Vu meter Problem

Hi All,
I have a problem with the meter of my summing mixer
when the output of the summing mixer is connected to another machine with no signal in input the meter are ok , but when i disconnect the output cables of the summing mixer (no load) the vu meter goes to full scale without any signal applied
How can i solve this problem ??
The vu meter have a buffer card mounted on the back

This question is like saying:
'My car doesn't go. Why?'
You need to supply A LOT more detail. But if the meter displays OK when loaded, and high when not loaded, it implies that the output impedance of your mixer is very high, or the loading is very low.

Audioman said:

Hi All,
I have a problem with the meter of my summing mixer
when the output of the summing mixer is connected to another machine with no signal in input the meter are ok , but when i disconnect the output cables of the summing mixer (no load) the vu meter goes to full scale without any signal applied
How can i solve this problem ??
The vu meter have a buffer card mounted on the back

Click to expand...

Is there an input termination (bleed) resistor on the meter input to ground?

JR

Hi radardoug ,
Tell me which informations you need to know for clearify the problem and i'll give you

radardoug said:

This question is like saying:
'My car doesn't go. Why?'
You need to supply A LOT more detail. But if the meter displays OK when loaded, and high when not loaded, it implies that the output impedance of your mixer is very high, or the loading is very low.

Click to expand...

Audioman said:

Hi All,
I have a problem with the meter of my summing mixer
when the output of the summing mixer is connected to another machine with no signal in input the meter are ok , but when i disconnect the output cables of the summing mixer (no load) the vu meter goes to full scale without any signal applied
How can i solve this problem ??
The vu meter have a buffer card mounted on the back

Click to expand...

It could be either a DC leak or an oscillation. Do you have a voltmeter? You may check if there's any DC; if not, that would suggest an oscillation. Some output stages are prone to oscillation when they are not loaded.  In order to be 100% sure you need an oscilloscope.

A schematic of the summing box would help.

Cheers

Ian

Audioman said:

I have a problem with the meter of my summing mixer

Click to expand...

with the Neumann V475-2 summing amp (transformer floating output) from another thread ?

when the output of the summing mixer is connected to another machine

Click to expand...

Wild guessing and depending on hook up maybe debalancing the output and tying one transformer secondary end to a reference voltage/gnd that your secret name (real VU?) meter connects to for reference ?

Hi Harpo
Yess the Neumann V475-2 same unit of the other thread
yess these are real vu meter (the vu meter and buffer card is taken from an old soundcraft)
in attached the schematic of the vu meter board



.

Harpo said:

with the Neumann V475-2 summing amp (transformer floating output) from another thread ?
Wild guessing and depending on hook up maybe debalancing the output and tying one transformer secondary end to a reference voltage/gnd that your secret name (real VU?) meter connects to for reference ?

Click to expand...

Hi All ,
I identified the problem of my vu meter and i need your Help /advice for solving the problem.
In my build i had use two separate PSU , one for the Neumann V475-2 (0V + 24V) and another for the Vu meter Card Buffer (+/- 15V)
When i connect the output of my summing mixer to the input audio of the vu meter the Vu meter PSU (+/- 15V) gave back a DC current (10V) on the audio circuit !!
So the vu meter goes to full scale
How can i solve this ??

Respective to the 0V point on the meter board, what is the voltage on pins 1 and 7 of the TL072?

Audioman said:

In my build i had use two separate PSU , one for the Neumann V475-2 (0V + 24V) and another for the Vu meter Card Buffer (+/- 15V)

Click to expand...

Do you use separate transformers or separate  windings on one transformer? 

Hi moamps ,
I use the same toridal transformer for the two Psu

moamps said:

Do you use separate transformers or separate  windings on one transformer?

Click to expand...

Could you sketch how did you connect secondaries of the transformer to your power supplies?
Also could you measure potential between common/ground pins of your power supplies (voltage between "0" of single PS for V475 and common/ground on the dual power supply of the VU meter buffer) when the buffer isn't connected to V475?