8 (7.1) channel analog volume control

[(*steve*)]

I'd guess you could get away with an 8 pin device. I'm not sure if you can parallel all the chips you need to control, but I assume you can.

 

[CommanderLake]

The PGA2311 has an SDO pin to daisy chain them together.
Hang on if I'm not allowed to leave the serial in on the picaxe disconnected what do I connect it to?
Do you think I should use separate supplies for digital and analog +5v or just use 1 symmetric supply?
Can I connect the ZCEN pin of all 4 chips to 1 output on the PIC for zero crossing detection?

 

[CommanderLake]

Have you given up on me?
Why are decoupling caps usually aluminium electrolytic then film? Cant I just use a big film cap?

 

[(*steve*)]

Hang on if I'm not allowed to leave the serial in on the picaxe disconnected what do I connect it to?

They specify exactly what you need to do. Essentially you keep the programming resistors in circuit and Bob's your uncle.

Do you think I should use separate supplies for digital and analog +5v or just use 1 symmetric supply?

Try with a single power supply first. If you have problems you may be able to get away with some decoupling.

Start simple.

Can I connect the ZCEN pin of all 4 chips to 1 output on the PIC for zero crossing detection?

I'll have to look that one up.

 

[(*steve*)]

Have you given up on me?
Why are decoupling caps usually aluminium electrolytic then film? Cant I just use a big film cap?

That's the reason -- physical size (and cost).

 

[(*steve*)]

Can I connect the ZCEN pin of all 4 chips to 1 output on the PIC for zero crossing detection?

Unless you want to programmatically urn this on and off, you can wire them all high or low as you might desire.

 

[CommanderLake]

Thanks for all your help, so to keep the SCEN high do I just connect them to the power supply with a resistor or something?
Also I just read about decoupling caps and the article said a smaller cap is required for higher frequency loads.

I came across a forum thread where someone discussed a voltage spike on the output of the PGA2311 during power down and this would cause a nasty pop and the solutions were a resistor from VD+ to VA+ or a relay, what are your thaughts on this?

Yea I can see why the film caps are small and backed by an alu cap because an equivalent film cap is huge!

I didn't know it needed programming resistors where's the schematic that shows all this I cant find much?

 

[(*steve*)]

Check out page 8 of this.

When the serial input goes high, the program stops and the boot loader takes over. So you leave those 2 resistors in circuit and it won't happen.

Yes, pulling high means connecting to +v. You almost certainly don't even need a resistor.

Note that you'll have to check that whatever PICAxe you get supports the protocol used by this chip (SPI?). I think it's standard, but better to be safe than sorry.

My thoughts are as before on the subject of decoupling. KISS. make adjustments later if you need to.

 

[CommanderLake]

On page 10 of the PGA2311 datasheet it says: The length of the shift regis-ter is 16 • N bits, where N is equal to the number of PGA2311 devices included in the chain.
does the • (dot) mean multiply?

 

[(*steve*)]

That sounds reasonable.

 

[CommanderLake]

The Diptrace schematic is coming along well, I have a 10k pot for the volume control with an ADC input but I'm having trouble deciding what phono connectors to get, do I want to run 16 wires to the phono sockets or use PCB sockets and get the case dimensions just right.

 

[(*steve*)]

Neater to have the connectors on the board, but it's your call (and you have identified the downside).

I'd be mocking one of these up on a breadboard before I went down the PCB route.

 

[(*steve*)]

Sorry, I'm not prepared to install software just to look at your layouts. Save them to an image or a pdf.

However, I consider it pointless to be worried about the PCB layout prior to breadboarding. (The schematic is obviously another issue)

 

[CommanderLake]

Dont you do PCB design?

 

[(*steve*)]

Not before I know what the final circuit design is.

 

[CommanderLake]

Can you recommend somewhere I can get the PCB made after I breadboard it?

 

[(*steve*)]

There are many places in China, and undoubtedly there will be some in whatever country you're in too. Maybe you can get away with veroboard.

You're getting ahead of yourself.

How are you going to design the PCB? Have you decided what type of solder mask you want? What about the finish -- gold, or just tinned copper? Are you after rapid delivery? Do you want several hundred of these boards? What about getting them to assemble the board? Who is the best supplier for the resistors you'll need? How many values will you need -- less may make it cheaper? What if some of the parts are counterfeit? What assurances will you require from suppliers? Are you concerned with RoHS? What about a CE mark so you can supply into Europe? Perhaps you should concern yourself with the translators you'll need to create documentation in all the languages required for Europe?

 

[CommanderLake]

I already ordered all the components from Farnell that's my favourite supplier and I dont intend on making it a product its just my personal solution I dont think I could handle the work required to resell my preamp project, I'm just trying to learn as much as I can about what is to come, immersion silver seems to be a popular finish but your the expert what would you recommend?
Here's my list of components I did order extras of the smaller components:

PGA2311PA
Harwin D2616-42
Harwin D2608-42
2-way terminal block (sticking with case mounted connectors)
3-way terminal block
Wima 0.1µF
Panasonic 10µF
Welwyn 22K
Welwyn 10K (I know 0.5w is too big but only 3 are needed, they're less fiddly to fit and the picture looks cool)
Neutrik white phono socket
Neutrik red phono socket
Neutrik black phono socket
Velleman K8042 (saves me designing one)
6v 50va and 20v 500va transformers from Airlink Transformers
and the PICAXE-08M2 Starter Pack

 

[(*steve*)]

Have you purchased (or do you have) a solderless breadboard?

 

[CommanderLake]

I got the solderless breadboard and a jump wire kit to go with it both from my local Maplin.