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I have a pre with a phono stage that wants to see 250k from the attenuator which follows it. The stepped series pot I have is good but a 46 position ladder or ldr would give me more gradual control. I found a kit LDR with self calibration from Tortuga audio that goes up to 99k and was thinking I could slap a 150k resistor on the ground leg to get me up to 250k seeing how the output hits the grid of the buffer tube that follows. Will the blocking resistor after the LDR damage it or harm its performance?
Anyone have an idea if this sounds workable?
Chas.
Follow Ups:
You should consider getting a different phono preamp (is it a phono preamp, or a phono preamp/linestage).
Only being able to drive a 250K load indicates a pretty crappy design with very high output impedance (maybe a bunch of 12AX7's). I wouldn't that it will drive cable capacitance very well either.
A 150K resistor between the LDR and ground will eliminate most of the positions you probably would use for normal listening.
The autocalibration would try to re-calibrate your 150k resistor.
You should speak to Morten Sissener at Tortuga about creating super-high impedance curves for his Tortuga boards, they are all digitally driven and variety of impedance curve "maps" could be created.
One thing though, LDR's do not operate well in impedance ranges higher than 30k as they become very non-linear and calibrating them becomes a real challenge. Another thing is their high 3rd order distortion that makes them useful in mostly "passive" attenuators where distortion is not amplifier any further.
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