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Old 9th July 2012, 02:38 PM   #1
Le Pick is offline Le Pick  Canada
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Default 50V Power Supply

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...


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Old 9th July 2012, 03:00 PM   #2
CBS240 is offline CBS240  United States
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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.
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Last edited by CBS240; 9th July 2012 at 03:15 PM.
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Old 9th July 2012, 03:04 PM   #3
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The "GND" terminal and the "-50VDC" terminal will be at about the same voltage.
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Old 9th July 2012, 03:42 PM   #4
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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 ...it will give you
+ and - 35 V and less power at output . In the meantime find a 35+35 V...300W transformer !
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Old 9th July 2012, 04:29 PM   #5
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Default Dual Rail PSU

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.
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Old 9th July 2012, 04:36 PM   #6
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25-0-25V will give you approx 34-0-34VDC. Which would be sufficient for the gain clones.
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Old 9th July 2012, 04:59 PM   #7
Le Pick is offline Le Pick  Canada
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Quote:
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?
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Old 9th July 2012, 05:01 PM   #8
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Not realy.

You will see voltage doublers but they aren't useful at these kind of currents.
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Old 9th July 2012, 05:03 PM   #9
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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.
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Old 9th July 2012, 06:55 PM   #10
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Why list the same question twice - This is against Forum Rules

Negtive Voltage ?????
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