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In pursuit of better sound and channel balance, I replaced the stereo 100K Noble pot in my Audio Note kit preamp with a 50K Alps HQ PRO. Now I've got very little rotation (like 8-9 o'clock) on the dial before my system gets too loud. This is a common enough issue as I've seen on different forums, but with so many solutions I am more confused now than before.
Question: what should I do to both get more range of dial motion while maintaining the sound quality this pot can deliver?
There appear to be several methods, and if you've compared I would really like to know what you like best.
Thanks,
Doug
Follow Ups:
I have a firm recommendation which will both improve your problem and is also likely to improve the sound quality.
It is to use a series resistor with the pot as below, in place of the 'upper half' of the pot.
Identify the pot connectors; input, wiper, earth. Input-earth will measure 50kohms; with pot set almost fully anticlockwise, wiper-earth will measure a very low value.
Disconnect the input lead from the pot and connect it via a resistor to the wiper. That's it; leave earth connections as they are, leave the output connection on the wiper terminal.
I suggest in your case a resistor about 75kohm. The pot will,in use, typically be at under 10kohm setting so the input resistance will be typically between 75k and 85k ohms; as the unit works well with a 100k pot this will be absolutely fine. The slight variation in input resistance in use will be of no consequence.
If it is still too sensitive, change the pot to say a 25k one and leave the series resistor as is.
Use a good quality resistor and you should get an improvement in sound quality; and use a low power rating! Takman carbon are good, but consider Shinkoh and definitely consider Charcroft Z-foil, Vishay bulk foil.
I always use this type of volume control now; I prefer it to a stepped attenuator! OK, I may be in a minority here but I know I'm not alone ...
Do please try this!
Regards
Mike
Thanks, Mike. Since it's an Audio Note preamp, my intent is to use tantalum resistors.
I'm hopeful that the sound quality is similar to what the pot sounds like with no resistors, as it is really nice! I haven't tried a stepped attenuator but the micro adjustability of a pot is something I like.
Thanks again.
Shame to amplify and attenuate and amplify to end up at a net attenuation from the source.
and possibly in practice, too! I may explore that but I like the sound of my active preamp quite a lot and so...
Then eliminate the voltage gain stage at the front of your amp.
There should be very little difference between a 100k pot and a 50 k pot as a gain control, unless the 50 k pot is linear taper and the original 100 k pot was audio (log) taper.
To check: take an unconnected pot, rotate carefully to halfway (12 o'clock) and measure the resistance from wiper to each end with an ohmmeter. A linear pot will show equal resistances, but a log pot will have a large difference.
I haven't measured them to compare, but from the specs they are each audio/log tapers.
So measure it anyhow. You don't really know until you check. There are a LOT of fakes out there, for one thing; for another mistakes still happen.
I spent quite a while figuring out why the left was weaker than the right; turned out the power supply resistor dropping voltage to the driver was waaaaay high out of spec.
And I measured before I soldered it in. It drifted - a LOT. Mistakes/ defects happen.
Will check!
How is the pot connected to the input stage? Is there another resistor to ground at the grid, a coupling cap, resistor in series? It sounds like more is going on than would be expected simply by changing from a 100K to a 50K.
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Buy Chinese. Bury freedom.
The pot is connected to ground per the pot schematics. No resistor, cap or anything else is in series with the ground.
The suggested methods I received to get more dial range are: 1) add a resistor (50K) to the input 2) add a resistor (50K) to ground 3) add a pair of resistors to get specific attenuation amounts--see link for suggested values from Goldpoint. Seems -20dB is their suggested starting point.
"The pot is connected to ground per the pot schematics. No resistor, cap or anything else is in series with the ground."
No, you misunderstood my questions. I was asking if there's a resistor to ground at the *grid* (effectively in parallel with the pot), or a series coupling cap and/or resistor to the *grid*. The values of any components like those might explain why the 50K pot acts so differently. They might also be a consideration in determining the best way to modify the circuit, if that ends up being necessary.
--------------------------
Buy Chinese. Bury freedom.
mt
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