Related to AG's post #21:
So from that explanation can I liken the JFET's purpose in the guitar amp to be more like an effects pedal and not a preamp as I thought?
My efficiency question was in reference to using the resistor/diode vs. an IC. In the same vein - am I choosing one over the other based on my applications current needs and not worry about efficiency.
Now for updating,
I pieced it all together - 78l05 powering the BT dongle, 7809 powering the bridged lm386 amp w/o a JFET, and driving an 8Ω 25 watt RMS speaker.
I've used it a few nights at work and am happy to report it still has all it's magic smoke. It works well for what it is but I get some noise from the BT unit. From looking around I've found the problem is likely a ground loop an can be fixed by adding an isolation transformer. Would something like this
DA103c work for me?
On another note I ordered some of the LM675 Staffan suggested and will try experimenting with some of those next. Should I start a new thread for those questions or just keep adding here?