I am presently looking into replacing the volume control on my tube amps. Original control was a 250k Ohmite type AB pot, used as a voltage divider with the wiper directly connected to the input grid of a 12ax7. I did replace it with a Burns conductive plastic type a while back and liked the change. I then started playing with resistors in place of the pot with the appropriate values to give me the same volume and total input impedance(250k). After a bit of reading I replaced those resistors with the same voltage divide ratio but with less overall input impedance, one with 70k total, then down to 25k.
Have not done extensive listening without other changes(room and tube changes), however, it does seem to give a bit more detail in the overall sound picture, best sound maybe with the 70k resistors in. I tried to maintain the same divider ratio/volume setting, close enough.
I read that at least a 1 to 10 ratio, output to input impedance should be maintained, easily done here. What about the effects of Miller capacitance? There has never been a resistor grid stopper in place. Not a tube expert here.
I am looking for some direction as to what should be the most optimum value for a type DACT control arangement. I expect to do a shunt type with an adjustment band over the range of my normal listening range with fairly fine steps. Not necessary to have the normal full range adjustment. The input will be a DAC with the output impedance somewhere around 15 ohms(2 x AD844 stacked). These are dc coupled. The interconnect are 40 inches(79pf) and the resistors are Mepco mil spec RN60. I will possible be using vishay bulk foils in the place of the Mepco's in the final version.
Not looking for a component advise, just value range for the overall input value.
Have not done extensive listening without other changes(room and tube changes), however, it does seem to give a bit more detail in the overall sound picture, best sound maybe with the 70k resistors in. I tried to maintain the same divider ratio/volume setting, close enough.
I read that at least a 1 to 10 ratio, output to input impedance should be maintained, easily done here. What about the effects of Miller capacitance? There has never been a resistor grid stopper in place. Not a tube expert here.
I am looking for some direction as to what should be the most optimum value for a type DACT control arangement. I expect to do a shunt type with an adjustment band over the range of my normal listening range with fairly fine steps. Not necessary to have the normal full range adjustment. The input will be a DAC with the output impedance somewhere around 15 ohms(2 x AD844 stacked). These are dc coupled. The interconnect are 40 inches(79pf) and the resistors are Mepco mil spec RN60. I will possible be using vishay bulk foils in the place of the Mepco's in the final version.
Not looking for a component advise, just value range for the overall input value.
From the 844 specs, you should use over 250 Ohms for the pair. I'd go with 1k to 10k total.
The 10k would be more compatible with other sources, if you ever use any.
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