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buddam 20th March 2017 08:05 PM

Pseudo Shunt wiring
 
Dear all

I recall there being 4 ways to wire a pot for the pseudo shunt mod, but the WAD FAQ section has been edited and only 1 pseudo shunt mod now appears. Does anyone have details of the original 4? I am in discussion with a colleague and it may be that my wiring was not pseudo-shunt at all (input shorted to output (ie pin 1 to 2), earth (pin 3) remaining separate.

Thanks

Adrian

A Stuart 21st March 2017 10:06 AM

Re: Pseudo Shunt wiring
 
I could be wrong here, but I think the nearest context for use of the pseudo word is in to "pseudo-logarithmic". Here, a linear potentiometer is used in conjuction with a pattern of fixed resistors to mimic the effect of a logarithmic potentiometer, conferring some technical advantage over logarithmic (- accuracy of balance??, choice of manufacturing material??) .
The modified shunt is still a true shunt, nothing pseudo about it.
Googling pseudo logarithmic potentiometer gives this near the top of the list plus many others:

https://www.maximintegrated.com/en/a...dex.mvp/id/838

Apologies if I have totally misunderstood.

Alastair

On re-reading, you probably want to Google "modified shunt potentiometer" instead, as I suspect it is not pseudo-whichever you want to know about. I start to recollect there were several ways a shunt could be modified, but the one in FAQ was considered best, probably because any electrical grunge generated at the wiper contact is electrically close to ground and far from the output.

Richard 21st March 2017 12:31 PM

Re: Pseudo Shunt wiring
 
2 Attachment(s)
Hi Both, I think Adrian's referring to the 2004 thread about the shunt pot mod. We went through 4 versions ABCD iirc. The final one is shown in the FAQ as a working drawing and photos with correct pin numbers for Alps Blue.

I've got the 4 drawings but the pinout numbers are wrong on C and D as I numbered the pins from the wrong end for the Alps not realizing they were already numbered on the pot :o so pins 1 and 3 are transposed (the Panasonic pot I was using doesn't have any numbers on it that's my excuse :D'oh!:).

It might be best if you say how yours is wired Adrian and I'll see which drawing it matches.

buddam 22nd March 2017 07:11 PM

Re: Pseudo Shunt wiring
 
Hi Richard

frightening to think that the pseudo-shunt discussion started in 2004! I have a Rose pre with Alps Blue and WAD Pre II with Panasonic Black. Both are wired similarly, but the 3 & $ pins of the Black are shorted together. On both the resistor is connected to both 1 & 2, but earth (3 or 3+4) is kept separate.

Hope that is clear

Adrian

Richard 23rd March 2017 08:24 PM

Re: Pseudo Shunt wiring
 
Hi Adrian, frightening indeed :eek:
How are you numbering the pins? It sounds like yours is wired as per the original idea and your numbering agrees with drawing A but that had the pins numbered the wrong way compared with Alps Blue numbering.
So there was the original way (in the thread) and how it ended up which was with the pot "inverted" and the wiper grounded.
Perhaps the easiest way for you to tell is whether or not your signal is conducted via the wiper (as originally), or is hard wired via the series resistor, so that only the ground is made via the wiper (final version as shown in FAQ) :thumbsup:

John Caswell 23rd March 2017 10:29 PM

Re: Pseudo Shunt wiring
 
I seem to remember that some of the pots, Panasonic? had four pins per track on them of which two were earthy pins which confused the issue somewhat.

John


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