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In Reply to: RE: Eagle pcb posted by nc on May 10, 2008 at 18:07:56
Thanks John,
Like a lot of posters here, I bought some 5AR8 tubes a couple of years ago meaning to give it a go but never got around to it - now's the time. I'm planning on building a Zeus amp (Susan Parker's design) & I was agonising over the best way to feed a balanced signal into a 600ohm input trafo but now this may well allow me to dipense with the input trafo & use this BDT preamp as both vol control & phase splitter.
Waht do you think - is this feasible? How would I bias the Mosfets if I substituted the BDT preamp in place of the I/P trafo. Sorry for the questions but as you can see I'm no Ee & struggle with the simplest of things!
Follow Ups:
It would work perfectly in this situation. The ground connection in the BDT schematic gets set to the bias voltage in your amp schematic, definately no need for the extra input transformer. You can adjust the load resistors after the transformer in the BDT schematic to be whatever value you need to get the gain to drive the amp. The BDT circuit can generate high levels of gain if you need it.
Using it this way makes a wonderful integrated amp, I'm actually going to be doing something similar (but with pentodes).
John S.
OK, just to make sure I got it - The output trafo of the BDT preamp replaces the input trafo of the Zeus amp - the Com+ & Com- of the BD preamp are tied together & get the bias voltage (~4.5V) applied here to bias the Mosfets of the Zeus amp?
I also asked a question above about how the VR might be scaled up for power amp use - I'm thinking of integrating this preamp onto a "baby Huey" circuit I have and having a preamp out option for feeding my Zeus.
The feed from the BDT to baby huey will probably be SE and not as elegant as the differential input into the Zeus
One final thing, could this VR be made into a High current/low voltage regulator - I need something along the lines of 8A/40V - burst not continuous & I need to be able to vary the voltage for a voltage controlled volume adjustment?
Forgot to include image & I would love a board with sockets on board!
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