Another quasi-complementary design

quasi · 11th March 2005, 12:42 PM

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

darkfenriz · 11th March 2005, 01:05 PM

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.

demogorgon · 11th March 2005, 01:19 PM

whoa.. and i almost understand how it works too..

Rudy · 11th March 2005, 01:25 PM

except for C12 everything seems to be okey

Rudy

quasi · 11th March 2005, 01:36 PM

Quote:

Originally posted by Rudy
except for C12 everything seems to be okey

Rudy

Please explain Rudy.

Rudy · 11th March 2005, 01:38 PM

The wirebridge between C12 and the output after the coil does not need to be there, probebly just a drawing error.

Rudy

audioPT · 11th March 2005, 01:43 PM

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?

richie00boy · 11th March 2005, 01:43 PM

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.

darkfenriz · 11th March 2005, 01:45 PM

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...

quasi · 11th March 2005, 01:53 PM

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

11th March 2005, 01:43 PM	#8
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	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. __________________ www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more

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11th March 2005, 01:05 PM	#2
darkfenriz diyAudio Member Join Date: Jun 2004 Location: Warsaw	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.

11th March 2005, 01:19 PM	#3
demogorgon diyAudio Member Join Date: Jul 2004 Location: Behind you.	whoa.. and i almost understand how it works too..

11th March 2005, 01:25 PM	#4
Rudy diyAudio Member Join Date: Feb 2003 Location: Belgium	except for C12 everything seems to be okey Rudy

11th March 2005, 01:38 PM	#6
Rudy diyAudio Member Join Date: Feb 2003 Location: Belgium	The wirebridge between C12 and the output after the coil does not need to be there, probebly just a drawing error. Rudy

11th March 2005, 01:45 PM	#9
darkfenriz diyAudio Member Join Date: Jun 2004 Location: Warsaw	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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