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Old 23rd December 2008, 02:50 PM   #1
Telstar is offline Telstar  Italy
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Default Volume control in the dac output stage

Greetings,

This idea is blinking in my mind.
I'm going to build a DAC based on Borbely dac age
http://www.borbelyaudio.com/pics/New_DAC_Age.pdf
and I want to have volume control in the DAC, which would be the easiest way imo to implement it in my chain.

First question, would it be within, before or after the output stage?
Second, my f3 power amp needs current, so what kind of conversion should be done?
Third, because i want remote and display, i was considering Tent VC:
http://www.tentlabs.com/Products/page31/page31.html
Fourth, I'm considering the lightspeed and i would probably prefer it to Tent attenuators. mmh.

Any suggestion and idea are welcome.
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Old 24th December 2008, 04:18 PM   #2
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One aspect of the Borbely DAC you referenced that I don't like is how he summed the differential output and then used a phase inverter recreate differential output. The advantage of using 4 1704's is so a phase splitter does not need to be used.

The attenuator goes after the DAC buffer and before the F3. If your attenuator has a buffer, then you maybe able to bypass the DAC's buffer to strip out circuitry in the signal path.

Other topologies to consider using:
* Pass x-BOSOZ or BOSOZ with CCS to convert the true balanced differential DAC output to single ended with a volume control on the output, and then to the F3.

* Pass B1 buffer after the summed output of the DAC to the F3.

-David
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Old 24th December 2008, 05:08 PM   #3
Telstar is offline Telstar  Italy
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Thank you for the reply, David. and merry christmas.

Quote:
Originally posted by dw8083
One aspect of the Borbely DAC you referenced that I don't like is how he summed the differential output and then used a phase inverter recreate differential output. The advantage of using 4 1704's is so a phase splitter does not need to be used.
I do not plan to use it straight as is, for instance i dont need balanced and i want to disable (remove) all filters and its switch.
I think borbely makes different output stages, which one do you suggest (not limited to his ones)?

I'm also thinking to double the dacs number and use 4 per channel, in single-ended mode.

Quote:

The attenuator goes after the DAC buffer and before the F3. If your attenuator has a buffer, then you maybe able to bypass the DAC's buffer to strip out circuitry in the signal path.

Other topologies to consider using:
* Pass x-BOSOZ or BOSOZ with CCS to convert the true balanced differential DAC output to single ended with a volume control on the output, and then to the F3.

* Pass B1 buffer after the summed output of the DAC to the F3.

-David
I'll either use George's lightspeed mk2 + a B1 buffer or a different version of LDR that has already a buffer(s).
In the first case my idea was to incorporate the lightspeed in the dac output stage (henche the thread title), with addition of a remote and display for the volume such as Tent labs.
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