The rectification effect between to dissimilar substances in contact is as a first approximation the difference in work function between the two substances.
For typical metals this is listed as -4.5 and for pure Carbon this is -5.0
From this the rectification effect of a typical wiper on a typical Carbon track is in fact very small and will only suffer any relevant increase in the case of the metal being oxidised, and just twisting the pot back and forth a few times is in practice sufficient to remove any oxidisation.
In a semiconductor such as Cadmium disulphide is connected via "Ohmic" connections to out put terminals. Exactly how Ohmic these are can vary widely, and in something like an LDR might well be far more of a Schottky barrier than any pot wiper, measurements I have seen seem to indicate this.
rcw
For typical metals this is listed as -4.5 and for pure Carbon this is -5.0
From this the rectification effect of a typical wiper on a typical Carbon track is in fact very small and will only suffer any relevant increase in the case of the metal being oxidised, and just twisting the pot back and forth a few times is in practice sufficient to remove any oxidisation.
In a semiconductor such as Cadmium disulphide is connected via "Ohmic" connections to out put terminals. Exactly how Ohmic these are can vary widely, and in something like an LDR might well be far more of a Schottky barrier than any pot wiper, measurements I have seen seem to indicate this.
rcw
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Yes, an Ohmic contact is one in which the electrons can cross a barrier with equal facility no matter what direction they are traveling in.
In quantum mechanics this means that the junction must be such that the electrons can tunnel through the barrier with equal ease in either direction, rather than having to cross a potential barrier that statistically favors one direction.
The mass production of semiconductor devices was enabled by developing methods of doing this, and how Ohmic the contacts actually are, is a major factor in performance.
rcw.
In quantum mechanics this means that the junction must be such that the electrons can tunnel through the barrier with equal ease in either direction, rather than having to cross a potential barrier that statistically favors one direction.
The mass production of semiconductor devices was enabled by developing methods of doing this, and how Ohmic the contacts actually are, is a major factor in performance.
rcw.
Curiously enough, there's no specific talk about this "diode problem" with the 'trimpots' on the Texas Component site, altho they do take a lot of trouble with the sophisticated contact system - they do emphasize the trouble taken with the connection between the resistance foil and the leads and altho this may have more to do with the physical durability of the junction of the 2 dissimilar metals, perhaps this does contribute to the better performance of these components
Just a quick question about DC coupling capacitors...
Most chip amps use a 2.2F DC coupling capacitor just after the volume pot, and I think I'm right in saying that is is supposed to protect the pot from DC. Does the Lightspeed attenuator need this cap, as I haven't used one with mine? If so, does it matter whether it is placed before or after the attenuator?
Most chip amps use a 2.2F DC coupling capacitor just after the volume pot, and I think I'm right in saying that is is supposed to protect the pot from DC. Does the Lightspeed attenuator need this cap, as I haven't used one with mine? If so, does it matter whether it is placed before or after the attenuator?
I recommend double filtering of the RF that flies around the modern home.
1. At the input to the power amp.
2. at the input to the box/screen that contains the power amp.
For 1. I use a 0.68us time constant, but any value from 0.3us to 1.5us are commonly used.
For 2. I use a 47pF directly across hot and return on the RCA input socket.
You may find that one or the other is adequate. But with all the radio transmitters around the modern home and in your neighbours', then I believe that more RF attenuation is better than audio contamination.
1. At the input to the power amp.
2. at the input to the box/screen that contains the power amp.
For 1. I use a 0.68us time constant, but any value from 0.3us to 1.5us are commonly used.
For 2. I use a 47pF directly across hot and return on the RCA input socket.
You may find that one or the other is adequate. But with all the radio transmitters around the modern home and in your neighbours', then I believe that more RF attenuation is better than audio contamination.
No sorry, only two channel for stereo use, a 7.1 would be a nightmare to do and get right, if at all. better off using one of these CT2 8 channel ones.
DACT audio attenuators
Cheers George
I have been trying to get my head around this but can't figure it out....
I am looking to replace the output capacitor of my dac with a better one, and I am trying to pick a value for this cap (as low as possible is best, as I want to use something good/expensive).
My setup:
Dac(tube output) --> Lightspeed --> Aikido LV preamp --> Pass F5
Can someone help me to select the right size output cap for the dac?
I don't want to use another buffer stage tbh.