Not on emitter.

Across the 0.47R Emitter resistors.

First measure the voltage drop across the 0.47R emitter resistor The amp shud be in idle mode. Volume down & the amp should be left on for around 10m to warm up to do this.

Measure each and post ur results. Do not turn the VR's

When i connect my multimeter, i dont get any reading

 

When i connect my multimeter, i dont get any reading

1) Make sure it's set to voltage mode
2) If it's a manual multimeter, set it to the 9 volt setting, and keep lowering it until you get a reading

 

1) Make sure it's set to voltage mode
2) If it's a manual multimeter, set it to the 9 volt setting, and keep lowering it until you get a reading

I had mine set down to lowest setting. Mine goes down to 200mV. I have one of those cheap $5 harbor-freight multimeters tho, im sure that doesnt help much

 

I had mine set down to lowest setting. Mine goes down to 200mV. I have one of those cheap $5 harbor-freight multimeters tho, im sure that doesnt help much

Did you have it on the AC or DC test setting?

 

Did you have it on the AC or DC test setting?

DC setting

 

Measure the base voltage at each out put transistor. Negative probe should be connected to ground.

Let the amp warm up before measurements.

The voltage range will be from 0.3VDC to 0.6VDC at the base of the out put devices.
Careful when u measure them. A slip of the probe and u will be crying.

 

Measure the base voltage at each out put transistor. Negative probe should be connected to ground.

Let the amp warm up before measurements.

The voltage range will be from 0.3VDC to 0.6VDC at the base of the out put devices.
Careful when u measure them. A slip of the probe and u will be crying.

Well this is weird. I have -30V on the first one, 0.73V on the second one, 0.36V on the third one, and -30V on the fourth one

 

It's OK.

Where did u ground the meter. Try to use the speaker ground as the ground to measure the voltage

Shooot ! I 4 got

It's not a complementary stage. What u get is correct.

U have to connect the meter across Base and emitter.

 

And if u cannot get the milliVoltmeter range then it is quite difficult to properly adjust the idle current. Which is same as the biasing or the 25mV voltage drop across the emitter resistor.

If everything is OK. U can remove the 22R resistors and solder the wires properly and do a test run on the amp.

 

It's OK.

Where did u ground the meter. Try to use the speaker ground as the ground to measure the voltage

Shooot ! I 4 got

It's not a complementary stage. What u get is correct.

U have to connect the meter across Base and emitter.

Okay i got 0.62 on the first 2 and 0.33 on the second 2

 

I am also noticing a slight bit of "hum" when i connect the speakers. Im guessing bad caps, which ill replace after everythings up and running

 

Just out of curiosity, I adjusted the pots on the amplifier board, to see if that would cancel out any hum. Not only did it cancel out the hum in the speakers, but now the 22R resistors arent even warm, and the heatsink is barely warm at all. I think the amplifier was obviously overbiased

 

The readings tells u tht it is indeed out of bias, u see the readings across each transistor shud be approx 0.55V.

0.33V won't even bias the transistor into linear region. 0.62V will saturate the transistor too soon..

The best way is to measure the 25mV across the emitter resistor.
The +25mV across the positive side and the -25mV across the negative side will cancel out giving u 0VDC at the speaker terminal when the transistors are properly biased.

 

The readings tells u tht it is indeed out of bias, u see the readings across each transistor shud be approx 0.55V.

0.33V won't even bias the transistor into linear region. 0.62V will saturate the transistor too soon..

The best way is to measure the 25mV across the emitter resistor.
The +25mV across the positive side and the -25mV across the negative side will cancel out giving u 0VDC at the speaker terminal when the transistors are properly biased.

I dont get any reading when i connect the multimeter across the resistors. I know my multimeter measures millivolts.

 

it's not easy without a millivoltmeter.

 

I dont get any reading when i connect the multimeter across the resistors.

Do you mean your reading is 0.0mV, when the meter is set to its 200mV scale? You really should not have any problem measuring in the necessary range. These cheap meters may not be super accurate at 20mV, but you should certainly get a reading that's within 10% or better. When mine reads 10.0mV, I believe it.

 

I have one of those cheap $5 harbor-freight multimeters...

This is it, right? Same as mine. I have a half dozen of them, all for free after coupons or rebates.

 

Okay i adjusted the pots to so that theres around 0.55V on the base of each transistor, but theres still some DC voltage on the speaker terminals, and I also hear this weird popping noise in the speaker if i turn the volume up with music playing through it

 

did u removed the 22R resistors?

 

did u removed the 22R resistors?

No, not yet