Hello,

@Kermit2 , the posted transformer is 2 X 18 Volts and can not be used to power the amplifier.

Bertus

 

'Twould have been sweet of ya to post the correct one when correcting my Mouser search function failures.

Meh.

 

Hello,

I would go for an ILP 43018 for a single amplifier.
For a stereo you could use the ILP 63018.
See attached datasheet.

Bertus

 

What is your designed power limit for the amp?
The transformer should have a bare minimum of 10% more VA rating. Preferably 25% more.

The theoretical maximum efficiency of a class B amplifier is 78.5%.
Using a full wave rectifier and capacitor filter, the DC output current is 0.62 times the secondary AC current and the DC output voltage is 1.41 times the secondary RMS AC voltage.
VAC = secondary RMS AC voltage
IAC = secondary RMS AC current
VDC = DC output voltage
IDC = DC output current
W = amplifier output power.
Taking the amplifier efficiency into account: IDC x VDC = W / 0.785
IAC = IDC / 0.62
VAC = VDC / 1.41
Transformer VA = IAC x VAC = IDC / 0.62 * VDC / 1.41 = (IDC x VDC) x 1.14
So Transformer VA = (W / 0.785) x 1.14 = 1.45 x W
So a bare minimum of 45% more than the amplifier output power.

 

like I said....3A secondary rating would be enough with plenty of smoothing cap

 

like I said....3A secondary rating would be enough with plenty of smoothing cap

How do I get 3 A secondary rating for the transformer in multisim or any simulator?

 

Also, are the diodes i used in the rectifier enough? The 1N4003G have a reverse voltage of 200 V and Curent of 1 A? I think I need to change the diodes to what can support 3A? Am I correct?

 

Hello,

For 3 Amps you could go for the 1N540X series.

Bertus

 

i used the 1n5402G diodes with 200 V and 3 A. added the 10000uF capacitors. it has 51 V and -51V. Do I need to treat the amplifier as a load for the supply and get its equivalent impedance and use it as a load for the supply? its only powering it to half of what it should. sorry, i still cant figure it out.

 

i used the 1n5402G diodes with 200 V and 3 A. added the 10000uF capacitors. it has 51 V and -51V. Do I need to treat the amplifier as a load for the supply and get its equivalent impedance and use it as a load for the supply? its only powering it to half of what it should. sorry, i still cant figure it out.
View attachment 128245

do i need more capacitors?

 

do i need more capacitors?

You have a 100uF capacitor across the transformer secondary. That would have an impedance of 31Ω and so a current of 1.6A would flow through that capacitor - not good. For the simulation, remove that capacitor. In the real world you might connect a capacitor with a much lower value, perhaps 100nF, to reduce high frequency interference from the mains supply reaching the amplifier.

 

How do I get 3 A secondary rating for the transformer in multisim or any simulator?

I was speaking for a practical situation.
If you choose your transformer depending on your sim you would be wrong.
You need plenty of extra power for the bass peaks.

Just connect amp to that PSU circuit and test your simulation. Why are you worried about "equivalent impedance" ?
And change those two 104uf to 100nf.

 

im only getting up to 30 W and the wave form is very distorted

 

I see two possible problems with the amplifier.
The maximum output voltage swing from Q2 is limited by the voltage drop across the emitter resistors to about 75% of the supply voltage.
Also, the diodes on the bases of the output transistors can turn off those transistors but the only source of current to turn them on is the 20k resistors. Try reducing the resistors in that chain by a factor of ten - 2k and 50Ω.

 

I see two possible problems with the amplifier.
The maximum output voltage swing from Q2 is limited by the voltage drop across the emitter resistors to about 75% of the supply voltage.
Also, the diodes on the bases of the output transistors can turn off those transistors but the only source of current to turn them on is the 20k resistors. Try reducing the resistors in that chain by a factor of ten - 2k and 50Ω.

It doesn't go up to 60 Watts when i make the 20k and 500 Ω to 2k and 50 Ω

 

i dont know anymore lol

 

Do not assume a 30W will deliver pure 30W when you start designing first.
Properly designed ones can deliver what it states and even that is under certain conditions.

 

It doesn't go up to 60 Watts when i make the 20k and 500 Ω to 2k and 50 Ω

You also need to address the lack of drive from Q2.

 

You also need to address the lack of drive from Q2.

what do you mean by lack of drive? can you please elaborate?

 

Because of the voltage drop across Re4, the maximum output swing of Q2 is about 80V so you've lost 20V of the available voltage.