P331 Tube Loading Amplifier (ALT ROCK)
P331 Tube Loading Amplifier (INDIE POP)
P331 Tube Loading Amplifier (ALT FOLK)
Audio Examples of both the original P331 and the P331 EVL on the same source material. Use chapter marker to go straight to EVL.
Both the Whitestone Audio P331 Tube Loading Amplifier and its “EVL twin” were developed to bring professional tracking, mix and mastering engineers versatile, elegant, precise and repeatable audio circuit variation. These are high-fidelity, hybrid vacuum tube /solid-state audio enhancement devices. They’re identical in their signal flow and control circuits, however we designed the P331-EVL to be more direct…more forward…less “polite” in its presentation.
So what are the differences?
Well let’s start with what’s the same. Like the original P331, the EVL version utilizes digitally controlled analog for all controls. Left/Right coherence is every bit as precise. The fully-differential solid-state output amplifier is unchanged. The LIFT circuit is also identical in both units, however, since the lifted frequencies are affected by the harmonics generated by the LOADING section…LIFT on the EVL will not sound exactly the same as the original P331.
The fully-differential tube LOADING amplifier in the EVL starts from a much different point. While the LOADING control is functionally the same as the original P331 in that it controls the 6SN7 tube’s operating point, it’s being pushed much harder from the start. It’s not like a distorted guitar amp…it’s still “mastering appropriate”. It’s simply a different, more forward “feel” than the original P331.
The XFORMER section is where the most differentiation occurs. We’re driving WAY more current at the EVL transformers …forcing them much further into saturation. The result is a more pronounced low-end presence, thrust and punch without becoming stuffy or losing clarity.
So what are the differences?
Well let’s start with what’s the same. Like the original P331, the EVL version utilizes digitally controlled analog for all controls. Left/Right coherence is every bit as precise. The fully-differential solid-state output amplifier is unchanged. While the LIFT circuit is also identical in both units, since the lifted frequencies are affected by the LOADING section…it will not sound exactly the same as the original P331.
The fully-differential tube LOADING amplifier in the EVL starts from a much different point. While the LOADING control is functionally the same as the P331 in that it controls the 6SN7 tube’s operating point, it’s being driven much harder from the start. It’s not like a distorted guitar amp…it’s still “mastering appropriate”. It’s simply a different “feel” than the original P331.
The XFORMER section is where the most differentiation occurs. We’re driving WAY more current at the transformers forcing them much further into saturation. The result is more low-end presence, thrust and punch without becoming stuffy or losing clarity.
In 1939, just a few weeks after the start of WWII in Europe, RCA Radiotron introduced the 6SN7 octal (8-pin) double triode tube to the American market. This was the birth of the true common ancestor of all modern double triodes used in high fidelity amplifiers. The 6SN7 is still in production after over 80 years, for good reason.
6SN7 vacuum tubes of the 1940s vintage were chosen for this amplifier due to their lower distortion capabilities that exceed that of the standard and ubiquitous 12A*7 variety. The 12A*7 varieties were incarnated due to commercial needs such that they were “better, cheaper, lighter” at the expense of embodying more distortion. With the advent of feedback, tube amplifiers could be mass produced with these less expensive 12A*7 style tubes using more feedback to reduce distortion.
While feedback reduces distortion, it also lowers overall amplifier gain. It might have been considered heresy to reduce the gain through feedback (and reduce distortion) in earlier tube designs since minimal gain was still extremely expensive prior to the 1950s. Thusly, earlier tube designs were lower distortion on purpose; especially for their critical role in modulation based communication systems that had more stringent requirements than the average 1950s guitar amplifier tube.
Notwithstanding, ultimate circuit topology can bring out more second harmonic characteristics than usual with any tube design. Hence the impetus for the variable circuit topologies within the P331 Tube Loading Amplifier to allow the user to do so as necessary or not at all.
(Ray LaMontagne, Bonnie Raitt, Aimee Mann, The Barr Brothers, Joe Henry)
Below is an email from Ryan after just 48 Hours with his new P331…
Here’s a note from the first client that gets to use the Whitestone. I told him I reprinted everything just because I needed to make a little change:
Damn, What did you change? These all sound like they are sitting perfect now! I can sign off on them, so good Ryan!
It’s a good start! Hopefully this project will be crossing Kim’s path soon.
Stampede Origin Studio
For any amplifier to be truly great you have to start with good clean power. The P331’s linear power supply is the most critical “component” for audio integrity next to the actual gain structure and circuit topologies within this amplifier. High voltage plate/anode tube power supplies start at around 320V DC and are filtered (up to 6 times) and smoothed with active regulators. It only uses film capacitors and real inductors (chokes) to remove ripple and noise from the high voltage power supplies.
(The War On Drugs, Kacy Musgraves, Arcade Fire, Bob Dylan, The Beatles)
“Seriously using it on more than half the work I’m doing. Scary good work tool. It has quickly become an essential tool, the most versatile box I’ve ever found to subtly colorize a track. Congrats to you and Dave!!!!”
The LOADING circuit is part of the fully differential (balanced) Class-A tube amplifier. It was designed to coerce an audio signal to hit the tube at different points on its response curve. As the gain increases through the tube, the signal is padded down in equal measure. This helps to ensure minimal audible level gain or loss, allowing you to audition the enhancement the tubes are imparting without drastic changes in level.
(NOTE: Parallel processing as illustrated in the block diagram below is only employed when LIFT is engaged.)
The LIFT circuit is a gentle parallel filter that enhances the highs, lows or both the highs and lows of the signal. Audio passes through the LIFT circuit before the LOADING circuit. When any of the LIFT filters are engaged, the audio is passed unscathed through the fully balanced P331 circuitry and blended with harmonic content of the LIFT and LOADING circuits working in concert.
(Bonnie Raitt, Bettye LaVette, Belly, Aimee Mann, The Milk Carton Kids)
My favorite things about using the P331 is how fun and easy it is to dial up gorgeous enhancements to a wide variety of sources…and how it’s the type of gear that encourages you to trust your ears and your instincts.