[AKSAphile]

Reading previous topic about transformer attenuation and also Hugh suggestion on PGA2310 use, I remembered that few years ago there was a project in Elektor electronics magazine where author developed a nice attenuator volume control around PGA 2310/2311 chip  controlled via PIC. 

Here is the link of the author page: http://www.dh3ben.de/html/electronics/pga2311_preamp.shtml


Another volume control option could be relay control. Here is the link: http://www.vaneijndhoven.net/jos/switchr/design.html

Author of this design has developed also a new RelaiXed balanced volume control with LM4562 buffers. But the problem is that his output is only balanced not single ended. So for the AKSA/LF amplifiers only project on the link should be suitable. 


The question is, could both (PGA2310 and relay control)  be used alone to power AKSA/LF or there should be buffer between volume control and power amplifier?

[AKSAphile]

The question is, could both (PGA2310 and relay control)  be used alone to power AKSA/LF or there should be buffer between volume control and power amplifier?

Have anybody some idea or experience with this type of volume control?

[AKSA]

Anyone with experience of this chip?

Andrej,

Google for the pdf application note - there are some indicative configurations, and instructions on the software.  It's not complete, but it's a guide.....

Hugh

[AKSAphile]

I studied both designs and find out that both have some advantages and disadvantages.

PGA 2310 is the most elegant solution. It is not just resistor network switch but also has output buffer. This buffer should be capable to run even 600 ohm impedance, but the output voltage will sag down a lot driving this low impedance load. The AKSA has a high input resistance so PGA 2310 could theoretically! drive the power amp directly. A disadvantage is that signal passing this opamp will definite get some coloration / distorsion to the sound compared to  classic pot. But on lucky side the added harmonic distorsion is VERY low.


Passive volume attenuation is for sure the cleanest option. No power supply noise, no added harmonic distorsion. Well it could be perfect, but here is the drawback: (hope you see attached pic)



Input resistance quite vary compared to classic pot which have static input resistance. Most CD players have output stage made of op amps and they will not complain driving higher than "normal" load. But the output resistance is low...


I am questioning myself how could typical CD player drive the AKSA/LF via relay volume control or even PGA 2310?

[Geoff-AU]

Some interesting volume controls there, thanks for putting those up AP!

That project has variable input impedance and (relatively) constant output impedance.  A passive pot has constant input impedance and variable output impedance.  I'm not enough of a guru to say which compromise is the better one off the top of my head!  I have A/B'd a passive pot with my active pre-amp (one of Rod Elliott's kits) and the passive sounded better initially but after a while seemed to be missing something (I used the same volume pots in each pre). 

Daresay the limiting resolution isn't in my volume control, but if I get around to building another pre it will have remote controlled volume one way or another!  Good to have some new concepts to explore in the meantime