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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)

Mixi 12th February 2018 08:17 AM

i'm returning to this topic after doing some reading of "The Art of Electronics" (Horowitz / Hill, 3rd Ed.). Earlier in this thread it was mentioned that a lower resistance pot puts more "load on the source". I never quite understood what exactly that was supposed to mean. Now I stumbled upon this sentence in the book mentioned above:

Signal sources (e.g., oscillators, amplifiers, and sensing de- vices) all have an equivalent internal resistance. Attaching a load whose resistance is less than or even comparable to the internal resistance will reduce the output considerably. This undesirable reduction of the open-circuit voltage (or signal) by the load is called “circuit loading.” Therefore you should strive to make Rload ≫Rinternal , be- cause a high-resistance load has little attenuating effect on the source

Is that explaining what "load on the source means"? It seems to make sense to me :-)

rayma 12th February 2018 03:06 PM

Quote:

Originally Posted by Mixi (https://www.diyaudio.com/forums/analog-line-level/219342-help-choosing-potentiometer-passive-preamplifier-post5338771.html#post5338771)
Is that explaining what "load on the source means"? It seems to make sense to me :-)

Yes, and distortion will usually increase with heavy loading, as well.

johnhenryharris 18th August 2018 03:56 AM

Just do away with the potentiometer and its problem and use Discrete well matched high quality resistors for the voltage divider, digitally controlled. Like This:
https://files.diyaudio.com/forums/im...bits_start.gif Home > Forums > Source & Line > Analog Line Level https://files.diyaudio.com/forums/im...allink_ltr.gif Preamp Control -Volume,input,mute, remote
Enjoy :)

DF96 18th August 2018 01:36 PM

This thread is about choosing a pot, not choosing something else.

Chris Daly 2nd September 2018 07:58 AM

Quote:

Originally Posted by DF96 (https://www.diyaudio.com/forums/analog-line-level/219342-help-choosing-potentiometer-passive-preamplifier-post5519863.html#post5519863)
This thread is about choosing a pot, not choosing something else.

Indeed, but that does not have to confine the pot, to its traditional fairly mundane use.

Is the ethos of the forum is to discover new things ? or to continually repeat the past.

In this case just celebrating variations of patent 1357773 Rheostat ,or drawings made by Sir Charles Wheatstone in 1843

Choosing a pot should as I see it equally have the ability, to encompass designs which enable the pot away from just processing audio signals - whilst acknowledging a pot is being chosen for duty somewhere in that circuit as part of a passive preamplifier.

ctrlx 2nd September 2018 09:43 AM

Quote:

Originally Posted by Mixi (https://www.diyaudio.com/forums/analog-line-level/219342-help-choosing-potentiometer-passive-preamplifier-post5338771.html#post5338771)
lower resistance pot puts more "load on the source". I never quite understood what exactly that was supposed to mean.



have you read post 1 of this thread?

diyralf 23rd September 2018 08:39 AM

Your design has several issues. Put an op amp (5532 or 5534) after DAC and after the pot (voltage follower). You need two/channel. BTW you need a log law pot.

diyralf 23rd September 2018 10:29 AM

additio: All mechanical pots have a left/right deviation of 3..20! dB at the end positions.
If you can't live with it, you have to change to other technologies: stepped attenuator, relay att, digital volume pot, etc.

diyralf 23rd September 2018 10:45 AM

Quote:

Originally Posted by scottjoplin (https://www.diyaudio.com/forums/analog-line-level/219342-help-choosing-potentiometer-passive-preamplifier-post5171597.html#post5171597)
It's a good idea to roll off the low frequency to avoid excessive excursion of speakers, particularly if a turntable is your source. Yes, 20Hz is about the limit of audibility


A good friend of mine (making audio devices for 40 years) once told me, that it is not the job of good audio devices to roll-off the signal and limit the bandwidth. If a signal is bothersome or dangerous, it has to be eliminated at the front of the source.

Chris Daly 27th September 2018 07:55 AM

Quote:

Originally Posted by diyralf (https://www.diyaudio.com/forums/analog-line-level/219342-help-choosing-potentiometer-passive-preamplifier-post5553815.html#post5553815)
A good friend of mine (making audio devices for 40 years) once told me, that it is not the job of good audio devices to roll-off the signal and limit the bandwidth. If a signal is bothersome or dangerous, it has to be eliminated at the front of the source.

He has instructed you wrongly, YouTube
The World Beyond 20kHz Article By Earthworks Audio Founder David E. Blackmer


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