1

MP573 Microphone preamplifier / MP573 Distorted sound and malfunction

« on: December 11, 2023, 08:46:43 PM »

Hi JP,

After several months enjoying the amp, I detect very distorted sound when I increase the gain above 30.

I checked the voltages and resistances:

Set up Guide

1 Short circuit ( OK )
3 TP2 / V+ without Input Trafo 24,64 with Input Trafo 24,51V
4 3.020 V decreasing smoothly until 2.994 and counting in 10 minutes

A 2.6V
B 4.1V
C 2.6V
D 13.6V
E 2V
F 12.9V
G 0.9V
H 4.1V
I 0.35V
J 3.5V
K 22.8V
L 3V

Trace signal

Sine signal 0.5VAC - 3.300 Hz -13.5dB
TP2 - Input trafo pin 7 - 0.94VAC
TP2 - TP1 0VAC
TP2 - Output trafo yellow wire 0.13VAC

Transformers resistance
Output transformer
Yellow Orange 7.8 ohms
Red Brown 6.7 ohms
Blue Green 21 ohms
Violet Black 20.9 ohms

Input transformer
2-4 25 ohms
3-5 25 ohms
7-9 138
8-10 141


Following the signal, I detect a problem between TP1 and TP2 and so on.

What is your diagnosis?

Many thanks!!!

2

MP573 Microphone preamplifier / Lunchbox Aux I/O vs MP573

« on: December 06, 2023, 06:21:49 PM »

Hi Jean Paul and everybody,

I have a question. I would like to have my MP573 working for tracking voices (Input in the Lunchbox direct to a mic) and alao I wanna use the MP573 for mixing signals in the DAW.

So, the only way I think for doing this without plug and amplug cables in the rear of the lunchbox is using the auxiliar I/O that my MIDAS Legend L10 has.

But it doesn't work.

Do you know if it's compatible or if there's a way of doing without a patchbay?

Many thanks!

Paco

3

EQ573 Equaliser / Problems checking the EQ573 II

« on: March 21, 2023, 10:42:37 AM »

Good morning Jean Pierre,

I have just to finish the EQ573II but I'm afraid there's something wrong with the assembly.

The checking figures are:

A -2,1V
B -14,6V
C -13,2V
D -11,1V
E -7,9V
F-5,6V
G  -0,7V
H -6,8V
I -13,2V
J -13,8V
K -7,9V
L -5,6V
M -6,1V
N -6,8V


I have to say that in the point A there's some sparks when I conect the O volts and the R48 resistor.

Could you guide me?

Thank you very much!

4

MP573 Microphone preamplifier / Question about Gain Staging

« on: February 12, 2023, 05:57:28 PM »

Hi everyone,

I am testing my new preamp and I have some questions, maybe you can help me.

In order to test the preamp behavior, I send a sine signal of 1 khz at -18 dB to the preamp. If I want to preserve in the DAW the same level od -18dB I must set the preamp like this:



obtaining this signal:




So, at this point, trying to test it without clipping, I put the preamp in Line mode in order to obtain the cleanest signal, con this configuration:



and this signal (very clean).



But, If I want to obtain more colour, boosting the output transformer, I get this:





It's almost the same signal, without any harmonics.

Is this normal? Maybe I'm doing something wrong?

Thank you so much for your advices!

Paco

5

MP573 Microphone preamplifier / No Input

« on: January 29, 2023, 04:34:36 PM »

Hi!

I just finished the assembly and I'm with the tests.

at point 3 I get 24.67V and 24.58 connecting the output of the transformer.

At point 4, I get 3.0V with the trim.

The problem is that I don't have output.

I have checked and got the following results:

A.2.6V
B.4.1
c. 22.6
d.13.6
e.2
f.13
G.0.9
h.4
I.0.34
J.3.4

I don't know how to measure point K, but I realize that at point L I get 0 Volts.

Can you help me?
Thank you!

6

MP573 Microphone preamplifier / 1N4004 Diode

« on: January 27, 2023, 05:45:01 PM »

Hi,

I can´t find 1 of the 5 1N4004 diodes in the kit. I have here a 1N4007 diode. Can I replace it safety?

Many thanks!