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Old 10th July 2014, 07:09 PM   #1
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Default Digital volume control for 7.1 preamp

I'm going to build a 7.1 preamp pretty soon, which I have not done before, and I was curious about the volume control mechanism used in these type of preamps.

Do they just use digital pots, and control these pots with some kind of ucontroller with memory (to store pot value after power down).

Such as this 2 of these (for 7.1):

Along with ucontrollers and push button (volume up and volume down) or a remote?
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Old 10th July 2014, 07:55 PM   #2
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Location: Tuscany, Italy
You could use 4 PGA2310/2311 if you want to control the volume of each channel independently.
The PGA is a stereo volume controller that can also act as a (simple) preamplifier since can set the volume level from -95 to +31 dB in step of 0.5 dB.
I'm currently using it with my "digitally controlled" preamp but you need a microcontroller to "dialog" with the PGA.


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Old 10th July 2014, 07:59 PM   #3
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I do it with a single CS3318....

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Old 10th July 2014, 10:23 PM   #4
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CS3318 looks good... thanks!
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Old 10th July 2014, 11:26 PM   #5
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Great chip, I didn't know it.
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Old 11th July 2014, 01:02 AM   #6
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I designed a USB mixer with the control pots on the PC screen.
I used Microchip digital pots.
Be aware that these pots need biasing correctly or you will get masses of distortion.
The Microchip pots need biasing at 2V5.
I also had fun with grounding on the mixer. The first pcb revision was rubbish with 1 volt hum on output. I had to complete separate power supply and audio grounds and only join them once at pcb edge where the power came in. This time the hum was negligible.

I used a 18f4550 PIC micro with USB and lots of I/O pins to drive the 6 digital pots.
They are quite easy to drive just being serial I/O.
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Old 11th July 2014, 03:18 AM   #7
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Here is another discussion with lots of info and ideas on what parts are available to you that may help,

DIY volume control open-source project

I have been planning such a project myself and I have been collecting Digital pots and switches for it for quite sometime now.

I have the several different PIC's including the PIC18F4550 as well.

In case that any one has not seen the latest here is a set of online courses and webinar's that Microchip has just started on July 1, 2014 for those of whom want to get in on learning to work with the PIC controllers.
I have been in on a few of these and they are great live classes and they are free!!!!

Online Training Calendar - Developer Help

Nigel, I would be interested in seeing any data or tricks you care to share on the interesting project you have done as well.
As I am just starting at PIC programming and interfacing with SPI and I2C
I will be following this project with great interest,Thanks!!



Last edited by geraldfryjr; 11th July 2014 at 03:43 AM.
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Old 12th July 2014, 09:32 AM   #8
maxw is offline maxw  United Kingdom
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Or 2x PGA4311 ICs.
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