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Old 8th Sep 2020, 7:21 pm   #1861
knobtwiddler
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Default Re: The Audiophoolery Thread.

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It's been reported that in blind tests people (on average) actually preferred the sound of music which had had a little 2nd harmonic added !
Although this is the generally held belief, it doesn't explain people's penchant for tape saturation, which is mainly 3rd harmonic. There's even a digital plug-in designed to emulate the characteristics of Studer reel machines (i doubt the original designers would be happy to know the foibles of their machines have been digitally emulated). Nor would it explain the fascination (incredible prices in some cases) for rare transformers (exclusively 3rd harmonic). I don't see much wrong with a little 2nd or 3rd - upper order odd harmonics generating IMD are what you want to worry about.

Watching a speaker distort on an FFT fed from a test mic can be an enlightening experience. The distortion comes on radically and abruptly at all harmonics, with little warning. If a system sounds clean, but edgy on transients, this could be a likely culprit.
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Old 8th Sep 2020, 10:24 pm   #1862
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Default Re: The Audiophoolery Thread.

An interesting valve amp here, make sure you put some sun glasses on before viewing the pictures in detail.

Just to show that what constitutes a good amp varies from person to person and this one could do gold plating.

https://newvalveproject.shutterfly.com/

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Old 8th Sep 2020, 10:34 pm   #1863
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Default Re: The Audiophoolery Thread.

The front panel looks to have considerable 1950s French styling influences.......
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Old 8th Sep 2020, 10:48 pm   #1864
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Default Re: The Audiophoolery Thread.

I thought myself that its plain UGLY. Bling Bling !
Oh well Just my opinion

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Old 8th Sep 2020, 11:06 pm   #1865
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Default Re: The Audiophoolery Thread.

That is a seriously impressive amp! (the Benchmark that is not the uber-bling valve amp!) I'm not surprised that Laurie Fincham was involved in the design. I talked with him several times when he was at KEF, and well before he decamped to the US to join THX.

Likewise I have not looked into THX's patent (the collaboration with Benchmark led to the AHB2). Halcro's is US patent 5,892,398

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Old 8th Sep 2020, 11:08 pm   #1866
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Default Re: The Audiophoolery Thread.

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What parameters were they not measuring?
The ones I had in mind while writing that were things like overdrive recovery and slew-rate limiting. In a period when the move to silicon from germanium was pretty much complete. People just hadn't realised that waveforms found in music could stress more parameters than simple frequency response and distortion of a single sine. Then the likes of Matti Otala started publishing papers. I suspect he went a bit overboard, but he had uncovered a legitimate concern and an area which wasn't being properly handled.

Every now and then someone brings out an amplifier where it looks like nobody checked the crossover distortion. Maybe it was blind cost-paring. How to do it well has been documented well (Self)

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Old 8th Sep 2020, 11:24 pm   #1867
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Default Re: The Audiophoolery Thread.

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Is part of the problem that crossover distortion occurs at a point where both output devices are so close to cut-off that the amp transiently has almost no open-loop gain ? Without open-loop gain feedback struggles to do much good.
This is prevalent in phase locked loops using phase/frequency detectors implemented in logic. They have a discontinuity at about zero phase difference, where operation is essentially a race hazard. Gain can go up as well as down, and exhibit hysteresis!

Makes a right b*gger of careful design. The fix is a bit of a cop-out, to bias it so operation sits off to one side.

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Old 8th Sep 2020, 11:32 pm   #1868
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Default Re: The Audiophoolery Thread.

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An interesting valve amp here, make sure you put some sun glasses on before viewing the pictures in detail.

Just to show that what constitutes a good amp varies from person to person and this one could do gold plating.
https://newvalveproject.shutterfly.com/
I think their market diminished substantially when Liberace popped his clogs.
They could have done one where the chassis top plate was grand piano shaped.

That amplifier looks about as tasteful as Captain Nemo's car...

But, really, someone needs to make KT88 with gold plate innards and top layer of the gettering so that the thing can be completed.

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Old 8th Sep 2020, 11:37 pm   #1869
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Default Re: The Audiophoolery Thread.

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Originally Posted by AdrianH View Post
An interesting valve amp here, make sure you put some sun glasses on before viewing the pictures in detail.

Just to show that what constitutes a good amp varies from person to person and this one could do gold plating.
https://newvalveproject.shutterfly.com/
I think their market diminished substantially when Liberace popped his clogs.
They could have done one where the chassis top plate was grand piano shaped.

That amplifier looks about as tasteful as Captain Nemo's car...

But, really, someone needs to make KT88 with gold plate innards and top layer of the gettering so that the thing can be completed.

David
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Old 8th Sep 2020, 11:37 pm   #1870
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Default Re: The Audiophoolery Thread.

Quote:
Originally Posted by GrimJosef View Post
Is part of the problem that crossover distortion occurs at a point where both output devices are so close to cut-off that the amp transiently has almost no open-loop gain ? Without open-loop gain feedback struggles to do much good.
This is prevalent in phase locked loops using phase/frequency detectors implemented in logic. They have a discontinuity at about zero phase difference, where operation is essentially a race hazard. Gain can go up as well as down, and exhibit hysteresis!

Makes a right b*gger of careful design. The fix is a bit of a cop-out, to bias it so operation sits off to one side.

David
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Old 9th Sep 2020, 12:18 am   #1871
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Default Re: The Audiophoolery Thread.

Quote:
Originally Posted by Radio Wrangler View Post
Quote:
Originally Posted by AdrianH View Post
An interesting valve amp here, make sure you put some sun glasses on before viewing the pictures in detail.

Just to show that what constitutes a good amp varies from person to person and this one could do gold plating.
https://newvalveproject.shutterfly.com/
I think their market diminished substantially when Liberace popped his clogs.
They could have done one where the chassis top plate was grand piano shaped.

That amplifier looks about as tasteful as Captain Nemo's car...

But, really, someone needs to make KT88 with gold plate innards and top layer of the gettering so that the thing can be completed.

David
Leak used a gold-anodised front panel for their pre-amps on the American market.
Gold-plating of grids and pins is quite common in special quality valves.
I've never seen anybody criticising the watch industry for using gold cases.
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Old 9th Sep 2020, 2:07 am   #1872
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Default Re: The Audiophoolery Thread.

I think that a significant element of the crossover distortion problem, namely the inherent asymmetry of the Lin quasi-complementary output stage, had been addressed, in terms of cause, effect and remedies, in the late 1960s by several circuit designers, including Bailey (WW 1968 May p.94ff), Shaw (WW 1969 June p.265ff) and Baxandall (WW 1969 September p.416ff.) Baxandall’s graphical explanation was quite clear. He reprised that work in 1977 (in Amos, Radio, TV & Audio Technical Reference Book), expanding it to show that the Quad triples (of 1967) achieved essentially the same result as his “Baxandall diode” of 1969. (Baxandall elsewhere claimed credit for suggesting the triples to Quad, but he did not claim to have originated the idea.)

In 1966, Bailey had noted the transistor amplifiers could be problematical in terms of listener fatigue, etc, and chose transformer drive as the best option at the time. His reasons for so doing were not covered in detail, though, until his write-up on his 1968 fully-complementary design, as mentioned above. In his 1966 article, (WW 1966 November p.542) he also addressed the germanium vs. silicon issue, including the comment: “In fact germanium transistors usually give far lower distortion due to their better linearity”. It would appear that the change from germanium to silicon, whilst generally beneficial, may have exacerbated the distortion issue.

With all of that work going on, with key points in the public domain, one might have expected equipment reviewers to have been well-informed as to the need to at least look at the known problem areas for transistor amplifiers. In fact my recollection is that some did, and for example Gordon J. King was on to the crossover distortion aspect in the late 1960s.

I also have the impression that some reviewers of the 1960s, such as Geoffrey Horn and John Borwick, made a lot more measurements than were actually published, and probably more than the commissioning magazines had paid for. Certainly, rereading Horn’s Gramophone review of the Radford STA25 left me with the impression that he had “poked and prodded” the machine to death in an effort to find fault. As well as on the technical side, these folk also had credibility in that they were music afficionados and regular concert goers, so were familiar the “original sound”, as it were.

Nonetheless, insofar as the reviewing industry generally might have missed the boat in fully observing, measuring, and commenting upon the key issues surrounding the valve-to- transistor transition, they might have helped open the door to what had become “audiophoolery”. Nonetheless, this was also the time when the hi-fi industry moved from niche to mass-market status. That alone would have been cause enough for the snake oil merchants to want a part of it. And the larger market more easily allowed the entry of manufacturers who had unusual or extreme views, both rational and otherwise (e.g. “no tone controls”). A bigger industry invited more magazines, and playing to the unusual and extremes (the tabloid approach as it were) was probably seen as the better business plan in terms of gaining sales.

Regarding the importance of the transient behaviour of amplifiers, not revealed by steady-state testing, it would appear that in a general sense it was known before its 1970s rediscovery. This piece at least slightly predates that time: “Good transient response. In addition to low phase and frequency distortion, other factors which are essential for the accurate reproduction of transient waveforms are the elimination of changes in effective gain due to current and voltage cut-off in any stages, the utmost care in the design of iron-cared components, and the reduction of the number of such components to a minimum. Changes in effective gain during "low-frequency" transients occur in amplifiers with output stages of the self-biased Class AB type, causing serious distortion which is not revealed by steady-state measurements. The transient causes the current in the output stage to rise, and this is followed, at a rate determined by the time-constant of the biasing network, by a rise in bias voltage which alters the effective gain of the amplifier.”


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Old 9th Sep 2020, 2:09 am   #1873
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Default Re: The Audiophoolery Thread.

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... The advantage is that it allows you to use two different cables for the high and low frequency, assuming of course that you believe different cables can sound different!

However, I would agree that bi-wiring with two runs of the same cable is indeed pointless.
Does this just boil down to a question of whether the cable's impedance is significant (i.e. audible) or not ? If it's not then one piece of cable will have no audible effect and multiple pieces will do nothing several times over. But if it is significant then running separate cables to the individual drivers might plausibly be audibly different from using just one cable. At the very least you could 'bi-wire' by putting two runs of the same cable simply in parallel - joining red to red and black to black both at the amp end and the speaker end. You'd have halved whatever resistive or inductive impedance they had and doubled the capacitative component and that ought to change the audible impact.
Perhaps look at it from the viewpoint of someone in the snake oil business, into which category the biwiring concept would seem to fall. Offering a cable pair consisting of two identical “blameless” constituents would probably not be very productive. Better I think to deliberately endow one of the pair, perhaps that on the HF side, with non-negligible impedance characteristics (magnitude and angle) such that it does have an audible (and a measurable effect). Thus the sound heard will be different to that with “monowiring” (say using the LF cable), and very likely different to that with the cables reversed. Then it is probably not hard to convince a would-be purchaser (who was probably at least somewhat open to the benefits of biwiring) that different equals better. It might have fooled a reviewer or to, as well. Job done!


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Old 9th Sep 2020, 5:07 am   #1874
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Default Re: The Audiophoolery Thread.

In some of those 'esoteric' speaker cables, it's quite apparent that the manufacturer/designer really bust a gut to endow them with extreme characteristics. It takes something pretty extreme to start affecting the sound directly.

Indirectly might be easier... the famous issue of Zobel diplexer networks becoming unfashionable with some amplifier manufacturers at the same time very high capacitance cables became fashionable. A lot of very expensive smoke got let out of some quite expensive black boxes.

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