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/diy/ - Do It Yourself


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1730852 No.1730852 [Reply] [Original]

Is it possible to use these 4 terminals in combination with 2 graetz bridge and 2 capacitor to power the amplifier?

Amplifier uses +/-36V
Transformer gives 31V, when converted to DC gives ~34 volts.

What would be consequences of using lower voltage than recommended?
Also how can I get negative voltage from this.
Broken transformer used center tap to separate + and -, but here I don't know if I have center tap.

>> No.1730853
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1730853

This is the transformer in question

>> No.1730854
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1730854

power supply in schematic

>> No.1730982

>>1730852
>Amplifier uses +/-36V
>Transformer gives 31V, when converted to DC gives ~34 volts.

the best that transformer can give you is +/-17V when converted properly to DC if it has center tap.

>What would be consequences of using lower voltage than recommended?
depends on the amplifier, if it doesn't need another stage to be powered with some specific voltage it only will give you less output power, ie. not so lowd as you want, maybe half power output.

Otherwise, look up for a appropriate transformer.
best option: 1 tranformer with center tap that gives you 36VAC in each side terminal.
not best but possible option: 2 single transformers (identical, with no center tap) that gives you 36V AC as output.

>Also how can I get negative voltage from this.

look for LM78XX and LM79XX voltage regulators to get an idea.

>> No.1730990
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1730990

>>1730982
I don't understand how it will give +/-17V max.
When run on simulations with full bridge rectifier, 42kOhm load and 4.7mF capacitor, it shows 29.5V

I accidentally set AC input as 36V, not 31V

>> No.1731004

>>1730990
if it is a transformer with center tap and the sides taps it gives you 31V then respect the center tap each other tap will give half voltage. But probably i got wrong what you described at first.

Don't trust simulations unless you know what you are simulating, 42kOhm load doesn't sound as a realistic load for an amplifier circuit. 4.7mF (assuming m is for mili and not micro) is a way too unrealistic value. Otherwise use "uF" for microfarads.

>> No.1731006

>>1731004
this transformer doesn't have center tap i believe. i measured all terminals in regards to all other terminals.

>>1730852
Those that do not have value written have 0V

42kOhms is probably too high of input impedance, but I have 2 capacitors 50V/4700uFarads lying around so I will use them (since they were with old transformer in the amp)

>> No.1731050
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1731050

>>1730852

it's super easy to get approx +/-36V from a 31Vac xformer. the only drawback with this circuit is it will supply half the current as if you used a proper center-tapped xformer. in other words, less power for your speakers, but guaranteed to work.

>> No.1731064

>>1731050
don't forget the ripple. with half wave rectifiers you get some awful ripple on voltage output if not properly filtered and regulated

>> No.1731097
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1731097

>>1730982
this is the amp. I presume there are no other stages.
>>1731050
Didn't know that, will look into it now.
but I don't know if the tradeoff is worth it, since I'm missing only 5V from the nominal value stated on the datasheet.
>>1731064
So a large capacitance should do the trick?

>> No.1731105

>>1731097
>So a large capacitance should do the trick?
not always, a capacitor, when discharged, acts as a shortcircuit allowing a peak of current run through the diodes, and as larger the capacitor is the longest will last this peak, if diodes are not set accordingly to this, or you just use large capacitors without knowing this you maybe will burn out some diodes.

Generally on bridges i've seen 1n4007 diodes which are desgined to tolerate ~1A of current through them without burning. If you know the diodes you are using you should respect the schematic values of components.

If you want to study all this stuff by yourself try looking for Electronics devices by Floyd book. There's a good introduction to the considerations you have to take in order to not blow out your shit.

>> No.1731115

>>1731105
>Electronics devices by Floyd book
Thank you for recommendation. I have managed to salvage some heavy duty full bridge rectifiers and diodes from earlier projects, so now is time to research the parts.

>> No.1731116

>>1731097
what kind of amplifier are you working on anon?
why so cryptic and not posting the whole circuit?
without values and stuff i can figure out too much, but those transistor at the right that seems to out of the same case of the rest of the cricuit look like they are part of a power stage, linked to the +-36V i pressume you are trying to make or fix, therefore the load involved is indeed much lower than the 4.2kOhm you stated before.

>> No.1731120
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1731120

>>1731116
Sorry, didn't want to smother you with unnecessary information. here is the actual schematic, but what is mostly salvageable are the 2 channel amps.

>> No.1731124
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1731124

>>1731116
Those 2 transistors on the right are NEC2SD388 nad NEC 2SB541. Power transistor, and they are "out" of the rest of the circuit because they are physically slapped on giant cooler.

>> No.1731131
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1731131

>>1731124
So actually I was thinking of seeing it as a black box. 4 wires: signal, +/-36V and GND, and make rest of functionalities around it (filters, inputs, separate port for headphones, possibly BT input, etc.)

pic is what I'm striving for

>> No.1731148

>>1731120
>>1731124
>>1731131

ok, so as i can see it is indeed a power stage, which means you'll lose some power at the output if you use less voltage than required, and maaaybe get a little of distortion (not sure about this) because the biasing of transistors of the running power stage will not reach proper voltage. You can try, i don't think you'll burn anything by trying but consider that you won't develop all the power on the output.

If you have all the original parts, why don't you just stick to the original schematic? Or is the transformer you posted here >>1730853
is burn out or something? If not i don't get why you're trying to lower the voltage supply

>> No.1731186

>>1731148
Original transformer is rattling alot. I triedsqueezing the plates, glue and tape, but it is just too much hum and buzz. Receiver is completely broken (unfortunately because mechanical solution was mesmerizing) and there is something wrong in the filter section. I tested with continuity and looked for visible faults, but to no avail.

Will try to hookup power supply connect it to speaker and see what i get out of that.

>> No.1731188

>>1731148
Forgot to mention in >>1731186.
The transformer in >>1730853 is from another amp (kenwood kaf 1030) and is in pristine condition. No rattling, stable voltage

>> No.1731383
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1731383

>>1730852
>Transformer gives 31V, when converted to DC gives ~34 volts.
31V x 1.41 - 2 = 42V. You'll get 42V DC.

>> No.1731466

>>1731383
>31V x 1.41 - 2 = 42V. You'll get 42V DC.

42Vdc open circuit. as soon as you put a load on it, it drops. bigger the load, bigger the drop.

>> No.1731491

>>1731466
Yeah, I'm familiar with square root of 2,
But unfortunately as >>1731466 said, it doesn't give me 42V

>> No.1731859

>>1731466
>42Vdc open circuit.
OC voltage would be close to 44 volts. If the sag is that big (44 -> 34 volts) then it means the transformer is overloaded big time. It's not OK to use it, it'll overheat and catch fire in no time.