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MP573 Microphone preamplifier / 300 Ohm not working + suddenly change in output volune
« Last post by Dolbah on October 05, 2024, 08:35:32 PM »I have 2 units. They outputed uneven volume for a while, so i disassembled them, reflowed some joints and measured TP2 and TP4 to check the bias of Q6.
The Q6 bias was not at 3.0 VDC, so i readjusted them and reassembled them. Tested, and i now have equal output gain from both unit.
The next day i was continuing recording with them and realized that the volume was uneven again. I forgot to pay attention to which unit it was so i am not sure if the volume was higher or lower than the other.
Both these units have been connected to EQ573-II erlier. I stopped using the cable link because one of the MP73s sometimes had some kind of internal feedback problem, making a small pulse making a small "swosh swosh" sound and the led lighting up. This was without any audio coming in to the unit.
This doen not happen without the EQs (also have EQs affected by this problem for a god while, but i have switched the polarity. Not ure if this can help cause this?) Maybe its the same MP573 unit.
I also had LM337T instead of an LM317T for U1, and you sent replacements.
Not sure if having the LM337T can have contributet to any of the symptoms i now experience?
I will disassemble again and try to get them equal once more. But if disassembling them resetts the problem, it makes me feel like there are some electrical components needing to discharge or something to make the unit functional.
One unit has non functional 300 Ohm too, not sure if this is the same untit.
Do you have any idea where to start looking for the cause of these issues?
The Q6 bias was not at 3.0 VDC, so i readjusted them and reassembled them. Tested, and i now have equal output gain from both unit.
The next day i was continuing recording with them and realized that the volume was uneven again. I forgot to pay attention to which unit it was so i am not sure if the volume was higher or lower than the other.
Both these units have been connected to EQ573-II erlier. I stopped using the cable link because one of the MP73s sometimes had some kind of internal feedback problem, making a small pulse making a small "swosh swosh" sound and the led lighting up. This was without any audio coming in to the unit.
This doen not happen without the EQs (also have EQs affected by this problem for a god while, but i have switched the polarity. Not ure if this can help cause this?) Maybe its the same MP573 unit.
I also had LM337T instead of an LM317T for U1, and you sent replacements.
Not sure if having the LM337T can have contributet to any of the symptoms i now experience?
I will disassemble again and try to get them equal once more. But if disassembling them resetts the problem, it makes me feel like there are some electrical components needing to discharge or something to make the unit functional.
One unit has non functional 300 Ohm too, not sure if this is the same untit.
Do you have any idea where to start looking for the cause of these issues?
