Volume control

[nlinus]

Hello!
I am building a preamp and found a digital volume control which i thougt looked good, the PGA2311.
Does anyone have any opinions about it? I am planning to use a PIC16f84 to control it.

/Linus Nilsson

[apassgear]

Linus,
No opinion since I never used one, but I would like to know what's this vol. control is all about since I have started also building a Balanced Zen Line Stage (BOSOZ). Will you be using a separate PS for this?

Do you have an Schematic that you could show?

[harvardian]

Hello,

BrianGT is also designing a PIC based control for one of the digital volume controls. He is also using a cool VFD display.

Do a search...

Dale

[MRehorst]

I did a volume control using an LM1972 a couple years ago, with a PIC16F84 controlling it. I am now working on another with some input switching using the PGA2310.

The first one used pushbuttons to set the levels. It worked very well, and sounded pretty good. The new one uses a rotary encoder so you get to turn a knob for volume.

I am designing a "generic" CPU board that will be connected to a separate analog board so I can use different analog circuits with the same CPU. I have designed in a lot more I/O than is required by this simple project so that if I want to do something more complex later I can use the same board. I am using a 16F874 which is ridiculous overkill, but again allows for a lot of future fooling around.

If I recall correctly, all the code for volume, mute, and reading keys took a total of 114 bytes of memory using the assembly language that MicroChip makes available for free. I put the CPU to sleep when it wasn't changing volume so it didn't generate any digital noise. The LM1972 is a good chip except for a sort of odd pinout which makes separating digital and analog grounds a bit difficult. I used an OPA2134 (?) for the opamp at the output.

Check the latest issue of Electronic Design magazine for a real neato single pin keyboard interface!

MR

[mlloyd1]

Do a search. There's been some useful stuff posted about these devices. There's a guy in the UK who is building/has built a very nice looking unit with this chip. His preamp is not discrete, but that's not important to your question.
mlloyd1
p.s. I just found the link http://www.mhennessy.f9.co.uk/preamp/analogue.htm

Originally posted by nlinus
Hello!
I am building a preamp and found a digital volume control which i thougt looked good, the PGA2311.
Does anyone have any opinions about it? I am planning to use a PIC16f84 to control it.

/Linus Nilsson

[mhennessy]

Hi All,

Hello!
I am building a preamp and found a digital volume control which i thougt looked good, the PGA2311.
Does anyone have any opinions about it? I am planning to use a PIC16f84 to control it.

/Linus Nilsson

As mlloyd1 says, I've done this just recently. There's quite a lot of info on my website, but please feel free to post or email me for help...

As you might have already realised by now, the PGA2310 is a better bet because it runs from +/-15V supply rails... If you haven't already done so, search this forum for PGA2310 for lots more info.

Good luck

Mark

[mlloyd1]

Oh, Hi Mark. Just wanted to say your preamp is a beautiful piece of work! I'm looking to do somethign similar when I can get some time .....

mlloyd1

Originally posted by mhennessy
Hi All,
...
As mlloyd1 says, I've done this just recently...

[dwk123]

For those that have used any of the 3310/2311/2310 chips, is there any major reason I couldn't drive these from a PC parallel port? I had been thinking of hooking up a 68hc11 on the serial port, and driving them with that, but now that I think about it a straight parallel port would be much simpler. I haven't looked at level/timing diagrams in exhaustive detail yet to ensure that it's feasible.

Since I'm using the PC as the source for all my audio/video, it's not an added component.

[BrianGT]

speaking of the volume control, my roommate who is helping me with it got back the analog volume control boards. They are pretty cool. He made them so that you can stack them on top of each other and then you only have to connect the digital connection to the top board. It is a pretty cool design. It makes it highly scalable. The boards are now populated, and I will get some pics soon. He made one mistake... mapped the +/- 15v to the opamps backwards, so he fried the opa2134 chips, and the pga2310 chip, so he had to reroute these two, and start with new chips. It appears to be working now.

Here is a pic of the unpopulated board. It is quite simple, and is based off the schematics on Mark Hennessy's website. Thanks Mark for the inspiration. I should have a finished prototype soon. The digital side is pretty much done. We haven't done the power supply yet, and are just using a bench supply for the analog stage now.

--
Brian

[mhennessy]

Hi Brian,

I'm impressed with your board layout, and very pleased that my site was helpful to you

You've been able to optimise the layout by freeing yourself from the mechanical constraints that I imposed on myself. I wanted to minimise the interconnections by using things like ribbon cable and PCB-mount phono sockets...

Your layout has lots of copper dedicated to earth, which is an excellent plan. One suggestion, though. I notice that there isn't a power supply decoupling capacitor at the input-end of the PCB. It might be worth trying to solder a couple on the back of the board during listening tests. It might not make any difference, but the PGA2310 datasheets made quite specific recommendations about it.

I notice that you've included gain on the input buffer. I added a very small amount of gain there to compensate for the losses in the input filter - this was only for the benefit of the fixed-level listen-source output that I provided, indeed I didn't bother for the surround-channels. So, you'd be able to simplify that end of the board if you wanted...

Out of interest, what do C15 and C25 do? I ask because they appear to be electrolytics! I guess that they are the 1nF caps that I used to set the -3dB point to 100kHz...

Very impressive work! I can't wait to see the assembled version... Which CAD package does your roommate use?


dwk123: If you are able to control the individual bits of a PC parallel port, then you should have no problem controlling these chips. You just need 3 lines for clock, data and latch (or strobe). You could also control the mute input with another bit - I mute via software. The timing diagrams in the datasheet should tell you everything, but feel free to ask for more info...