Using blue Alps as vol control

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MEPER

MEPER

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Joined 2017
#1
I purchased some Blue Alps (50k and 10k) to be used for various pre-amp builds. They seems to be "good enough" for "high-end" use so I don't have to spend 400 USD for e.g. a Khozmo every time (used that for BA-3 pre). But I was a bit surprised how bad the channel match are in these Alps. Only one of the 10k is spot-on. So what do you do? …..just use them without checking the channel match and close the eyes? 🙂
For the 50k stereo pots a typical variation between channels if I set at 1 o'clock is something like 12.7k and 12.3k …. 0.4 k difference out of 12k ….so that is 3-4 %. I think that is a lot? ….I have not calculated what that relates to in dB between channels…...so maybe I should do that before complaining to much…...I would like < 1 dB channel error.
Are "stock" Blue Alps "Pass Lab certified"?
 
#8
You need to measure the attenuation instead of the absolute resistance value at the wiper, because the resistive elements may vary by up to 10% or more, and the attenuation may still be better than that.

In practice, the ratio Rwiper/Rtotal will give you the attenuation.
 
#9
MEPER said:
It seems Alps only guarantee <2-3dB tracking error.


Good idea with 100k Lin and shunted wiper. Then I have to find a good quality 100k lin. It seems Alps don't specify lin/log so I assume they are all log.
Click to expand...

I'm pretty much same clueless in Law and Medicine .... but that doesn't mean that there are no laws and cures

:clown:
first rule of Engineering - you need to learn where and how to find and extract needed information
 
#11
Zung said:
In practice, the ratio Rwiper/Rtotal will give you the attenuation.
Click to expand...


The above mentioned 50k. One channel measure 47.1 k and the other 47.5k (why do they call them 50k pots?). But the error from wiper to one end is not consistent. It depends on the wiper setting. So I can not just add a 0.4 k resistor to the resistive element but I may be able to correct the error a bit.


A typical setting measuring the side that goes from 0 - 47k:
34.5/47 = 0.734
35.2/47 = 0.749
So with 1V in I get 0.734V out in one channel and 0.749 out in other channel. Relative to 1V it is -2.69 dB vs -2.51 dB ….so that it not much of a difference.....?
 
#14
Wait until you're confronted with contact rectification, resistive element composition (carbon/cermet/conductive plastic), wiper geometry, and so on, and you still have to wire it up with OFC/silver/litz/solid core..., and solder with Sn/Pb/Ag.

Dealing with the unknown is a lot more fun! 🙂
 
#19
ColinA123 said:
My opinion.
I tried the DACT attenuator, it felt nice with soft clicks.
However I found the larger ones with Dale resistors sounded cleaner. (To my old ears)
I use twin mono ladder type as passive attenuator between music server and F6 amp
https://www.ebay.co.uk/str/ATOPELEC/DALE-23-Step-Mono-Ladder-Type-/_i.html?_storecat=3427425219 (Other suppliers are available)
Click to expand...

from experience - I don't trust these switches , unless I didn't opened it and put some quality grease in ( Vaseline at least)

some of them even need patient de-burring of all edges inside , or you'll get no contact situation in less than a year

I'm using 2 section/24 position ones for my Iron :Pumpkin: as relay command - greased with Mo-Si , both sections in parallel .... that way I can trust them ..... while I had 4 problematic pre-finished attenuators , of 5 I bought several years ago , and all of them gone Dodo in less than a year

however - they're cheap , just buy more 🙂
 
#20
So we are back to a Elma switch for quality if stepped attenuator or maybe Khozmo…..will see how my is doing after a year or just Alps.....for a "normal" type pot. Don't know if wire wound pots is an option...….
 
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