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

[tiefbassuebertr]

about
http://www.accuphase.com/cat/e-250_e.pdf
I read:

How AAVA-II works:
AAVA-II operates by feeding the music signal to a V-I (volt-
age - current) converting amplifi er where it is weighted in 16
steps [1/2, 1/22, ..., 1/215, 1/216].
The 16 current steps are
turned on or off by 16 current switches, and the combina-
tion of switch settings determines the overall volume. The
switching operation is controlled by a CPU according to the
position of the volume control knob. The combined signal
current forms a variable gain circuit that adjusts the volume.
Finally, the combined current is converted back into a music
signal voltage by an I-V (current - voltage) converter.

Are there any experiences from this kind of a level attenuator without any resistors in the signal path?

[DF96]

This whole complicated circuit (well, more complicated than two resistors anyway) contains no resistors? Does it use switched capacitors instead? Or are we to believe that a whole set of p-n junctions can be matched so accurately that the outcome is more linear than a resistor? Is not a current switch a resistor, of sorts?

This sounds like more straining at gnats and swallowing camels!

[DavesNotHere]

digital controlled VCA

http://www.thatcorp.com/datashts/dn02.pdf

[Javin5]

A digtally controlled attenuator. There are a couple of chips that do the same. Not sure if this is realized in discrete form or if it is on an IC.

Of course the music signals flows still through resistors, as with any gain control chip or any relay controlled attenuator. I respect Accuphase very much, but I don't see the big advantage of this, compared to other simple, established solutions.

[udailey]

If they sent the signal down the interconnects as current and THEN went back to voltage it would make more sense as it would be nearly impervious to EMI RFI which is turned into voltage in the cables anyway. Like CAST from Krell.

[tvi]

Might this be the patent?
JP 2004104269 SIGNAL SWITCH AND VARIABLE GAIN AMPLIFIER PROVIDED WITH THE SAME

The switch comprises a fixed current drive circuit having a voltage-current conversion gain for converting an input signal voltage applied to an input terminal to a current to output, a current-voltage converter circuit for converting an output current from the drive circuit to a voltage to output, a plurality of signal switching circuits connected in parallel between the input terminal and the input of the current-voltage converter circuit, each composed of a series switch circuit connected between the input of the current-voltage converter circuit and the output of the drive circuit and a short-circuit switch circuit connected between the drive circuit output and the ground, and a switch control circuit for controlling the switch circuits.; The switch control circuit changes over the switching of switches in the plurality of parallel-connected signal switching circuits singly or multiply with specified time intervals one after another to control the gain

Its in Japanese

[Leon08]

This is interesting approach, but I think it's too complicated for volume control. Maybe it's really as good as they claim, but it's very bulky and expensive.So this is for some rich audiophils, wich don't know what to do with their money.

[maxw]

I've looked at this before and think this type of volume control is really interesting, I would love to make one. If someone gave me a schematic I would design a PCB.

I like it because:
- it's so precise compared to everything else
- lower distortion than PGA2310 etc
- Simple concept
- No click sounds. Pretty much all relay volume controls click when all relays flip (like at step 64/128 etc)

There is some more info here on page 2:
http://www.axissaudio.com/pdfs/C-2400.pdf

Mark Levinson use the same concept too:
http://www.marklevinson.com/image_library/32AB_lo.jpg

bbp built one a while back. He used DG413 analog switches but these days there are better ones like DG611 or ADG1221. He also measured he version and achieved higher specs than the PGA. Here are his threads:
Solid State Volume controls
Ultra high precision digital control attenuator
Promotion: Hi-end Volume Control Module,Ultimate Attenuator for Audio

[barmanekm]

I was thinking about designing something similiar, but have no time currently. Electric circuit seems not to be a big deal. More interesting is interfacing switches to volume know. I was thinking about absolute one turn encoder and some simple uC, like 8051. Is this a correct idea? Or anyone has more simple way to do it?

[maxw]

Originally Posted by barmanekm

More interesting is interfacing switches to volume know. I was thinking about absolute one turn encoder and some simple uC, like 8051. Is this a correct idea? Or anyone has more simple way to do it?

You are on the right track. Personally I would use an arduino and a standard encoder since there is a much bigger range available as opposed to absolute encoders.