With a lack of 2 ohm specs / tests / ratings - I would assume that both of these designs would do well into difficult loads...
But the Bryston probably better (66% rise with halving impedance, as opposed to 60% rise)
What I would dearly love to see from amp manufacturers/designers is charts like the one Quad published for the 606
View attachment 393739
But - and here I undermine some of my own points
- the 606 rises only 30% into a 4ohm load going from 135W to 175W... it really isn't a high current design.
However, it is, by design (and spec), unconditionally stable into any load... - as long as the required performance is under the continuous rating line, distortion figures are well controlled, and high fidelity results are pretty much assured.
The DRX3.4 keeps pumping out sound into my 1.6ohm speakers - no protection mode kicking in, but the symptoms of increased distortion (not clipping) are quite audible.
The weight rule of thumb applied to both the Bryston and Parasound, would indicate that at circa 20kg and 30kg, both of these would be robust designs capable of handling difficult loads.
Tracking down specs or test result at 2ohm would provide a better indication - but those are rare.
Thank you, so now you must understand why I have been countering your points about this whole "high current" hype/hearsay/vague at best term being thrown around often even when just talking about AVR amps. Also with due respect, I know you know the theories behind this, but your presentation could mislead those who don't have sufficient EE principles/theories, at least due to over simplification.
May be we can agree on some sort of a summary of this discussion by saying that we cannot assume one amp is of "higher" current design than another by simply based on the point presented in your earlier post because (reference the Quad graph), as well as some of my posts, and that there are at least the following factors to consider as well, namely:
1) continuous rating versus short term (then how long, example: transient only, 20 ms, 200 ms, 10 min, 15 min., or indefinite, ie literally/truly continuous?
2) types of power transformer used, this is a tough one because 99.9% of the time we won't know the characteristic of the transformer, even if we see the nameplate, you can have two 1000 VA 120V/80V transformer, yet one could have much better current capability and/or lower voltage drop than the other.
3) Weight, if use alone is not reliable as in 2) two transformers of the same 1000 VA and voltage rating could have very different weight depending on how they are designed and constructed, and keep in mind the size of the enclosure, materials used, also affect weight, same for the heatsinks.
4) Other cooling technique based on a combination of passive and active (such as fans) obviously would greatly affect the weight of the amp.
5) Again, as shown in your Quad amp's graph, two different amps with similar or even identical 4 ohm specs could be very different at different load phase angles because their designs may be different enough such that the output device's SOA characteristic curves could be quite different, making one performing much worse at higher phase angles while the other may not be affected much, an extreme example would be like a Purifi modules based, or even those tiny class D chip amps used by the likes of the Fosi, Ayima amps vs an Emotiva class AB amp, let alone those class AB Denon/Marantz AVR amps.
We both know full well there are many well known factors such as the level of THD used for the rated output, class AB, AAB, class D with switching PS, class D with linear PS etc., but those are obvious factors so we don't need to elaborate on.
Feel free to add as many factors, there are no shortages of them, making it, as I mentioned in the beginning difficult to say one amp, or AVR is high current because of the 4 ohm/8 ohm rated output ratio.
Back to my 4B SST vs A21 example, the two slightly different ratio is not much to go on as the 4B SST's output ratings are based 0.007% THD, whereas the A21's based on the much higher 0.2% THD. As you well know, if Bryston had used the same 0.2% THD, it's 4 ohm rating could have been much higher based on the typical class AB amp's output vs THD curve. Now feel free to Google for their weight specs, and be surprised to see that the less "powerful" Parasound amp is about 8-10 lbs heavier. Bryston used two 600 VA transformer (sort of monoblock design lol..) and the Parasound claimed a single 1200 VA transformer, so here's a case of equal VA gives a little (significant enough though) output capabilities, even when the Bryston's use of two smaller TX had obviously put them at disadvantage in terms of the way the specs are presented.
Finally, the more recent designs typically have protective schemes based on voltage and current sensing, many used ICs to help improve versatility and accuracy.
The Onkyo RZ50's issue, in my opinion, has a lot to do with their design team's choice of protective scheme/philosophy.
Based on available information, I am comfortable in saying the RZ50's voltage and current capabilities are practically the same as the Denon AVR-X3800H, X4800H and the Marantz Cinema 40 and Cinema 50. The variance in weight of those units are likely mostly size and materials used, of the enclosure and the design of the combination of passive and active cooling, not so much the power supplies themselves. The differences Amir found on the bench are most likely due to the different protective schemes used.
By the way, one of the point you made, seems to make sense but in practice it is of little use:
So rules of thumb - if you want a guarantee that the amp can handle low impedance / difficult (EPDR) loads, then look for 2 ohm specs, or in their absence look for amps that ramp up nicely into 4 ohm - if they do that, chances are they will be ok - yeah it ain't guaranteed! - And contrarian designs like the Quad can complicate things too!
That's because you won't find too many amps, so let alone integrated and AVR amps, even real power amps typically do NOT provide 2 Ohm output ratings with clearly stated test conditions. They almost always provide such so called output into 2 ohms based on unspecified test duration, and THD level. So, in that case, just about any amps, yes including AVR amps, can have a 2 ohm rating if they chose to do so. And, even those that provide 2 ohm rated output that would double down from 4 ohm, you can assume it is transient, or say very short duration based, and surely we can consider that "high current" but we both know such info would be anectotal at best!
Finally, examples time, to show a couple separate/power amps that can almost double down:
Benchmark AHB2 - 100 W/190 W 8/4 ohms measured under the same conditions based on their website info.
NAD M23 - >200W/380W 8/4 ohms, spec is not 100% clear but seem to indicate it's for under the same THD level and 20-20K Hz, like Benchmark's.
You will be hard pressed to find more than a couple power amps that comes close the the above's 1.9 ratio, if you do, please provide the test conditions such as Benchmark and NAD, those are not the best to begin with, but seems close enough.
Try McIntosh, Passlab, two biggies when it comes to presumably high power/current capabile, you won't find such specs.
So, I guess one more point we could perhaps agree on, that is forget about "high current" for most (say 90%) integrated and AVR (say 99%) AVR amps if you use the criteria of close to 2:1 4 ohm/8ohm rated output measured under the same test conditions. And, there is
no such thing as double down, though admittedly, the two examples used above should be considered close enough, at 1.9.
As for QUAD, yes we agree their published curve is great though I am not sure if they would provide one for all of them power amps. I can tell you though, as I might have done it before, I have never seen one single QUAD amp that passed the torture test of 1 ohm regardless of any meaningful test duration, yet at least one Denon AVR had pass such an 1 ohm test. That's ironic right? Obviously I would say that, all else being equal, just about any Quad power amp would be much preferred to any Denon AVR amps lol, just show that the issue is complicated when it comes to the narrative typically found on forums.
The post is too long, and I am too lazy to spell/grammar check, so sorry about any such errors.
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