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Volume control placement: DAC or Modulus-86?
Volume control placement: DAC or Modulus-86?
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Old 25th October 2017, 08:52 AM   #1
zgtc is online now zgtc  Europe
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Volume control placement: DAC or Modulus-86?
Default Volume control placement: DAC or Modulus-86?

Hi,

I ask about Modulus-86 specifically because I bought them and intend to use them in balanced mode. Probably only source will be a soekris dam1021 (4V RMS buffered balanced output), maybe I get an AKM with balanced output though.

Is it better to have a digital volume control at DAC and no volume on the amp (same as amp at full volume, I guess) or, no volume on the DAC (programmatically set full volume) and place an analogue volume control on the amp?

Gut feeling tells me 1st option would be easier since second would need to take into account impedance changes and so on. Also, which is better in terms of sound quality?

Thank you
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Old 26th October 2017, 08:42 AM   #2
AndrewT is offline AndrewT  Scotland
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It is not easy to find a balanced volume control. Those that attempt it, generally destroy the balance of impedance that is fundamental to the common mode rejection ratio (CMRR).

There are volume controls designed to fit into balanced impedance circuits, but these convert the balanced impedance signal to unbalanced. Adjust the attenuation/gain. Then convert back from unbalanced to balanced impedance.
B.Putzeys' balanced volume control is an example of such a double conversion device.
The output of B.Putzeys' circuit is described in AN003 by Jensen.
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File Type: pdf The G Word13pages.pdf (730.7 KB, 17 views)
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Last edited by AndrewT; 26th October 2017 at 08:45 AM.
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Old 26th October 2017, 08:48 AM   #3
AndrewT is offline AndrewT  Scotland
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If you need balanced impedance for the CMRR of interference then you must keep the balanced impedance all the way from DAC to Amplifier.

Check the DAC with adjustable volume, maintains the balanced impedance on it's output.
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Old 26th October 2017, 12:05 PM   #4
zgtc is online now zgtc  Europe
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Volume control placement: DAC or Modulus-86?
Quote:
Originally Posted by AndrewT View Post
It is not easy to find a balanced volume control. (...) There are volume controls designed to fit into balanced impedance circuits, but these convert the balanced impedance signal to unbalanced. Adjust the attenuation/gain. Then convert back from unbalanced to balanced impedance. (...) If you need balanced impedance for the CMRR of interference then you must keep the balanced impedance all the way from DAC to Amplifier.
I see this option (volume control on the amp) is way too complex for my skills.

Quote:
Originally Posted by AndrewT View Post
B.Putzeys' balanced volume control is an example of such a double conversion device.
The output of B.Putzeys' circuit is described in AN003 by Jensen.
Wow, nice articles, thank you! Will need some time to digest though

Quote:
Originally Posted by AndrewT View Post
Check the DAC with adjustable volume, maintains the balanced impedance on it's output.
I think placing the volume on the DAC will be the easiest approach in my case (balanced input to amp). That simplifies design a lot as well, since DAC chassis can have all the rotaries (source and vol) and input/output, then leave the amp chassis with a simple on/off and output to speakers. Does this make sense?

Thank you again
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Old 26th October 2017, 01:10 PM   #5
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by zgtc View Post
I see this option (volume control on the amp) is way too complex for my skills...............
It is my opinion that the power amplifier belongs at the speaker with very short speaker cables.

If one places the power amplifiers beside their speakers, then it is not operationally convenient to locate all the volume controls at the (widely) distributed power amplifiers.
It would be nice to have a local volume control near to, or at least accessible from the listening seat.

That puts an "in amp volume control" out of the equation.
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Old 26th October 2017, 01:20 PM   #6
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Volume control placement: DAC or Modulus-86?
Quote:
Originally Posted by AndrewT View Post
It is my opinion that the power amplifier belongs at the speaker with very short speaker cables.

If one places the power amplifiers beside their speakers, then it is not operationally convenient to locate all the volume controls at the (widely) distributed power amplifiers.
It would be nice to have a local volume control near to, or at least accessible from the listening seat.

That puts an "in amp volume control" out of the equation.

This makes a lot of sense. Maybe thinking about the vol in the amp is due to the usual approach used by the consumer audio equipment.
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