Diy subwoofer amplifier burns

[Lazer]

Made this simple subwoofer amplifier based on the mj15024 and mj15025. But after som playing the r4 burns and the opamp turns to ****.
Cant see why this is happening!!
Some suggestions?

[Netlist]

Are the values of the resistors on the drawing the actual ones?
I think it's a bit strange that you can even get sound out of this schematic. Simulations gives very strange results. We need some opamp gurus here.

/Hugo

[pinkmouse]

I agree, R1 and R2 seem very high

Surely C1 should also be directly in the output of the op amp, you are feeding the bias from the top transistor straight back into the chip.

Is the voltage divider set up by R3 and R4 supposed to reduce the output swing to what the chip can handle as feedback?

I am not a great electronics guru, and this circuit confuses me greatly.

[sivan_and]

CRAP!!

[zagisrule!]

Hehehe...

You have some major issues with that circuit buddy.

Problem #1: What is the 1uF doing there? My guess is that you want it to pass audio to the bases of the BJT's? If so you need two of them. And if you want any bass out of the thing you need to up capacitance to at least 100uF, 200+ being more reasonable especially considering this is a sub amp.

Problem #2: Your emitter resistors are way too big! 1 ohm or less to encourage load sharing (when using multiple BJT's in parallel - in this case you don't even really need them).

Problem #3: Your feedback circuit is way out of whack, the lower resistor need to have a much lower value. The gain the way it is is over 100 and that is not feasable unless your input level is extremely low. Try making R4 1K or so for a gain of 11.

Problem #4: If you want to utilize a DC servo for output offset correction you will need to add resistors from the output of the op-amp to the bases of the BJT's to allow a DC current path for the op-amp to adjust the bias and keep offset managable.

I have attached a modified circuit diagram to try that should keep you from blowing things up!

The caps and resistors I added are flexible as far as values go, maybe 1K or so for the DC servo resistors, and anything over 200uF for those caps.





-Matt

[sivan_and]

My suggestions....

[zagisrule!]

I wouldn't go much under 10K.

You might also want to add compensation capacitors.










-Matt

[Carondimonio]

Maybe I' m stupid, but it seems to me that the lower Transistor is REVERSED!

Cheers,

Bruno

[GregoryD]

Well there are multiple problems with the schematic as shown:
1. The MJ15025 is drawn/installed incorrectly. The collector needs to connect to the -V rail. The emitter connects to R2.
2. As already stated, R1 and R2 surely cannot be 10K ohms. These are typically less than 1 ohm.
3. Make sure there is some resistor (about 50K) installed from pin 3 of the op-amp to ground.
4. The gain of the op-amp circuit is set to 101... this is really high, maybe change R4 to around 470 ohms.
5. Consider adding a capacitor in series with R4 if a high-offset voltage op-amp is being used.
6. Consider a small capacitor around R3 to help supress any oscillations that may become evident when you get this thing working.
7. As already stated, the wire going from pin 1 of the op-amp to the base of the MJ15024 needs to be removed and replaced with another capacitor just like C1. This will allow the bias circuitry to work properly. C1 and the new capacitor that you add need to be higher in value... about 100 times higher.

Good Luck!
GregoryD

[GregoryD]

Also... make sure that the op-amp you are using is capable of the high supply voltages. It needs to be rated for +-18V operation. Check your P.S. voltages and make sure they don't exceed the max. ratings of the op-amp. You may need to lower the values of R5 and R6 after you get the circuit working to bias the output devices correctly.

Later,
GregoryD