Log or Lin?

[Aidan135711]

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?

[richie00boy]

It depends on the input impedance of the chip amp. If you want to use a 100k pot which is quite high impedance, I would try a linear pot.

[Aidan135711]

I just checked the datasheet and it shows 10k pot on input.My mistake.
So,if I use 10k pot ,should it be log or lin?

[jaudio]

Use a log.

[Profsparks]

Just found this on another post, enjoy!

http://www.penguinlovers.net/audio/Attenuator.html


Cheers
Sparks

[richie00boy]

Yes if 10k use logarithmic.

[AndrewT]

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.

[danielwritesbac]

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.

[Aidan135711]

I just read profsparks link about building a ladder stepped att.
I might have a go at making one of those,however in his resistor calculator table,should position 1 read -80db not -8db,or am I mis-understanding something?

http://www.penguinlovers.net/audio/Attenuator.html

[AndrewT]

-80db or -infinitydb are the choices. The 8 is an attempt to write the symbol for infinity which is similar to an 8 on it's side with the right hand end open.
If Rg=0 then attenuation is theoretically infinity.
If Rg = 1r0 then attenuation is -80db.