The Golden Ratio -

JCA Circuits GR1.6 “Golden Ratio” Amplifiers

Original Production Run 2005-2010

Final Production Run 2020-2023

The (3) amplifiers featured in the photos above represent the final production run which concluded in 2023.

I built a total of 17 of these including 2x prototype(s). 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.

Testimonials

“To us, it is among the best 1X12 20 Watt amplifiers we have ever reviewed” Tone Quest Report

“Everything that ToneQuest says about the JCA GR 1.6 is correct…. it’s literally the best small combo amps I have ever had!.. if anything, I think TONEQUEST understated how great this amp really is!” N. bessie

“Well, I finally cranked this baby up…OMG! Like Riding a Wild Horse, WOW…Woman Tone X5, Yikes….I think a 100 Watt version would be a useful military weapon (:” Huey Redwine

“JCA GR1.6 Golden Ratio Amp. “Dumble Killer”. Best 1×12 boutique combo ever built.” The Black Lodge

“If a Trainwreck was the sound of the 90’s, then this amp is the sound of the future” Kenn Mogel/Psychedelphia

“Purring look, roaring sound!” Vintage Guitar Magazine

“It’s really a super inspiring beast to play, and I’ve been very happy with so far, I feel it is upping my game due to the touch responsive qualities and the fact that you play it as well as your guitar, putting you in an ‘inspiration loop’…it gives back everything you put into it. Massive sustain, uber thick cleans, plenty of gain available if you go there, very transparent, bloomy and chime-y. Reminds me of a Trainwreck Rocket style amp I once played.” Baemer

“For me, there was nothing like the JCA Circuits GR 1.6. Just a spectacular combo amp, with all the right knobbies and switchies.” pima1234

“A buddy said the Golden Ratio is an amalgamation of many classic medium/small amps, with a level of refinement similar to what the Trainwreck Rocket was to the AC30. I’m paraphrasing and I hope it makes sense but it’s quite the compliment. Your amps are remembered as being at that level.” Elijah Robinson

“The best news of 2021, JCA is back and supplying the world with sonic goodness once again! Those Vibes look fantastic, I should purchase them both but I’ve already placed my order for a ‘Dumble Killer’ (Golden Ratio). Thank you for returning to the industry, we missed you terribly. I wish JCA all the luck and success out there, you deserve it!” Jessica Harvey

“I was fortunate enough to make JCA’s acquaintance, and he invited me over to the shop to have a look at his gear. I got a sneak peak of what he was building for you, the Dumble Killer. It’s not only going to sound great, it’s going to look great too. Exquisite attention to detail through and through.” Jae Haeme

“Jason, Just letting you know how completely thrilled I am with your fantastic amp! With the right pedal, I can finally accurately recreate Alex Lifeson’s unique and elusive tone on Limelight. I don’t know whether or not your amp has any similarities to the Marshall Club and Country (different tubes and power rating of course), but I am so happy with it, all around. It can do almost anything. My tech noted the high build quality and he’s not easily impressed.. Thanks so much!” J.H.

“Okay, Jason, I got the amp home and unpacked it…I’ve got one word for you. RIDICULOUS. Holy shit, man this thing sounds GREAT! It sound EXACTLY how you described it which, to be honest, is usually not the case. I mean I obviously expected it to sound really good or I wouldn’t have sold stuff at a loss and scrambled to buy it. But WOW. Super great cleans, Marshall roar, and that Trainwreck feedback hanging on the ends of the notes when it’s cranked up. And it cleans up with my guitar volume. I still haven’t touched the EQ, cut or trim, just the switches and volume knob. Thank you. THANK YOU.” J.P.

“I just got a JCA Circuits GR (Golden Ratio) 1.6. It’s the best low wattage combo amp I have ever had, played or heard! A truly magical piece of gear!” N. Bessie

“If you relish the prospect of jumping from the sound of a blackface Deluxe (without reverb) to a high gain Marshall short stack with all the dimensional bloom and harmonic character of a hand-wired tube amplifier, the GR 1.6 performs this nifty trick better than just about any amp we have reviewed. A Marshall PA20 can’t do it… the reissue 1974X 1×12 combo can’t do it… and the AC15 won’t do it. The DR. Z MAZ18 comes close, as does the Balls M18, but both lack a bit of the Fender DNA we hear in the GR 1.6. This is an extraordinarily toneful amplifier, created with an equally extraordinary voice, feel and attitude.” Tone Quest Report

“Given its laid-back appearance, we were expecting the amp to purr like kitten, but what we got was a roar! The 6V6s didn’t produce that sedate, scooped Fender-like clean tone; rather it more closely resembled a blackface or tweed on steroids, with an abundance of natural overtones and overdrive and very present upper midrange.” Vintage Guitar Magazine

“The elusive and very rare “Golden Ratio” reviewed by Tone Quest Report and Vintage Guitar both touting “best 1×12 combo we have ever reviewed”. Very few were made, around 20 from what I have read. Super high quality Dumble style boutique build!!!” Mountain Cat Guitars

“Up for consideration is an incredible combo amp. The amp that garnered the glowing review in the Tone Quest report, linked to below. Jason Arthur (JCA) studied with Ken Fischer and his amazing design makes this obvious. This amp has been played by folks with some incredible ears and chops, who had input in the final design as available here, including making the recommendation to have the Celestion Blue re-coned with hemp by A Broun Soun in San Rafael. CA. A Review of this particular amp is available here. Very few in existence – dual 6v6. flavors of Trainwreck Rocket and Tweed Deluxe, Fender Blackface Deluxe. Highly touch sensitive, truly amazing clean sustain and bloom. very touch sensitive. Chimey clean to mean all controlled via guitar volume.” Guitars Electric

“Jason C Arthur (JCA) was a protégée of Ken Fischer (Trainwreck) in the 1990s. He built 12-14 of these amps back in the mid-’00s that are unlike anything else I’ve ever played. The MOST touch sensitive amps you can imagine. 9-10 years ago, I was able to buy the #1 Golden Ratio 1.6 from the builder who’d kept it as his personal amp since it was built. That was the actual amp that was sent to the ToneQuest Report and garnered a glowing review. I later was able to acquire this one as well, the only difference being the speaker and faceplate color. The #1 amp now lives with a good friend of mine, and I’ve babied this one for awhile now.

Being so few of these in the world, and owing to the fact that they came out prior to the days of YouTube gear reviews, there are virtually no clips online. But there are plenty of glowing reviews, from the aforementioned 2008 ToneQuest Report to a handful of folks of this forum who have tried one. The vibe of this amp is influenced by Trainwreck, as it’s got plenty of gain on tap and cleans up better than anything else with the volume knob. But it reminds me very much of a Jim Kelley in the way it sustains and has lots of tweakability with the switches, trim knob and EQ. It’s been referred to as a “Dumble Killer”, although I don’t think that’s accurate, unless you’re talking about an Ultraphonix Dumble. The trim knob let’s you tighten it up like a proper hotrodded Marshall or get a bit looser and fatter like a tweed (switched to Hi Tilt and Plush) or a Vox (when switched to Lo Tilt and Lean). Being a 6V6 amp, the cleans are pretty Fender-y but with slightly more prominent midrange. It’s a room-filling 20 watts, with a very full low end…” SCMAVL @ The Gear Page

“This amp is very unique. I’d be hard pressed to label it as a clone of anything. It’s got the Blackface Fender in there. Marshall crunch. TW / Dumble sustain (I’ve only played clones admittedly). And it seems like it can do all that at the same time if asked. It can also be a nearly transparent voice for your guitar. I’ve played an ES-175 through it with haunting clean jazz tones.

It’s a GREAT pedal platform amp. Driving the input can get you thick tones at modest volume. It will throw some sound waves at you as well if you crank it up along with those pedals. I tried 90 watt Celestron Cream in there and it was phenomenal. Loud, full 3d tone. I’m running a Vintage 30 in it atm.

And then it surprises you with juicy distortion with a voice all it’s own. LP’s sustain like crazy as one would hope. Strat’s chime and snarl like they should, and Tele’s give all the twang and spank you could ask for. Can be touch sensitive and also creamy and full using your touch or volume knob. The settings are very interactive. It works great with attenuators as well.

It’s really an amazing amp that should have an IR done on it if that was at all possible.” AJLo @ The Gear Page

“After spending some quality time with Jason’s “Golden ratio” amplifier here are some thoughts on my experience. Before delving into the details, I’ve been playing guitar for over 30 years mostly in cover bands or hidden away in some studio tracking all while tinkering endlessly chasing sounds..
After indeterminate amounts of amplifier purchases I ended up designing and building two of my own which have satisfied my needs to what seemingly has no end; However as guitarists do- we all suffer gear acquisition syndrome! So who isn’t up for trying something new?!
Being a Dumble and Trainwreck enthusiast; Jason’s amplifiers’ instantly caught my attention.

Some of you might know but for those who don’t; Finding a truly responsive amplifier capable of cleaning up when dialed to scream is difficult. Not many amps actually pull this dynamic off.
The Golden Ratio is legitimately dynamic and not just with guitar volume knob work, this amp breathes with every pick strike. Once you’ve gotten a feel for the amps behavior – you’ll hit new planes of expression musically.

The Golden Ratio’s power/volume from its tube rectified dual 6V6 output section is astonishing.
Pairing the Celestion Blue with this amp dishes out superlative fidelity. The Alnico blue just works and hits that sweet midrange spot well seasoned with tight bass response and just enough top end bite to make the first couple of folks in the front row hop (as they should!). I was particularly fond of the Hi-Tilt and Plush setting with a 62 Stratocaster reissue which dished out Fender black panel vibes but with way better midrange content, no bass flub, none of that ugly power supply sag that squelched your pick response and dynamic response. Goosing the front end with any drive pedal was eargasmic. As a pedal platform the GR had enough capacity to cleanly handle looping + playing, delays, mod effects galore all while holding it together even with a battery of drive pedals fed into the front end.

From a build perspective dare I say no other guitar amplifier is intently overbuilt in this fashion.
We’re not talking about standard off the shelf parts or some kit built here- this is original recipe!
Starting with a machined extruded aluminum chassis, ¼” wall thickness, elegantly milled pockets for tube sockets, pots and jacks- this chassis is indestructible; very Boeing B-29 like thought applied in design. Jason’s amplifier is truly crafted in a “Build it once” and “Enjoy it forever” mindset. Inside the chassis you’ll find top shelf resistors, capacitors and pots, even the wire is better than what most fine cars use today. Expertly built cabinet work, even the rubber feet command authority.
Every part has been strategically selected and it shines thru sonically and visually.

If you have the opportunity grab one of these amplifiers, DO IT.
It’s truly a breath of fresh air that will last a lifetime.

Mike “Norton” Suchodolski (Retrolinear, Inc.)

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.

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