[sdiy] Prophet 5 power supply

[Oakley Sound]

Hi all,

Has anyone tried upgrading the Prophet Five's power supply? I have one
and it needs a new transformer because the present one hums audibly. Its
a simple power supply design in the rev 3.2 and 3.3. But the problem is
that it is too simple.

Firstly there are no protection diodes around any of the three terminal
regulators. This is easily rectified [ :-) ] by adding the missing
diodes. Secondly the rear heatsink gets really really hot. OK, its not
quite as hot as JP-8, but its hot enough to get me worried.

The +5V rail is a 7805 with a diode on its GND leg taking the output to
5.6V. This regulator takes its feed from the 26V unregulated voltage that
also feeds the +15V regulator. Now dropping nearly 21V at around 800mA is
sure going to cook the little fella and the heatsink gets rather warm.

It seems to be asking for a separate low voltage feed from another
smaller transformer for this regulator alone. Anyone done this, and did
you have any problems with the u-proc reset line that takes its signal
from the raw 26V supply?

Alternatively, I was thinking of a pre-regulator design for the 7805. Or
possibly even a switch mode [shudder..] unit to replace the whole lot.

I'm cross posting this to AH and Synth-DIY so please watch your replies.

Many thanks,

Tony

www.oakleysound.com