Ok today I tested both MTX152, the ones that I adjusted bias to 1.5mv, both of them work and sound great, no distortion, nice clean power. However the last MTX152 with low filter on and low HZ adjusting pot set low the woofer destorts badly but at higher hz works fine. RCA are plugged in and stereo deck is at low volume. This does not happen with first MTX152. I already changed the OP amps, what could cause this?
If you move the body of any of the potentiometers does it make a difference?
Even if it doesn't, the pot could still be defective.
Don't try removing a pot from the working amp and installing it in the other amp. You have to take special care in removing the pots to prevent damaging them.
If you pull both boards and set the pots the same (various positions where the amp produces the noise), you can compare the resistance between the terminals on the pots to see if one varies significantly from the other.
Even if it doesn't, the pot could still be defective.
Don't try removing a pot from the working amp and installing it in the other amp. You have to take special care in removing the pots to prevent damaging them.
If you pull both boards and set the pots the same (various positions where the amp produces the noise), you can compare the resistance between the terminals on the pots to see if one varies significantly from the other.
Meter on diode check
MPSW42:
With the red probe on the center leg, you should read ~0.65v to both outer legs. With the probes reversed, you should read an open circuit.
MPSW56:
With the black probe on the center leg, you should read ~0.65v to both outer legs. With the probes reversed, you should read an open circuit.
MPSW42:
With the red probe on the center leg, you should read ~0.65v to both outer legs. With the probes reversed, you should read an open circuit.
MPSW56:
With the black probe on the center leg, you should read ~0.65v to both outer legs. With the probes reversed, you should read an open circuit.
Thanks, got that figured out.
On another 500D post I did not know the value of Capacitor C215 that is accross plus B+ and ground you told me this: "I don't know the value of the cap under the terminal block. If it's across the B+ and ground terminals, a 0.1uf mylar should be close enough." So I went and got 0.1Uf mylar 16v(asuming 12v supply power to amp)
http://www.diyaudio.com/forums/showthread.php?postid=1416348#post1416348
Well I got good 500d now and that capacitor has numbers Z5U 475M 50V so I asume that is 4.7uF 50V capacitor with Temperature Coefficient Z5U . I wonder if the one you told me before is totaly wrong cap to go there.
can you use radial instead of mylar ?
On another 500D post I did not know the value of Capacitor C215 that is accross plus B+ and ground you told me this: "I don't know the value of the cap under the terminal block. If it's across the B+ and ground terminals, a 0.1uf mylar should be close enough." So I went and got 0.1Uf mylar 16v(asuming 12v supply power to amp)
http://www.diyaudio.com/forums/showthread.php?postid=1416348#post1416348
Well I got good 500d now and that capacitor has numbers Z5U 475M 50V so I asume that is 4.7uF 50V capacitor with Temperature Coefficient Z5U . I wonder if the one you told me before is totaly wrong cap to go there.
can you use radial instead of mylar ?
'Radial' means that both leads come out of the same end of the cap.
A film cap is probably the best option. There are already several large electrolytics across B+ and ground.. The Mylar/polyester film capacitor is used to bypass the high frequency noise (not audible) that isn't bypassed by the electrolytics.
A film cap is probably the best option. There are already several large electrolytics across B+ and ground.. The Mylar/polyester film capacitor is used to bypass the high frequency noise (not audible) that isn't bypassed by the electrolytics.
As I mentioned before, the capacitors shunt (bypass) high frequency noise to ground.
The capacitor is placed at the terminals so that's it's most effective at shunting the noise and prevents it from getting into/out of the amp.
Aluminum electrolytics are not as good as ceramic or film capacitors because they have relatively high ESL (Equivalent Series Inductance) and the loss (inability to pass efficiently pass current) at higher frequencies is greater.
When low impedance at high frequencies is needed and the total capacitance needed is not significant, ceramic, film or tantalum capacitors are used.
The value used is up the the designer, in most cases. You can vary the capacitance significantly and make no audible difference. If the amp must pass certain tests for noise (on the power supply lines), the designer may have to increase the capacitance to meet spec. 0.1uf is a good starting point. If the amp is generating too much high frequency noise on the supply lines (across B+ and ground), the designer may increase the value.
The capacitor is placed at the terminals so that's it's most effective at shunting the noise and prevents it from getting into/out of the amp.
Aluminum electrolytics are not as good as ceramic or film capacitors because they have relatively high ESL (Equivalent Series Inductance) and the loss (inability to pass efficiently pass current) at higher frequencies is greater.
When low impedance at high frequencies is needed and the total capacitance needed is not significant, ceramic, film or tantalum capacitors are used.
The value used is up the the designer, in most cases. You can vary the capacitance significantly and make no audible difference. If the amp must pass certain tests for noise (on the power supply lines), the designer may have to increase the capacitance to meet spec. 0.1uf is a good starting point. If the amp is generating too much high frequency noise on the supply lines (across B+ and ground), the designer may increase the value.
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