Paralleled Transistors

Is there any truth to the argument that many paralleled output transistors, despite strong attempts to match closely, will smear music signals as they are not identical. How about those designers. using only N channel mosfet pairs rather than complimentary P Channel devices? Just curious whether using larger more powerful Mosfets, and thus fewer pairs, is better in any way than let’s say 12 smaller pairs (24) per channel? Thanks for helping me to understand.
Not really. The more transistors paralleled results in less current through each transistor. The benefits are: less distortion and less of a beta drop, making any inherent beta mismatch not a great factor (and further reduced by emitter resistors that enable each to share current more evenly). The reduction in distortion, especially at 4-ohm loads and lower, probably negates any mismatch.

However, there is no free lunch. More transistors in parallel will make it harder for the amp to control parasitic oscillations. It will also require the voltage amplification stage bias circuitry to source more current for the multiple transistor bases, which may also require inserting a driver stage before the output. All of this drives up the cost rapidly. Considering there are excellent high power transistors available (On-Semi NJW0281G), it doesn’t make economic sense to put a lot of transistors in modest powered amplifiers.

As far as mosfets go, Nelson Pass is the one to ask. Mosfets are less linear, have higher internal capacitance (must be charged/discharged very rapidly at high frequency signals) and they require voltage swings of 5 volts (instead of 0.6) at the gate for them to conduct. Yet Pass makes them work great.
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Very interesting and informative posts .....thank you to all. I recently auditioned a Danish Gato amplifier which uses one pair of large N Channel Mosfets per channel.(200/400/700 wpc) The sound was very pleasing, with a natural tonality, similar to a class A Gryphon type sound. Curious!
Short answer: no. Everyone parallels devices. Also paralleling them is not really related to complementary pairs (NPN and PNP) which are used to achieve DC coupling to speakers. Which almost everyone does.
Exceptions: tubes and some really oddball, very low power FET amps.
I’d argue that if you want to go to the trouble and cost to parallel up a gazillion devices, you could get some theoretical benefits. Nelson Pass certainly thinks so.
Ps: after posting this i saw that Nelson's name was being bantered about above, but for the opposite reasons i was. Nelson once designed, or tried to, a power amp using hundreds of tiny N-channel JFET TO-92 devices that he really liked.
pps: In sane-land, i recently completed  a design for a headphone amplifier with no loop/global feedback. This adds to the output impedance issue noted above, but is inherently stable into any load (including some crazy impedance 'phones). Among other things, it parallels quite a few to-92 NPN and PNP devices to achieve power handling temperature margin, and linearity. And it just rocks.

There was an extensive discussion on Audiogon about a year ago, when the late great Roger Modjeski hosted a thread entitled something like, "Ask an amplifier designer a question."

We discussed paralleling and matching transistors at some length.

Further to your question, I like epitaxial output transistors from Sanken (beware of counterfeits). Their higher power transistors tend to be slower, which you can absolutely hear as imprecise. Hence, if you want to hear the best your topology can do, you have to parallel.