HEHE...My amplifier is almost ready...

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I almost finished building my p3a...

now i need a power supply.

25V 300VA costs about 80$ (380 israeli Shekels)..

so this is too much for me.

i have a 33V transformer but with only to wires coming out...

i changed it with a small circuit with 2 diodes + 2 4700uF caps...

but now i have 45 VDC (+45_0_-45) and i need 35 VDC...

what can i do to change it?
 
benmanf said:
I almost finished building my p3a...

now i need a power supply.

25V 300VA costs about 80$ (380 israeli Shekels)..

so this is too much for me.

i have a 33V transformer but with only to wires coming out...

i changed it with a small circuit with 2 diodes + 2 4700uF caps...

but now i have 45 VDC (+45_0_-45) and i need 35 VDC...

what can i do to change it?


can't really change voltage, just be sure your bias is not affected by the overvoltage. you could also build a powerFET feedback regulator and reference it to 35V for both POS and NEG sides(more complicated). Otherwise your circuit will produce more heat.
 
Shalom friend with P3A

Good amplifier.

I have a supply, that will make you free of voltage problems from now to eternity.

Can receive high voltage in the input... around max 75 volts... output regulated, and stabilized....voltage start zener voltage more a couple or volts... this case 17 because of zener.... you can reduce zener.... or increase a little if you want.... once adjusted.... can put fire on the P3A.... and voltage will stay the way you adjusted.

I am using 30 years this schematic.... made first by Ampex, to Video Tape Professional Recorders.... and them Sony used.... and them milions used it.


Expensive.... can be or not.... i like to make short circuits in the output, without fuse or protection... this way i put DC voltage in short and i measure maximum current...... if, lets say, 20 ampéres.... them i put 4 times this capacity in output transistors.

Your case on transistor each side will be enough with fuses to protect supply... if you put, lets see, 6 transistors positive side and six transistor negative size.... you can go kidding melting coins in your house or making small electrical soldering jobs.

If not fused.... if amplifiers damage, and no fuses..... amplifier will melt, speaker also, speaker wire also, and supply output wire will be very very hot!

When finished the destruction..... go to measure supply.... OK!...in order!.... you will spend money once.... it will survive for decades, and will be good to a lot of amplifiers...just turn trimpot and adjust plus and minus voltage you want. Maximum stable voltage is aroud 5 volts less the maximum voltage.... regulation stays around 5 percent.

Carlos
 

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benmanf said:
I almost finished building my p3a...

now i need a power supply.

25V 300VA costs about 80$ (380 israeli Shekels)..

so this is too much for me.

i have a 33V transformer but with only to wires coming out...

i changed it with a small circuit with 2 diodes + 2 4700uF caps...

but now i have 45 VDC (+45_0_-45) and i need 35 VDC...

what can i do to change it?

Sorry if it's a dumb question.
How did you get +45 _ 0 _ -45 from a transformer that only has 2 wires coming out?
--
Danny
 
Hello friends, let i enter this subject too

I prefer, always to dismount transformer, and re-wire it again.

Only if secondary is over primary windings.

Count the turn coils, and buy two wires half the original diameter and same length..... make the secondary turns again with hand.

I put those informations, deeply in our forum, 2 monthes ago, to a Israeli friend of us.

Another idea is to buy another one and connect the way i scratch.

And, of course, the Joensd way is the easier way, very good way, but i do not know the power results, this way, i asked him, direct mailing him, same explanations about this subject.

regards,

Carlos
 

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And, of course, the Joensd way is the easier way, very good way, but i do not know the power results, this way, i asked him, direct mailing him, same explanations about this subject.
If I understand you correctly then well, the current is obviously halved as the one secondary winding is supplying 2 rails.
Of course this is a one-way-rectifier so rectified voltage will be a bit lower than with two-way rectified.
Again, I don´t think that this is recommended to use with high power applications.

You´ll find this circuit usually in general electronics books where it is referred to as voltage doubler.
 
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