Ah, that probably is your problem. Check out this excerpt from the VU meter spec:
The harmonic distortion introduced in a 600-ohm circuit, caused by bridging the volume indicator across it, is less than 0.3 percent under the worst possible condition (no loss in the variable attenuator).
"Variable attenuator" in the above statement refers to a switchable VU meter range extender, if used.
Since the output impedance of your circuit has been built-out by your T-attenuator to a value close to 600 ohms, I guess you could say your meter is meeting the spec :wink: 0.3% of added distortion was considered pretty minimal back in 1939, when the VU standard was adopted. Of course, the distortion added by the meter would be less if the source Z were less than 600 ohms; but in your case, if that added 0.3% is not acceptable, I guess you're looking at an active buffer.
If you really want to avoid the active buffer, there are two other solutions you might find workable:
1. Switch the meter out-of-circuit after lining up your operating levels.
2. Add a range-extending attenuator to the meter, or simply increase the 3600-ohm series resistor to a higher value. 0VU will no longer equal +4dBM, but this will buffer the line from the meter somewhat and reduce distortion. You'll just have to remember that your "zero" level falls at a particular point below zero on the meter. You could make this range extender switchable so that you could have it switched out while setting your levels, then switch it in before you begin recording.
A T- or bridged-T attenuator designed for 3900 ohms is a suitable range extender for a VU meter, when used in addition to the 3600-ohm series resistor.
