Ampex 351 Tube Preamp

This used to be the audio electronics for the Ampex 351 series recorder (not 350). We saved 10 of these from a dumpster in 1996 and set to rebuilding them, optimizing the mic preamp path.

We gave it these handy options -

• Polarity Reverse Switch

• Phantom Power Switch

• -20 dB Pad (where "input" switch was)

• 600Ω Output Attenuator

• Meter Defeat Switch (meter introduces a minor level of distortion (not something we added, but the nature of the original beast))

They are set for a maximum of 65dB gain, and are shockingly quiet. You can use ribbon mics with them on quiet acoustic passages with no problem. At roughly 15kHz there is a 1 to 1.5dB rise in response. From 10 Hz to 14kHz, and 17kHz to 35kHz the response is flat.

The output attenuator is a great feature in that it allows you to overdrive the preamp for a desired color, while maintaining a usable output level. If you like having an extremely high output for some reason, you can kill the meter, keeping the needle from pinning all day (meter defeat switch).

They are used mostly on bass, guitar, vocals, and strings.

4 of these are installed in Studio B, 2 in Studio A.