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correct value for Volume pot - NJ MMB

G

grahamdocman

pfm Member
I'm now preparing to assemble components for my build:
In his BOM Neil suggest a 20K volume pot. The ELMA and GOLDPOINT are way out of my budget

Two questions:
  1. 20K (especially as a ladder stepped attentuator - my preferred choice) seems quite difficult to come by, but 25K is very common - is it OK to use a 25K 'Pot'
  2. if a 25K pot will do without having to alter other component values: has any one experience of or tried the EIZZ Pots - I'm finding it very hard to find any objective assessments.
If it has to be 20K, the I'll try building my own using a Blore Edwards or Valab 4 Pole 24 way base

All thoughts appreciated
 
A cheap Chinese switched resistor volume pot will give better balance and can be customised with your choice of resistors if you want
 
25K will be fine. Depending on your sources, you can probably drop down to 10K if you had to.
 
Thanks - I think I'm getting there and have found a "calculator" to populate my DIY ladder pot for 20K input impedance, it even gives me the nearest available resistor values to the theoretical resistor values.

BUT the calculator has also confused me:
https://www.hificollective.co.uk/sites/default/files/elma-shunt-a47-calculator.xlsx

It gives two examples for a 24 'step' ladder , one is with "no load", the other is for a "1M Ohm load".
Which do I choose and can you advise me (if I need the "load" version), what should I assume the NJ MMB load to be ?

As ever, thanks for your help
 
The load is the input impedance of the line stage, which is about 62K. It will only make a marginal difference - the gain change on the first few steps will be slightly bigger than the ones further down. But if you worry about such things, that would be a good value to use.
 
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