The 405 only had a single set of output devices for 100W. This meant the SOA protection could not safely allow much current into 4R loads.
Later current dumpers used closer to AB bias on the output devices.
the snorting wasnt so much about it being a chipamp, more about you saying you had 'designed' a chipamp
At some stage it may register that what I'm really interested in are the subtle refinements that allow the next level of SQ to emerge ... this can be done by modifying a Krell, designing a gainclone, or, heavens to betsy, optimising an Aldi TV. Otherwise, all I'm doing is a YAPA, and variants thereof; which is not really interesting, it will be more of the same -- pretty easy to get technical performance as good as one would want these days, with no guarantees of subjectively excellent performance.
As an example of what I'm after, I was just running the UULE with AC/DC, Stiff Upper Lip, as loud as the plastic carcase would allow: it met two key criteria, no change in tonality as the volume went right down and up, apart from the plastic starting to rattle and buzz; and, it had that mysterious, 'timing', element right ... the songs were driving hard, and your body was instinctively bouncing with the beat. This had a lot to do with the fact that the cymbals were super clean and shimmering, there was no hardness to the sound ...
As an example of what I'm after, I was just running the UULE with AC/DC, Stiff Upper Lip, as loud as the plastic carcase would allow: it met two key criteria, no change in tonality as the volume went right down and up, apart from the plastic starting to rattle and buzz; and, it had that mysterious, 'timing', element right ... the songs were driving hard, and your body was instinctively bouncing with the beat. This had a lot to do with the fact that the cymbals were super clean and shimmering, there was no hardness to the sound ...
A customer had a pair of Gale 401 speakers , 4 ohms or less . He introduced me to the parallel bridge idea that Quad recommended for less than 4 R . A 5 K pot taken to the L and R input . A cheap speaker connected between L and R red terminals . Play music Quad said , adjust the pot until there is least output . They pointed out it would be frequency dependent as even the 405 had some variation . Then connect red to red as output ( black is already connected ) . The results were rather good . Never tried it with the mK 2 , suspect it would be even better .
If I owned a 405 I think I would buy an extra one . Also I would note the phase of the and and check the overall phase . Drums kicking backwards do not sound right , that is if not intended . As is said " transients are always positive " ( ???? ) .
Brown's Restaurant Oxford had some 405's which we estimated were running into less than 1 R for years . They didn't sound very happy . Years later the 8 of them ( ? ) were dumped on my work bench . " Sell these Nige " . I tested all of them and was happy to do absolutely nothing . I sold them and gave them a years guarantee . None ever came back . I was told later they were so unhappy as to mechanically throb when playing music at Brown's . Neither the guy who put them on the work bench or myself installed the original system .
Well, simply using an op amp for the input stage of a power op amp is neither new, nor enough. It's just a start, one does need to get the rest of it right for the whole thig to be significant.
While I'm a devout believer in discrete, especially in power amps, I must admit to having heard several of the op amp input kind which did sound anything from good to glorious. Also, I've heard many more which were easy to forget.
Ultimately, my own Karan Acoustics KA-i180 (2x180/250W into 8/4 Ohms, you don't want to know its price) uses Burr-Brown op amps throughout, including its power amp input stages (BB 2604). And I swear by it, it's still the best overall integrated amp I have ever heard to this day.
Those were the days when speaker equirements were thought of only in terms of avalable power in Volts. Few thought of the possible current requirements as well.
Look over the SAE schematics of the day and you'll see the same thing - single ended outputs, sometimes with stacking, for power outputs as high as 200 Wrms/8 Ohms (model 2200, 2400, etc). And that was no novice on the block, that was James Bongiorno.
Such were the times.
By the early 80ies, this changed for the better.
One unit I can think of which was a whopping exception to this rule was the Studer/reVox 740 power amp. It was rated at 100/185W into 8/4 Ohms, and it used 3 pairs of custom Motorola 250W devices per channel. Each channel was supported by two 33,000 uF capacitors. This was very unusual at the time.
none of this is achieved by increasing power supply cap size ... you'de have to see the posts we are referring to and the string of references to dinky amps, while slinging mud at just about everything based on reports from hifi shows, rather than ownership. i'm by no means anti-opamps, not in the slightest! I use them in various roles in my system to great effect. that and discrete solid state (no tubes for me) are about half half in my system.
If done well, multiloop and/or hybrid discrete/opamp composite amps can be excellent and do require some chops with PCB layout and parasitics too, particularly if they are fast and/or wide bandwidth. but that is a pretty different thing to applying some basic power supply parts swapping with little or no objective testing to confirm, which is what was described.
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However it was done, the end recording is quite odd, and doesn't engage. Another 'audiophile' recording goes to the other extreme, a piano recital in a huge space, like being in an enormous bathroom; a single note echos and echos ...
The overall impression is that these recordings are highly contrived, 'natural' is the last word I would apply to them ...
In my experience, swapping some non descripit caps of say 4,700 or 6,800 uF, as are mostly used in cheap gear, for quality caps from a reputable source will improve the sound. What is not know is how much, could be anything from small to impressive, depending on the ciruit inside.
Generally, you can expect more oomph from the circuit, as its energy reservoirs can hold more after swapping.
However, while improvents will happen, this cannot turn a so-so device into a High End one no matter what we stick in. In the end, the circuits will be the limiting factor.
On the other hand, one cannot expect wonders from a very loose power supply; it'll do well with higher, but not so well with the lower impedances it may encounter. Bob Carver used to pack in from 5 upwards pairs of very solid power transistors in his Phase Linear power amp, but grossly underrated capacitors, like a pair of 6,800 uF caps per channel feeding a 200 Wrms plus nominal output. As a result, his power amps always sounded somehow lean and starved, especially so when driving below 6 Ohm impedance loads.
Lastly, and obviously, it's not at all the same thing regarding cap quality, not just sheer quantity, they also need to have quality. My personal candidates for quality replacement come from BC Components (Vishay), Fisher & Tausche and Siemens (both from Germany) and Nichicon. I refer to values from 4,700 uF upwards, mostly 10,000 uF in parallel. Currently also 22,000 uF in my Marantz amps, no place for more than two.
This really shouldn't surprise anyone - a cheap device will also use cheap'n'cheerful caps, so even replacing these with better ones will yield audible benefits. When increased as well, the benefits will just become more obvious.
Hallelujah!
Right on!
Op amps are really no different from any electronic component in that it's up to the designer to use them fully and properly. Like everything else, they are not inherently good or bad, you just have to use the right one for the job.
And the Good Lord knows one has one's choice of them.
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