F4 power amplifier

[albertli]

Populated Veteran's boards, but still waiting for the TL431 and the K170/J74 pair.

 

[Yunick]

Nice chassi! Those heatsinks look massive

What mosfets are you using?

 

[Nelson Pass]

"I finally have the funds to purchase a few tubes of Fairchild fet's for my F4, Could you please comment on the part number which won't exhibit the distortion as mentioned before."


The Fairchild FQA12P20 are good P channel parts.

 

[albertli]

-Nice chassi! Those heatsinks look massive

What mosfets are you using-


I brought 4 of them from ebay and they are 12"H x 121/2"W x 4" fin. I thought I could try running higher bias.

Those mosfet are 2SK1530/2SJ201.

 

[nonoise]

Thank you very much Mr Pass

 

[dadello]

F4 psu problem

Hello everybody,
this is my psu I have a problem with: fuse is slow blow rated at 2A (more than needed for 240VAC), toroidal is new from trafomatic 300VA with secondary 18-0-18, 3x22000uF caps per rail, and two thermistors cl60 (one in the primary, the other between psu earth to chassis).
This psu is almost the same I used in my previous Aleph2, I only changed the toroidal.
Without connecting ground from filter caps, I have 24,8VDC on each rail, and everything seems working properly.
The problem happens with the earth of psu connected, and fuse blows into two seconds.
Any suggestions? Thanks
D.

 

[albertli]

My F4 is singing for 4 hours now at 270mv with heatsink at 30C , mosfets at 40C and o.47 3w resistors at 48C.
I wonder if I run at higher bias would hurt the 0.47 3w resisitors.

 

[Tea-Bag]

alberti. I have a set of those crazy Aavid heatsinks. I think 300mv is the max. Maybe you can put a whole balanced amp in one chassis. That may warm it up.

 

[albertli]

The sound is a bit too thin and not warm so far. Maybe it's the problem of temperate too low, and or need more time to break-in.

 

[SCD]

Alberti
Once you put a front and a top on it, it will likely warm up a bit.
Looks real nice

 

[albertli]

SCD
May I ask where about are you in Vancouver.

 

[SCD]

Hello Alberti:
I am over on the Island. About 1/2 way up in Campbell River

 

[EUVL]

> The sound is a bit too thin and not warm so far.

Add another 2 pairs of MOSFET per channel perhaps ??
I am sure you bought enough of them to try this out.




Patrick

PS My Aleph-X has 12 FETs per channel, and there are enough people who have 16. I think Nelson use something like 24, if my head still functions properly.

 

[Nelson Pass]

My F4 is singing for 4 hours now at 270mv with heatsink at 30C , mosfets at 40C and o.47 3w resistors at 48C.
I wonder if I run at higher bias would hurt the 0.47 3w resisitors.

If you have lots of heat sinking and your rails are at 24V or so, then the max
is around 700-900 mV. That will warm it up.

 

[Gyuri]

Hello Papa!
Do we get some beautiful new game for Christmas?
Although the old ones are not all of them, an example are not yet for me yet F5.
And I got not bored of the even older ones.
Gyuri

 

[Nelson Pass]

Hello Papa!
Do we get some beautiful new game for Christmas?
Although the old ones are not all of them, an example are not yet for me yet F5.
And I got not bored of the even older ones.
Gyuri

You have been exceptionally good this year, so for Xmas you get
a nice surprise.

A little bit of old and new to keep you warm through the winter.

 

[carpenter]

Hahahah.....

Speaking of warm: who needs a snow plow when you have class A amplifiers to keep the driveway clear!

 

[Babowana]

..., so for Xmas you get a nice surprise.

Gyuri, congratulations!

 

[albertli]

Patrick,

I certainly will try couple more pair just for warming up the heatsink and see how it go. I've to do this in the later days for I've to go Christmas shopping with my love one for the love ones.


-If you have lots of heat sinking and your rails are at 24V or so, then the max
is around 700-900 mV. That will warm it up.-

Nelson,

Thanks for the advice. I'm running both rails at 25v and 23v after loading. Both channels are running at 300mv now and it takes 3 hours to warm the heatsink at 36C. mosfets 50C and the 0.47R 60C. I don't know I would burn the 0.47R if I run the amp on more higher current.........

Wish everyone a Safe and Merry Christmas, Happy New Year too.

 

[EUVL]

0.9V across 0R47 is 1.9A. The resistor will see 1.7W; bit high but still OK. The transistor will see almost 50W, which is definitely high.

Therefore paralleling more FETs is the better solution, if money is no issue in that sense. I would suggest 1.3A per FET, which is about 600mV across 0R47.


Patrick