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Le Pick 9th July 2012 02:38 PM

50V Power Supply
1 Attachment(s)
Hi, i'm making an Amplifier based on two L12-2 Power Amps from ebay.
But as for the power supply I'm a bit comfused.
So, lets say that I have a toroid transformer 25-0-25 that I wire in series to output 50V, going to a bridge rectifier, then to 4 caps and a negative voltage generator (based on Voltages Regulators).

-First, is the output is still going to be -50v/GND/+50v with proper Voltage regulators?
-Second, what could be the proper voltage regulator for the power supply?
-And Third, is my schematic a good start or a bad idea?

I've roughly made a schematic, in the attachement, for what i think could be Ok...

Le Pick

CBS240 9th July 2012 03:00 PM

25V * sqrt(2) is 35.35V. Then you have the diode drop, so you will end up with ~34.5V, so from 25-0-25VAC you will have +/-34.5Vdc from across the filter caps before the regulator.

The circuit requires +/-50V, so with a diode drop you need ~51/sqrt(2) or ~36VAC....36-0-36. You need to reference the filter caps to the centertap or GND so you need two sets of filter caps to get +50VDC/GND/-50VDC.

Speedskater 9th July 2012 03:04 PM

The "GND" terminal and the "-50VDC" terminal will be at about the same voltage.

picowallspeaker 9th July 2012 03:42 PM

That PSU schematic is just wrong for many reasons :
1)you have to understand what a dual supply intended to be used with a power amplifier is , which brings to
2)that you don't need a regulated PSU for it ,then ..
3) the loudspeaker asks for current from the two poles , which are the output from the power transistors ( or mosfet ) and ground , so you just can't create a 'ground' ...

So , if the amplifier gives full power of 120 W on a 8Ω load with a dual 50 V supply ,
for the initial start-up you can power it up with your transformer will give you
+ and - 35 V and less power at output . In the meantime find a 35+35 V...300W transformer !

KatieandDad 9th July 2012 04:29 PM

Dual Rail PSU
1 Attachment(s)
Let's let a picture paint a thousand words:

This is OVERKILL but explains the issue.

You require +50 - 0 - -50V PSU. Therefore in a high power situation you must have two secondaries, which indeed you have.

Each secondary MUST be capable of producing 50V in its own right, therefore you need a minimum of ~35V AC.

Ideally you would need about 37-0-37V AC to give you an unregulated 50-0-50 VDC but 35-0-35V AC would be close enough.

There are a number of ways of obtaining 50-0-50V DC from a 35-0-35 or 0-35 + 0-35V AC supply but they all require a split secondary winding.

KatieandDad 9th July 2012 04:36 PM

25-0-25V will give you approx 34-0-34VDC. Which would be sufficient for the gain clones.

Le Pick 9th July 2012 04:59 PM


Ideally you would need about 37-0-37V AC to give you an unregulated 50-0-50 VDC but 35-0-35V AC would be close enough.
Assuming that I already have my transformer (Oups) that push 25-0-25 is there any way to do something with it or I did a bad mistake?

KatieandDad 9th July 2012 05:01 PM

Not realy.

You will see voltage doublers but they aren't useful at these kind of currents.

KatieandDad 9th July 2012 05:03 PM

You could go SMPS with a Buck Regulator to increase the voltage but I would either just live with the transformers you have got or sell them and buy the 35-0-35 that you are looking for.

The 25-0-25V is popular for the Pass F5 so you might not be too out of pocket.

KatieandDad 9th July 2012 06:55 PM

Why list the same question twice - This is against Forum Rules

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