i don't know if this amp is precisely like other MTX amps but you should have a transistor with it's 3rd leg connected to the remote terminal. If it doesn't have a 0 ohm connection, The resistance between them should be very low.
It's probably going to be an MPSA56 and it should be between the remote terminal and the 339. It should have a circuit board designation that begins with a 4. It may be shorted.
It's probably going to be an MPSA56 and it should be between the remote terminal and the 339. It should have a circuit board designation that begins with a 4. It may be shorted.
yes it is MPSA56 Q427, two outer legs show continuity, so it is shorted, remote goes trough one diode and then goes to the outer leg of MPSA56, I already bought fe so I can change it now and see. But what would make the AMP run so hot just at idle? Something is driving the output FETs to its limit?
Unless this amp is significantly different than other MTX amps, you should have voltage on many of the pins of the 494 and the 339.
If the amp is switching properly, reinstall the power supply FETs and clamp the transistors to the heatsink. Measure the voltage across the 0.1 ohm source resistors on the output transistors. If it's above ~5mv, reduce the bias setting. 5mv is a good starting point if it's too high.
If the amp is switching properly, reinstall the power supply FETs and clamp the transistors to the heatsink. Measure the voltage across the 0.1 ohm source resistors on the output transistors. If it's above ~5mv, reduce the bias setting. 5mv is a good starting point if it's too high.
Ok, am testing the amp with 10 amp fuse installed and amp turnes on and after FETs warm up the fuse pops. On those resistors where do I put black DVOM prong and where do I put red prong for testing? Where do you adjust the bias? Those two adjusting VR pots on the board? counterclockwise reduces the voltage?
The probes will go on each end of the 0.1 ohm resistor.
The two pots are the bias controls. If no one has turned the one on the cool channel, measure the voltage across the 0.1 ohm source resistors in that channel to determine what it should be in the other channel.
Generally, CCW reduces the bias current. Only turn the one on the channel that's getting hot.
The two pots are the bias controls. If no one has turned the one on the cool channel, measure the voltage across the 0.1 ohm source resistors in that channel to determine what it should be in the other channel.
Generally, CCW reduces the bias current. Only turn the one on the channel that's getting hot.
Ok, I got it. I connected my GOOD mtx152 to read the what is the proper voltage and am getting in right channel 1.5mv and left channel 3.5mv, on a good amp. So even this one is off?
The one that we are fixing right now, I adjusted it to 5.0mv, turning the pot clockwise decreases the reading of Mv accross the resistor, so I asume the higher the reading on the reistor the less current goes to FET?
The one that we are fixing right now, I adjusted it to 5.0mv, turning the pot clockwise decreases the reading of Mv accross the resistor, so I asume the higher the reading on the reistor the less current goes to FET?
Higher voltage = more idle current. Watch the amp meter on your supply. More current through the outputs = more current from the 12v supply.
The same current passes through the outputs and the resistors. They are all in series.
A few amps have the pots reversed (which is actually a smart thing to do).
The bias current isn't absolutely critical. As long as a tiny bit of current is passing through the outputs, it should be OK. The actual idle current will probably drift slightly with temperature anyway. I'd set it to 5mv at the temperature where it's the highest (if it drifts).
The same current passes through the outputs and the resistors. They are all in series.
A few amps have the pots reversed (which is actually a smart thing to do).
The bias current isn't absolutely critical. As long as a tiny bit of current is passing through the outputs, it should be OK. The actual idle current will probably drift slightly with temperature anyway. I'd set it to 5mv at the temperature where it's the highest (if it drifts).
Do you have the red probe on one end of the 0.1 ohm resistor and the black probe on the other end of the same resistor?
The voltage you're looking for is absolute voltage (-0.005 will be the same as 0.005 if you reverse the leads). Do you mean the voltage got closer to 0v when you turned the pot CCW?
The voltage you're looking for is absolute voltage (-0.005 will be the same as 0.005 if you reverse the leads). Do you mean the voltage got closer to 0v when you turned the pot CCW?
If the bias current is too low, the amp's output may be distorted.
On most amps, the distortion is crossover/notch distortion. In these amps, the bias determines the voltage across the drivers. The bias transistor is connected to the drivers or pre-drivers.
On some (maybe all) of the MTX full range amps, insufficient bias current will prevent the output from swinging as close to the rails as it should/could when the amp is driven hard. In the MTX amps, the bias control determines the current through the differential amplifier pair.
On most amps, the distortion is crossover/notch distortion. In these amps, the bias determines the voltage across the drivers. The bias transistor is connected to the drivers or pre-drivers.
On some (maybe all) of the MTX full range amps, insufficient bias current will prevent the output from swinging as close to the rails as it should/could when the amp is driven hard. In the MTX amps, the bias control determines the current through the differential amplifier pair.
So if I got one good MTX amp that works and bias voltage is at 1.5mv cold amp. That means I can set this one at 1.5mv? The amp works great and deliveres smooth bass so if my good amp is at 1.5mv then I can set this one at 1.5mv and then test it?
What would cause an amp to distort the woofers when no RCA jack are plugged in and low pass filter is set at its lowest settings 20hz and then I adjust the gain at maximum and the woofer distorts badly?
What would cause an amp to distort the woofers when no RCA jack are plugged in and low pass filter is set at its lowest settings 20hz and then I adjust the gain at maximum and the woofer distorts badly?
Well then, I will go from 1.5mv then, I just don't want to blow another FET.
this second MTX152 was doing it, am yet to test it after I installed all new OP amps and new tl074cn. But at maximum gain, RCA unplugged, and then when I go from 80hz to 20hz of minimum low pass adjustment knob the woofer would destort, like braaaaaaaaaaaaa. What would cause this? I was reading your website and it says there that some amps may do this new out of the box
this second MTX152 was doing it, am yet to test it after I installed all new OP amps and new tl074cn. But at maximum gain, RCA unplugged, and then when I go from 80hz to 20hz of minimum low pass adjustment knob the woofer would destort, like braaaaaaaaaaaaa. What would cause this? I was reading your website and it says there that some amps may do this new out of the box
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