Chris, you’re up early (or late, if you’re on the West Coast). In principle, I don’t immediately see why a pot. could not be combined with an active I/V op-amp to form a Baxandall type volume control. I’m not sure that would buy you anything beyond the elimnation of one op-amp, though.
Regarding the OP’s situation, he is wondering whether he might specifically modify his AN DAC 4.1, which utilizes a passive I/V circuit (resistor + transformer), and not the typical op-amp based trans-impedance I/V stage.
Regarding the OP’s situation, he is wondering whether he might specifically modify his AN DAC 4.1, which utilizes a passive I/V circuit (resistor + transformer), and not the typical op-amp based trans-impedance I/V stage.
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You could use a (non-carbon) logarithmic 330 ohm potmeter (if you can get one somewhere) connected in reverse: DAC output to the wiper, one side to ground, the other to the transformer.
The impedance driving the transformer then stays roughly constant. I assume this is an advantage when you want to keep its frequency response constant, although for distortion, the lower the impedance the better. The DAC sees a better short at low volume settings. When the wiper temporarily loses contact, you temporarily get silence rather than maximum volume.
The impedance driving the transformer then stays roughly constant. I assume this is an advantage when you want to keep its frequency response constant, although for distortion, the lower the impedance the better. The DAC sees a better short at low volume settings. When the wiper temporarily loses contact, you temporarily get silence rather than maximum volume.
@MarcelvdG that's a good idea. Basically it's voltage divider that keeps the primary resistance consistent.
I will give it a try with a couple of fixed resistor (eg 330Ohm + 3.3 Ohm for 40dB attenuation) an hear how that performs from a sound quality and nosie perspective. If the result is good I can look more into the potentiometer option.. or I could use a 20 posistions rotary switch and a bunch of resistors.
The alternative, and probably easier way to go solve the volume control, is to use a voltage divider between the 2 stages of the buffered output.
Basically replacing R2 in the circuit below, with a stepped potentiomenter with the wiper connected to the grid of V1(b).
I will give it a try with a couple of fixed resistor (eg 330Ohm + 3.3 Ohm for 40dB attenuation) an hear how that performs from a sound quality and nosie perspective. If the result is good I can look more into the potentiometer option.. or I could use a 20 posistions rotary switch and a bunch of resistors.
The alternative, and probably easier way to go solve the volume control, is to use a voltage divider between the 2 stages of the buffered output.
Basically replacing R2 in the circuit below, with a stepped potentiomenter with the wiper connected to the grid of V1(b).
Attachments
You will have more chance finding a linear pot of low value.
Use a fake log scheme.
https://sound-au.com/project01.htm
Use a fake log scheme.
https://sound-au.com/project01.htm
I wholeheartedly agree! 1M log pots are available, 500k will do as well, I think. Because of the high value + associated wire, they have bigger chance of picking up noise, so mounting the pot physically close and using short wires is recommended. Use a shaft to extend the shaft.