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Old 28th March 2011, 09:16 AM   #1
hpt is offline hpt  Australia
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Default dual outputs from LTP / SOX / symmetrical amplifier

Hello everybody,

please excuse me if I come across as being new to the field - I kind of am.

As part of a uni project I am asked to explore ways in which to utilise the super-symmetry zen (in particular son of zen) as a power amplifier.

With out going into any details why, let me say that I am wishing to explore ways in which to implement the super-symmetry son of zen as the input stage of a two or three stage amplifier (as much as I am sure this will annoy some people). I am aware of the relative merits and lack thereof in doing so.

So I am thinking it will achieve the best results in trying to reduce the number of stages, except I wish to come up with a push-pull output stage, be it class A or AB. And whether I have a push-pull VAS or incorporate voltage gain in the first or last stage I don't know yet. 'Designing' these further stages is not an issue. Knowing that the resulting amp will be viable, I cannot predict.

I have been inspired by A. W. Newby's Long Tailed Pair Zen: Long Tailed Pair Zen, A W Newby, Jan 2007

This gives me confidence that there is at least some foreseeable possibility of utilising the SOX (son of zen xploited) as an input stage, being that it is the first example of a complementary style amp with signal taken from both outputs of the LTP.

So I have seen very few amps that take both outputs from the LTP. Is this because most three-stage amps do not use a push-pull VAS, but a single-ended VAS? And Newby's LTP Zen doesn't use a VAS but goes straight to the push-pull output stage?

Are there any reasons from the LTP's perspective why they are not commonly used this way, or is it more to do with convenience of not having a push-pull VAS?

So do you think it is possible or a good idea (or not) to explore implementing the the son of zen xploited as an input stage to push-pull stages? Would it be best to get the voltage gain in the SOX input stage and just have the output for power handling?

What becomes the situation with global negative feedback? Should I try to incorporate it into the SUSY feedback loops? Or need I not worry... The traditional global NFB to inverting diff amp input, I am not sure will work when using a balanced input signal to both diff amp terminals???

I cannot find any specific information on Nelsons commercial amplifiers, which I understand, but I assume his X amps are perhaps something like what I am describing? I think SOX with a MANY voltage-follower FET output stage.

Well, just seeking ideas at this point. I do not have the experience to know that what I propose to do will necessarily be viable, but I do have the skills to walk through design calculations and simulations in order to get it working (should it be viable). I am in the dark at the moment, and would like some advice so that I know I won't dedicate all my time at the beginning for a lost cause.

I hope I am not making a fool of myself.

Cheers,

HPT
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Old 11th May 2011, 10:08 AM   #2
hpt is offline hpt  Australia
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Sorry for the bump, but does anybody have any comments on this?
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Old 11th May 2011, 11:49 AM   #3
flg is offline flg  United States
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You could use a complimentary differential version? Ala John Curl. That would deffinatly be tarting it up a little but, then you have all the output phases and feedback points you would need for most any style output
Check out the JC3 power amp for starters. There might be some answers/ideas there.
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Old 11th May 2011, 12:17 PM   #4
hpt is offline hpt  Australia
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Quote:
Originally Posted by flg View Post
You could use a complimentary differential version? Ala John Curl. That would deffinatly be tarting it up a little but, then you have all the output phases and feedback points you would need for most any style output
Check out the JC3 power amp for starters. There might be some answers/ideas there.
Thank you very much, I have had a look at the JC-3 and this should help but is not exactly what I am after.

Without explaining why, let me say that I wish to (need to) take two oppositely phased signals from a single LTP. IE. Not using complementray LTP. The amp will take a balanced input. I may use a second LTP as another gain stage, in which case two oppositely phased signals become inputs to the next LTP stage, and then two oppositely phased outputs are taken from this to drive a load in a bridged fashion.

I am also interested in seeing any schematics where a SUSY diff amp has been used as the input to other stages.

Cheers.
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Old 11th May 2011, 01:00 PM   #5
flg is offline flg  United States
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Try a search on "UGS Adventures" I think
It has the comp diff but you can see where you might go...
Actually there are many circuits out there but can't think of one at the moment. Aleph X maybe
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