
Blue Jinn
Rider of the ARPocalypse
Hello,
For some reason, I can't seem to get my head around this. I have a 12AX7 preamp built from a circuit in a 1991? EM. It's pretty conventional two stage with a "drive" pot on the second tube grid. Basically like the "McTube" with a Baxandall tone control between the two stages.
Anyway, has a pot on the output for volume control. Even with the volume control down it is still way too hot, so I was thinking of eliminating hte pot* and putting a 10k or 15k:600 trafo on the output, to knock the signal down, with a side benefit to lower the output impedance (can't find the circuit right now, but assuming it's fairly high as comes straight off the plate via a cap and a 2.2k resistor to the top of I think a 50k or 100k pot.)
I don't have balanced I/O on anything it's going to connect to so I planned to just pull the "+ side" of the trafo just past the blocking capacitor on the tube, and then run the "+ side" of the secondary to the tip on the TS connector, and then ground the other trafo connectors. The whole thing is in a metal chassis, and signal ground and chassis ground are all the same.
Or, would it be better to isolate the signal ground, and take + and - from the transformer secondary? (Grounding - at the console input.)
* I've read elsewhere that putting a pot in front of a transformer can have undesired effects.
For some reason, I can't seem to get my head around this. I have a 12AX7 preamp built from a circuit in a 1991? EM. It's pretty conventional two stage with a "drive" pot on the second tube grid. Basically like the "McTube" with a Baxandall tone control between the two stages.
Anyway, has a pot on the output for volume control. Even with the volume control down it is still way too hot, so I was thinking of eliminating hte pot* and putting a 10k or 15k:600 trafo on the output, to knock the signal down, with a side benefit to lower the output impedance (can't find the circuit right now, but assuming it's fairly high as comes straight off the plate via a cap and a 2.2k resistor to the top of I think a 50k or 100k pot.)
I don't have balanced I/O on anything it's going to connect to so I planned to just pull the "+ side" of the trafo just past the blocking capacitor on the tube, and then run the "+ side" of the secondary to the tip on the TS connector, and then ground the other trafo connectors. The whole thing is in a metal chassis, and signal ground and chassis ground are all the same.
Or, would it be better to isolate the signal ground, and take + and - from the transformer secondary? (Grounding - at the console input.)
* I've read elsewhere that putting a pot in front of a transformer can have undesired effects.
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