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Old 7th December 2008, 09:05 AM   #1
rhysh is offline rhysh  United Kingdom
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Default Intrest Check : Pretty Simple Digital Preamp / Volume Control

I am in the process of designing a pcb for a digital preamp & volume control. The volume level is controlled by a PGA2320, which is connected via serial to a ATtiny44 microcontroller. A rotary encoder or pushbuttons can be used to set the volume level, aswell as a pushbutton to fully mute the system. The PGA2320's gain can be turned on or off with a onboard jumper.

On the input side of the PGA2320, i am using a OPA2134 buffer, with a gain of 0db, or 6db (user set), and on the output side i am using another OPA2134, with a gain of 6db, which is also user ajustable.

This board features single ended input, the outputs are balanced AND single ended , (balanced via drv134 opamps on board). The whole thing only needs to be powered by a split rail 15v supply as there is additional regulation on board. I expect the final board size to be around 3"x2".

The board features seperate analogue and digital grounds, aswell as surface mount IC's to keep board size and costs down. I expect the whole thing to not cost much more then $40 to build.

A quick run thru the I/O,

Power: 15+/-
Audio In: Single ended via molex KK
Audio Out: Single ended via pads, Balanced via pads.
Rotary Encoder: 3 pin rotary encoder via molex KK
Mute: Mute button via molex KK
Mute LED: Wire pads on board.

SMD resistors are used in the digital sections, and standard thru hole resistors are used in all signal paths.

If anyone is intrested, or has any comments feel free to let me know!
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Old 7th December 2008, 09:55 AM   #2
rhysh is offline rhysh  United Kingdom
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Here is the unfinished version 1 of the board.

Click the image to open in full size.

I expect the pcb to cost under $10 hopefully. I may be able to offer pre programmed AVR's for everyone that wants them.
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Old 7th December 2008, 10:28 AM   #3
Dr_EM is offline Dr_EM  United Kingdom
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Am certainly interested as I will eventually need 6-8 channels of volume control for my system and planned to use PGA2320 for this. My questions is can multiple units be linked together to form an accurate multichannel control via one rotary (for tri-amplification in my case)? Also, how easily could this be linked to a remote control system (ie, not through the use of a motorised encoder)?

Nice to see your in the UK too, makes shipping easier and less costly!
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Old 7th December 2008, 10:38 AM   #4
rhysh is offline rhysh  United Kingdom
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Quote:
Originally posted by Dr.EM
Am certainly interested as I will eventually need 6-8 channels of volume control for my system and planned to use PGA2320 for this. My questions is can multiple units be linked together to form an accurate multichannel control via one rotary (for tri-amplification in my case)? Also, how easily could this be linked to a remote control system (ie, not through the use of a motorised encoder)?

Nice to see your in the UK too, makes shipping easier and less costly!
Thanks for the reply, i am going to be including points on the board, so they can be stacked and controlled by the same microcontroller.

You will be able to use the identical board, but in slave mode, so you just dont populate the AVR, some resistors and a couple of pin headers.

By remote control system, do you meen linked to a existing remote control system, or have one built in? Basicly i have designed this board as totally simple preamp, so i have disgarded the idea of having LCD's and IR etc, but it can be done, on a external board by using another microcontroller to convert IR protocol to a rotary encoder standard, instead of a rotary encoder itself.
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Old 7th December 2008, 11:21 AM   #5
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Quote:
Originally posted by rhysh
.....using another microcontroller to convert IR protocol to a rotary encoder standard, instead of a rotary encoder itself.
I would be VERY interested in something like this. I have an existing remote I would like to have a receiver capable of learning it's vol up/down signals and output a rotary encoder signal.
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Old 7th December 2008, 11:22 AM   #6
rhysh is offline rhysh  United Kingdom
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Quote:
Originally posted by theAnonymous1


I would be VERY interested in something like this. I have an existing remote I would like to have a receiver capable of learning it's vol up/down signals and output a rotary encoder signal.

I will look into this, but im not the most advanced programmer.
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Old 7th December 2008, 12:32 PM   #7
Dr_EM is offline Dr_EM  United Kingdom
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The remote control feature is something I could live without, just I bought this:

http://www.maplin.co.uk/Module.aspx?ModuleNo=220037

with the intention of implementing it thus. I'm sure I can figure out a way regardless, or just manage without it (one of the buttons on that system will effectively jump the volume to full so mabye it's best not to use ). Main thing is they can be daisy chained for multiple channels

I see you're using the SMD PGA chip. In the UK the DIP actually looks to be cheaper (Farnell). Do you know of a cheap supplier for this chip? at farnells prices several will be expensive. Am trying to chase up a set of DIP I ordered from Taiwan ages ago actually. Were very cheap but alas haven't arrived
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Old 7th December 2008, 12:36 PM   #8
rhysh is offline rhysh  United Kingdom
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Quote:
Originally posted by Dr.EM
The remote control feature is something I could live without, just I bought this:

http://www.maplin.co.uk/Module.aspx?ModuleNo=220037

with the intention of implementing it thus. I'm sure I can figure out a way regardless, or just manage without it (one of the buttons on that system will effectively jump the volume to full so mabye it's best not to use ). Main thing is they can be daisy chained for multiple channels

I see you're using the SMD PGA chip. In the UK the DIP actually looks to be cheaper (Farnell). Do you know of a cheap supplier for this chip? at farnells prices several will be expensive. Am trying to chase up a set of DIP I ordered from Taiwan ages ago actually. Were very cheap but alas haven't arrived
Hi again, i am buying my PGA's from digikey in the US, works out a lot cheaper, if you are intrested i can order you the required amount in when i order mine, they come out around 8 pounds each.

If i do decide to do the remote control feature, it will come along later as a daughterboard.

Hope this helps!
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Old 7th December 2008, 03:47 PM   #9
rhysh is offline rhysh  United Kingdom
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Quote:
Originally posted by theAnonymous1
I have >100 peices of PGA2320 if anyone needs some.

How much would you be offering them for?

Rhys
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Old 7th December 2008, 03:47 PM   #10
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I have >100 peices of PGA2320 if anyone needs some.

rhysh, maybe we can work out a trade if you think you can put together an IR controller like mentioned above.
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