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Ho jmcd (not to be confused with jcvd)
In general the birdged-T is just a notch circuit with very low-q. This means the notch is not likely to be too deep. In this application, peter used it to add a mid dip when the pot resistance is zero and it does nothing when the pot is at full resistance. The pot is in the ground connection of the T so it decouples it or engages it. being a passive circuit there can only be amplitude cut and more cut.
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I also note that the third gain stage has a 68k plate resistor and 9k total Rk (I think TUT3 may have specified Rk = 68k)
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Hi jmcd
Correct on both counts. This version is just a straight mid-dip with no control. The V2B stage has a bootstrapped grid-leak for slightly increased input impedance, thus reducing loading on the T. The gain of the stage is also low, mostly to make up for loss through the
Pete did have a ground pot in another model.
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There is a lot of potential for turning this into a guitar amp rather than a bass amp. adding bypass caps on the input stages gets you most of the way there.
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Thanks KOC,
I started by replacing the original filter caps and adding one extra stage of filtering for the preamp, and then I re-worked the random grounding scheme into your Galactic scheme. I'll modify the bias circuit when I have some free time (next week?).
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Hi jmcd
Yes, the simulations look good. The passband around a bridged-T is usually asymmetric.
The first tuning looks like it is supposed to reduce the response hump at speaker resonance, and/or to get rid of some of the 'woofiness" with the typical thumpy country bass tones of the day.
The second tuning would be good for guitar use.
You can make the bridge-T tunable or switchable, as you might suspect.