If you are going into the microphone preamp with a U87AI and the gain is set to -20db then something is very wrong. The -20db will take the output of my CM47fet LDC microphone 2" out from a kick drum without any clipping.
My guess is you are over driving whatever the Neve 1073 is feeding?
1) Does the U87AI work without clipping distortion if you go into a different preamp... this could anything like a Behringer, Mackie or M-Audio. You are not comparing sound quality but just want assure that the 87AI working correctly and there is not a service problem with the 1073N or the U87.
2) If you plug a SM57, 58 into the Neve does is work in the same audio chain without clipping. I was just recording our CM87 with a Vintage Neve preamp and for vocals we had the input gain set at -40db of gain on an Etta James type vocal. Our CM87 has a nominal output with 3db of a U87AI.
3) Does the Neve 1073N work with any other LDC microphones without clipping distortion or can you measure the phantom supply and make sure there is actually 48v reaching the U87 when it is plugged in?
4) Plug a set of 50 ohm headphones into the line output of the 1073. Now, the output impedance is 75 ohms but this is a NEVE and it should be about drive a 50-600 ohm set of headphones without clipping distortion.
The Neumann U87AI specs are as follows:-
Maximum output voltage 390 mV
Dynamic range of the microphone amplifier (A-weighted) 105 dB
Supply voltage (P48, IEC 61938) 48 V ± 4 V
Current consumption (P48, IEC 61938) 0.8 mA
390mv is an output level of -6dbu before the on-set of distortion.
So, if you set the NEVE for -20 then you have 14db of headroom. However, my guess is the Neve gain should be set to around -40 for the average close vocal which is a level of about .007v.
Now, there is a Hi/Lo switch on the rear of the 1073 that sets the transformer input impedance. It should be set to Hi (1.2K) for a condenser microphones and dynamic microphones. In Low (300 ohms) the transformer will have 6db more gain which is useful for ribbon microphones. However, this shouldn't create clipping distortion just that the gain switch should be set for one position lower for the same output level.
I love solving analogue audio electronics problems as that has been my passion for nearly 45 years now.
So, first determine the U87AI is working correctly into a different preamp and that the Neve doesn't distort with a dynamic microphone.
Cheers, Dave Thomas
Originally Posted by londonengineer
The 1073(N) has plenty of headroom, the big question here is a) what are you plugging it into, and b) by what method. If you give exact details someone will probably work out what's happening.
To me it sounds like it's being plugged into a mic input on an interface as you haven't given any details to suggest otherwise.