Hans Polak's 64-step VolCB and 4InputSelect boards. For simplicity, it uses two rotary encoders, one to select input, the other - volume. Use it as a starting point.
Amazing - thank you! With three young children around I don't have much time to code, so this is a huge help.

Already using the 16-step controller, which is excellent!!
 
Dear All,

I built the circuit with the original board from eurocircuit that I got with the Linear Audio book.
I am having only the hot phase out. Strange that this affects both channels and both inputs in the same way I am kind of puzzled. I am trying to trace the signal.

At R7/R16 I see the two phases (My input has phases shifted 180 degrees).
When I get to R2/13, on one side I see the signal in opposite phases on the other side they have the same phase.

Not sure how this is possible.

Any hint ?

Thanks,

D.
 
It is a common misconception that balanced output must have two anti-phase ground referenced signals on hot and cold wires, even though some balanced outputs do work like that. To quote the original article (page 3):
Take-home messages
Differential transmission of audio doesn’t mean you need to make a symmetrical voltage.
An input that expects a symmetrical signal is not differential because it’s trying to involve a third node into the equation whereas voltages are only measured between two nodes.
The BPPBP circuit is not designed to drive both hot and cold outputs in anti phase - it should be clear from the schematic. You get one output signal between the hot and the cold wires, not two ground referenced signals in anti phase.
 
This is my plain vanilla implementation.
Partly done with scrap parts:
The chassis is from an old Russian multi channel analyzer
The transformer from a Japanese signal generator
The panels used to be a door

The only interesting bit is the mechanical demultiplier that I also took from the signal generator. I still have to produce a decent concentric knob, but basically when you turn the outer ring you act straight on the pot.
When you use the inner ring (where the knob is now connected) the pot turns very slowly. I hope that this device, together with a mechanical stopper (also to be done tomorrow), will make the system usable. I only made measurements so far, will listen tomorrow.

Regards,

Davide
 

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