Choosing the right potensio's value??50k/100k/1M?

thomgun_lc · 13th October 2005, 08:38 AM

Hi, i'm confusing about choose the right potensio's value. Usually people using 50k pot (assumed they don't use a preamp). In a basic theory, max value of the input's pot will give the best result, there is no drop voltage.It's necessary to keep our GC to have HI-Z in.
But, why GC'ers using 50k/20k as an input pot?Why they don't use a higher value like 100k/1M?
Using a lower value will causing drop voltage?is it right?
Need ur opinion please

Nordic · 13th October 2005, 09:00 AM

If I read the datasheet correctly Rin is supposed to be between 10k and 100k.....

slackman · 13th October 2005, 10:18 AM

Usuaslly potis with higher values tend to produce more noise than low-value pots...

Michael

PierreG · 13th October 2005, 12:07 PM

Quote:

Originally posted by Nordic
If I read the datasheet correctly Rin is supposed to be between 10k and 100k.....

What datasheet are you talking about?

Ropie · 13th October 2005, 03:26 PM

Quote:

Originally posted by PierreG

What datasheet are you talking about?

I would think the LM3875 datasheet.

Nordic · 13th October 2005, 03:55 PM

Correction it is Rf1 wich is recommended to be between 10 and 100k... lthough it does warn against big values for RIN

...page14

"The desired input impedance is set by RIN. Very high values
can cause board layout problems and DC offsets at the
output. The value for the feedback resistance, Rf1, should be
chosen to be a relatively large value (10 kÙ–100 kÙ), and
the other feedback resistance, Ri, is calculated using standard
op amp configuration gain equations."

thomgun_lc · 14th October 2005, 03:04 AM

So,do you agree if we using 1M pot?not using 50k pot?As far as i know, high Zin is important to keep the voltage to the chipamp from the source. Ussually after pot, we add a resistor (22k) to ground, why we don't use 1M to keep in High Zin?

13th October 2005, 08:38 AM	#1
thomgun_lc diyAudio Member Join Date: Mar 2005 Location: Indonesia	Choosing the right potensio's value??50k/100k/1M? Hi, i'm confusing about choose the right potensio's value. Usually people using 50k pot (assumed they don't use a preamp). In a basic theory, max value of the input's pot will give the best result, there is no drop voltage.It's necessary to keep our GC to have HI-Z in. But, why GC'ers using 50k/20k as an input pot?Why they don't use a higher value like 100k/1M? Using a lower value will causing drop voltage?is it right? Need ur opinion please

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13th October 2005, 09:00 AM	#2
Nordic diyAudio Member Join Date: Sep 2005	If I read the datasheet correctly Rin is supposed to be between 10k and 100k.....

13th October 2005, 10:18 AM	#3
slackman diyAudio Member Join Date: Mar 2005 Location: Germany, lower saxonny (Bremervörde)	Usuaslly potis with higher values tend to produce more noise than low-value pots... Michael

13th October 2005, 03:55 PM	#6
Nordic diyAudio Member Join Date: Sep 2005	Correction it is Rf1 wich is recommended to be between 10 and 100k... lthough it does warn against big values for RIN ...page14 "The desired input impedance is set by RIN. Very high values can cause board layout problems and DC offsets at the output. The value for the feedback resistance, Rf1, should be chosen to be a relatively large value (10 kÙ–100 kÙ), and the other feedback resistance, Ri, is calculated using standard op amp configuration gain equations."

14th October 2005, 03:04 AM	#7
thomgun_lc diyAudio Member Join Date: Mar 2005 Location: Indonesia	So,do you agree if we using 1M pot?not using 50k pot?As far as i know, high Zin is important to keep the voltage to the chipamp from the source. Ussually after pot, we add a resistor (22k) to ground, why we don't use 1M to keep in High Zin?

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