Mosfet power follower (Pavel Macura)

[naim35]

Hello forum,

last week I finished my follower. I build it like the drawing 4 of Pavels web side discribes, http://www.pha.inecnet.cz/macura/fig_4.gif.

At first i could´nt reach the 2,2A Iq, but Pavel told me that I should use a BZX83 Zener, thanks Pavel. I use a 3.3V Zener, so point B from T102 is 3.6V and Iq reach 2,6A.
With my 4 Ohm loudspeaker the amp has about 13W power per channel enough for a good household-noise level.

The sound is absolut fantastic, pretty fast, not sharp, absolut transpatent. I´m very happy with it.

It runs very hot, with an Iq like this (2,6A) i have to buy another heatsink. The housing is not yet completely finished, maybe I will make the front in wood. The photos show still the first starting period, I will tight the cables more beautifully in the future.

Best regards from Hamburg

Martin

[naim35]

I hope it will succeed to sent more pics. I dont know how it works to sent more pics than one.

Martin

[naim35]

Picture Three

[naim35]

at first the last picture,

Best regards

Martin

[AndrewT]

Hi,
How hot is the heatsink?
The transformer and caps will be running much hotter than need be.
Can you re-organise the mounting to introduce a big ventilation space between the heatsink and the other components?
regards Andrew T.

[Upupa Epops]

Is screw for toroid fitting made from plast ?

[naim35]

Originally posted by AndrewT
Hi,
How hot is the heatsink?

The transformer and caps will be running much hotter than need be.

Can you re-organise the mounting to introduce a big ventilation space between the heatsink and the other components?
regards Andrew T.

I still did not measure it, but I think if the amp runs one hour the temp. is about 55°C or a bit higher, it is hard to touch the heatsink a little bit longer.

The Transformer is about 30-35°C and the caps are not hot.

Maybe if I will go to a second heatsink, but I think it is not necessary.
I would not use a ventilation. If I should get a termal runaway I reduce Iq. But with two heatsink like this I am on the secure side.

Regards

Martin

[naim35]

Originally posted by Upupa Epops
Is screw for toroid fitting made from plast ?

Yes it is. It is PEEK.

best regards

Martin

[AndrewT]

Hi,
if the heatsink is over 55degC then the base of the caps must be even higher than this!
Can you get in there to measure this?
No don't bother measuring the inside of the caps just wait until they tell you they are too hot - big bang is english for too dam hot.
One side of the transformer is also going to be running at elevated temp.
If you can alter your layout then try. Spacers and/or a separating plate might be enough.
Your output transistors will thank you for an easier life with 2 heatsinks by lasting longer.
regards Andrew T.