Hi all! Long time lurker, first time poster...
I am planning on building a simple passive pre for use between a source with 560 ohm output impedance and an amplifier with 47kohm input impedance. I would like to use a stepped attenuator (specifically I will use either one of the series or shunt models from Khozmo (https://khozmo.com/). Does the formula for minimum load presented to the source by a potentiometer + amp in the sticky-ed thread (the formula given is 1 / (1/Resistance of potentiometer+ 1/Impedance of amp) also work for series and shunt stepped attenuators? If not, how do I find the load presented by these to the source when connected to an amplifier? Finally, how does one determine the maximum load presented by a series or shunt stepped attenuator + a source to the amplifier?
I hope this isn't discussed elsewhere! Thanks in advance for your help and patience 🙂
I am planning on building a simple passive pre for use between a source with 560 ohm output impedance and an amplifier with 47kohm input impedance. I would like to use a stepped attenuator (specifically I will use either one of the series or shunt models from Khozmo (https://khozmo.com/). Does the formula for minimum load presented to the source by a potentiometer + amp in the sticky-ed thread (the formula given is 1 / (1/Resistance of potentiometer+ 1/Impedance of amp) also work for series and shunt stepped attenuators? If not, how do I find the load presented by these to the source when connected to an amplifier? Finally, how does one determine the maximum load presented by a series or shunt stepped attenuator + a source to the amplifier?
I hope this isn't discussed elsewhere! Thanks in advance for your help and patience 🙂
Might be helpful to take a look at: http://www.eijndhoven.net/jos/attenuator-calculator/index.html
EDIT: Its also possible to design stepped attenuators that more closely emulate pots, although some might require more relays or switch contacts than the attenuators described at the link above.
EDIT: Its also possible to design stepped attenuators that more closely emulate pots, although some might require more relays or switch contacts than the attenuators described at the link above.
Last edited:
Great thank you for this. So basically what I'm getting is that a 10k log series stepped attenuator ideally presents a constant impedance of 10k to the source. So am I right in thinking that the minimum load presented by the attenuator + amp will be 1/(1/impedance of attenuator + 1/impedance of amp)?
If you look at the default example attenuator on the page I linked to, the last 10k resistor at the right should be taken to represent the amplifier input impedance in parallel with the actual value of resistor at the right. Otherwise the attenuator will not look like a 10k load to the source device under all switch conditions. Hope that makes sense?