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Old 11th March 2005, 12:42 PM   #1
quasi is offline quasi  Australia
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Default Another quasi-complimentary design

This one is a variation of a PA amp that I built many years ago. The changes were prompted by learnings made during my post "Power Amp Under Development".

I haven't built it yet. Whadya'll think?

Cheers
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Old 11th March 2005, 01:05 PM   #2
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hi quasi
it seems very nice, just take care to mje350's thermal and miller C imbalance. I think they should be nicely matched and very close to each other on the same heatsink. 39p caps 2% or better.
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Old 11th March 2005, 01:19 PM   #3
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whoa.. and i almost understand how it works too..
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Old 11th March 2005, 01:25 PM   #4
Rudy is offline Rudy  Belgium
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except for C12 everything seems to be okey

Rudy
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Old 11th March 2005, 01:36 PM   #5
quasi is offline quasi  Australia
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Quote:
Originally posted by Rudy
except for C12 everything seems to be okey

Rudy
Please explain Rudy.
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Old 11th March 2005, 01:38 PM   #6
Rudy is offline Rudy  Belgium
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The wirebridge between C12 and the output after the coil does not need to be there, probebly just a drawing error.

Rudy
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Old 11th March 2005, 01:43 PM   #7
audioPT is offline audioPT  Portugal
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Default Re: Another quasi-complimentary design

Quote:
Originally posted by quasi
This one is a variation of a PA amp that I built many years ago. The changes were prompted by learnings made during my post "Power Amp Under Development".

I haven't built it yet. Whadya'll think?

Cheers

Off-Topic - Quasi, with software did you used?
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Old 11th March 2005, 01:43 PM   #8
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D5 needs an additional normal diode in series with it to prevent output rail spikes due to reactive load from reaching up to the upper MOSFET gate and turning it on spuriously.
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Old 11th March 2005, 01:45 PM   #9
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about LRC filter
Yes, it creates 'resonance' load
the impedance is reasonably high up to 30kHz, then is loweing down to 0.689ohm at 660kHz and rises again to 0.702 ohm at HF.
Not sure about phase...
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Old 11th March 2005, 01:53 PM   #10
quasi is offline quasi  Australia
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Default Re: Re: Another quasi-complimentary design

Quote:
Originally posted by darkfenriz
hi quasi
it seems very nice, just take care to mje350's thermal and miller C imbalance. I think they should be nicely matched and very close to each other on the same heatsink. 39p caps 2% or better.
Thanks Darkfenriz. Yes your comments are well received. The 2 MJE350's should be on the same heatsink. The two 4R7 resistors are there to help reduce mismatches between these transistors. Your advise about the two 39pF capacitors is noted.


Quote:
Originally posted by demogorgon
whoa.. and i almost understand how it works too..
whoa....me too. The main difference with this amp and som eothers is the tempreture compensation built into the constant current source of the second stage and the way the FETS are driven.

Quote:
Originally posted by Rudy
The wirebridge between C12 and the output after the coil does not need to be there, probebly just a drawing error.

Rudy
Yes, the high frequency load impedance will be more gradual and predictable if I remove the link.


Quote:
Originally posted by audioPT



Off-Topic - Quasi, with software did you used?
I used a software package called sPlan.

Quote:
Originally posted by richie00boy
D5 needs an additional normal diode in series with it to prevent output rail spikes due to reactive load from reaching up to the upper MOSFET gate and turning it on spuriously.
I read lots of good advice from you. Yes I will put diodes in series with both zeners.


Cheers
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