If Marantz made STK's, theyd be golden
I see the modules have a stigma attached to them depending on who makes them, (as usual) referring to Warren's 1st post.
Abuse a solid state amp by overheating it repeatedly, it will eventually fail, doesnt matter if it's STK's, Kenwood Trio's (Sanken), or Toshiba discrete outputs. Basically, all solid state complimentary Class AB amps sound the same, the differences are about 90 percent in the power supply, and the other 10 percent cannot be heard....only imagined. Those that say the metal plates on STK modules are too small are'nt getting out their rulers and making any measurements, by comparison most modules I've seen have more surface area than a combined set of discrete output pair.(Even TO-3 types) Digging a little more deeper into the thermal foray, You will find that the junction to case thermal coefficient of these devices are not as low (efficient)as a discrete power transistor in most cases, and this accounts for just about all of the "these things fail under heat" opinions. It is ESSENTIAL that these devices have as good of thermal coupling to their heatsinks as can be had, make sure thay are gooped up well, secured tightly, and you'll be fine. This will not make up for the above thermal coeffiecient, as that is a function of heat transfer within the device itself, BUT, The above mentioned thermal "weakness" is adequate however, to protect the units when operated within spec and sinked adequately.
There is absolutely NO reason you should "keep the volume down" or "leave Your tone controls flat" if You use a unit employing these modules than You would any other solid state devices. Driving them into clipping also is no more an issue for STK modules than it is for a discrete design. There is No reason to operate into strictly an 8 ohm load, most of the modules are safe into 4 ohms, and yep they get hot as hell just like discrete outputs under those conditions. I have repaired dozens of receivers and amps that had blown output stages, and there have been just as many with roached discrete output transistors as there have been STK modules.
Well designed amps have thermal protection, again, does not have to be (and is not in my experience) more elaborate protection because STK modules are employed, thats just good design regardless. Heat is the arch enemy of all solid state electronics, period.
With an adequate power supply behind them, as in the case of the Sanyo 2050 receiver for instance, they DO sound just as good as a discrete output design. Once again, the stigma determines the sound here, not the ears, as has pretty much been the case around here forever with anything labeled Sanyo. And as for advanced topology and circuit designs, it all depends on the STK, as some do have CCS's employed for their input stages, as well as other advancements that were being developed and employed at the time. Some have very advanced designs that sport specs just as perfect as their discrete amp counterparts. As we all know, ears dont hear numbers and if one skimps in other areas of the design (as Warren mentioned), any amp can sound crappy regardless of its schematic. If you were blind to what an amp employed (discrete vs. STK) and all you could view was the test equipment, You simply could not determine from the measurements which amp You were testing.
In the beginning of their use, STK modules were NOT a cost cutting measure from a parts only standpoint, in fact, they were more expensive than discrete output counterparts of the same power level, the savings came in labor, You just bolt them on with two screws to a flat, undrilled surface, no sockets, no mica insulators and extra wiring to the power transistors.
Why do KR9600's fail, has nothing to do with their modules, has everything to do with the fact that they get abused because of what they are, by mostly the non-audio loving groups. "Check this out man, this was my Dad's- it' got 200 WATT's dude, I can rattle my playstation controller right off the top of this iPod dock, watch man"......................
Not being able to replace the Yamaha's STK module without oscillations is clearly a result of poor design, something is wrong there, and it aint the STK's, I have replaced many of these on 25 year old receivers, and never had a problem with a "new" replacement STK module. A commercially produced amplifier should never oscillate.....ever. Someone dropped the ball on design there, or there was way more cost cutting going on at Yahama than even, oh my gosh, that crappy Sanyo stuff. Of course, the models being mentioned are not Vintage receivers to my knowledge, and basically anything produced after about 1980, had nowhere near the overbuild mentality incorporated into it, as units that fit into this time frame (before 80).....
SO here's my advice, if you use a receiver built after the Vintage era (the Real Vintage era), then I would suggest Warren's advice, keep the volume way low, turn off Your loudness and leave your tone controls to flat, regardless of whether Your unit employs STK's or has twenty four discrete devices in parallel, and use strictly 8 ohm loads, but for those of You that have SX-780's for instance, go ahead and push all You want and enjoy, Your no more likely to fail than anything else, and 100 times less likely than anything built later by Pioneer, like those with "V" in their model numbers, or ones that say "elite" on them..........
