Hello,
In a new AD1865 based DAC, I'm thinking about volume control, but not in the traditional way. What if I would build a 24 step step 200 Ohm log "pot" and use it as I/V resistor before the triode preamp?
At the moment I use 200 Ohm resistor, but as I know if I reduce the resistor, the voltage over the resistor will drop. Can I reduce to zero?
Problems I'm thinking about:
I'm wondering did any of you experimented with this?
Thanks,
JG
In a new AD1865 based DAC, I'm thinking about volume control, but not in the traditional way. What if I would build a 24 step step 200 Ohm log "pot" and use it as I/V resistor before the triode preamp?
At the moment I use 200 Ohm resistor, but as I know if I reduce the resistor, the voltage over the resistor will drop. Can I reduce to zero?
Problems I'm thinking about:
- the resistor will be more "complex". Even if I do not put the resistors in series, but connect all to ground on one end and select single resistor. As I see I should be able to pick from E96 line. Does a little additional inductance matter here?
- the resistors (or the selected resistor at a given setting) will not be a tantalum or caddock or similar, only ordinary metal film resistor. I do not know how much difference it makes. Maybe I loose more here than what I gain with the lack of volume control later
- during switching, the resistance will go high momentary, resulting loud transient noise into the amps.
I'm wondering did any of you experimented with this?
Thanks,
JG
- With the volume control before the triode, you will always get the full triode noise.
I have no experience with any such circuit.
I have no experience with any such circuit.
In order to have zero voltage drop, it is necessary to have zero current through the "resistor", hints at the links below.
https://www.analog.com/media/en/tra...dbooks/system-applications-guide/Section3.pdf
http://www.ecircuitcenter.com/Circuits/op_PGA/op_pga.htm
I've also given DAC volume controls considerable thought and ended up with likely the same (or perhaps similar) idea as you. Tap the I/V resistor at 1 or 2dB intervals and switch between them. In fact I have already implemented such a scheme on an earlier DAC design. Since I have an LC filter prior to my I/V resistor, I can't just lower the R to reduce gain as that'll upset the termination of the filter. Hence a tapped attenuator - I used 74HC4051s to build the mux, having around 60ohm on-resistance. Seeing as they're cheap they could be paralleled I guess to lower the on-resistance.
With your I/V resistor of 200R, this makes a very low noise volume control provided your switches are also low on-resistance.
With your I/V resistor of 200R, this makes a very low noise volume control provided your switches are also low on-resistance.
