So i have a amplifier which i want to test is a class d amplifier i think and uses stk459 2x 15w stereo amplifier and in the datasheet says that it uses typical voltage +- 19 volts which is 38 volts so because i don't have bipolar power supply i wanted to ask if i can power the amp with +40volts on one rail and 0v on the other rail without destroying the chip or anything on it.Thanks

 

No, the amplifier will need the separate positive and negative supplies.

 

No, the amplifier will need the separate positive and negative supplies.

So how can i convert the unipolar supply to a bipolar supply

 

What is the 40V supply which you have?

 

What is the 40V supply which you have?[/QU
I use two 20v smps supply in series.

 

Two 20V supplies in series is just what the amplifier needs. Connect the junction of the two supplies to the amplifier 0V.

 

Two 20V supplies in series is just what the amplifier needs. Connect the junction of the two supplies to the amplifier 0V.

i found thisis that what you saying because i didn't understand you well

 

The Sanyo STK459 is a very old class-AB amplifier module. Class-D was not invented for audio amplifiers then.
Any audio amplifier can use a single supply or a dual supply if its input is biased at half the supply voltage and a coupling capacitor blocks DC to the speaker.

Here are schematics of a similar audio amplifier with a dual supply and a single supply:

 

The Sanyo STK459 is a very old class-AB amplifier module. Class-D was not invented for audio amplifiers then.
Any audio amplifier can use a single supply or a dual supply if its input is biased at half the supply voltage and a coupling capacitor blocks DC to the speaker.

Here are schematics of a similar audio amplifier with a dual supply and a single supply:

I didn't understand you well.I conect the 40v supply but with coupling capacitor for blocking dc and the input to be biased at half volage to what?

 

If you use a 40V single supply then make a voltage divider with 3 resistors as shown on the Single Supply schematic I posted so that the amplifier + input is biased at half the supply voltage. 2 resistors are in series to make a 20VDC voltage divider that is fed to the amplifier + input by the third resistor. Then the amplifier output will also be biased at 20VDC by the negative feedback so that it can swing up and down.

Also add the series output capacitor to block the 20VDC voltage at the amplifier output from damaging the speaker.

 

I do not suggest using resistors as a voltage divider because the division will not be even when the load current changes.
In post #4 you were asked what 40 volt supply you were using, and your response in post #5 was that it was two 20 volt smps in series. Then a circuit was shown which was not relevant to the discussion because it was not what was needed.
If your "40 volt" power supply is indeed two 20 volt supplies connected in series, then the connection between them is the connection between the positive of one supply and the negative terminal of the other supply. Using that junction as the common would allow you to have the required voltages of +20 volts relative to the common and negative 20 volts relative to the common. I can not supply a picture of the circuit that I just described, but it is both simple and obvious.

 

I do not suggest using resistors as a voltage divider because the division will not be even when the load current changes.

ALL single supply audio amplifiers and opamps are biased with resistors producing a voltage divider because the amplifier input current is extremely low. The datasheets show the tiny input current then simply made the current in the divider 10 times more.

 

ALL single supply audio amplifiers and opamps are biased with resistors producing a voltage divider because the amplifier input current is extremely low. The datasheets show the tiny input current then simply made the current in the divider 10 times more.

In a power amplifier stage the common voltage point will often have some current from the output section flowing and by using a resistor divider that is adding an additional feedback path as the current changes the voltage. AND, it is likely that a stereo amplifier has additional circuits that may only be connected across one of the supply sections. We are not given that information, but in most integrated amplifiers, the earlier stages do not run on the same voltage as the output devices.
In addition, if the TS does have that supply made from 2 of the 20 volt supplies in series, it makes the most sense to use it as a dual voltage supply. I base this suggestion on the response given in post #5, that the 40 volt supply is really two 20 volt supplies in series.

 

Since he has two 20V batteries, do they produce enough current?
The STK459 amplifier module produces 15W per channel into 8 ohms when powered by 40V. It is about 55% efficient. Then the total power from the battery is 54W and its maximum current is 54W/40V= 1.35A. The amplifier probably will not be blasting its maximum power continuously so less average current will be fine.

Here is an amplifier using it:

 

Batteries were never mentioned, only SMPS (switch mode Power Supplies. I have several of those and the small ones are rated 3.16 amps, which is about 60 watts. That particular power supply is very common and so it may be the same as what the TS has.
THEREFORE we should wait for the TS to respond before coming up with a lot of guesses, most of which will be off-target, except for those that are far off target.

 

I dont't know what brend smps i have but i've tested them and they can upstand up to 2.5 Ampiers each which will be more than enough to power the amplifier

 

I do not suggest using resistors as a voltage divider because the division will not be even when the load current changes.
In post #4 you were asked what 40 volt supply you were using, and your response in post #5 was that it was two 20 volt smps in series. Then a circuit was shown which was not relevant to the discussion because it was not what was needed.
If your "40 volt" power supply is indeed two 20 volt supplies connected in series, then the connection between them is the connection between the positive of one supply and the negative terminal of the other supply. Using that junction as the common would allow you to have the required voltages of +20 volts relative to the common and negative 20 volts relative to the common. I can not supply a picture of the circuit that I just described, but it is both simple and obvious.

Although I agree that using the node between the two supplies makes the most sense in this case, I don't see @Audioguru 's suggestion as being problematic, other than using a few extra parts. The voltage divider he's proposing is only to bias a low power input signal, not to carry any significant current, unless I've misunderstood something. Isn't this how most single supply audio amps (phones, MP3 players, etc.) work?

 

I tried the both methodes and the two supplies method worked better for me beacose with the one resistor from the voltage devider was overheatig and also i didn't see difference between using the both methodes.

 

I tried the both methodes and the two supplies method worked better for me beacose with the one resistor from the voltage devider was overheatig and also i didn't see difference between using the both methodes.

Interesting - I guess I was wrong then!

If the amp worked the way I had expected, none of the resistors would get warm at all. Sorry for posting bad information, but I'm glad you found your answer regardless.

 

Interesting - I guess I was wrong then!

If the amp worked the way I had expected, none of the resistors would get warm at all. Sorry for posting bad information, but I'm glad you found your answer regardless.

No problem you just wanted to help