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Matched transistors for analog experiments

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RoGeorge:
Looking for factory matched BJT transistors, but I wouldn't mind finding some matched JFET or MOSFET either.  They are for experimenting with long tails, current mirrors and alike.  This is hobby level, so I don't want to break the bank buying $30/1pair of famous NOS part numbers.

I've looked at mouser, and for 'transistors array' it returns all kind of darlington and drivers and H bridges.  When searching for 'matched transistors' there are only 3 part numbers, decent price (less than $0.5-$1/pcs), but they are all pnp pairs.

There are some ROHM pairs from their THAT300 series, advertised in a mouser "what's new" page, but they do not appear as products for sale, only advertised and no link to buy.

The matched transistors are for casual learning and experimenting with discrete analog IC-like structures.  Required specs are as good as possible, but at very low cost, less than $1/pair.

- What paired transistors part numbers to look for, and what search term to use?
- Will factory matched be better matched than hand-matching from a casual bag of 20..50 THT discrete transistors of the same type?

Andy Watson:

--- Quote from: RoGeorge on February 13, 2024, 09:04:10 pm ---- What paired transistors part numbers to look for, and what search term to use?

--- End quote ---
Try "dual transistor"

In my limited experience, you will struggle to match individual transistors to the same level that is easily and readily obtained with transistors that are on the same die. I believe CA3046 are still available.

Kleinstein:
There are a few cheap dual BJTs (e.g. SOT23-6). They offer some degree of matching, though not as good as the higher cost SSM2212 or THAT300.
Examples are FMBM5551, NST45011.
THT duals are rare however and can get expensive.

For JFETs there is the SK2145 as the prime candidate for a cheap pair - though already connected source to source.  There are also some more dual JFETs, but not all offer good matching, at least not guaranteed.
For high performance the JFE2140 is a candidate to look at, though more in the $4 range, still not super expensive.

Chances are manual matching could be more accurate (at least for the parameters tested), if one starts with transistors that are quite uniform or accepts a low yield (e.g. only use the best 1 or 2 pairs out of 20).

magic:

--- Quote from: RoGeorge on February 13, 2024, 09:04:10 pm ---Required specs are as good as possible, but at very low cost, less than $1/pair.
--- End quote ---
This virtually rules out monolithic pairs, unless you manage to find some obsolete transistor arrays on eBay or similar sites. I think I have seen a 5-NPN array for $2 once. You can probably forget PNP.

If you look at dual transistors in SOT23-6, some of them are offered with ±2mV offset guarantee. IIRC suppliers were NXP and Diodes and part numbers were quite generic: xxx847xx, xxx3404xxx, xxx5551xxx or their PNP analogs. I imagine these may be very handy for mass production.

The Vbe spread in a bag of 2N3904/3906 or BC847/857 from decent manufacturers like Fairchild (now ON semi, I suppose) is very small, a few mV. You will easily harvest multiple pairs with 2mV or even 1mV offset. Test with DMM diode mode, one probe on E and one on BC shorted together. Or get the AVR transistor tester, which will also show β.


I hope you know that 2mV matching only holds if internal junction temperatures stay within 1°C of each other. Only realistic if power dissipation is very low or equalized.

djsb:
Alfa in latvia still make a LM194/394 equivalent. They are discussed in this thread

https://www.diyaudio.com/community/threads/lm194-lm394.333623/

They can be bought from Erica synths or Thonk in the UK.

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