Handling Heavy Amps

@cundare2 If you don't mind some correction, the 3rd harmonic isn't 'nasty'. Musically its an octave and a 5th above the fundamental tone. Its well-known that it is innocuous such that this fact is often only mentioned in passing in engineering tomes like this one (see page 10).

The primary distortion that a properly working reel to reel (or any other analog tape recorder) makes is the 3rd harmonic. I don't hear people complaining about reel to reel sound, can we put this one to bed?

The 3rd harmonic is present in any amplifier. It is useful in tube amps for masking higher ordered harmonics and is a big reason for tube amps sounding smooth as a result. It tends to be more suppressed in solid state designs so the high orders in solid state tend to be unmasked, especially if distortion rises with frequency, which is quite common.

The period of amplifiers with TIM issues was about 10-15 years earlier than you suggest. Marshall Leach designed his rather famous amplifier in the 1970s to get around this problem. However its helpful to understand that TIM by itself isn't a thing- tunes out is was just distortion caused by how the feedback is received in the amplifier design. Its caused by the input differential voltage amplifier having to drive a high capacitance, and you can get situations where the feedback is unable to control the voltage amplifier, resulting in distortion. The problem was solved by degenerating the gain of the input differential amplifier, thus reducing the compensation capacitance it had to drive.

We use a lot of feedback in our class D (as its a self-oscillating design) but the feedback is able to control the amplifier properly with any signal right up to clipping. So its immune to this problem.

IMO your 2nd paragraph in the post above doesn't make sense. You do have to be precise when talking to lawyers and engineers :) 

The 'supersonic, low-amplitude line noise' to which you refer really isn't a thing! When designing a class D amplifier, its not enough to build it to meet FCC subpart 15 or EU radiation directives; you have to make it considerably more quiet than that so noise doesn't interfere with digital audio devices connected to the amp. So quite literally the noise you mentioned doesn't exist in a successful design. In our case the class D is quieter than most tube amps, not just in the speaker but also radiated noise (if the tube amp uses a solid state power supply).  So this does mean less radiated noise than most solid state class A or AB amps.

FWIW, due to the fact that GaNFETs have no leads at all, they tend to have very low parasitic inductances, so its easier to control switching noise. This is important because GaNFETs can switch at some pretty high speeds; perhaps a couple of orders magnitude higher than the actual switching frequency of the amp itself. So you have to make sure everything is cleanly done, otherwise you may well have the outputs switching at 60MHz and heating up a bit as a result :)

Had my Accuphase-P-4600 amp audition today. The amplifier is a beautifully designed component. Extremely well built  The sound was also beautifully musical with a wide and deep soundstage. The bass was very impactful. Actually the overall sound was different than I was expecting. I was expecting a warmer sound instead it was a delicately refined neutral sound that was slightly on the warm side of neutral in the midrange. However the highs were very neutral and extended with a perceptible airiness. My dilemma now is that while I really enjoyed this sound presentation it wasn’t significantly better to my ears than the Bryston that would justify twice the price  So I will struggle with this decision  If it was around $9 or $10k instead of $14k I’d probably go for it as it would be close to the Bryston at $7,800  I’m going back to listen to the Bryston again next Tuesday and also to hear the Pass X250.8  Actually wanted to hear the X150.8 but they don’t have one to demonstrate  Then it will be decision time  

All good ideas to resolve weight issues.

My dilemma now is that while I really enjoyed this sound presentation it wasn’t significantly better to my ears than the Bryston that would justify twice the price  So I will struggle with this decision  If it was around $9 or $10k instead of $14k I’d probably go for it as it would be close to the Bryston at $7,800

@jfrmusic Here is a poorly understood fact: High end audio is not driven by price, its driven by intention. That is why a less expensive component is able to be better than a more expensive component, sometimes one that might be multiples of price more. Not in all cases depending on the intention of the designers of the components in question.

Seems to me you have your answer on this one. I don't seen any dilemma or downside.

Here's another thing to be aware of: the Veblen Effect.

This is the idea that if you pay more, you're getting greater value, which is not always the case- in fact it tends to be a blind spot.

So ignore the price- that has nothing to do with it.

Well you have a point but I usually go with my gut instincts. I tried to convince myself that the Accuphase was not worth the additional cost but deep down I know it was the best amp I’ve auditioned and I really liked its sound characteristics. I would purchase it if it was the lower priced component. So I called the dealer back this morning and told him my dilemma and after a brief discussion he gave me a great deal that included delivery and setup.  And he’s 90 minutes from me. I can usually tell when I make the right instinctive decision. I feel exceptionally calm after and full of anticipation. My search for my amplifier is completed. Expecting delivery of the Accuphase P-4600 sometime in late April. It’s allotted to the next shipment from Japan.