Talk:Valve audio amplifier - technical

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Contents 1 lethal voltages 2 Class B and rock concerts 3 nfb and class B 4 Component Quality 5 SET

[edit] lethal voltages

were the article mentions that SETs operate a lethal voltages it should be changed. Its not the volts that will kill you, its the amps(milliamps in this case). The average static shock people commonly get can be thousands of volts yet not do any damage because the amperage is so low.

[edit] Class B and rock concerts

"For this reason class B amplifiers are arguably well suited to eg pop and rock music where high sound levels predominate"

This seems to give the impression that class AB and B are unsuited to other music types, which is clearly not the case.

More to the point, the suitability of class B to high power music has nothing to do with the quoted reason, rather it is down to practicalities, including costs. When running huge output powers, high efficiency means less power consumption, more manageable levels of heat dissipation, and lower component diss equals lower amp cost. The relationship between output and distortion is minor in comparison. Tabby (talk) 01:02, 18 December 2007 (UTC)

[edit] nfb and class B

"Following its invention by Black, negative feedback (NFB) has been almost universally adopted in most amplifiers (of all types) and universally in amplifiers operating other than in class A, to provide substantially improved measured distortion performance, flatter frequency response, and more repeatable performance irrespective of component variations."

Almost, but I had a pocket dictaphone using class B and no nfb. It sounded terrible. Early 70s, with very minimalistic discrete transistor circuitry, though class B because it was battery powered. At least the use of germanium rather than silicon reduced the xover distortion a fair bit, making it terrible rather than unintelligible.

I tweaked the article. Tabby (talk) 01:02, 18 December 2007 (UTC)

[edit] Component Quality

"Today's circuits in most cases remain similar to circuits from the golden age, however they benefit from dramatic advances in ancillary component quality (notably capacitors)"

Surely the main component quality issue in old kit is not caps, but switches.

AFAIK modern caps are no better than old, despite the fact that there seems to be a lot of mythology built up around bad caps since the 90s. Tabby (talk) 01:02, 18 December 2007 (UTC)

[edit] SET

Using term "SET" to describe the common cathode voltage amplification stage is not standard practise in texts. The term SET almost always refers to power amplification, specifically the output stage. Also note the word triode within its definition. This article largely ignores the pentode device and therefore falls woefully short of justifying its title description. Using the term "common cathode" gain stage and noting that the explanation is based upon the triode might be a first step in rectifying these shortfalls. —Preceding unsigned comment added by 121.72.27.120 (talk) 22:25, 5 June 2008 (UTC) I overlooked logging in before above comment RichardJ Christie (talk) 22:28, 5 June 2008 (UTC)

Removed this: "This stage is often used as the input stage for power amps with unbalanced inputs, to buffer the input signal and provide some initial gain. "

Reasons: 1)it's not very common usage; 2) the stage has poor buffering characteristics, more commonly a cathode follower cct is used for such buffering; 3)there is no definition of "unbalanced" does the author mean "paraphase"? 4) commonly used differential splitters and drivers provide gain and cannot be described as common cathode RichardJ Christie (talk) 22:48, 5 June 2008 (UTC)