bijaker1 Posted May 1, 2012 Share Posted May 1, 2012 Hello Everyone, I plan on buying an HRT Music Streamer II DAC to feed 2 Marantz MA500 monoblocks. In order to keep volume control in the analog domain without buying a preamp, I plan on making a passive volume control from scratch. The max output voltage of the DAC is 2.25V and the output impedance reportedly 200Ohm. The monoblocks have 30kOhm input impedance with a sensitivity of 1V. For this reason the volume control is designed to drop the DACs voltage to 1V from 2.25V at 0 attenuation. Attached is a picture of the circuit so far. I do though have a question: what is more important, presenting a high input impedance to the DAC (by the volume control) or presenting a low output impedance to the amps? I can increase the size (max resistance) of the left/right pots (right now at 5kOhm max) and increase the input impedance or decrease the size of the pots to decrease output impedance. Thanks for all the help! EDIT: The label "Amp_Left" should read "Left_Input" meaning the left input to the amp, modeled by the 30kOhm resistor. Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted May 1, 2012 Share Posted May 1, 2012 You're making this more complicated than is necessary. Drop me an email if you want to discuss alternative ways of doing this. Maynard Quote Link to comment Share on other sites More sharing options...
bijaker1 Posted May 1, 2012 Author Share Posted May 1, 2012 Thanks Maynard []. Email Sent, let me know if you don't get it. If anyone else has input on the design I would very much appreciate it [] Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted May 1, 2012 Share Posted May 1, 2012 Sent reply to your email. Will check mail again in a few hours--- Maynard Quote Link to comment Share on other sites More sharing options...
Guest " " Posted May 1, 2012 Share Posted May 1, 2012 The best approach is to use a TVC. Quote Link to comment Share on other sites More sharing options...
Greg Oshiro Posted May 2, 2012 Share Posted May 2, 2012 <snip> For this reason the volume control is designed to drop the DACs voltage to 1V from 2.25V at 0 attenuation.<snip> You might discover that more attenuation is required. I recommend allowing space and connection points for series resistors followed by shunt resistors in front of the pots. <snip>what is more important, presenting a high input impedance to the DAC (by the volume control) or presenting a low output impedance to the amps?<snip> As usual, "It depends ..." I think the input impedance only needs to be high enough so the DAC output does not distort. I'm not familiar with the HRT DAC. Maybe sending this query to their tech support folks is in order. If there is significant capacitance loading the output, as in long cables between the output of the volume control and the amps, lower output impedance will cause less high-frequency rolloff. Quote Link to comment Share on other sites More sharing options...
Greg Oshiro Posted May 2, 2012 Share Posted May 2, 2012 deleted erroneous double post Quote Link to comment Share on other sites More sharing options...
babadono Posted May 3, 2012 Share Posted May 3, 2012 My 2 cents: Your circuit is increasing the output impedance of the DAC so keep the cable length distance from the output of your volume control to the input of your amp as short as possible. The higher the impedance the more high frequency rolloff effect of the capacitance of the cable. And just a silly question: Do the monoblocks have level controls? If so this circuit is superflous. babadono Quote Link to comment Share on other sites More sharing options...
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