Tonebender mk2 thermistor shunt musings

[cspar]

Following a recent topic that started with a mk2 analysis and then moved into a bit of a discussion on temperature compensation in general, I happened opon an old thread with a question about using a peticular thermistor in a mk2.

That topic sums up like this;

...it should be possible - with some heavy design work or experimenting - to use a NTC in the application, think of it this way, you want to have the increase in temp to increase a current that fights against the leakage.

So for the last week or so the idea of using a NTC thermistor as/or in parallel with the feedback shunt resistor and maybe sharing a heatsink with a transistor has been in the back of my mind.

I've already got more parts lists than money and don't see myself getting any thermistors to experiment with anytime soon.

Nonetheless, I'm curious about if and how effective it might be.

Do any of you gurus that are better at math and more familiar with obscure components have any thoughts on this?

Shunt musings, anyone?

[antonis]

No maths needed..

Just replace any resistor with thermistor V-C transfer function (OK, some maths degree indeed is needed..) or, more plain, particular resistance for particular temperature..
(consider NTC as a CCW working pot wired as variable resistor -  all manufactures provide resistance/temperature tables..)

[Gus]

This has been covered using some different methods in the past

One was a servo
http://www.hollis.co.uk/john/rockface.jpg

another was a meter and a external bias control (in a Joe G. thread. I forgot what it was called)

[PRR]

What part needs stabilizing? Q2 Q3 are a plain old Fuzzface, that's stable. Q1 should not even work at all, without leakage. What do you select for? Possibly Vc. Which can be stabilized many simple ways. If you insist on a sub-standard device at Q1, it may need an external servo.

[cspar]

What part needs stabilizing?

My question more specifically than I stated is, could a selected NTC thermistor as the shunt resistor help with consistency of the circuit over a wide temperature range?

I was already thinking about aspects that Antonis has pointed out and was curious about frequency response and maybe something I wasn't even thinking about in the mix.

Thanks Gus, I'll look into that Hollis design more. Is this the one of Joe's that you're refuring to?


I'm generally curious about the concept of thermistor regulating germanium transistors though.

There's not a lot of information out there that I've found and this seemed like a good question to ask in hoping to add info to the results of "thermistor" when you use the search function while learning something myself, since I didn't find the answer searching 

Does anyone know of a patent or white paper that touches on the subject in any way?