Class S amplification

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#3
actually Class S is more like quad current dumping,
in that it has a small class A amplifier and a powerful class B amplifier linked together.
However at this point the similarity ends, the principals of operation are different. But without looking it up I can't reliably give any more detail.
 
#4
That sounds pretty good to me Class A input married to Class B output. Do you know if they are a good design? I am asking because you don't seem to see these around anymore.
Also, are Class S difficult designs to realise?

Gareth
 
#8
I've certainly seen it used to mean Sandman topology, but I wouldn't rule out it being used to define some other topology.
I suspect over the years Class S has been used for Sandman and Switching (now known as Class D).
 
#9
I don't have a link but back when I was doing research (couple years ago) into different classes Class S was originally defined as what we call Class D today. Class D also was defined but the difference was the LC network on the output. The classes A - H and S were mostly defined nearly 100 years ago. There is a Class E & F but are not very well know (used in communications similar to how Class C is used in radio transmission). In the last 10 years we have seen Class T, I and now XD which are not real classes at all. Class T and I are Class D (Class I being Class BD) and XD being a version of Class AB (or B depending on who you ask). The class of an amplifier is a general description with some having subclasses such as Class D having AD and BD (how the output waveform works) and then tube amplifiers having subclasses based on biasing. Sometimes people get too caught up in trying use a class definition too specifically. But I do hate marketing classes such as T, I and XD.

-SL
 
#10
SpittinLLama said:
I don't have a link but back when I was doing research (couple years ago) into different classes Class S was originally defined as what we call Class D today. Class D also was defined but the difference was the LC network on the output. The classes A - H and S were mostly defined nearly 100 years ago. There is a Class E & F but are not very well know (used in communications similar to how Class C is used in radio transmission). In the last 10 years we have seen Class T, I and now XD which are not real classes at all. Class T and I are Class D (Class I being Class BD) and XD being a version of Class AB (or B depending on who you ask). The class of an amplifier is a general description with some having subclasses such as Class D having AD and BD (how the output waveform works) and then tube amplifiers having subclasses based on biasing. Sometimes people get too caught up in trying use a class definition too specifically. But I do hate marketing classes such as T, I and XD.

-SL
Click to expand...


Thanks LLama,
I thought that Class D used PWM and Class S was a Class A input feeding a Class B output....do you know if this topology is a good design if implemented properly?

Gareth
 
#12
Yes, the comment is a little confusing, as class B amplifiers are usually driven by a class A VAS.

In the case of Sandman topology (avoiding the term class S) , the load is driven by a small class A amplifier via one side of a bridge network. The error signal derived from the bridge is fed to the following high power class B amplifier. The output of this high power is feeds the load from the other side of the bridge network.
I think the idea is that the class B stage tries to keep the demands on the Class A amplifier very low, so it is effectively driving a high impedance load. And can be designed to perform very well under these conditions.

Just for comparison the Quad Current Dumper has a Class A feeding the load via a bridge network, but in this case it also directly drives the following Class B stage. The output of which feeds the bridge, but this time the error signal is fed back to the class A stage.
The idea is that the bridge combines the output from the two amplifiers and increases the feedback when the Class B stage (Current Dumpers) are in operation, this change in feedback corrects the non linearity introduced by the class B stage. I think the class A stage works a little harder in this topology.
 
#13
below we see Sandman’s iterative circuit.
Click to expand...

12-2-2004_Sandman11.gif


Each cascading amplifier receives the distortion from its
preceding amplifier and works to cancel it at its output.
Three amplifiers are shown, but many more could be used,
each being less in power than the preceding. (Note the
increasing in value series resistors at each output. This
would imply that each succeeding amplifier would have to
have an ever greater gain than the preceding.)
By the way, this arrangement is somewhat similar to
the Quad current dumping scheme, but not exactly.
Click to expand...

🙂/sreten.
 
#15
Just for the record, the circuit above is by sandman but is a feed forward scheme and was not called Class 'S'

The Sandman Class 'S', is described in a few of JLH's books,
the circuit diagram is shown on this web link page 180.
http://books.google.co.uk/books?id=...Im6X6TbErqlw4f3TsaIzas6dQ&hl=en#PRA1-PA180,M1

hopefully the link works 🙂

Note: I think Technic's called there version class AA, and you can find references to this on this forum
 
#16
Symon said:
Just for the record, the circuit above is by sandman but is a feed forward scheme and was not called Class 'S'

The Sandman Class 'S', is described in a few of JLH's books,
the circuit diagram is shown on this web link page 180.
http://books.google.co.uk/books?id=...Im6X6TbErqlw4f3TsaIzas6dQ&hl=en#PRA1-PA180,M1

hopefully the link works 🙂

Note: I think Technic's called there version class AA, and you can find references to this on this forum
Click to expand...


Ah, so that's what Class AA was. Thanks for the link. I've just got hold of a book by JLH called Audio Electronics. I think I will try to get a read of it on Sunday.

Thanks
Gareth

Edit..I remember when I was younger on holidays on the South Coast one of my Grandparents friends had the Quad II/22 (you know the ugly grey colour) and ESL53's (with the ?brass? front and wooden legs), and was amazed with the sound. Do you know what type of design the II/22 is?
 
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