Amp with DC out

[nonprof]

Hello!

Good Day!

I have this problems in mono 850 Watts rms amplifier. This is China made amplifier.

Problems:
1. 14V DC out
2. When subwoofer is connected it produces whinning sound and popping but still has a clear music.

Symptoms:

When speaker is not connected:
1. DC out at 14VDC but not protect, rail voltages are normal.

When speaker is connected:
1. Positive rail voltage increases up to twice from its operating voltages
63VDC -> 115VDC.
2. Negative rail decreases from -63VDC to -55VDC.
3. Produces whinning sound and popping but still has clear music.

Thank you so much! Please help....

 

[Perry Babin]

With nothing connected to the amp, what's the resistance from the B+ terminal to the secondary center tap or to the negative speaker terminal?

 

[dotneck335]

I don't know what's wrong, but it sure is a DAMN good reason to fuse your speakers, methinks!!

 

[nonprof]

With nothing connected to the amp, what's the resistance from the B+ terminal to the secondary center tap or to the negative speaker terminal?

No resistance between -speaker to B+. Sometimes DC out reaches >30Volts and goes down...

thank you.

 

[Perry Babin]

By 'no resistance', do you mean infinite resistance or 0 ohms?

 

[nonprof]

sorry...definitely not zero ohms or any leakage resistance. ill give a try again. thanks

 

[nonprof]

By 'no resistance', do you mean infinite resistance or 0 ohms?

Hello Perry,

Resistance is above 75K ohms and still rising.

And DC out sometimes around >24VDC without speaker connected. If you connect speaker the one of the rail voltage increases from 63VDC -> 112VDC.

 

[Perry Babin]

If you had the black probe on the primary ground, place it on the secondary center-tap.

Does the rail voltage shift up when using the secondary center tap as the reference?

 

[nonprof]

If you had the black probe on the primary ground, place it on the secondary center-tap.

Does the rail voltage shift up when using the secondary center tap as the reference?

Ill do this...

But I verified that primary GND and secondary GND along with GND terminal are connected with physical PCB connection.

Thanks.

 

[Perry Babin]

OK. If the rail voltage is higher than the output of the secondary windings from the power transformer, the amp likely has a defective driver circuit for the output stage.