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...
Board...
(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?
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...
An externally hosted image should be here but it was not working when we last tested it.
Board...
An externally hosted image should be here but it was not working when we last tested it.
(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?
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.
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
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
Hi,
I dont really have any intention to implament a input selector, this would mean a bigger microcontroller, new firmware, bigger power supply etc.
I dont really have any intention to implament a input selector, this would mean a bigger microcontroller, new firmware, bigger power supply etc.
rhysh said:
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 🙂
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
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
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.
Yes, i have used them both in previous projects, infact the schematic was drawn with 2320's, i dont know why i wrote 2310...
Rhysh, Does TI make a 10k version of this volume control? I have found that some projects will not respond fully with the 100k attenuation.
Tad
Tad
Decoupling caps
I am sure you already planned it, but just in case...
I would definitively add power supply decoupling capacitors (10 or 100 nF) close to each PGA2320.
Nice work
Cheers
Andy
I am sure you already planned it, but just in case...
I would definitively add power supply decoupling capacitors (10 or 100 nF) close to each PGA2320.
Nice work
Cheers
Andy
Rhysh,
What type of encoder are you using on this volume control? Are they expensive?
Is a buffer really necessary for most applications being driven by a CD player? I thought the PGA units had small op-amps already imbedded in them so they can drive 600 ohm loads.
I am in on this when boards eventually become available.
And next up a relay/mosfet based volume control which has only one set of resistors in the line at a time. Maybe? It would be nice to learn how to program the controllers for one of these.
Tad
What type of encoder are you using on this volume control? Are they expensive?
Is a buffer really necessary for most applications being driven by a CD player? I thought the PGA units had small op-amps already imbedded in them so they can drive 600 ohm loads.
I am in on this when boards eventually become available.
And next up a relay/mosfet based volume control which has only one set of resistors in the line at a time. Maybe? It would be nice to learn how to program the controllers for one of these.
Tad
tryonziess said:
Hi,
Rotary encoders are cheap, you can get high quality optical encoders for not a lot of money.
Not necessary for most applications but it would be nice maybe, im going to get my act together with this now as i need a volume control!
I was thinking about a relay based control, but there are allready loads of them out there so there wouldnt really be any reason for another one!
Im thinking of ways to power this thing now, i may use a PCB mount transformer etc or just use a wall wart and split the supply...
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