Whitestone Audio Instruments P331 Tube Loading Amplifier had its genesis when my wife (and multi-Grammy® nominated mastering engineer) Kim Rosen was looking for a custom piece of analog gear for her new mastering room. Something unique.

We ended up brainstorming on an idea for a versatile tube stage for her analog chain. Much of the way Kim works is exploiting the sound of the input and output gain stages of some of her favorite equalizers and compressors with actual processing bypassed. Just the enhancement some of these analog gain circuits provide often times is just the thing to add a bit of “magic”. The goal for the P331 was to capture this kind of enhancement potential in a line amplifier that delivers the natural clarity of a well-designed tube circuit. At the same time, we wanted to bring fully switched controls that introduce harmonics and other carefully implemented, and repeatable, non-linearities to enhance the signal without harming the recording’s original intent. We really had no idea what we were getting ourselves in to! 

For the next five years we worked with our electrical engineer, (who’s other position of employment involves projects he doesn’t have clearance to discuss) on how to implement the features we envisioned…circuit design, prototypes…add features, scrap features, new prototypes, listen…tweak… build revisions…listen some more…tweak some more…over and over. We’re so happy we didn’t throw in the towel (we nearly did on several occasions) because we feel what we’ve ultimately created is a truly unique, truly exceptional processing device.

We wanted the P331 to have just a few great sounding and useful features. Chief among them being its Class A fully-differential (balanced) tube amplifier designed around 6SN7 dual triode vacuum tubes.  This tube was introduced in 1939 and while the 6SN7 is somewhat rare in pro audio applications, it is relied upon in the hi-fi market for its inherent “clean and silky” characteristics in audiophile preamps. The tubes are still in production and can be purchased new without hassle. 

Taking mixes to new levels without harming what’s already there is what the world’s best mastering engineers dedicate their life’s work to achieving. With that in mind we set upon designing features into the P331 that never sound overly processed, unnatural or heavy-handed. From the gentle parallel LIFT filter to the optional output transformers and clean solid-state output gain, all aspects of the P331 were designed to provide a tool which helps achieve that elusive element, that “something special” which is difficult to describe but unmistakable when heard.

We believe a great sounding recording is the sum of an accumulation of subtleties. With the Whitestone P331 Tube Loading Amplifier, we’ve worked to put a palette of these subtleties at your fingertips.

Dave Rosen