How to match transistors - Planning on stuffing some op amps

[Category 5]

Fabio sent me some of his awesome boards, and i can hardly wait to start stuffing the op amps.

Only thing I am not straight on is how to do the transistor matching. Fabio suggested buying them in big lots (like 100) which is fine, but then how can I match them once I have them.

I wanth the op-amps to sound good, so I thought I'd better ask before I screw things up.

Shane

 

[Gus]

I would build the part of the circuit they are used in as the best way.

Calculate the currents and voltages and try to test then at the points they are used at. The Hfe changes with Ic alot with some transistors so maybe a two point match would be better low Ic and high Ic

 

[tony dB]

:?:
how much "deviation" from spec can one expect with these transistors?
And, what will be the mismatch result in, in such case?
I just finished soldering 24 Melcors without really paying attention
Wouldn't mind having to redo a bunch of work if this yields higher quality

Tony

 

[daArry]

Hey

think this was originally posted by sum1 else round these parts, but here it is again:

http://www.notapplicable.co.uk/audiolab/905-matching-transistor.gif

:thumb:

 

[BuzAllen]

Some multimeters have the functionality to test both Vbe and Hfe. I have a fluke 863 that does Vbe and some other meter (cant remember name) measures Hfe. I know that some craftsman meters have the Hfe function and I have seen it on many others. I don't know what Ic they measure at, but it's a simple and quick method.

I usually match Vbe to within a few mV and Hfe to within about 10%

Brian

 

[Category 5]

Anyone know what hte 741 chips is? Can I just use

TI UA741CP Op Amp? There are also National and Fairchild variants.

Shane

 

[NewYorkDave]

You must be young if you're asking what a 741 is :wink:

Yes, the UA741 is the same thing. And the LM741...

 

[robomatique]

I am also new to this and am about to stuff some melcors. My multimeter can measure Hfe, should I match according to that or should I try to find something where I can measure Vbe?

Which transistors should I match?

Thanks

Robert

 

[daArry]

match the input BC's

 

[gyraf]

Vbe is important for low input DC offset.

But if you run DC-servo or capacitor-coupled, don't worry too much about this spec.

Jakob E.

 

[Flatpicker]

What about setting the DVM to "Diode Check" and measuring across the B-E junction just like you would a diode - would matching Vbe's this way be good enough?

 

[matta]

Hey Guys,

I?m also trying to figure out how to match input transistors for some
Melcors, but I have read another post from PRR saying that in the good old days
they may not have matched them at all his comments were:

The Melcor may have been assembled
from run-of-the-mill transistors, without any pretense (or need) of high DC
accuracy. IIRC: Even a perfectly matched pair will be unbalanced in that
design. And that is part of the charming sound of the older less
sophisticated designs.

I have learnt how to use my multimeter diode?s checker to distinguish NPN
and PNP transistors as well as measuring what I think is vbe (Many thanks to
Frank for this very important lesson! I Never got to clarify if that was vbe
I was measuring as I had a power failure and we were cut off). I don?t
know how accurate it is for matching transistors vbe this was and wondering if anyone had
an answer to Flatpickers question?

My DVM doesn?t measure Hfe and I have looked at the Atlas
DC55 which was mentioned in a previous post, but maybe it is not necessary
to do so if their is another way of measuring Hfe and from the looks of it
the % variation on the Hfe of the Atlas might be too broad.
(http://www.groupdiy.com/index.php?topic=560)

Thanks

Matt