A New approach of Volume Control: AAVA (Accuphase Analog Vari-gain Amplifier)

[jan.didden]

I can understand they use this convoluted way instead of just getting a high performance MDAC. As a manufacturer you need to be able to distinguish yourself from the competition, even if the performance suffers a bit.

Jan

 

[DF96]

You are surely not expecting me to believe that some high-end audio deliberately degrades performance in order to enhance marketing?

 

[MarcelvdG]

Isn't this just a sort of discrete current switching DAC??

Jan

Yes, but apparently with a transadmittance amplifier for each switch, so switch resistance variations with signal cause even less distortion than in a normal multiplying DAC loaded by a virtual ground. Unfortunately the schematics in the patent and in the brochure don't provide any information about those amplifiers other than that they exist.

 

[trung224]

Unfortunately the schematics in the patent and in the brochure don't provide any information about those amplifiers other than that they exist.

You can search the schematic of Accuphase C2810 Preamp to see the implementation of this circuit. Just Google Accuphase C-2810 service manual and you can see it, don't need to guess

 

[jan.didden]

You are surely not expecting me to believe that some high-end audio deliberately degrades performance in order to enhance marketing?

That's not what I said.

Jan

 

[jan.didden]

You can search the schematic of Accuphase C2810 Preamp to see the implementation of this circuit. Just Google Accuphase C-2810 service manual and you can see it, don't need to guess

I don't know where you are, I can't get to that service manual. Do you have a specific link please?

Jan

 

[trung224]

I'm in Germany.

here is the link
ACCUPHASE C-2810 Service Manual download, schematics, eeprom, repair info for electronics experts

It is safe, as I downloaded so many service manual from this website

 

[MarcelvdG]

Thanks! It's another model, but with the same kind of volume control.

One unit transadmittance amplifier is shown in the attachment. They use a low-offset low-bias-current op-amp to force the signal voltage across R313. Whatever offset current there still may be is conducted to ground via R315 and C304 conducts the signal current to the switch.

That answers the questions I had: the AC coupling eliminates the offset, there is no bias current source noise added to the output signal with this topology and the fact that R315 reduces the impedance that drives the switch is taken for granted.

 

[Bonsai]

I would think in the actual Accuphase implementation, they are using 16 resistors to create the weighted currents into the summing junction from the buffer. You could simplify it and just use 6~8 and still get reasonable control IMV.