475K ohms output resistor

[tpatton]

Could someone knowledgeable please confirm for me that the 475K ohms resistor at the Seduction output (to ground) is not especially important to the sound?  I know from much experience that the opposite is true of the 47K5 ohms imput load resistor, but not so for the 475K ohms resistor at the output, I think I recall being told.

[Paul Joppa]

Yes, that's correct. It exists to allow the output capacitor to charge, but the input resistor of the preamp to which the Seduction is connected will swamp out the 475K resistor. For the same reason, the value is not critical, as long as it's large.

That said, we have not conducted listening tests. In theory it can't possibly have any noticeable effect, but theory has been inadequate before.  :^)

[tpatton]

Paul J, could you please tell me what "swamp out" means?  I'm wondering because I don't use an active preamp, but rather a shunt passive, signal resistor 12K ohms, shunt resistor variable but usually around 2K2 ohms (16 db attenuation) or 3K ohms (14 db attenuation) with the Seduction.  I've forgotten what a typical active preamp will have as an input resistance (if I ever knew).  In my situation, is that 475K ohms resistor at the Seduction's output still "swamped out"?  If not, would its sound quality then possibly matter? 

[Paul Joppa]

The Foreplay III has about 50K input impedance; I think the range from 10K to 100K covers most preamp inputs.

What I'm thinking is that something like 90% of the output current goes through the preamp input resistor, or the cable capacitance. Any nonlinearity or noise generated in the 475K resistor will be a small fraction of current through that resistor, and the total current is less than 10 percent of the other currents. So unless those other components (cable capacitance and preamp input resistance are at least 10 times better than the 475K resistor, you will hear them first.

But as I said, no careful experiments have been done. To my ears, capacitors are much more problematical that resistors. Your ears may vary though!

[tpatton]

Thanks, Paul, for this detailed spelling-out of your earlier "swamping" comment.  The only resistor upgrade that has ever impressed me, in a tube component, is in the 47K ohms input load resistors, where I've heard (as have others I've urged to make this change) how much TX2352 Vishays help.  Their quality is easily tested in a passive preamp, where there's little else in the circuit, and I've done a lot of testing there.  But capacitors are huge, in my experience.  I sold the first Seduction I built, and took out some "boutique" .47 uF output caps and put the stock caps back in--and found that I couldn't stand to listen to it that way.  I advised the buyer to go for something better--Obbligato Gold Premiums, as I recall--and he was impressed by the improvement.  I'm aware that Bottlehead stock components are carefully chosen, and are often as good as or better than the "upgrades" someone might replace them by--for example, Causasian Blackplate regards the Panasonic 220 uF power supply caps in the Seduction as better than the JJ Tesla ones I got to go there, and I believe him, and the JJ's are sitting idle in a drawer, probably never to be used.