Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: worth on May 22, 2011, 03:08:03 pm
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Although lifting the tonestack ground gives a huge boost.... a lot of high end is lost. What can be done to retain some clarity when completely lifting the ground ?
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The apparent increased treble in the normal tonestack operation is due to the fact that the midrange is cut so heavily that the treble seems boosted by comparison.
If you need more treble, you will have to lose some mid/bass somewhere to give the impression of more treble.
If you don't turn the volume knob up all the way, you could use a small cap between the non-grounded outside lug of the volume pot and the wiper (center lug). Typical values are anywhere from 50-330pF. This seems to cut the bass and boost treble, but the drawback is the tone changes with a change in volume (low volume = extreme treble; max volume = no apparent treble boost).
You might switch in a smaller cathode bypass cap on a stage to give a fixed bass reduction; the switch for the cap could be on a DPDT switch which also performs the tonestack ground lift. You would have to experiment with how small of a bypass cap to use; typical values might be 5uF (almost no bass reduction) to as small as 0.47uF (*very* bright). The switch could be wired to have the small cap always wired across the cathode resistor, with a bigger cap added in parallel for the full-range sound when the tonestack is operative.
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Following HotBluePlates lead
with respect, Tubenit
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Its funny in looking at this it was like a little lightbulb went of i had looked at it enough and even used it once and just got it I can be such a dork sometimes :l2: Tubnit i noticed in your PAB switches on other amps you put up you will use like 47k or 68k on one side and then a 150k on the other do ever notice a real need when have such a swing like that on lifting your mid pot .Thanks Bill
I was just curious
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notice a real need when have such a swing like that on lifting your mid pot
Yes
With respect, Tubenit
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Tubnit what I noticed in that one you drew above you have a pot as a variable resister I like that idea its funny I would have never even thought about that Im thinking fixed on one side of the switch and the variable resister on the other.
Thanks Bill