23 step attenuator potentiometer/vishay resistors -

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Offline dmannnnn

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Reply #15 on: October 26, 2009, 03:16:41 PM
... Unless the series attenuator is wired as a shunt, but then switching noise becomes a problem even with the better switches.  If the switch breaks contact at all, there is no attenuation to the amp.  This will cause some serious popping. ...
That does not happen if you wire the shunt attenuator as we do in the Foreplay III.


Yes, when I use the term 'shunt' I am referring to the wiring that Voltsecond shows on his page (fig1.0).   I don't really don't know how else to refer to that style of attenuator wiring.  The standard FPIII wiring works great.  When I first built the FP I thought it was just a standard series attenuator wiring.  I can see now that it is a little different.

 For some reason I found the wiring scheme on VS's page very intriguing so I tried it and liked the results (as long as the switch contacts are bombproof).  I liked the idea that there was a direct connection from the input to the amp grid with only a single resistor in the path and the switched resistors only on the wire leading to ground.

I remembered a previous post where you stated that these newer styles were not actually ladder attenuators, so I just refer to them as 'ladder style.'  I'm still not sure what a true ladder attenuator is.

Harmon Kardon T60 - Hagerman Bugle - Cal Audio Labs CL15
ForePlayIII - Paramount 300B's
Klipsch RF-7/Altec Model 14/Magnepan MG12


Offline Grainger49

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Reply #16 on: October 27, 2009, 12:02:01 AM
I think PJ is saying that there are a number of wiring schemes that can be called "shunt."  VoltSecond calls the FP III wiring "Shunt Mode Pot Typical" and many use the "Shunt Mode Pot Easiest."  

Also, the volume wiring in the FP III is one of many improvements that were made in that design revision to eliminate noise or problems that only some users had with the FP 2.  The list is long and highlights the sophistication of this improved design.
« Last Edit: October 27, 2009, 10:12:35 AM by Grainger49 »