The Inferno - Welcome

JCA Circuits “Hi Power” Inferno Amplifier

“You’ve shown me a lot of amps today. Why didn’t you tell me you had THIS amp, Jason?” Steve Kimock

“THIS might be the best guitar amplifier ever!” Brian T

Named for Dante’s “Inferno” and inspired by the thought that “Hell Is Other People”, this is the JCA Circuits Inferno Amplifier. This is a one off amp which I built for myself back in 2010/2011. I’ve received several offers for this amplifier over the years which have been politely declined for a variety of reasons.
 

Besides fabricating the chassis line for the entire run of GR 1.6 amps, the brilliant, incredibly talented machinist named Michael Gent also helped design and construct this series of chassis for the Inferno. Michael retired several years ago and it’s extremely unlikely that I would look into producing a chassis like this ever again. The chassis isn’t important per se, as much as the constraints it placed on how it was built-which dictated layout and construction. The layout and construction I needed to use definitely dictates it’s performance. Honestly, I’d never build amplifiers using these techniques again due to inherent difficulty/material costs. However, it sounds unbelievable and performs at the very top of the curve, IMO.
 

Inferno utilizes concepts I originally uncovered while designing/building the Purpleheart amp throughout the 1990’s. Inferno was conceived to be the ultimate fixed bias, interchangeable output tube head. Inferno also includes concepts from the GR 1.6 preamp with the The Hi/Lo Tilt & Lean/Plush controls. These controls are proprietary and unique circuits I designed to work within the preamp/EQ section to give a large variety of tones and performance from the fewest parts in the signal path. They are unique, super effective, and function perfectly for any style of music, IMO.
 

Inferno can be considered to be more of plug straight in and play type of amplifier. However, it also makes an excellent pedal platform. Due to the mildly higher gain within the preamp, it can require more care and attention from the user when setting up reverbs and delays. This amp plays well with fuzz/distortion/overdrives, compressors, and modulation without much fuss.
 
The signal cleans up perfectly-like all of my creations-with the guitar volume. The drive, push, and sensitivity of this circuit is exemplary and is unlike anything else out there to my knowledge. Like all of my amplifiers, the noise floor on this amplifier is among the lowest of ANY amplifier I’ve ever experienced. Signal emerges from a literal inky black background in space and presents itself quite prominently to the listener. It truly is among the very best vacuum tube amplifiers in terms of performance-at any price point and design topology.
 
Please note-this is NOT a clone of a Trainwreck in any way. It simply pays homage to my friend and mentor-Ken Fischer with it’s cabinetry design/appearance. If you look fairly closely at Inferno and a Trainwreck Amplifier, the difference becomes readily apparent. Also, JCA Circuits amplifiers are typically cleaner with more headroom, are less compressed, and are designed to be more pedal friendly than a ‘Wreck. I love to use pedalboards and am a fan of trippy, atmospheric guitar tones like Gilmour, Edge, Fripp, Summers, Lifeson, Robin Guthrie, Johnny Buckland, Billy Corgan, Anthony Gonzalez-M83, Michael Jurin-Stellastarr, John Squire-Stone Roses, Kimock, Hendrix, Trevor Rabin, Phil Manzanera, Etc. For that reason, I prefer tons of headroom and a rich lower midrange which stays the hell out of its own way.

The circuit architecture of Inferno is along the lines of highly tweaked Plexi Marshall/5F6A Bassman/AC30 Top Boost using a 2+1 cascade preamp with the cathode follower. The cathode follower is a personal favorite of mine-I use it a lot in guitar, bass, and stereo designs. That’s an entirely different universe altogether than Kenny’s amazing cold clipper/3rd gain stage preamp designs used in his Express, Liverpool, and Dirty Little Monster preamps. Just to keep the peace on the homestead…

•6V6/5992, KT-66, or EL-34 Class AB1 Output Stage

•6V6 Duet Approximately 22 Watts RMS @ Clipping , EL-34 & KT66 Duet Approximately 35 Watts RMS @ Clipping

•Adjustable fixed bias output stage. Provides concentric 10 turn dial counter & test points for convenient approximate adjustment and swapping of output tubes.

•Like the Purpleheart & Golden Ratio Amps, the Inferno Preamp is also 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 in the treble phase cancellation tone stack. It completely changes the operating parameters of the entire tone stack and generates several different and unique harmonic spreads

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

•Treble, Middle, Bass, Cut, Presence, and Negative Feedback Controls

•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 Silver/Teflon Signal Wire

•Custom, Proprietary CNC Milled Chassis

JCA Circuits “Lo Watt” Inferno Amplifier

“I love this Inferno amplifier! My daughter and I cut the most amazing album with it. You have to hear it…” Dennis K.

The concept is to use either single OR parallel, single ended, mixed output tubes for power. I always liked the Palmer DREI concept. This worked out very nicely. I love single ended power amplifiers for audio and guitar. However, IMO they have many shortcomings and need to be worked in the right places to get them to really perform at the highest levels.

A single volume/gain control, deep switch, and a unique, proprietary “Loop Gain” switch. It’s basically a nuclear powered “Champ” with a big output stage, massive power supply, and 2+1 cascade preamp (cathode follower) driving the output tube(s) directly.

The cabinet was built (along with the Inferno Hi Power) by a very eccentric and talented woodworker named Dan Hudock of Green Lane, PA. It’s made of solid quilted cherry and the leftover valence piece from the Inferno Hi Power. Dan really did a nice job on both of these cabinets. They cost me deep in the purse… He did the joinery/planing/assembly. I performed the final sanding, finishing, oil, etc.

The Inferno can utilize either a single/parallel 6V6/5992 OR a single 6L6GC/KT66 deployed. The average transfer characteristics allow for it in this design. It produces about a maximum of about 10 Watts RMS @ Clipping.

The Inferno Lo Watt has a ton of clean, clear, useable headroom until about 6 watts RMS. Then all hell breaks loose. It remains tight, fat, and controllable throughout its entire power range. It’s full of crunchy harmonics and sustain. Think “Calvary Cross” by Linda and Richard Thompson (I Want To See The Bright Lights Tonight). Really quite the experience-especially if you aren’t prepared for it. I always liked it driving an EVM12L, Altec 417-8C, or a single Tone Tubby Ceramic 10.

•Single 6V6/5992/6L6GC/KT66 OR parallel 6V6/5992’s Class A1 Output Stage

•Approximately between 4-10 Watts RMS @ Clipping

•Like the Purpleheart, Golden Ratio, and Inferno Hi Power Amps, the Inferno Lo Watt’s Preamp is also a riff on the basic architecture of an 1959 SLP Plexi 2+1 cascade cathode follower driving the output tubes directly-minus the tone stack!

•Volume, Deep, and Loop Gain Controls

•Loop Gain bootstraps the cathode follower