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-   -   Help in choosing a potentiometer as a "Passive preamplifier" (https://www.diyaudio.com/forums/analog-line-level/219342-help-choosing-potentiometer-passive-preamplifier.html)

sreten 16th September 2012 09:13 PM

Hi,

The best ~ 10K pot is a ~ 100K linear with an ~ 15K for pseudologarithmic.

rgds, sreten.

Esperado 13th November 2012 09:36 PM

Potentiometers are not the most transparent device to tune the volume. Mobile contact+carbon resistance are far to be ideal. (noise, grainy sound)
Better to go for metallic resistance arrays, mechanically (rotators) or electronically switched. You can even set that way a constant source impedance for your amp, where it behave the best. (low pass filter in it, square waves overshoots etc.)

DF96 14th November 2012 10:39 AM

Much of the music we hear will have already gone through a number of carbon pots and carbon film resistors. The contact resistance is not too much of a problem provided the next stage has a high input impedance, and no DC current draw. Switches can introduce clicks unless DC is kept well away.

Some people prefer switched attentuators and they may in theory be best, but many have also been disappointed to find that they can't have them without also introducing extra coupling capacitors and ground resistors. As in all engineering, you have to choose your compromises carefully.

MLStrand56 2nd December 2012 09:58 AM

Quote:

Originally Posted by deChrLam (https://www.diyaudio.com/forums/analog-line-level/219342-help-choosing-potentiometer-passive-preamplifier-post3157081.html#post3157081)
I think I should just use a 10K logarithmic potentiometer to get a nice pure sound

Can you please explain why you chose a logrithmic pot, over a linear pot? A linear pot gives you more precise control of the output level.

Japanese components typically use logrithmic pots, because they give the false sense of a much bigger amplifier. American/European components typically use linear pots, because they are more acurate.

MLStrand56

sreten 2nd December 2012 10:58 AM

Quote:

Originally Posted by MLStrand56 (https://www.diyaudio.com/forums/analog-line-level/219342-help-choosing-potentiometer-passive-preamplifier-post3266793.html#post3266793)
Can you please explain why you chose a logrithmic pot, over a linear pot?
A linear pot gives you more precise control of the output level.

Hi,

A linear pot will give you awful control of volume levels, not precise at all.

The best way is a linear pot with a log law faking resistor.
It will have far better channel matching than a dual log.

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example from ESP of a linear pot + log law faking resistor

Channel matching at low levels can be improved further by adding
a resistor that gives a minimum gain, rather that zero, at zero.

rgds, sreten.

AndrewT 2nd December 2012 11:11 AM

Quote:

Originally Posted by MLStrand56 (https://www.diyaudio.com/forums/analog-line-level/219342-help-choosing-potentiometer-passive-preamplifier-post3266793.html#post3266793)
........................... A linear pot gives you more precise control of the output level.

Japanese components typically use logrithmic pots, because they give the false sense of a much bigger amplifier. American/European components typically use linear pots, because they are more acurate.
................

misquotes and misinformation !

DF96 2nd December 2012 03:31 PM

In a conventional pot (whatever law) the worst piece of resistance is the wiper-track interface. Therefore you want as little current as possible through this resistance, so any resistance variation does as little damage as possible. Adding a law-changing resistor to a linear pot does the very opposite. OK in an emergency if the right pot is not available, but I would avoid it when possible.

Esperado 2nd December 2012 08:15 PM

Quote:

Originally Posted by MLStrand56 (https://www.diyaudio.com/forums/analog-line-level/219342-help-choosing-potentiometer-passive-preamplifier-post3266793.html#post3266793)
Can you please explain why you chose a logrithmic pot, over a linear pot? A linear pot gives you more precise control of the output level.
Japanese components typically use logrithmic pots, because they give the false sense of a much bigger amplifier. American/European components typically use linear pots, because they are more acurate.

The sensibility of our ears is logarithmic. A perfect logarithmic pot will gives-you the feel of the same volume increment for each same angle increment, while a linear pot will up most of the power at its beginning.
A pseudo logarythmic pot (they are all pseudo) is make of several superposed carbon slices at various places. It is more prone to generate parasitic noises when you move-it.

Quote:

Originally Posted by DF96 (https://www.diyaudio.com/forums/analog-line-level/219342-help-choosing-potentiometer-passive-preamplifier-post3241091.html#post3241091)
Much of the music we hear will have already gone through a number of carbon pots and carbon film resistors. The contact resistance is not too much of a problem provided the next stage has a high input impedance, and no DC current draw. Switches can introduce clicks unless DC is kept well away.

I have mitigate comments about you entry. In fact, in professional mixing desks, we use plastic Penny and Gilles linear potentiometers. And more and more records are produced in the Digital domain.
Despite i'm very suspicious about "audiophile" differences, i found carbon resistances to sound a little grainy, comparing to metallic ones.
Too the relative precision between the two channels of a traditional potentiometer is far to be perfect, and can lead to a little change in the balance between the two channels. reason why we used rotators and array of resistance in our amps.
Not to forget you can find very good sounding cheap circuit we can use as remote control resistances array based. As an example: http://cgi.ebay.fr/CS3310-Crystal-Volume-Remote-Control-Preamplifier-Kit-/260706392408.

Did-you agree ?

Wayne Parham 20th February 2013 03:05 PM

Quote:

Originally Posted by DF96 (https://www.diyaudio.com/forums/analog-line-level/219342-help-choosing-potentiometer-passive-preamplifier-post3267162.html#post3267162)
In a conventional pot (whatever law) the worst piece of resistance is the wiper-track interface.

I built a remote control using an Analog Devices AD5206 RDAC, and while it was inititially intended to drive an LDR (which would pass the audio signal), I connected one up to pass the audio signal through the resistor in the AD5206.

It is a linear pot, but the firmware that controls it uses a logarithmic function to control the pot, so the taper is truly logarithmic. As an aside, there are no mechanical potentiometers that have a true log taper - all are approximations.

The AD5206 device sounds very, very good to me. No noise, just purity. Don't know if it was a "proud papa" thing or not, but I ended up selling all my preamps and going solely with this type of arrangement instead.

Here's a write-up of my experience with this approach:

AudioLapDance 20th February 2013 06:09 PM

Ohh, the Analog Devices AD5206 RDAC does up to 6 ch! (AD5204 = 4ch) That would be great for anyone with a 5.1 setup (HT, surround, ... etc) and those with active crossovers (2 and 3 way!)

Are there any opamps onboard or is it just the resistor network?


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