VBIGC multi-amping / PGA2310 questions

[sergiusz]

Hello All !

First of all thanks to Joe Rasmussen for his contribution and the valve buffered gainclone !!!!

A am a very newbie to DIY so as a first project I built a prototype VBIGC on wood and I love the sound very much! I have little hum on my speakers but that could be an issue of the "prototype" ground wiring

Now I want to go a step further and make some PCB's and make things neat. However I have two questions:

I want a bi-amped system. I thought about using two LM3875 and one 6922's for each channel. However, how do I apply the grounding in such a configuration? I planned to make one PCB for each LM3875 following the grounding recommendations on Joe's site. Thus on each PCB I'd have a power ground point and a signal ground point. Afterwards I'd wire all the grounds (altogether eight) to a common ground point. Is this a good solution?

2. This is a short question: How can I integrate a PGA2310? Is it straight-forward, so I can remove the 50k pot and replace it using the PGA2310?

Thanks in advance and sorry for the newbish questions,
Serge

[janneman]

Serge,

How do you plan to implement the power supply? Do you plan to have separate supplies for each channel? In that case you can also ground the amps per channel. What about the xover filters? Are these passive, after the amps, or active, before the amps?
This all has a possible bearing on the optimum grounding strategy.

I don't see any problem with the PGA23??, but the answers on the other questions may impact on that as well.

Basically, what I am saying is, the grounding is just one issue of the total system topology. You should decide on that first, and then work top-down.

Jan Didden

[sek]

Hello,

about the PGA: You're aware you need a controller for the volume control to work this way?

That said, I guess it works like any other kind of volume control, as the PGAs keep (analog) signal ground separated from their (digital) control ground. That involves a separate power supply for the PGA, of course.

What signal voltage levels do you plan to feed from the PGA to the Valves? You'd probably need some attenuation (plain voltage divider?) here, but otherwise I don't see any problems.

BTW, do You know Elektor's PGA-based pre amp?

Ciao,
Sebastian.

[sergiusz]

Hello janneman,

Thanks for the very fast answer!

The filters are passive xovers in the loudspeakers. I made a bi-amping terminal at my 2,5way speakers. The terminal provides sepereate cables for the "1,5way" part and the "1way" part of my speaker thus they are electronically "independent".

Regarding xformers, here are my initial plans:
2x250VA each handling 2xLM3875
2x50VA each handling 1x6922 (both "halfs" of the valve)
1x20VA handling 2x6922 filaments, the digital part (PGA2310, AVR Attiny26 uP) and the analogue part of the PGA.

Each LM3875 chip will be given a seperate rectifier circuit as well as each half of the 6922's, the filaments, the analogue part of the PGA2310 and the digital part (PGA2310, AVT uP).

[sergiusz]

@sek Yes I know the Elektor PGA-based preamp and am actually inspired by it :-) I just want add some more logic to be handled by the AVR uP using a 74HC595 shift register which then switches input relays (see http://www.rotgradpsi.de/mc/amp51/amp51simpleana3i.gif).

The analogue and digital part of the PGA would be supplied by the same xformer but would have seperate rectifiers, I hope that's sufficient.