Arfa Daily wrote:


Now this amp has a PIC onboard that (as well as controlling the footswitch
functions, also) senses the inserted jack in the input socket.
But, in addition, it also disables the Bias control circuitry, so as well
as muting the signal to the Power Amp, it also puts -100v bias onto the
output valves, thus cutting them off completely, unless a plug is in the
input socket.

But what I didn't know was that the PIC also gets a signal from the
Speaker jack sockets, and will again not take off the -100v bias unless
THIS also has a plug in it.


Whilst it's all very clever sticking a micro in there, realistically, what
is the point ?


** None so blind as those who will not see.


When has a shorted input, as is the case with most amps with
a switched input socket, ever caused any kind of problem ?

** It does not mute nor put the amp in standby.


And if you really want
to shut the output stage off along with the rest of the amp, what was wrong
with a standby switch ?

** Requires an intelligent human operator.

When I see some of this stuff, I can't help but
think that it is design for the sake of the designer's ego.

** Lucky your mad ideas are not anybody's concern.

What the uP does in this examples is useful, clever and makes great selling points too - the number ONE thing a guitar amp has to do is sell well in an extremely oversupplied market.

The uP in the Blackstar extends output valve life, biases them precisely and protects them in case of open circuit operation.

The only other amps I know with even this last features are some Rivera models - where the output valves cathode connection to ground is open until a speaker plug is fitted.

My only worry is obtaining replacement uPs in a few years time.


.... Phil