Re: Strategy for automated bias control


Ian Iveson wrote:
> Hello everybody!
>
> Finally set to work on my IR remote. There is so much cheap stuff in
> a microprocessor these days that may as well rope it in to other
> functions too. One such is bias control.
>
> The plan so far is to have the micro read the current in each output
> valve and reset the grid bias voltage to achieve a target current. A
> resistor ladder or DAC will be used for each valve, with the micro's
> own ADC used for reading current.
>
> The idea is that the bias will be incremented or reset, if
> necessary, each time the amp is switched off, if it has reached its
> stable operating temperature. Normally, the micro will be asleep
> between IR instructions, with all clocks switched off.
>
> The advantage of this approach is that it is off-line, and so
> non-intrusive, and yet seems to achieve everything that a normal
> servo-bias system does.
>
> Reality check, please. Have I missed something? Yes I know it may
> seem OTT to some...
>
> cheers, Ian

I'm not an engineer, but I like the idea of pinning down tube circuits
with a microprocessor that is not in the audio path but monitors bias,
cooling fans, etc. I've built some robot projects with my son for
science faire that we programmed in Basic, from this place:

http://www.parallax.com/

It was fascinating.

For something as critical as bias, I would think you would need
something "failsafe", whereby if the processor crashes a bootstrap of
some kind can take over with another resistor, or at worst cut power.

Also see lots of possibilities for controlling tone switching that can
change out caps in the tone stack, motorized pots, etc. all controlling
what is basically a vintage tube audio path.

Good Luck

.

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