Having troubles when I tried to build a stereo power amplifier

[Yuegui]

Hello fellow harmonycentral forum users, I am having a bit of trouble with the specs of the components needed. I’m trying to build this BA5417 stereo power amplifier

 

BA5417 is a stereo amplifier IC with a lot of good features like thermal shut down, standby function, soft clipping, wide operating voltage range etc. The IC can deliver 5W per channel into 4 ohm loud speakers at 12V DC supply voltage. The BA5417 has excellent sound quality and low THD (total harmonic distortion) around 0.1% at F=1kHz; Pout=0.5W. For more details, you can read the BA5417 datasheet: http://www.rohm.com/web/in/datasheet/BA5417/ba5406-e

 

Description

Setup and working of this stereo power amplifier circuit(More information about power amplifier: http://www.apogeeweb.net/article/73.html) is somewhat similar to the BA5406 based stereo amplifier circuit published previously. C10 and C11 are DC decoupling capacitors which block any DC level present in the input signals. C2 and C6 couples the amplifiers left and right power outputs to the corresponding loud speakers. C1 and C5 are bootstrap capacitors. Bootstrapping is a method in which a portion of the amplifiers is taken and applied to the input. The prime objective of bootstrapping is to improve the input impedance. Networks R1,C3 and R2,C7 are meant for improving the high frequency stability of the circuit. C4 is the power supply filter capacitor. S1 is the standby switch. C8 is a filter capacitor. R3 and R4 sets the gain of the left and right channels of the amplifier in conjunction with the 39K internal feedback resistors.

 

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I see the notes said that

 

• Supply voltage range of BA5417 is from 6 to 15V DC.
  
• The recommended supply voltage for this circuit is 12V DC.
  
• The power supply must be well regulated and filtered.
  
• BA5417 requires a heatsink.
  

 

The circuit can be assembled on a perf board without much degradation in performance. But I was curious on the specs of the components needed. I imagine voltage on any component must be greater than the voltage of my power source, so the lowest voltage capacitor I’m using is rated for 25v and I’ll be using a 12v power source. Additionally, what wattage must the resistors be rated at? Could I assume that R1 and R2 must be able to handle 5 watts because they are on the same lines as the speakers? My final question is regarding the speakers. I understand that when using a circuit that accommodates 4ohm loudspeakers, using 8ohm speakers will be safe for the circuit, but is there a way I can optimize the circuit for 8ohm speakers instead?

[WRGKMC]

The circuit can be assembled on a perf board without much degradation in performance. But I was curious on the specs of the components needed. I imagine voltage on any component must be greater than the voltage of my power source, so the lowest voltage capacitor I’m using is rated for 25v and I’ll be using a 12v power source.

 

Double the voltage should be fine

 

Additionally, what wattage must the resistors be rated at? Could I assume that R1 and R2 must be able to handle 5 watts because they are on the same lines as the speakers?

 

You need to study your owns law. Current splits in a parallel circuit. Two the resistors also have a low value cap which will only pass certain frequencies not the entire current load. A cap will behave like a resistor with a different resistance depending on frequency. The higher you go up in frequency, the lower the 'resistance' value of the capacitor. The cap across the woofer bypasses or shunts the higher frequencies, making the higher frequency voltages smaller. This makes less high frequency content available for the woofer.

 

I suspect those are added to make the speaker output more linear. As far as a resistor, I suspect a 1/4 watt resistor will do fine. Remember, 5 watts is the maximum output. Its doubtful you'd ever run this amp at maximum volume with a maximum full frequency input. Audio doesn't produce a steady current its constantly rising and falling and its mainly the bass frequencies you have to watch out for. Those resistors will only be seeing the high frequencies and at a far lower current level therefore a lower wattage.

 

My final question is regarding the speakers. I understand that when using a circuit that accommodates 4ohm loudspeakers, using 8ohm speakers will be safe for the circuit, but is there a way I can optimize the circuit for 8ohm speakers instead?

 

You shouldn't have to do anything but because the impedance is higher the wattage is going to drop so the speakers wont be as loud. The only thing that's going to happen is the wattage is going to be lower by 1/3 to 1/2.