[Chris]

Hi JP. 
I'm sorry if my English is not good I will try to make myself understood as best I can.
I just finished my first Mp573, all tests are good except my LED.
Indeed, it is never green and as soon as I speak into the microphone, it turns red immediately whatever the gain. 
can you help me to find the problem (error in the direction of the LED maybe)

I have a second problem. At very high gain, I have a buzz from the transformer (I Suppose) that goes round and round (like a melody). What can it come from ?

Thanks for your help. 

Friendly 

Chris

[Chris]

I solved the LED problem. I had indeed reversed it.
There is still the problem of Buzz from 30/40 dB. Can you help me on this point please.
Chris

[Chris]

A = 2,52
B = 4,06
C = 22,4
D = 13,37
E = 2,0
F = 12,73
G = 0,01
H = 1,1
I = 0,00
J = 0,44
K = 0,43
L = 0,02

[JPK]

How far is the pre from the lunchbox PSU?
The input transformer of the MP573 is sensitive to radiated noise. Make sure there is no power device too close.

[Chris]

Thanks for your answer. I will try to take it away from the food to see if it changes anything.
I have done the requested voltage tests (see before) and I contact abnormal differences. What can it come from? What do you think?
Sincerely

[Chris]

Indeed, I just moved the lunch box a few centimeters and the problem seems solved.

Why then, are my G to L voltage tests not as they should be?

[JPK]

With the values shown for G to L, you shouldn't get any output!
Did you connect the output transformer when measuring?

[Chris]

Oops!! indeed, it's my fault. Everything is ok! Sorry for the inconvenience. I am a beginner in DIY. Everything is perfect. Thank you for your time.