the many ways of cv controll

[zipzap]

this is not mean´t to be a "double thread", i was just wondereing what should be matched when people talk about matched components like transistors, like here http://www.uni-bonn.de/~uzs159/

Besides - What methodes do you know for making a circuit cv controllable? We´ve all learned a bit about LED/LDR in the thread next door, so thats one way for cv-variable resistance.
What if you have a pot with all three lugs conected and you want cv instead?
I have used cmos swiches to shortcut pots, eg for glide on/off in a sequencer - also some kind of cv-controll. I have seen a pulse-vco controlling a counter that openes/closes some swiches that connect resistors or cabs to the signal path. depending on the speed the result "looks" like a certain value. kind of digital controll.
Must be many other ways.
How do transistors, mosfets and otas work in this context?

[Scott Stites]

Hey Zip,

Normally the transistors are matched for Vbe (voltage from base to emitter).

I've been searching for the schemo I've used - from the Moog Modular manual I think it was - can't find it!

In the meantime, here are a some links:

Jim Patchell's method:

http://www.oldcrows.net/~patchell/matcher/matcher.html

Don Tillman's Method:

http://www.till.com/articles/QuadTrapVCO/vcocore.html

Here's one I've never seen before:

http://www.elektroda.net/cir/index/Measuring%20&%20Test%20Circuits/TRANSISTOR%20MATCHING%20CIRCUIT.htm

The schemo I'm thinking about had a circuit for NPN and for PNP (I believe there was a mistake on the PNP schematic).

You're idea about listing all the different CV control mechanisms is a good one. I'll have to think about it a bit.

Take care,
Scott

[bugbrand]

Am I right in thinking the SSM2210 Dual Matched NPN chip should be useful? - states its a direct replacement for lm394

http://www.analog.com/en/prod/0,2877,SSM2210,00.html

You can get them as samples.

[zipzap]

As samples? Do you mean for free? how?
I guess its very useful for exp-converters in vcos. But if i build a moog filter and want to use a certain transistor, i have to handmatch them i guess?

[mosc]

[Scott Stites]

Dang - you're right, Howard! Never caught that. The mistake I was thinking was one that was on the Moog procedure that I had (no current limiting resistor on the PNP part).

Cheers,
Scott

[toppobrillo]

hey isthis it?

[zipzap]

In one of the links it said transistors should be matched under the conditions of the circuit. How´s that to do?
What i just did was use 12 Volts, collector via 220k, base via 500k to + and emitter to ground.
Now when i mach my ts in this way, is it likley that they won´t mach in a different enviorment? - Should the whole testing done with a set of different resistors?

[mosc]

The Vbe test is just one measurment. Another key one to test would be the beta, or current gain. The Vbe test is a good convenient one if the transistors are of the same type, like 2N2222 or whatever. The same type implies that more or less they are made to the same specs already. It would be best to get transistors from the same manufacturer in the same lot.

The best way to get matched transistors is to purchase matched pairs which are from the same wafer and put into a common package so the temperatures track.

[Uncle Krunkus]

Don't forget to only handle them with tweezers while you're testing them. The warmth from your fingers is enough to render all results pointless.