[sdiy] Matched transistors - critical parameters?

[Matthew Smith]

Oren, Ian, All, thanks for the feedback on this.

As I haven't looked into the theory of the circuits in question and am 
just taking a "cookbook" approach at present, I wasn't sure if the lack 
of gain in the new devices might be an issue.

If this is all about heat, I don't see a problem.

The DMMT5551 (and DMMT5401 for PNP) from Diodes Inc., are "intrinsically 
matched," which is explained as being built on adjacent dies from a 
single wafer. So, with the constant improvement in fabrication 
technologies, I wouldn't be at all surprised if electrical matching were 
not as good as, if not better, than what might be considered dinosaurs, 
in silicon terms.

As far as heat matching is concerned, and I realise I could well be 
wrong on this, I can't see how the two dies, encapsulated in an area of 
about 1.5 square millimetres or less, wouldn't be isothermal as near as 
dammit. Not sure about the thermal conductivity of the lead bonding but, 
even with emitters connected externally, there is still a thermal path 
going that way.

I'm trying to cram an entire synth, with modern components, into as 
small a space as possible (all on one board, hard-wired.) No accuracy is 
required, as this will not be played in the conventional sense, but will 
receive control voltages from optical feedback in a multi-sensory 
sculpture. This is why I was asking about getting control voltages out 
of LDRs the other day, and why the LM358 VCOs caught my interest.

Hey, if I like the sound of it, I can always break it out into modular.


-- 
Matthew Smith

Business: http://www.smiffytech.com
Blog:     http://www.smiffysplace.com
Linkedin: http://www.linkedin.com/in/smiffy
Flickr:   http://www.flickr.com/photos/msmiffy
Twitter:  http://twitter.com/smiffy

ABN 16 391 203 815