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In Reply to: RE: The Bob Crump TKD pot mod for the blowtorch preamp posted by fastcat on June 14, 2021 at 14:45:29
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Have Fun and Enjoy the Music
"Still Working the Problem"
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I think the idea behind the addition of the resistors (which
are 10X the value of the pot itself) is to have a hard soldered
parallel resistor network such that the actual pot acts as a
variable shunt to the entire assembly. Overall input resistance
is only a bit lower, and part of the pot becomes a hard connected
network of HQ resistors. The net result is slightly better sound
from the pot.
I did a similar trick with an ALPS blue velvet 100K audio taper
pot (using 10K metal film resistors) that brought down the input
resistance to a little below 10K, and provided a partially hard
wired variable resistor network. The precision resistors might
even improve the channel balance a bit(stereo).
.
Have Fun and Enjoy the Music
"Still Working the Problem"
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There's no virtue in being old,
it just takes a long time
...but nothing on the "why". Apparently John Curl thought there was a positive result from the late Mr. Crump's mod though.
One of my tube preamps may be regaining some lost real estate if the new, much smaller, B+ regulator works out. That will allow me to install a physically larger, hopefully better, pot or attenuator than the Alps blue I've been using for years.
The phono section needs to see 250K though, which is why I was curious if the Crump mod increased the impedance.
I'll do more searching on the subject.
Bob was an interesting man.At T.H.E. Show, 2000 Las Vegas.
He and John were in the room next door to where we were showing our OTL amplifier. VPI was handing out turntables to anyone who wanted them. Elliott was following up to do the set up.
Well, he messed up Bob's. He didn't add enough damping fluid to do anything and the platter was crooked.
Bob threatened to throw the turntable into the pool. He was going on and on about what a piece of S___ it was, etc. I grabbed the damping fluid and an Allen wrench.
John said I saved the turntable. He said Bob would have thrown it into the pool for sure.
Fun memories.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 07/01/21 07/01/21
I have read that Bob was very good with picking particular
components for the sound quality they produced - for the
circuits that John designed. Do you know anything about
all that, or how Bob got to be so good at that?
I guess it comes down to his exceptional hearing & experimentation. I made a bunch of raw cables for Bob, which he then terminated himself. I was cautioned (by my boss) to make sure I always oriented the cables off the spool, because he could tell if one was reversed. Bob helped me tweak my soldering skills too.
No. My only contact with Bob was for that two day show.
He was funny though.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
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