Not long ago I dealt with an unobtainium STK. It can be done. This was a lower powered one so the ubiquitous LM3886 was just fine. I thought of just putting in pre out jacks but nope, the tone controls were in the global feedback loop.
Bottom line is that STKs are not a performance issue at all. Look at the internal diagram of them and see that this is how you would design it anyway. Seriously. And you have the bias regulator really really thermally coupled. Someone really should make modern replacements but alas, there is simply not that much demand.
There are three major types. One is the Darlington power pack which only has the outputs, drivers and bias regulator. The transistors in those are just as good as anything out there, they do not have more nonlinearity which would cause distortion, and other important amp specs are determined largely by the design, not the STK. The 0029 up to the 0100 series are like this. The performance is up to the designer for the most part, as stated - a shortcut.
Then there are the really integrated ones that are the whole power amp section on a chip. Engineers don't just save money using them, they save time and PC board space. And holes. Back in 1990s if you called a circuit board manufacturer for a price, before he even wanted to know anything like the size or whatever, he asked "How many holes ?". I know why. And that same reason is why SMDs have profilerated so well. That stuff is hard to drill and mill. Actually for holes they punch it. You'll notice in some things they just punch a row of holes and break it, it is actually cheaper and faster to do that than to cut or drill it.
That is one of the major reasons that ICs, including the STKs became so popular.
And then came the SVI series. Mainly Panasonic/Technics, These were a cut above, some new class A. Expensive as hell too, I got a Technics amp in the boneyard, the ?I?C for it is A HUNDRED BUCKS. That is the B&D price and I really do not want to get it anywhere else, not THAT part.
And then we get to the Sonys for example that use the STK module to drive the outputs. Now that sucks. They get to say it is a discrete output stage, but got out of designing is by using an IC. I don't want to get into trouble here because I know the owner of this site likes Sony and has some killer Sony stuff. but the fact is, their mid line **** is **** IMO. The ESS line is totally different. But the BPC is as bad as the Pioneer BPC. And all of them are as bad as it gets as far as I am concerned.
Thing is, it is not so much that they made their own ICs, they didn't. Sanken or whoever made them and all they do is set up the right transistors, and two resistors to set the gain and the engineering is done. Anything having to do with sound quality was not done in house. You did not buy a Sony, you bought a brand X with a Sony output and transformer. This is my problem with it.
And then, some will say that ICs, not just STKs but any ICs in the audio path simply have too damn many transistors. I do not disagree. I do not totally agree but the got a point. Every damn thing that audio goes through affects it and there is no argument about that. but then there is the pretty much highly regarded Yamaha "Wedge". I refuse to work on them. A circuit like that SHOULD be in an IC.
Engineering wise, I am a faithful follower of the KISS church. Keep It Simple Stupid ! Consider audio like water. A straight pipe flows best. When you convolute it all over the place you lose that straightness, the immediacy, the something. How do you spell that French phrase Je Ne Say Qua ? It means that which cannot be described.
But sensitive testing devices CAN describe it. Bob Carver proved that a long time ago.
There is yet another speaker wire thread, I am not getting into it even though the point has been proven to me. My boss many years ago said OK, on the test bench setup which was not the best of speakers but good enough to hear ****, take this brand new package of elcheapo speaker wire and put it in line with your bench speakers. There was no question, it sounded ALOT different. I was convinced right then and there.
Anyway, using STK Darlington power packs you still get YOUR sound in an amp. But when you take to using the driver ICs, you just took yourself out of the loop. You are no longer an audio designer, your job is to make the bluetooth n **** work. The wifi. The surround sound, not the sound. And they have all done it. All the mid fi manufacturers seem to have gone the same way. If you want something new and really good, you know that boat in the backyard ? Sell it.
Try to imagine now, in fact some of you are qualified to do so and if so, do comment.
What would it cost to build this stuff today ? Start with something relatively easy, say a Piojneer SX-850. Think you could do it for a grand ? And the numbers do not warrant it. Let's take it a step further, a Marantz 4270. You could buy a Corvette for that kind of money.
Anyway, the main problem with STKs is not being able to get them. Sonically they are no different than any other bunch of transistors, and in fact are probably matched better. But now people like me have to figure out how to build a replacement for them because it is so damn hard to get a new one. I will take a 2SC3281 and 2SA1302 and screw them in the mounting holes along with the drivers right on top of them. But then I have to deal with the bias. It is not adjustable, it has to be right the first time. I can do it, but not for the $14 the STK used to cost twenty years ago. (and we bitched about that)
I can outdo almost all STKs with more modern components, however the class A ones not really. The SVI ones, understand if I refit an amp it will no longer be "new class A". I am simply not willing to do it. I can get it running, but it will not be class A, sorry. You want that you need to send B&D a hundred bucks for one of the few last ICs you can get for it.
But for most of them I can find what is needed to make it work. And it might not be pretty but it will work reliably and sound good.
Nother thing I have noticed, remember how the FTC rules only apply to the front two channels of a surround amp ? Well I have noticed that alot of them have discrete components on those channel;ls but use a chip for the rest, center, surround etc.
Why are they doing that ? Why ? Because that is where their ratings are. Even a Carver, has a custom IC for voltage amp and discrete outputs on the main fronts, and a big STK for all of the other channels. (HR895 IIRC)
Actually, I can't really bitch about STKs because eventually you might just have to pay me to get past the problem of not being able to get one. Only thing is, if it comes to a Technics new class A amp or receiver, I am removing the brand name and model number because it would be unethical to sell one that is not class A without disclosure.
OK this is plenty long and you are probably tired of it. Get some sleep. (I am on a FUBARed schedule myself, there is no hope for me)
