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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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In Reply to: RE: preamp with paralled outputs degrading audio posted by genelex on September 16, 2014 at 19:22:50:
That's opamp based circuitry. It's quite possible that the I/P impedance is different when the unit is powered on and when it's powered off.
More than 1 SS recording device has required buffering, when used in combination with tubed phono sections. Remember, BJTs are inherently low impedance devices. BJT circuits elevate the I/P impedance by the application of NFB. Take the power away and you have the low impedance of the base/emitter junction.
Constructing a JFET buffer is not difficult. Assemble a regulated bipolar PSU from a "Rat Shack" 25.2 VCT trafo, 4X Schottky diodes, and 7812/7912 3 terminal regulator ICs. The only cap. in the signal path is between the FET's source electrode and the load. The minimum coupling capacitance is 3.3 μF. That will work (barely) into the IHF "standard" load of 10 K.
Eli D.
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