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Old 12th May 2010, 09:19 AM   #1
sekhar is offline sekhar  India
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Smile Which is Beter Quasi Or Non Quasi

which sounds better a quasicomplementary amp or a complementary amp as i going to make a amp in the range of 150 to 200W rms I was just thinking which topology to use .................

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Old 12th May 2010, 09:57 AM   #2
AKSA is offline AKSA  Australia
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Quasi sounds better providing there is diode, resistor and cap all in parallel between phase inverter and output rail.

Full complementary measures better by far.

Take your pick.

Hugh
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Old 12th May 2010, 10:47 AM   #3
Mooly is offline Mooly  United Kingdom
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Hi Hugh, as soon as I saw the thread title I guessed it might be yourself responding.
Just to go off the original OP's thread slightly, did you see this thread of mine,

Very unusual old quasi complementary design... which sounded great at the time.

I missed the VAS PNP stage off, but the main question was that it was a quasi design but with the darlington arrangement as shown on only one side of the LTP.
Wondered what your reaction might be to that... I always remembered it sounded really good at the time, and never found out why it had been designed like that.
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Old 13th May 2010, 07:32 PM   #4
sekhar is offline sekhar  India
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quasi and nt quasi seems to show nt much difference in THD spec in simulation wat do u people say ?????????????????????////
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Old 13th May 2010, 08:58 PM   #5
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I have designed both quasi and comp output MOSFET amplifiers.

I personally preferred the quasi to listen to but found it not quite as easy to bias and set the dc offset due to extra transistors in the output driver stage moving around with temperature, despite using a Vbe miltiplier.
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Old 13th May 2010, 09:15 PM   #6
sekhar is offline sekhar  India
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so wat do u recommend Quasi or nt quasi for true audio experience ???????????????
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Old 13th May 2010, 09:19 PM   #7
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Originally Posted by sekhar View Post
so wat do u recommend Quasi or nt quasi for true audio experience ???????????????
I prefer the sound of quasi.

But if you are going to design or build a quasi then care needs to be taken with bias and DC offset. I found I needed a bit more bias current on the quasi which can cause thermal problems if you run too much bias current.
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Old 13th May 2010, 10:37 PM   #8
Bigun is online now Bigun  Canada
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Quote:
Originally Posted by Mooly View Post
Hi Hugh, as soon as I saw the thread title I guessed it might be yourself responding.
Just to go off the original OP's thread slightly, did you see this thread of mine,

Very unusual old quasi complementary design... which sounded great at the time.

I missed the VAS PNP stage off, but the main question was that it was a quasi design but with the darlington arrangement as shown on only one side of the LTP.
Wondered what your reaction might be to that... I always remembered it sounded really good at the time, and never found out why it had been designed like that.
Is it to do with voltage drops difference between the upper and lower outputs ?
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Old 13th May 2010, 10:48 PM   #9
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Quote:
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Is it to do with voltage drops difference between the upper and lower outputs ?
The top driver is an emitter follower so has a gain of one.

The bottom driver is an inverter with a gain of 1 unless you add a Baxandall diode, in which case it has a much higehr gain and also drives the mosfet gate harder just like the top driver.
This extra gain of course disturbs the balance and then most often yuou find you need a 220pf from c-b on the lower driver.
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Old 14th May 2010, 06:05 AM   #10
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by Bigun View Post
Is it to do with voltage drops difference between the upper and lower outputs ?
I don't really know what the idea was, and have never found any reference to this old design anywhere on the web. The design was AC coupled, so any DC drift didn't matter... I don't know.
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