XAR: Digital Balanced Volume Control - diyAudio
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Old 15th March 2009, 09:36 PM   #1
rhysh is offline rhysh  United Kingdom
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Default XAR: Digital Balanced Volume Control

So today i was thinking, after i have upgraded my system to balanced, how am i going to change the volume?

I had a few requirments;

Supports balanced audio
Accuracy between channels
Very little wiring
Cheap
Small
Transparent
Last but not least, high quality

So what did i come out with?

A volume control system, that will take PCB mounted XLR jacks that uses a pair of PGA2310's to alter the volume level controlled by a AVR ATTINY44 microcontroller, interfaced by a rotary encoder.

The thing i love about this design, is that there is no need for signal hookup wire! All that is needed is a 15V +/- supply to make this thing work.

How big is the board?

Tiny! we are talking 44mm x 108mm. I ask you to find a smaller volume control that also offers onboard connectors.

Okay so lets have a look...

Schematic...
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Board...
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(Board routing looks messy becuase of the resolution. This is not the case.)

If there is enough intrest, i will be doing a group buy on this, along with offering pre programmed microcontrollers.

Its not finished, i need to mess around with the decoupling and power supply but you get the basic idea. Its designed to fit at the back of a hammond enclosure and still leave enough room for an IEC connector, so a linear power supply can be used.

It is a true volume control only, gain is disabled.

So there we have it, a near 100% accurate balanced volume control that can be built for less then $50?
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Old 15th March 2009, 10:00 PM   #2
rhysh is offline rhysh  United Kingdom
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I forgot to mention, as i am going to be using rather long interconnects, im going to add a simple opamp buffer to the PCB.
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Old 16th March 2009, 10:19 AM   #3
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Rhysh, You can count me in for a set of these when they are up and running. Tad
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Old 16th March 2009, 12:55 PM   #4
SRMcGee is online now SRMcGee  United States
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rhysh:

Looks very promising! But how much more effort would be required to add source selector capability? It would be nice to have 2 or 3 sets of balanced inputs and perhaps a single-ended input set as well.

Regards,
Scott
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Old 16th March 2009, 03:20 PM   #5
rhysh is offline rhysh  United Kingdom
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Hi,

I dont really have any intention to implament a input selector, this would mean a bigger microcontroller, new firmware, bigger power supply etc.
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Old 16th March 2009, 04:07 PM   #6
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Default Re: XAR: Digital Balanced Volume Control

Quote:
Originally posted by rhysh
Transparent
Last but not least, high quality


What kind of preamp would such a volume control suit without becoming a transparency eye-sore? Probably one designed around 5534 or similar opamps. At least it will be well balanced
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Old 16th March 2009, 06:21 PM   #7
rhysh is offline rhysh  United Kingdom
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Power supply is now onboard, all that is needed is a 12v wallwart.
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Old 16th March 2009, 07:13 PM   #8
rhysh is offline rhysh  United Kingdom
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Click the image to open in full size.
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Old 17th March 2009, 04:34 PM   #9
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Rhysh,
I have read some of the threads concerning the solid state volume controls. Is the Texas Instruments version considered to be close to the head of the line in this area. Tad
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Old 17th March 2009, 09:52 PM   #10
rhysh is offline rhysh  United Kingdom
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I would say the Texas Instruments version is the best out of the standard range, but this is debaitable like everything else. I couldnt tell the diffrence between a PGA and a stepper.
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