+/- rail from one trafo

[pro]

Hi all
A silly question:
If I have a trafo 0-46 VAC and I want a +/- 31VDC, is correct the arrangement in the schematic, or I just do the big bang?
Thank You

[woody]

I don't think that will work. You might check out post 4290 in
the Pass F5 thread it's suposed to work.

[pro]

Thanks Woody, I'll give a look.
Regards

[bobodioulasso]

Hi all A silly question:

Your proposal does not work . You can use the one of post 4290. I use it with my F5 and some other class AB amp.
One 10k resistor has to be tweaked under load to get accurate symetrical voltages. If no tweak, there is a slow drift that equilibrates at a few volts difference between the two halves.
You can google Quad 606 ( and 909) amplifier which uses this PSU.

[pro]

What transistors are the two that You use, just small one type BC550/60 or bigger?
Regards

[bobodioulasso]

In the Quad, they use 2 amps capable devices. Personally, i use BD139/140 which i had on hand. There is no need of a heatsink at all.

[pro]

Thanks a lot Bobo
Regards

[EUVL]

> You might check out post 4290 in the Pass F5 thread it's suposed to work.

http://www.diyaudio.com/forums/showt...74#post1864574

http://www.diyaudio.com/forums/attac...amp=1245948705

I have built this about 5 years ago, but with some slight modifications.
Firstly I put a resistor between the two base of the transistor pair, instead of shorting them. The value of this resistor is chosen such that it creates about 1.5V across the two base connections, and hence bias them to Class A. I also added low value emitter degenerating resistors (depending on your current consumption) to create bias stability.

A yet simpler solution is to use a high voltage power opamp (say capable of 200mA and +/-40V rails) connected as a follower and connect the inpout to the mid-point of the 10k resistors. The output of the opamp is your virtual ground, and the opamp is to be powered by the two rails.

But you have to bear in mind that such a system cannot sustain constant current draw from one rail to ground continuously, unless you use very high power devices capable of delivering the continuous working current.


Patrick

[EUVL]

> In the Quad, they use 2 amps capable devices. Personally, i use BD139/140 which i had on hand. There is no need of a heatsink at all.

That all depends on the application (how much current).


Patrick

[pro]

The ampli is supposed to be an AB class mosfet with 400mA bias for the two mosfet (200mA each) for two channel, so, less the 1 amp continuosly and a max power (with +/-31VCC) of 40W.
Regards