Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TerryD on November 22, 2015, 12:39:23 pm
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In this Bugera hd 55, schematics below, Could I just disengage the presence control pot from it's present presence function and then use that same pot for a cut control that I would rig up?
What would I need to do to disengage the presence control pot from it's present function without messing up the amp?
http://bmamps.com/Schematics/Bugera/V55-Schematic.pdf (http://bmamps.com/Schematics/Bugera/V55-Schematic.pdf)
Thanks,
Terry
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Could I just disengage the presence control pot
don't know your *why*, but just put a 10k fixed R where the pot is and then you have a fixed presence :icon_biggrin:
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The amp has "presence" in spades. I'm trying to get rid of thin brittle highs. A cut control would be of greater service "if" I can redeem this amp at all.
Would the 10 K resister give me like 0 presence, which is what I have it on now.
Thanks, Terry
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What would I need to do to disengage the presence control pot from it's present function without messing up the amp?
Where do you normally set the Presence control? Zero? Halfway? Full-up?
If you normally set at zero, You could just disconnect the pot and C50 from the circuit. Presence control gone.
If you want a cut control, It is normally a larger value than 20kΩ, so you'd need a new pot. I think the pots in this amp are board-mounted, so you'll have some trouble removing that entire board to desolder the Presence pot. I don't know if you'll have enough space with the board re-installed to have a panel-mounted pot to stay clear of that board.
To add a Cut control, you'd need to have the new pot wired as a rheostat (wiper & 1 outside leg used), with a coupling cap from each phase inverter plate going into the Cut pot. The challenge is you might need several caps on hand, as you may not like the sound/action of one value, and replace them to get the function you like. At least that's what I went through when I added a Cut control to an amp.
There are several threads going on this amp; one thread would help keep the train of thought clearer...
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This actually seems like a user friendly board. But your right, getting a pot off a board is not child's play. There might be room inside. Seems like plenty of room but I'd like to be able to get at the cut control. The plan I'm using for the cut control is from a Matchless amp and I can't see the value of the pot. What's a good pot value for this?
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http://el34world.com/charts/Schematics/files/matchless/matchless_dc30_old.pdf
this shows a 250k. I installed the "brilliance" circuit from the clubman on one of my builds, don't use it, it does kill the volume, but at the expense of otherwise good tone