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Re: Which is the BEST step attenuator

192.169.41.33

Posted by DG on August 5, 1999 at 06:47:07

In Reply to: Re: Which is the BEST step attenuator posted by Thorsten on August 5, 1999 at 03:07:07:

>>>I find the shunt design gets you to or exceeds a ladder attenuator quality without the cost. Are you
familiar with this design.<<<

We have tried that. Surprisngly (or actually not surprisingly) it does not give the same performance.
My personal Take is that we hear the effects of the quite severe loading (low input Impedance) of the
Shunt-Attenuator scheme on the preceeding stages.

Anyway, in one of the Euridice Preamp's (we build two of them recently) my Friend Jon used a Shunt
Attenuator using a single 20k Vishay Series Resistors and suitable (mostly Holco) shunt Resistors. The
other used a classic 100k Ladder Attenuator with Holco Resistors. All other Details of the Preamp's
(Parts, Valves, output transformers and Powersupplies) where at this point identical between the two
Preamp's.

Still, the Preamp with the Ladder Attenuator consitently sounded SUBSTANTIALLY better. Since
then both Preamp's have been converted to Ladder Attenuation using Holco Resistors for most
positiona and with Vishay's in the most often used positions.

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A better comparison would have been to have both ladder and shunt attenuators having the same input impedances. Otherwise you wouldn't know if you are listening to impedance related distortion or other distortions of the signal path like solder junctions.

The true test is when a certain attenuation level is selected, both the series and shunt resistance of the ladder and shunt designs have the same values, then any difference in sound quality would be due to everything else except impedance matching.

That's exactly what I did in a few scenarios using exactly the same series and shunt resistor values. The results in order of quality:

1) just 2 resistors with no switches - best result

2) Shunt design with one shunt resistor only for each selection and ladder design - the same sound - actually tantamounts to the same design if viewed statically in this one controlled case

3) Shunt design with shunt using series step attenuator - in the test case the shunt comprised a series of ten resistors adding up to the same resistance value as the above cases)

4) Series Step attenuator in normal cofiguration (like regular pots)

5) Shunt Design with Conductive plastic pot as shunt

6) Conductive plastic pot in regular configuration.

The point I was trying to make was referring to (2) where you can get the same (sometimes better) sound from a shunt design compared to a ladder attenuator but at a lower cost since you use half the amount of resistors and usually have less solder junctions that the signal has to pass through

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