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Bel Canto and Digital Volume Control

I am considering eliminating my preamp from the chain as all my sources are now digital. I have a concern about dropping bits and how much of that is acceptable when using the digital volume controls included with some DACs. So much effort goes into obtaining the most resolution possible in the design of a DAC it seems a shame to jut start throwing that away by dropping bits. I will also be driving 2 amps (a powered sub and a stereo power amp) with the line outs from the DAC.
Are there any issues when driving two amps with the outputs of the line output from a DAC? I don't know what current capability, what impedance loads they will tolerate, etc. How low can the volume be set on (for example Bel Canto's DAC3) before the data loss becomes audible?
I also consider including a passive attenuator in the chain so I could control the volume without dropping bits from the data.
Thanks in advance for your input.
patrickp

Showing 3 responses by patrickp

patrickp OP
59 posts
 
Some of the digital controls do; the true digital ones that work in the digital domain exclusively. That is the type I intended to refer to. Wadia has a nice white paper with some explanation.

http://www.wadia.com/technology/technicalpapers/Digital_Volume_Control_2.pdf
patrickp OP
59 posts
 
All -

I think I may have handle on the digital volume thing. Please feel free to provide additional insight and education as required.

My speaker amp:
90db/w/m Speaker rating + 61db amp gain (1200watt @ 4 ohms) = 151db SPL max
(I know that would kill both my speakers and my ears)

Assuming a low level average listening level of 60db?
(I used the average conversational level of 40db-80db as a point of reference)

Average CD recording level usually at -20 to -6 peaks
(It seems this recommended as a target for setting levels in the mixing studio)

Attenuation required for the average listening at low level is -70db?
(max possible gain less attenuation to get to the low level listening volume assuming the recoding level indicated for CD’s)

Id I understand it correctly 6 bits will provide 64 potential levels of attenuation. That would still leave be with 18 bits of resolution when using a 24bit digital volume control. That seems to be almost about the limit that may be realized with current state electronics. It’s likely all I can hear anyway.

That would seem to dictate about 1.25db of attenuation per step.

Thanks in advance all -
patrickp OP
59 posts
 
In regards to the attenuator IC -
Is there a pin compatible version that provides 1 - 1.5db / step instead of the .5/db commonly used? I don't mind losing a bit of 'fine tuning' in the remote in order to preserve another bit or so of resolution.

If that is not available I suppose I could to the sensible and easy solution and use a quality audio resistor or two into my XLR patch to provide the attenuation. - or heaven forbid I get a more reasonably powered amplifier. LOL
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