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Post by Tommy Boy on Jan 12, 2008 22:20:52 GMT -7
Can someone help me with what "Dead end class A" or "Single Ended Class A" power means? Amp makers seems to tout this as a good thing so I am wondering what it means.
Thanks.
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Post by zdogma on Jan 13, 2008 5:09:26 GMT -7
Can someone help me with what "Dead end class A" or "Single Ended Class A" power means? Amp makers seems to tout this as a good thing so I am wondering what it means. Thanks. One tube operating in class A produces your output power. A lot of high end audio amps and a fair number of low wattage guitar amps (Fender Champ, THD Univalve, Dr. Z's Mini Z, many others) are built this way. www.passlabs.com/downloads/articles/seclassa.pdf
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Post by John on Jan 13, 2008 7:21:24 GMT -7
I tried to read a bit of the link above, and sheesh...that's getting technical.
In simpler terms....
I don't know what dead end class A is, but..
Single ended class A is usually where there is only one power tube for the power amp. This is opposed to 2 or 4 tubes which work in a 'push-pull' format, where one 'side' (one or two tubes) will handle one side of the wave (think half the string vibration) and the other tubes handle the other half. Kind of like running, where one leg is hitting the ground and moving you forward, while the other doesn't...they never work together.
But with one tube, it has to hande both cycles. So it's always firing all the time, and there is never a rest period like the push-pull. This can give a unique tone.
There is also 'parallel single ended class A'. This is where the signal is split/divided and can be used with more than one tube. (almost always just two, and the signal is combined after going through the tubes ). But it still operates with that 'always firing/on' situation (class A). Even though there are two tubes, they do not behave in that push-pull way (class AB)
Class A seems to be presented to the public as a 'magic tone heaven' type of thing. And that Class AB (push-pull) is terrible and sounds poor. But there are many classic fantastic sounding amps over the years that are Class AB push pull:
Tweed Fender Bassman Blackface Fender Deluxe Marshall Plexi Marshall JTM45 Marshall JCM800
I could go on listing for a long time, but you get the idea.
And now I open the floor to more knowledgeable people than me to tell everyone where I've gotten it wrong.
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Post by zdogma on Jan 13, 2008 11:39:47 GMT -7
I tried to read a bit of the link above, and sheesh...that's getting technical. Yeah, I wasn't sure how much detail to give... There is also 'parallel single ended class A'. This is where the signal is split/divided and can be used with more than one tube. (almost always just two, and the signal is combined after going through the tubes ). But it still operates with that 'always firing/on' situation (class A). Even though there are two tubes, they do not behave in that push-pull way (class AB) I have one of these, great amp, sounds good at any volume level (my Kingsley Deluxe is parallel single ended). The THD bivalve is like this as well. Class A seems to be presented to the public as a 'magic tone heaven' type of thing. I totally agree, Z only makes one true class A amp (I think...the Mini Z, correct me if I'm wrong), and all of his amps sound great to my ear. Many of the amps that are claimed to be class A really aren't in any case.
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Post by Tommy Boy on Jan 14, 2008 12:20:19 GMT -7
Thanks, that helps.
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Post by Phil (aka Phil) on Jan 15, 2008 8:11:59 GMT -7
The whole "Class A" thing has been discussed many times on many different forums and web sites. I think one of the best explanations is on Randall Aiken's web site (www.aikenamps.com) in the Tech section. The reality is that a lot of amp manufacturers do tout "Class A" as a selling feature, when in fact the vast majority of the amps that are advertised as such are in reality push/pull (even number of output tubes) cathode biased amps that operate in Class AB for the majority of the time. I think the whole thing got started with the Vox AC/30 and the perception that they sounded so good because they were Class A. There are a lot of reasons why the AC/30 sounds so good, such as it's minimal circuit path, lack of negative feedback, cathode biasing, and Vox "blue" speakers, but it's a Class AB1 amp. Any single power tube amp is by definition a Class A amp, as gtrman3 said.
Phil
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Post by edoetsch on Mar 8, 2008 2:23:18 GMT -7
the more I read about class A is that the only way to guarentee it is to buy an amp with a single output tube.
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Post by dixiechicken on Mar 9, 2008 9:35:05 GMT -7
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Post by Strato on Mar 10, 2008 0:10:19 GMT -7
This cancels out any even order harmonics created in the power stage, correct?
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Post by dixiechicken on Mar 10, 2008 7:34:53 GMT -7
I don't know for certain - but I don't think so.
Or let me re-phrase it to a question - why would even order harmonics be cancelled in single-ended parallell class A amp.
If the even order harmonics from the two output tubes working in parallel - somehow somewhere gets get phase-shifted 180 degres with respect to each other - yes then they would be cancelled if their respective amplitudes are the same.
Cheers: Dixiechicken!
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