[mbogner]

Hey,

I build a MP512 one year ago and it worked fine. I didn't use it much, and when I used it now I realized, that there's something wrong.
It has a realtively high noise level nad pretty much no low-end. The signal sounds filtered.
Anyone an idea how that could have happened?

Thanks, Malte

[JPK]

This is probably a balancing issue. I would consider 3 possibilities:
- The input transformer doesn't receive the 2 phases. Check the solder joints on the input transformer, RLY1 and RLY2.
- The output transformer doesn't send the 2 phases. Check the solder joints on the output transformer and pot P2.
- It is an external connexion issue.

[mbogner]

Thanks for the reply!
I checked all the solder joints, but the problem remains the same.
I would exclude an external issue, since I tried different cables and slots in the 500 Box

[mbogner]

It is especially in the high impedance setting. I'm concious that it has an emphasis on the higher frequencies, but it seems very big, especially compared to the MP573.
The noise is gone though

[JPK]

Measure the DC resistor between input hot and cold, with the power on and gain on MID or HIGH --> 36 ohms.
Measure the DC resistor between output hot and cold, with pad at max --> 37 ohms.

[mbogner]

Thank you. I'm not sure where to measure. Could you tell the resistor numbers?

[JPK]

The measurement must be done on the input and output XLR between pins 2 & 3.

[mbogner]

Those values are correct

[JPK]

It is especially in the high impedance setting. I'm concious that it has an emphasis on the higher frequencies, but it seems very big
There is no impedance setting in the MP512, only gain setting. In the high gain setting there should be no obvious change in the frequency response.

What is the PCB revision of your unit (green or black PCB)?

[mbogner]

It's black

[JPK]

Do the test Try to follow the signal here and check the levels you get.