Very simple quasi complimentary MOSFET amplifier

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E

EmeryBB

Member
Joined 2015
bandol83 said:
Hi,

This is not a quasi complementary since it does not use a combination of MOSFET and Bipolar in the output stage :(

I have increased the size of the capacitors to 13 mm but I have to move a lot of things, however I have found that the 1 W resistor were far too big therefor I could reduce them :) During the modification I also modified some value based on the schematic drawn by DACZ (I hope that they are the last ones ?) and I found that the capacitor C7 had a wrong connection because the previous version didn't use a Zener diode ! By the way I have seen that it is possible to replace the Zener diode by a blue LED ? From my experience in tubes amplifier, it seems that LED are less noisier than Zener because they are used in the direct way and not reversed... What do you suggest ?

I have attached the schematic and the PCB for your comments.

Best regards,
Marc
Click to expand...

7K2 in R13??
 
B

bandol83

R.I.P.
Joined 2004
Hi EmeryBB, Hi Schillg11,

Thank you for finding the typing error on R13, the correct value is 1k2 on DACZ schematic :)

I have also reduced the size to 99 mm, but the mounting holes will be very close to the PCB edges :eek:

Finally I have made some cosmetic changes on the PCB to optimize some tracks and make the serigraph more readable... I hope this version will be OK to produce the boards ?

Best regards,
Marc
 

Attachments

  • Schema Quasi.pdf
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  • PCB Quasi.png
    PCB Quasi.png
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B

bandol83

R.I.P.
Joined 2004
Hi,

This is probably the last version before I send it to the PCB manufacturer, I have checked twice and make some tracks shorter, I hope I didn't forget anything, if you find some errors please tell me :)

I have a 300 VA transformer with 2 x 35 V AC output : http://www.farnell.com/datasheets/2...16.403529732.1531758856-1429063303.1527947097
This will give about 45 to 47 V DC after rectifier and 2 x 10'000 uF capacitors, do you think it will not be too much with a NJW3281G bipolar and a IRFP240 MOSFET and that I can use it for a stereo amplifier ?

Marc
 

Attachments

  • Schema Quasi.pdf
    141.2 KB · Views: 196
  • PCB Quasi.png
    PCB Quasi.png
    180.6 KB · Views: 883
M

motronix

Disabled Account
Joined 2012
ebay.com/usr/motronix2012
bandol83 said:
Hi,

I have a 300 VA transformer with 2 x 35 V AC output : http://www.farnell.com/datasheets/2...16.403529732.1531758856-1429063303.1527947097
This will give about 45 to 47 V DC after rectifier and 2 x 10'000 uF capacitors, do you think it will not be too much with a NJW3281G bipolar and a IRFP240 MOSFET and that I can use it for a stereo amplifier ?

Marc
Click to expand...

The voltage will be 49V to 52V DC after rectifier.
This NJW3281 & IRFP240 can work with no problem up to 85V
 
E

ermine22

Member
Joined 2015
First power-up behaviour

I am just getting around to firing up the DACZ boards that I built several months ago. My usual procedure is to power circuits with my programmable bench PSU at this stage - using over-current protection to protect both the board and me. When I power the boards with 25VDC and a max of 3A, the over-current protection always kicks in instantly on both boards. I am using LED's in the circuit and both light momentarily. Is this expected behaviour?
 
B

bandol83

R.I.P.
Joined 2004
Thanks for the tip Bangla, I see the picture of your coil on the post 1581 and it look very nice :) I have also been impressed by the nice green coil of xrk971 on post 1470 and the coil of dirttracker73 on post 1743... When I try to make a coil it look like an old spring, may be this is because I have used a wire too small ?

Should I buy the one you recommended (1.32 mm) or should I buy the 1.5 mm as indicated somewhere in this thread ?

I am already a customer of TME and I like their Toroidy transformer that I have recommended for the EL34 Baby Huey amplifier... I like the fact that they have a very fast shipping service :)

Rgds
Marc
 
nigelwright7557

nigelwright7557

Member
Joined 2008
murtonpikesystems.co.uk
Mooly said:
Higher values will "play safe" and make the design more tolerant of any compromised layout and so on. That was my reasonlng. It removes a potential source of trouble for you.



Yes, its workable although it may need need more refinement to get the very best from it.
Click to expand...

A 390r gate resistor also makes less likely damage further back if mosfet's blow GS or GD.
 
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