svart-hvitt
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The measurements Amir performed are extremely limited. (no doubt due to time constraints). I certainly feel a categorical recommendation or lack thereof is a very unwise position to take.
What we can see, is the performance exceeded rated specifications by a wide margin (factors of 10+) for the parameters Amir tested. This was as expected and as I predicted. Frequency response tests appear to exceed spec also, but Amir has not specified the power output level he tested FR at. The standard and the spec is 1W. We can only guess what he used.
The high level preamplifer inputs were driven with a signal to give the same level out as in (2V). There is absolutely no point using a preamplifier that is specified with an 18dB gain and then winding back the attenuator to give unity gain for testing purposes. All preamplifiers are tested and specified at the wide open position and have been forever. The rated output of the preamplifier is 1.07V from a 134mV input. He fed it 2V and wound back the attenuator. You test a preamplifier at its rated input and output, not some made up number that suits you. We may be merely seeing non-linearities and noise (hum) etc, from being buried in the multiple stages of the AAVA volume control (see below).
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I had hoped Amir would investigate this unusual implementation and test it at various increments/levels to give some insight into its performance or lack thereof. I'm not convinced piling VI buffers in line is a good idea, but who knows. Accuphase have been touting their AAVA for several years now.
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One cannot characterize the performance of an amplifier with only one resistive load test (4 ohms), which is half the standard, and make no comparisons between different loads and different numbers of channels driven. There is no reactive testing, transient (IHF/EIA) testing, power bandwidth, shorted input residual, comparisons of various inputs, crosstalk
There is zero discussion on the topology as the cover was likely not removed (understandable if it was on loan) and therefore we can only surmise as to the reasons for the burst of HF hash on the FFT. I have offered a possible reason in a previous post, but Accuphase is unlikely to have released a product into the wild with such an issue. It may be operator influenced perhaps.
The power amplifier stage is conventional and of a decent standard according to what I see on Accuphase's brochure.
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What we can see is Accuphase appear to have decoupled supplies for the VA, the driver stage and the output stage and we know they will have high quality regulated supplies for the preamplifier stages. Amir makes the statement the preamplifier supplies are being affected by the output. This is perfectly normal in integrated amplifers with single transformers when operated at high powers into low impedances.
Comparisions to the Hypex are flawed. The Hypex units have not demonstrated they can hit their specifications. Nor have they demonstrated they can be trusted not to shut down at inopportune times. Their power supplies overheat and are failing in the marketplace. The Accuphase wasn't pre-condtioned, or tested for 5 minutes at full rated power either.
I take the whole review with a grain of salt.
That said, further investigation would clear up a whole lot of the above. Time contraints are a b#tch.
Hmmm...seems like lack of measurements standardization - which is for everyone to see and debate - is haunting @amirm ’s review?
Such standardization would consume more time. But it would probably be worth it, wouldn’t you agree?
Standardization is a theme that I come back to so often, I wanted to add that «furthermore, I consider that Carthage must be destroyed»