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Old 10th September 2004, 10:13 AM   #1
pro is offline pro  Italy
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Default Quasi or full complementary.

Hi averybody.
I am gonna building a new 100W mosfet amp for loadspeaker's woofer.
The bubt that I have is if build a quasi ar e full complementary amp.
Could pls somebady explain to me whitch are the main advantages and disadvantages of both circuitary, both for electrical quality and sonic quality.
Thank you.
Ciao.
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Old 10th September 2004, 02:54 PM   #2
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Full complementary is usually a little more expensive due to
P types part cost, but is easier to make perform well due to
it's simplicity, and is also usually more stable.
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Old 10th September 2004, 05:01 PM   #3
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Thanks Mr. Pass.
Nothing to say about sonic cacacter of both?
Ciao
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Old 12th September 2004, 03:31 AM   #4
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According to Self...

Quasi's are an old technology when it was uncomming to find P and N types in complementary characteristics. Now that consideration is virtually a nonworry. The quasi has more distortion than a full complementary but can be made to perform pretty well with careful design.
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Old 13th September 2004, 10:39 PM   #5
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Quasi-complementary amps are harder to design because one of the output transistors act as a voltage amplifier and the other acts as a current amplifier. These two amplifier stages need different types of driver circuits, and this is tricky to design. Now if you insist on using two of the same type output transistors, you could make a transformer coupled push-pull. This would of course require a good size hunk of iron for a 100Wrms amp, but would work all the same. You use two audio transformers. The input transformer is used as a phase spitter and the second is the output transformer, used to connect to the speaker. I have made small amps, like 10-15W using this type of topology. It requires fewer componants.

This is not the cheapest way though. The cheapest way is to direct couple a complementary output stage to the speaker but this can have some design hazzards unless you know what you're doing.
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Old 14th September 2004, 06:52 AM   #6
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The question is:
if nowaday a quasi complementary seems to have no good reasons for to be alive (difficult to tune, problems with crosstalk, etc etc) , why so many people use it (I found a lot of schematics on the web).
Could it have some better sonic signature respect to a full cpmplementary? (Distorsion spectrum or something else).
Ciao.
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Old 14th September 2004, 06:28 PM   #7
azira is offline azira  United States
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One reason is that patents expire. A lot of those designs (Citation 12 for example) are old designs who are out of patent protection and therefore the schematics can be published.
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Old 14th September 2004, 09:26 PM   #8
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It used to be very hard to find complementary power MOSFET devices because P-ch was hard to find and match up. In the new wonderful modern times we live in, , you can find these componants much easier. A decade or so ago if you wanted to make a MOSFET amp, your best bet was quasi-complementary, class-A, or transformer coupled push-pull. It will be much easier and cheaper to make a complementary amp anymore. Times do change my friend.

Get in touch with Fairchild for mosfet's they have a large selection.
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