The Golden Ratio

JCA Circuits GR1.6 “Golden Ratio” Amplifiers (2005-2023)

First (Original) Production Run 2005-2010

Second (Final) Production Run 2020-2023

The (3) amplifiers featured in the photos above represent the final production run which concluded in 2023. The snakeskin version sold in July 2023. Both the B&W Face and Gold Face versions currently reside within my personal collection. The B&W Face version is extra special because it has the double distinction of being the final build of the second production run (circa 2023) and is also the last GR 1.6 to be built.

The GR1.6 featured below in Cocoa Levant/Brown Face is the final unit built from the first production run circa 2010, and also resides within my personal collection. There are (4) of these Cocoa/Brown Face versions. The rest are Black/Gold Face versions plus the ones pictured above.

Also, I don’t keep extensive notes on builds. Amplifiers don’t leave the shop until they are maxed out according to what I sense at the time. I figure at that point they’re born, they will live a life, and eventually they’ll die. Like everything else subject to the Second Law(Thermodynamics), these instruments will reside in a state of constant change in between each of those events. They simply are until they are no longer.

It’s no longer possible to build more GR1.6’s in this configuration due to some of the unique, proprietary parts no longer being available. Specifically, the Japanese made Azuma/Angela ceramic tube sockets, custom proprietary chassis, custom Ohmite 2 watt carbon film signal resistors, and Dave Allen’s wonderful TP40D power transformers.

The body of JCA Circuits’ work to date enjoys a wonderful reputation, receives impressive reviews & owner testimonials, and is often compared to the very best examples in the State of the Art.

The brilliant, incredibly talented machinist named Michael Gent, who helped me design and build the CNC .300″ thick milled aluminum chassis retired several years ago. Dave Allen provided the power transformers for ALL of the the GR 1.6’s including these. He was kind enough to provide me these last three power transformers in 2021 to complete this run-right before he sold the company. Each GR1.6 are examples of the finest construction techniques, circuit design, and musical performance on full display within each.

I spent approximately 1.5 weeks physically constructing each amplifier. I’m not the “fastest” builder. I AM the most meticulous. From that point, I then spent approximately 3 months daily, for hours on end, playing each one, going between each chassis, each speaker, each tube, and each cabinet combination paying the closest attention to and tweaking/lining each up to maximize it’s own performance. Then, I spent dozens of additional hours with a guitar in hand, critiquing each with every combination cabinet, guitar, and pedal I have. I’m a musician and play multiple instruments-drums, guitars, and synths. My ears, hands, and brain reveal whether the feedback loop between myself, the instruments, the ensemble, the room, and the audience is right. Once I am pleased with all of that, then I consider the amplifier available.

•6V6 Duet for Approximately 20 Watts RMS Output Power @ Clipping/Class AB1

•Split cathode bias-there is a separate bias resistor and bypass capacitor network for each 6V6 phase.

•Preamp is a proprietary take on the basic architecture of an 1959/SLP Plexi/5F6A bassman-a 2+1 cascade cathode follower driving the tone stack

•Hi/Lo Tilt is a resistor/capaticor network within the tone stack. It completely changes the operating parameters of the entire stack generating a vastly different and unique harmonic spread with each

•Lean/Plush changes the slope of the tone stack network

•Trim provides fine adjustment of the Lean/Plush effect

•Ohmite RCN Series 2 Watt/750 Volt Carbon Film Signal Resistors

•Mallory 150 Series Metallized Polyester Signal Capacitors

•Angela/Azuma Made In Japan Ceramic & Silver Tube Sockets

•PEC 2 Watt Carbon Composition & Clarostat/Honeywell 2 Watt Conductive Plastic Signal Pots

•Alpha Signal Wire

•Custom, Proprietary CNC Milled Chassis