Its datasheet shows how much lower its output power will be with a lower supply voltage.

Its datasheet shows how much higher its power supply current will be and how much more its output power and heating will be.

I don't know since you are just copying the circuit.

You must plan the entire design of a power supply, not just its voltage.
The datasheet shows that with a 50V supply, two bridged LM3875 ICs driving 80W into an 8 ohm load causes the amps to heat with a total of 66W. That heat must be dissipated by a huge heatsink.

Since 66W must be dissipated as heat and an additonal 80W is dissipated by the load then the total power from the power supply is 146W.
Simple arithmatic shows a power supply current of 2.92A which is way higher than the max from the little regulators in the power supply circuit you found.

Why use regulators? They aren't needed with a huge 37V/4A transformer and 10,000uF of filtering. The amp won't be operating at max power continuously so a 2A or 3A transformer will be OK. Double its current for stereo.

__________________
Uncle $crooge

 

You don't need anything in that circuit to the right of the two 4700uF capacitors, and you need a lower voltage transformer as I mentioned above.

A 15-0-15 transformer would work fine.

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The circuit will drive an 8 ohm speaker to 60W with a 15V-0-15V transformer and the supply current will be 2.4A max. A 50VA to 100VA (1.7A to 3.33A) transformer would be fine.

__________________
Uncle $crooge

 

i made the power supply and it works +35 to -35

but...but...i counldnt find the IC LM3875 so tht project is no more
now am looking for something else to submit to my professor
10 watt amp or a 20 watt amp....easy to make as i dont hav much time left saturday is the date for submission

 

I thought you wanted +25V and -25V?.

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I think he used a 25V-0V-25V transformer by mistake.

__________________
Uncle $crooge

 

Oh yeah, Philips have about 76 IC amps and ST Micro also have 70.
Maybe they are available in your country.
http://www.semiconductors.philips.co...215/index.html
http://www.st.com/stonline/stappl/pr...X_DOC&latest=N

__________________
Uncle $crooge

 

variable dual power supply
max +35 to min -35
i thght it is needed in so many circuits..why not make sumthin tht can be used over and over

thnx...i look into these ics...

 

It's doubtful if it's powerful enough to run audio amplifiers?, they take a fair amount of power - unless you've built it with huge heatsinks and descrete regulators?.

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LM 337 and LM 317
is it enuff?
or should i add something more to it?
no heatsinks though...
i'll add them

 

NO!, far too small, Audioguru mentioned that earlier - also you should fit as large a heatsinks as you can, because even at fairly low currents they will get really hot at lower voltages.

Try doing the maths - W=VxI.

With 35V in, and (for example) 12V out, you're dropping 23V across the IC. If you draw 1A then the IC is dissipating 23x1=23W as heat. With 0.5A, it's 23x0.5=11.5W - with no heatsink it will probably only handle 1-2W?.

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how about this one?
it'll give me + - 22 but thts enuff for me
no voltage regulators.. though

Attached Images

ps_679.gif (4.4 KB, 601 views)

 

Audio amps don't need voltage regulators.
The LM317 and LM337 supply 1.5A only when their output voltage is near their input voltage. They reduce their output current when they are set to lower output voltages to protect themselves, only 150mA.

Of course they need heatsinks with fins, because power= VI.
If your heatsinks aren't big enough, the regulators will shut-down when they get too hot.

Attached Images

lm317.png (33.0 KB, 598 views)

__________________
Uncle $crooge

 

i wish you guys were my teachers

thnx
btw where did you guys graduated from?

 

The simple PSU you posted is like the one I mentioned earlier, it's all that's needed for an audio amplifier.

Personally I never graduated from anywhere :lol:

I left school at 16 and went to work doing radio/TV repairs, after the first year I started attending technical college on day release, one day a week.
It was a four year course called ETV, I skipped ETV1 and started directly in ETV2 (as I already had O Level physics), I passed ETV2 with distinction and went to ETV3, I passed ETV3 with Distinction Grade 1 (the higher mark they gave). Because of this high mark I skipped ETV4 and moved to a technicians course in the third year, called T3 - this was a six or seven year course (as fas as I can remember?).

Anyway, this was a seriously BAD move - T3 was a complete waste of time!, I was learning nothing, and just wasting a day and night of my life every week, so after the Christmas break I stopped going any more :lol:

So I never actually finshed ANY electronics course :twisted:

This hasn't stopped me being Sharp UK TV Service Engineer of the year twice, and Grundig UK Satellite Engineer of the year once 8)

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