Need A Resistor Value

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I received this amp, mtx 8100d. The problem was that it had both power supply resistors are shot. I replace them with 68ohms, but i think the value are wrong. Because i get a hissing sounding coming from the transformer. I know rockfords have this problem, but usually mtx are very quiet amps.


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there r435 and r436
 
Hi swordfish689

That value should work fine. You can almost use any value from 10 to 100 ohms. try pressing your finger on the transformer in differant spots and see if the sound go's away. I've had to do this with rockfords then if it quiets down, I would put some glue on the windings to suppress it. Does the amp work?

Martin
 
In the 1501 that I have here, they are 39.2 ohms.The board layouts look the same and the resistors have the same designations so the value should be right.

Some of those amplifiers are extremely noisy. After repairing it, run it hard. The power supply and the output FETs should all operate at roughly the same temperature. If either set of FETs is running significantly hotter than the other, you may want to check it a little more thoroughly.
 
Thanks for the replies. The only thing that i replaced were the 8 power fets, 2 resistors near the fets, and one diode that seemed to be overheated, it still worked, but i didn't want to take any chances. It turns on and works, the only thing i don't like is the sound of the transformer, making a loud hissing sounding. Also it has no gain, its full all the time, the first time i connected it to my sub it rattled the windows. Scared the **** out of me. I need to check the op-amps. Thanks again.
 
If the RCA jack shield 'bell' isn't soldered to the RCA jack 'frame', solder them together. Apply heat from the outside of the frame and apply solder to the inside of the frame. If the shield ground is not solidly connected, the amp will oscillate at ~100hz at full power. The newer RCAs are soldered.

The amps do have problems with failing op-amps that cause low frequency oscillation but I've never seen a failed op-amp cause full power oscillation.
 
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