Linear to Log POT using resistor

Linear to Log POT using resistor

Have any of you guys tried it :?:

I've been doing a little research & it looks like a good idea but is there a downside to it... quality or sound wise?

+ Linear's are cheaper & easier to get in various values.

I would like to try it in an API 312 style pre (18 or 20k rev log) & thought I'd see what you guys thought maybe even give some tips or advise either way :green:

Thanks,
Kevin - khstudio

In basic volume controls it works very well, and gives you the chance to tweak the range (how fast the volume raises).

But as far as I know, the arrangement doesn't work well in API-ish preamps, it was probably Fabio who beat this to death and came to the conclusion. It will "work" but the range is dumb.

thanks,
I thought there might be a catch...

I probably should have ordered the dual 10k rev-log's from JLM and wired them in series if I knew it would be so hard to find them in the 15-20k range I can only seem to find 10 & 25k.

Kevin

We've discussed this several times - try a search..!

The scheme works for converting a lin pot to a log-like potential divider - but you sacrifice the constant-impedance load of a real log pot.

Jakob E.

I did try searching... maybe mis-spelled... or abreviated wrong.

You answered my question anyway.

thanks

This might be usefull http://sound.westhost.com/project01.htm

The scheme works for converting a lin pot to a log-like potential divider - but you sacrifice the constant-impedance load of a real log pot.

Jakob E.[/quote]

A pot has no impedance aspect, its a passive device like a resistor.

[quote author="Mike Keith"]A pot has no impedance aspect, its a passive device like a resistor.[/quote]

Huh? :?

[quote author="khstudio"]18 or 20k rev log[/quote]

You can turn a B pot into an A pot, but you can't turn anything into a C pot. Like Jakob said, this comes up every once in a while, mainly fueled by the faulty "Secret Lives of Pots" article by R. G. Keen...

[quote author="khstudio"]I can only seem to find 10 & 25k.[/quote]

Oh, c'mon - just use the 25K and be happy!

Peace,
Al.

25K is what API uses, all you have to do is change the feedback resistor value...

'A pot has no impedance aspect, its a passive device like a resistor.'

Click to expand...

nothing personal dude, but you really need to study electronics some more.

so your saying the value of a pot changes with frequency?
Never heard of that in my 30 years in electronics...

[quote author="Mike Keith"]so your saying the value of a pot changes with frequency?
Never heard of that in my 30 years in electronics...[/quote]

So, what's the appropriate amount of Xl & Xc to cross the border from resistance to impedance? What if theres' less of the other? :shock:

A pot has inductive reactance?

Are we talking audio band or Microwave frequency?
2 wires close together will have a small amount of capacitance, 2 traces on a pcb will also...
this is a waste of time.....

But it still IS impedance. Sure, it's mostly pure resistance but if you put a 1k resistor in front of your op-amp buffer, the thing has 1k output impedance over the audio range. If you put a 1H choke there, you couldn't say one specific output impedance but you'd have to state one at various frequencies.

[quote author="Mike Keith"]A pot has no impedance aspect, its a passive device like a resistor.[/quote]

You're saying a passive device doesn't have an impedance?

http://en.wikipedia.org/wiki/Impedance

Google hit no:1 for "impedance".

Check for "impedance for different devices".

Hmm.. I sense word-splitting.. :grin:

To me, resistance is (zero-Hz) impedance, but YMMW..

A forum search finds e.g.:

http://www.groupdiy.com/index.php?topic=42609

Jakob E.

To split hairs, the cable that we use has far more cap. and inductance than that pot does... and using cable is unavoidable...
So what do you do about that???

[quote author="Mike Keith"]So what do you do about that???[/quote]

I avoid cables with too high a capacitance, gear with too high an output impedance and make the cables shorter.