New doo-dad: resistor replacer

[funch]

I just ran across this link in the Hagerman Audio Circle:http://www.buildanamp.com/Resistor-Replacer-RR.htm

 

[earfanatic]

Interesting. There is a passive volume control / preamp project with LDR-s, folks like it. The magic behind it is actually some distortion it is different from resistors. At diyaudio someone measured them.
It is something like the difference in solid state amplifiers and tube amplifiers. People just like tube amplifiers, I think the effect is similar with LDR-s. Once I tried it and for my ears it sounded very good.

 

[Telstar]

I heard a LDR preamp made by a friend of mine and I couldn't hear any distortion. And it didnt add tubelike sound either.
I think not all designs with LDRs are equal and i'm not sure what they measured (but cant find that post/thread over diyaudio, and I would like to know).
 

 

[DingoSmuggler]

Check out the application notes for silonex's audiohm range of ldr based optocouplers for some useful info
http://www.silonex.com/audiohm/levelcontrol.html

 

[macm75]

I'd never go back to a pot or attenuator for volume control.  That being said, I can only assume the LDR "resistor replacer" would be phenomenal in the position of a critical resistor point, say the cathode of a valve - only issue, like any resistor, is the wattage.

 

[funch]

BTW, here's the thread in Audio Circle where I found the link: http://www.audiocircle.com/index.php?topic=111983.0

 

[earfanatic]

Quote:

I heard a LDR preamp made by a friend of mine and I couldn't hear any distortion. And it didnt add tubelike sound either.
I think not all designs with LDRs are equal and i'm not sure what they measured (but cant find that post/thread over diyaudio, and I would like to know).
 

 
Here You are, read this topic page 134-135. Nelson Pass did the measurements on Silonex LDR-s (the one used in many passive diy preamps too).
On the page 135 he does a THD vs input voltage graph with 10k input at different attenuation levels. With a 2V input signal the THD is between 0.3-0.4%
With 1V signal the THD is much lower. It could be better attenuating low voltage signals.
And as you said there could be different configurations in different designs, that changes everything.

 

[Telstar]

I remember that thread, I think I abandoned after the THD measurements
0.1% is just not acceptable for me. But I would like someome to measure the newest designs, there are a couple on diyaudio.
 
one day maybe... for now i'm sticking to resistors which have -150db third harmonic with 10Vpp.