[sdiy] AN299 VCO (was: SDIY list troubles)

[Paul Perry]

Certainly it works, by many accounts.
The thing is, it may not work, if one (for example) swaps the heating and
the temperature sensing transistors.
It's one of those things that one might think would not matter..
And, when laying out a PCB, it might be easier to lay out with them swapped.
I just mention this, to save someone being led astray.

As for the best matched pair - I find it hard to believe that the
transistors on the wafer are wired up differently according to where the
best pair is. That would make the chips very expensive indeed!

paul perry Melbourne australia

-----Original Message-----
From: Ian Fritz 

>I've heard that too, but I don't understand it.  Aren't Q1 and Q2 the best 
>matched pair, wherever they are located on the die?  I mean, on the wafer 
>the matched pairs aren't always in the same relative location.

>But the important point is that several list members have reported that the

>circuit works, so people shouldn't be put off from building it because of 
>one or two failures.