add a volume control to a dac with dc offset

nightanole · 3rd May 2011, 01:11 PM

I have an amb gamma2 dac that uses a single rail for the output buffer so its mid point is 2.5v instead of 0v. So it needs cap coupled. I want to add a volume control to the unit since it is my only source. However im having trouble finding a way to add a pot to the unit without adding yet another set of decoupling caps.

My goal is to have a cap coupled output, and only use 1 set of caps in the signal path.

this is what one idea i came up with.

I connected the pot to analog mid rail so there is no dc going into the pot.

s3tup · 5th May 2011, 02:13 PM

And now your DAC's output goes directly to it's analog voltage reference pin. A no-go.
Simple pot connected to ground should do the trick, but then you get "hrrr" noises when you spin the pot.
Otherwise, put the pot after the DAC's buffer and decoupling cap, and then you'll have a problem with linearity of volume control - which will be affected by devices you connect to the DAC (their input resistance).

3rd May 2011, 01:11 PM	#1
nightanole diyAudio Member Join Date: Feb 2009	add a volume control to a dac with dc offset I have an amb gamma2 dac that uses a single rail for the output buffer so its mid point is 2.5v instead of 0v. So it needs cap coupled. I want to add a volume control to the unit since it is my only source. However im having trouble finding a way to add a pot to the unit without adding yet another set of decoupling caps. My goal is to have a cap coupled output, and only use 1 set of caps in the signal path. this is what one idea i came up with. I connected the pot to analog mid rail so there is no dc going into the pot.

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5th May 2011, 02:13 PM	#2
s3tup diyAudio Member Join Date: Dec 2004 Location: Israel	And now your DAC's output goes directly to it's analog voltage reference pin. A no-go. Simple pot connected to ground should do the trick, but then you get "hrrr" noises when you spin the pot. Otherwise, put the pot after the DAC's buffer and decoupling cap, and then you'll have a problem with linearity of volume control - which will be affected by devices you connect to the DAC (their input resistance).