Stereo Audio power amplifier 2 x 40W - 80W

[audioguru2]

Your transformer has a sine-wave RMS value of 28VAC.
Its peak voltage is 28 x 1.414= 39.6VDC.
The two rectifier diodes in series will drop it to about 37.6VDC at full output which is far less than 55VDC.
At clipping, the amplifier will make a sine-wave at its output of about 69Vp-p which is 24.4V RMS. Therefore it produces 74W RMS into 8 ohms.

The 38VAC transformer will have a peak voltage of 53.7VDC. After the rectifier diodes it will be 51.7VDC at full output.
At clipping, the amplifier will make a sine-wave at its output of about 96Vp-p which is 34V RMS. Therefore it produces about 144W into 8 ohms. Nearly double the power of the smaller transformer. 

 

[faizanbrohi]

ok you are right but how much ampere should i have , a transformer of 2x38VDC @ how many amperes ??? A . what i think it would 500VA so if i multiply by power factor which i don't know , but assuming , it to be 0.5 , it is 300W that is 4A , so the transformer should be rated at 2x38VDC @ 4A , or else .. what do you suggest  ???

 

[c3r14l.k1l4]

Hi,

you'll need a supply with the voltage the schematic was designed to. About it's current, the more the better (the circuit will only use the required amperes). The problem is that if your transformer has less power, the circuit will cause the transformer to dissipate more power (incresing it's temperature) and therefore... kaput 

Don't forget to have a rectifier bridge with support for more than 1.5x the maximum current you'll need.

 

[audioguru2]

A class-AB amplifier is about 50% efficient at clipping, so a stereo amplifier with 144W output from each channel will have a supply power requirement of 576VA which is a current of 7.6A. Amplifiers don't work at full power continuously so a smaller transformer with a current of 5A will be fine.

 

[faizanbrohi]

i have studyed just now that Class AB is about 79% efficient and Class A transformer coupled have 50% efficiency. However as far as the transformer is concerned , i have decided , a transformer of 2 x 38VAC @ 6A , with 2 x 12VDC @ 1 A for something(the other winding is seperate for from the first BUT IN THE SAME HOUSING) other then powering up a amplfier . i mean for the Detector circuits and the 10 band VU LED meter that i will insert in it .

i will also need a bridge of 35A @ 230V , well i will begin in it later , seems like a tough project and a little expensive too . i will keep it as a mega audio project and now i will make the First Audio AMplfier i posted with PCB . i am going to draw a schematic and post it sooon.

Wish me good luck in the exams , tommorow is my Solid state Devices and Basic Electrical Engineering paperz.

 

[c3r14l.k1l4]

Good luck man!

I'm just waiting for the results of one disciplin (DataBases 2), the others are done. (I'm from informatics engineering).

 

[faizanbrohi]

There is a big problem , i asked my friend today and he says , MJE15024 and MJE15025 is not available here  :-[ , can you please suggest a replacement

 

[audioguru2]

I don't know which transistors you can buy in your country. The output transistors in the schematic I posted have only one of them available at an American distributor.

 

[faizanbrohi]

I Found something else also , the part number in the schematic i posted is MJE15024 and MJE 15025 which is wrong , it should be MJ15024 and MJ15025 , however MJE15030 and MJE15031 are correct numbers

 

[faizanbrohi]

i Have looked it up in farnell , i found the transistors by searching and selecting my country . My distributer is makkays , so i will be looking to contact makkays . However i glitch that makkays have these transistors  on hand. if not they have to import .

But still they cost around 5.5 pounds . which is approximatiley Rs 550 and it is really very expensice for a transisitor.

 

[faizanbrohi]

Well Thank God I got the Transistors at a low price , farnell is toooo expensive , i have bargained for Rs 1000 for  8 transistors , one transistors cost Rs 125 which is 1.25 pounds and 0.73 dollars i guess. so really low price. Well BEsides That i also have a 8 transisitor heatsink for only Rs 175 , which is 1.75 punds or 1 dollar approx.

So I want to ask if this M250 can be used as a amplfier in the 500W inverter to increase power. and then use a power transformer afterwords..

 

[audioguru2]

I want to ask if this M250 can be used as a amplfier in the 500W inverter to increase power? Then use a power transformer afterwords..

The 500W inverter won't work with an amplifier. The M250 amplifier can be used in a sine-wave inverter.
If you use 8 car batteries in series to feed it positive and negative 48V, its output power will be only about 115W to about 200W and can be used with a 30VAC stepup transformer.

 

[faizanbrohi]

so if different channels are used can it produce more power

 

[faizanbrohi]

IF there are common connections . what will happen parallel voltage is same only current divides , and we have a lot of current no problemooo one car battery is about 55A @ 12V , the one which i have

Here is an idea , what do you think

View attachment 39366

 

[audioguru2]

so if different channels are used can it produce more power

Amplifier outputs should not be paralleled without adding series resistors. The resistors will waste power and cause poor voltage regulation.

IF there are common connections . what will happen parallel voltage is same only current divides , and we have a lot of current no problemooo one car battery is about 55A @ 12V , the one which i have

Eight 12V batteries in series can power many amplifiers. But then the charge in the batteries won't last very long.

 

[faizanbrohi]

It is getting all in all expensive to build a sine wave inverter. Well Good news i will send some pictures of the heatsink i bought for the M250.

 

[faizanbrohi]

HEre is a picture of heatsink

View attachment 39368

View attachment 39369

 

[audioguru2]

You have a nice big heatsink, but you will be surprised at the amount of heat that your linear sine-wave inverter will make and a fan is probably also needed.

 

[faizanbrohi]

Well Here is another Amplfier i found of 1.5 KW how is this Baby . this can drive upto 1.5KW , this is insanity , but wait just calculate how many batteries  Godd Help me . No way , i neeed something like a ferroresonant transformer and a square wave inverter that's allll  ;D

Further More this is the fans Pic , i am just asking do i include two fans on one heatsink or not  ???. I am Eager to use one fan per heatsink . THe Fans are rated 12V @2.2W and 200mA approx . and no i am not using these heatsinks for the inverter , i am using them first for the M250 Amplfier , Stereo 500W x 2 , 250 Watt per channel .

View attachment 39371

View attachment 39372

 

[audioguru2]

i am using them first for the M250 Amplfier , Stereo 500W x 2 , 250 Watt per channel .

Are your speakers 4 ohms? The amplifier makes 250W into 4 ohms or 144W (maybe 150W) into 8 ohms per channel. I don't know if it can have 2 channels bridged to make 500W into 8 ohms.