Sound Skulptor forums

Build help and troubleshooting => MP573 Microphone preamplifier => Topic started by: Chris on April 06, 2021, 02:11:43 PM

Title: Led pb and slight noise at high gain
Post by: Chris on April 06, 2021, 02:11:43 PM

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

Title: Re: Led pb and slight noise at high gain
Post by: Chris on April 06, 2021, 06:27:25 PM

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

Title: Re: Led pb and slight noise at high gain
Post by: Chris on April 06, 2021, 07:10:19 PM

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

Title: Re: Led pb and slight noise at high gain
Post by: JPK on April 07, 2021, 09:39:50 AM

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.

Title: Re: Led pb and slight noise at high gain
Post by: Chris on April 07, 2021, 09:55:41 AM

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

Title: Re: Led pb and slight noise at high gain
Post by: Chris on April 07, 2021, 10:24:58 AM

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?

Title: Re: Led pb and slight noise at high gain
Post by: JPK on April 07, 2021, 11:27:54 AM

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

Title: Re: Led pb and slight noise at high gain
Post by: Chris on April 07, 2021, 11:50:23 AM

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. ;)