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July 15, 2024, 06:45:08 AM

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Transistor power amp component matching

Started by Miyagi_83, June 02, 2024, 11:26:20 AM

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Hello, everyone.
First of all, I'm sorry if this question has been asked and dealt with before. I have done some searching, but haven't been able to figure out a straightforward answer. I'm new to solid state amplification. Now, to the point.
I've been looking at Rod Elliott's 40W power amp design and I don't know which components should be matched. I started reading teemuk's book, but for now it's quite a bit to digest, so I'm taking my time.
So, should I look for matched pairs of any devices found here?
The whole article:

Circuit diagram:

Thanks for any input.


Matched components are not really needed and are a waste of money unless you get them from a trusted source.

If you are using ESP's circuit boards, make sure you don't mix up the two R24s and Q12s. The amp won't work and you will likely damage several components.


J M Fahey

No power transistors in parallel here, you only have single Q8 on positive rail and Q11 on the negative one, so nothing to match.

Now in higher power amps where you have multiple transistors in parallel, as in Gibson G105 (or something like that) being discussed in another thread, where they use parallel 2N6254, yes, there you need it.

That said, modern transistors are *so* consistent that if same brand and type and from same batch (say you order 4 or 8 together from Mouser - Digikey - etc.) they *will* be very close, by default.

I often buy power transistors in bulk, say 20-25 units in a "stick".
Used to measure all and attach small labels to each ... not any more, incredibly consistent.

Only justified if, say, one transistor is made by, say, Fairchild and the other by ST or ON, or one was bought in 2014 and another in 2023 or some similar separated vintage.

Even so, low value emitter/ballast resistors (0.1  0.22  0.33 ohm) tend to even out current very well.


¡Muchas gracias, Señor Fahey!  :)
That definitely makes life easier, doesn't it? This info will come in handy one day, once I feel I'm ready to design and build my first high power transistor amplifier. I'm not going to rush it, though 😅