Tube Amps / Music Electronics
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|previous: Ray Ivers Gil,
|7/12/2000 8:50 PM|
|Gil Ayan||Re: Trip + Presence + Why Dumble's Way?|
Thanks, we sure did.
I was talking about the physical pot itself. As you will see, the whole feedback loop is scaled:
1. Feedback resistor: (M) 100K, (D) 4.7K (off which tap in the Marshall? Important point, and I don't know!)
2. Ground resistor on feedabck side: (M) 4.7K, (D 390
3. Pot: (M) 25K, (D) 2K
4. Cap: (M) .1uF, (D) 1uF
Even if the Dumble has roughyl twice the negative feedback, I wonder why the choice of "scaled down" values. The PI's "tail" is (M) 10K, (D) 24K...
Right. But the breakpoint is not that different... In the extreme case, i.e. with the presence wide open, the Marshall sees 4.7K//.1uF, and the Dumble 390//1uF, the Dumble's frequency breakpoint being HIGHER, the way I see it...
I guess I don't see that quite in the same way. The feedback loop is negative, so having a higher impedance wouldn't result in more noise in this particular case, would it? I guess if it was a regular gain stage, sure, lower impedance would definitely mean more stability.
As I said, I am not sure I readily see a good "reason" for doing things that way. Probably nothing more than Fender Blackface legacy, where the feedback resistors were all "scaled down" with respect to the Bassman, as well.
|Ray Ivers Gil,|
Steve Ahola Gil: