Cannot see answers to my questions below. +4dBm should be adjusted to read 0VU. so 2 or 3 is more than needed.erhard58 wrote: ↑Fri Nov 17, 2023 11:49 amthank you for your quick reply, I appreciate it.
In this post, you mentioned that the 3K3 buffer resistor may need to be lowered, dated October 26, so I just started to experiment with a value and see what happens.
It was doing the same, ie no VU meter movement after power down and power up again with no resistor value changes, so lowering it to 1K, as far as I can see, has no effect on what it is doing when powered down and back up again.
I am using a TN-73-HS-9213H VU meter.
The measured internal DC resistance is 50 OHMS on a digital meter. It has no diodes or resistors inside.
Using +4dBm, I only get a max deflection between 3 and 2 on the VU meter.
Any advise would be appreciated, thank you.
Wow that resistance is very low for a meter. Can you cal +4dBu = +4dBm = (1.23vac RMS on multimeter) to correct 0VU?
and then if you put in +7dBu does the meter show +3 ?
If not let me know as the output 3k3 ressitor on the buffer will have to be made smaller in value.
To answer your question as follows:
What power rail is the buffer running on? Volts & Amps? 12VDC @ 1.5A
Is it SMPS? Is the power supply running anything else? It uses a 7812 regulator, well filtered and running nothing else
Input reference level to the buffer? Balanced or unbalanced? If unbalanced have you tied -in to 0v? unbalanced and yes, I tried -in to 0V
What are the meter specs for the meters you have tried? see above
Is it wired in with other audio gear etc in the same case? no, one driver per VU meter
If so how are the power supplies wired? Photos are best for this.
Can you cal +4dBu = +4dBm = (1.23vac RMS on multimeter at input) to correct 0VU?
and then if you put in +7dBu does the meter show +3 ?
What is feeding the input of the buffer?
I have a pair of TN-73-HS-9213H VU meters here and my notes written on them say
"Meter works on buffers without mod for +4dBm = 0VU but are 1000uA 55ohm so needle movement is too slow for VU meter.
Changing series 3k3 to 2k2 resistor makes VU scale accurate and needle moves faster but still too slow for real VU"
TN-73-HS-9213H on right with backlight on in photos attached
Tests for -5 +3VU & 0VU with 2k2 fitted for R7R