Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: AHeck on July 26, 2023, 09:35:45 pm
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Good evening. I'm trying to figure out A good way (if not the best way) to convert a bass signal to line level with good headroom. Would this work considering:
1) Using a 12AU7
2) Loading the AC voltage divider with 15K
3) The 5:1 transformer
4) A signal of .1VAC
5) All pots wide open
Are my Voltages close or should I try again?
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I'm both new here and new at audio signals, so take what I say with a grain of salt. :icon_biggrin:
I would probably tap my output phono jack on the preamp side of the transformer and remove the ground connection from the -ve DI pin on the output side. My understanding is the balanced connection is that way because the +ve and -ve line signals are inverted with respect to each other for the length of the cable. This makes it easier to remove common mode noise at the receiving end. In the drawing you linked, you have the -ve line tied to ground, which is a reference point. See Figure 5 in this link for what I mean: https://en.wikipedia.org/wiki/Balanced_circuit
That said, I don't have an answer for your other questions, although I am also interested in the proper technique. :occasion14:
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In the drawing you linked, you have the -ve line tied to ground, which is a reference point. :occasion14:
Yes indeed, You're absolutely right. I totally mucked up that schematic. Thanks for the heads up.
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Here's a corrected signal voltage schematic.
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Your phone jack will not work because it needs one side of the transformer connected to ground. You need a Switchcraft 12B stereo jack for the phone jack. Then when you plug in a standard phone plug one side of the transformer will automagically be grounded. Remove the plug to use the XLR balanced output.
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Your phone jack will not work because it needs one side of the transformer connected to ground. You need a Switchcraft 12B stereo jack for the phone jack. Then when you plug in a standard phone plug one side of the transformer will automagically be grounded. Remove the plug to use the XLR balanced output.
Yessir. Many thanks.
If you have a moment, does everything look as though it might work to output a line level to an audio interface or pro audio style power amp?
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I think it will work fine. Why a 2.2µF coupling cap? If output level needs adjusting, you can juggle that 22K/47K voltage divider.
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Why a 2.2µF coupling cap?
The whole project was cobbled together from the original Alembic schematic, Frog Pedal's PCB with an added SMPS power supply, and another source that was using the transformer and the rather large coupling cap. Since I'll be using it for bass guitar, I kept the cap big.
Thanks for the second pair of eyes.