Log or Lin?

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Aidan135711

Member
2008-02-10 11:40 am
Finally got my LM4766T amp going.Now I need a pot.
Ready made stepped attenuators are too expensive and I can't seem to find enough info on how to build my own so I choose to use some sort of high accuracy stereo pot.
Do I use a 100k log or 100k lin pot for input?
Or can someone show me the way to some stepped att. diagrams?
 
Hi,
you can use a lin with log faking resistor added.

The slight advantage of the lin track is better matching of resistance. This can affect balance between channels and becomes a bigger problem at high attenuation rates.

When mimicing a log pot with a lin pot+faking resistor it is usual to select a lin~=10times log value and then add a wiper to signal ground resistor ~10%to 15% of lin pot value.
eg 10klog or 100klin+12k resistor.
 
Hi guys!

I've noticed that some sources, usually (not always) headphone sources, may have a cap at the output that causes the bass to vanish if a 10k pot is used.

Unless tried, you wouldn't believe that Alpha's A20K ($1) plus ordinary 24 gauge solid conductor copper, could be a viable solution.

Whether that's true or not, it can give you a baseline from which to evaluate other options.
 
Clarification

AndrewT: Could you clarify your "fake log pot"? Between what should you put the resistor? Was it just between the pot and the signal ground? Probably it's just my English, that makes me not understand this... :eek: :confused:

I'm thinking of buying a simple Remote with preinstalled 100k (probably lin - not specified) pot.

Another thing: If you do this fake log pot, will that also resolve the problem with added noise with a high value pot (I guess it will, but ask the qst anyway...)?

Thank you!
Sincerely
Andy
 
Re: Clarification

andySweden said:
Could you clarify your "fake log pot"? Between what should you put the resistor? ...................
Another thing: If you do this fake log pot, will that also resolve the problem with added noise with a high value pot .....

the faking resistor goes between the wiper and the audio/input ground.
Zin of the amplifier can also provide the faking resistor value if there is no DC blocking cap between pot and Zin. But 100k varies Rs too much for many power amps.

The amp sees a worst case source resistance of [100k+Rs]/4 // 12k ~=8k1. this is still much higher than the 2k5 seen when a 10klog is used. But lower than 25k without the faking resistor.

Have you tried the search facility on the Forum, or even Google?
 
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