AoS

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alfer
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Re: AoS

Unread post by alfer » Fri Aug 24, 2018 9:51 am

Let us spare a thought for the forum that draws members thanks to the Earl of Wrexham's USP.
Strip out the obvious USP stuff and it isn't isn't as alive as Wam or PFM. Man who does not want his picture shown insists on others pictures, all sorts. :lol:

alfer
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Re: AoS

Unread post by alfer » Mon Aug 27, 2018 3:06 pm

Where is t’owner did he pop over to Ireland. Or is he busy writting his Book ‘Successful Forum Management and Popularity’

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Dr Bunsen Honeydew
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Re: AoS

Unread post by Dr Bunsen Honeydew » Wed Aug 29, 2018 10:58 am

More ignorance amoungst the pretend AoS gurus. Krell is not Class A it is a highly biased Class AB, they just invented bullshit names for it.

keepitsimplestupid
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Re: AoS

Unread post by keepitsimplestupid » Thu Aug 30, 2018 9:25 am

I thought that the KSA 50, 100 and 200 models were Class A, and everything else that followed was not? Certainly the KSA 200 I rebuilt was Class A, with 600mV across the emitter resistor for each of the 36 output devices.

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Dr Bunsen Honeydew
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Re: AoS

Unread post by Dr Bunsen Honeydew » Thu Aug 30, 2018 10:16 am

Do they have a split rail, are they complimentary or quasi complimentary, if so they are Class AB. Anyway it is simple physics it is *impossible* to build a Class A amps with those power levels.

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Re: AoS

Unread post by keepitsimplestupid » Thu Aug 30, 2018 7:34 pm

36 Bipolar output devices, 60mV bias, 45v +/- rails, Class A to over 100 watts. Obviously it's AB eventually, but the numbers look like the KSA 200 was Class A to nigh on 170 watts.

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Dr Bunsen Honeydew
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Re: AoS

Unread post by Dr Bunsen Honeydew » Thu Aug 30, 2018 7:51 pm

It is a Class AB circuit all the time it is just highly biased to A. Amps like this a 10 to a penny, real Class A amps are rare, and this IS NOT REAL CLASS A IT IS BULLSHIT PER USUAL, it is the same trick Marco tries to pull with his valve amp.

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Dr Bunsen Honeydew
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Re: AoS

Unread post by Dr Bunsen Honeydew » Thu Aug 30, 2018 8:07 pm

It is not even real class A, as an AB in A is still not real A. A real A circuit is simple and is single ended.

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Re: AoS

Unread post by keepitsimplestupid » Fri Aug 31, 2018 11:13 am

Sure, a single ended circuit has to be Class A, but the reverse doesn't doesn't have to be true, Class A amps can be single ended or push pull.

As long as the output device conducts through 360 degrees of the input signal waveform it's Class A. (that's the engineering definition of the circuit topology).

I'll leave it there.

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Re: AoS

Unread post by Dr Bunsen Honeydew » Fri Aug 31, 2018 11:43 am

I think you need to read about it. A Class AB cannot be Class A even when within its pre-bias levels, it is two devices from a complimentary circuit running in parallel so cannot be Class A. The original terms of reference has been twisted for marketing purposes.

I quote.
We have seen that the power output of an amplifier is the product of the voltage and current, (P = V*I) applied to the load, while the power input is the product of the DC voltage and current taken from the power supply.

Although the amplification of a Class A amplifier, (where the output transistor conducts 100% of the time) can be high, the efficiency of the conversion from the DC power supply to an AC power output is generally poor at less than 50%. However if we modify the Class A amplifier circuit to operate in Class B mode, (where each transistor conducts for only 50% of the time) the collector current flows in each transistor for only 180o of the cycle. The advantage here is that the DC-to-AC conversion efficiency is much higher at about 75%.

One way to produce an amplifier with the high efficiency output of the Class B configuration as a simulated Class A configuration is to create an amplifier circuit which is a combination of the previous two classes resulting in a new type of amplifier circuit called a Class AB Amplifier. Then the Class AB amplifier output stage combines a simulated version of the Class A amplifier and the Class B amplifier while minimising the problems of low efficiency and distortion associated with them.

As we said above, the Class AB Amplifier is a combination of Classes A and B in that for small power outputs the amplifier operates as a simulated class A amplifier but changes to a class B amplifier for larger current outputs. This action is achieved by pre-biasing the two transistors in the amplifiers output stage. Then each transistor will conduct between 180o and 360o of the time depending on the amount of current output and pre-biasing. Thus the amplifier output stage operates as a Class AB amplifier.

***************************************************************************

Amplifier classes A and B go back to the 1st World War where early single ended circuits were all there was, so radio transmitters were low power, so Class B was invented. They are different and always will be. The term AB is a marketing construct but has become accepted as a highly pre-biased Class B but it is still a highly biased Class B it is not a Class A. That can ONLY be single ended, even the Sugden circuit broke those rules and is not true Class A. I call it simulated Class A.

You want Class A then buy a 300B valve amp etc, they are Class A, it is possible to build a single ended transistor amp but very few were available commercially. Tim de P did one.

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