THD Electronics
Name origins
Copyright issues prevented Marshall from naming THD Electronics after himself, (as Marshall Amplification had been established in the 1960). Marshall also decided against naming the company after his first name because, in his words, hois going to spend $2,500 on an ndy Amp?” Instead he chose THD, the acronym for otal harmonic distortion.
(Total harmonic distortion) is one of the ways that amplifiers are rated, says Marshall. nd in the hi-fi world, where people are quite conscious of total harmonic distortion, everybody goes for the lowest possible amount of distortion. In the guitar amp world, people tend to go for the most. So it was slightly tongue-in-cheek, but more of an inside joke.”
Marshall has said that THD alternatively means wo Hairy Dogs, referring to his bearded collies, Truffles and Tobler and with the addition of a third dog, Piper, hree Hairy Dogs.
Amplifier basics
Exterior
THD amplifier heads have a unique perforated steel cage, which is removable (via captive thumbscrews) if the amplifier is added to a rack or installed in a cabinet. Aside from the different faceplates, the UniValve, BiValve-30 and Flexi-50 look nearly identical. Although THD does not offer a hard-sided carrying case, they do make a soft-sided case for their amplifier heads.
Vacuum tubes
All THD amplifiers utilize vacuum tubes for their preamp and power amp sections. Until the release of the Flexi-50 amplifier, they were all Class-A, (The Flexi-50 is Class-AB). This is why early THD UniValve-prototypes were sometimes referred to as the ure Class A Head.
Printed circuit boards
Unlike the vast majority of high-end, outique-style guitar amplifiers, THD amplifiers are hand-built, but not hand-wired oint-to-point. Instead, they utilize printed circuit boards (PCBs). There is some controversy in the guitar amplifier community about using PCBs as opposed to point-to-point wiring in tube amplifiers. THD escaped much of this criticism by using thick boards with large ground planes to reduce noise, as well as through-plating and use of Teflon wire for durability. THD also does not mount their electro-mechanical components like jacks, potentiometers, switches and tube sockets to the board.
An identifying feature of THD boards is the addition of famous quotes to the printing on the board. These circuit board quotes include:
lie can travel halfway around the world while the truth is putting on its shoes. ark Twain
xperience is the one thing you cannot get for nothing. scar Wilde
on play what there. Play what not there. iles Davis
ove is a perky elf dancing a merry little jig and then suddenly he turns on you with a miniature machine gun. att Groening
First vintage reissue amplifier
In 1987, THD Electronics put the first vintage reissue vacuum tube guitar amplifier into production, the 4-10 amp. It was modeled after a 1959 Fender Bassman and, unlike the weed covered Peavey Classic Amplifiers of the 1970s (which were covered in vinyl made to look like weed) the 4-10 was covered in authentic cotton tweed, the first since Fender and Gibson stopped production of tweed amplifiers in 1960. The 4-10 was in production from 1987-1993. In 1989 a head-only and 2-10 version were released as well.
THD Plexi amplifier
The next amplifier in production was the Plexi, manufactured from 1990-1993. Although it, too, was physically styled after the Fender Bassman (and was also available in tweed,) electronically and sonically, it was meant to mimic an early JMP Marshall. In 1992, Guitar Player Magazine conducted a one-to-one test with a 1973 JMP Marshall 50-watt amplifier head, and found the two sounded ery close. From 1990-1991, a very limited run of THD 50-watt bass amplifiers was also produced. These bass amplifiers were dubbed the lassic Bass Head. For the last 18 months of the Plexi production, several minor circuit changes were made, prompting THD to rename it the ype-O.
2×12 extension cabinet
In 1990, THD also started production on a 2×12 extension cabinet for guitar amplifiers (the 2 refers to the cabinet having two speakers, the 12 refers to the size of the speakers, in this case 12 inches.) The back of the speaker cabinet is orted, (also known as ented) which tunes the cabinet to give it substantially more bass-response than either an open-back or sealed cabinet can. The two-inch lot-port in the back of the cabinet, s designed to offer the air and breath you get from an open-back design, while giving more bottom end and overall efficiency than can be had from a sealed cabinet. Fifteen years after it started production, THD 2×12 extension cabinet won Guitar Player Magazine Reader Choice Award for best speaker cabinet. Although usually covered in black vinyl, cream, brown and blue paisley-colored 2×12 extension cabinets were manufactured as well.
Hot Plate power attenuator
The Hot Plate power attenuator was first released by THD in 1994. It was designed to act as a type of master volume control for tube-based amplifiers, without sacrificing the distorted sounds such amplifiers make when they are played at full volume. The concept started in the late 1980 as a way to in-house test the company amplifiers without the technicians suffering hearing loss.
The Hot Plate works by being installed between the amplifier and the speaker cabinet (if any is used), absorbing the majority of the signal from the amplifier and passing only a small amount to the speaker. The remaining power is converted to heat. The UniValve and BiValve-30 amplifiers have Hot Plates built into them; the Flexi-50 has a foot-switchable master volume control in lieu of a Hot Plate. The Hot Plate is manufactured in five different colors; each color corresponds to the specific amplifier impedance that the Hot Plate is optimized for (the impedances should be matched.) The colors and impedances are: gold- 2 ohms, green- 2.7 ohms, red- 4 ohms, purple- 8 ohms, and blue- 16 ohms.
The Hot Plate has a Line Out jack, which can be used to send a DI signal to the mixer, or to insert equalization, time effects, and possibly a solid-state amplifier between the distorting tube power amp and the guitar speaker. The Line Out (or DI) signal can be blended with a miked guitar speaker at the mixing console. The Load setting enables using the Hot Plate as a pure dummy load, with no guitar speaker.
Yellow Jacket tube converters
The Yellow Jacket was also released in 1994. Yellow Jackets are a type of adapter that allows the existing power tubes in a guitar amplifier to be replaced with EL84 power tubes without rebiasing the amplifier. In 1994, Guitar World Magazine conducted a test in which Yellow Jackets were installed in a 100-watt Marshall Plexi Reissue. The resulting tones were imilar to those of a Vox AC30 although the amplifier was not as loud as it had been before the modification. There are several sets of Yellow Jacket tube converters, their designations relate to the type of amplifier they are converting.
UniValve amplifier
The UniValve is a 15-watt amplifier head released in 2001. Although it operates with only one output tube, it was designed to take a wide range of output tubes without needing to be rebiased. The UniValve was the first-ever recipient of Guitarist Magazine uitarist Gold award, under their revised scoring standards. The etched design on the amplifier front panel was made to resemble the work of artists and architects Charles Rennie Mackintosh and Frank Lloyd Wright. As of 2004, only around 1,300 UniValves had been produced. Their serial numbers start with 000, although model number 000 was given to the THD dealer who coined the amplifier name. Billy Gibbons (of the band ZZ Top) requested serial number 007, and model 666 (which is written on the back of the UniValve chassis in red ink) is owned by a former THD employee.
BiValve-30 amplifier
As the name would suggest, the BiValve-30 amplifier head is a 30-watt amplifier with two output valves. It was released by THD in 2002. Like the UniValve, the BiValve-30 was designed be auto-biasing. It is one of only a very few single-ended parallel tube amplifiers ever produced, and is the only one with separate primary windings on the output transformer for each power tube, allowing different tube types to blend in the magnetic realm instead of simply connecting the plates of the two power tubes. It, too, has a chemically-etched stainless steel faceplate, although THD chose a marine theme for the BiValve-30. Also, the BiValve-30 uses screen printing on the faceplate in addition to etching. In 2002, the BiValve-30 received a uitarist Choice award from Guitarist Magazine, after being rated a 4.5 out of 5 possible stars. In that test, the BiValve-30 was given a slightly lower score in the alue for money category, and the accompanying written review stated: definitely an amp for the well-heeled purist.
Flexi-50 amplifier
The Flexi-50 amplifier head was released in 2003, and made its debut at that year Music Live event in the UK. It is a 50-watt, class AB amplifier, meant to reate an idealized (Marshall) lexi tone. As a ubtle homage to the Plexi, the Flexi faceplate is gold Plexiglas. Like its predecessors, the Flexi-50 was designed to take the same range of vacuum tubes that the UniValve and BiValve-30 can. However, the Flexi is not self-biasing. Instead, it has three bias test-points on the rear panel for manually biasing the amplifier when the tubes are changed. It received a Guitarist Choice Award from Guitarist Magazine in April 2004, and a Guitar Player Magazine Editor Pick Award in December of that year as well.
Notable customers
THD has traditionally shied away from formal endorsers. However, the company does have many professional customers. Some clients include Jeff Beck (The Yardbirds), Peter Buck (R.E.M.), Eric Clapton, Charlie Daniels, Bob Dylan, John Fogerty (Credence Clearwater Revival), Billy Gibbons (ZZ Top), Paul Gilbert (Mr. Big), Kirk Hammett (Metallica), Mick Jagger (The Rolling Stones), Mark Knopfler (Dire Straits), Mick Mars (Mtley Cre), Steve Miller, Bob Mould (Hsker D, Sugar), Jimmy Page (Led Zeppelin), Prince, Chris Poland (Megadeth, Ohm), Brian Setzer (Stray Cats, Brian Setzer Orchestra), Dan Spitz (Anthrax), George Thorogood, Eddie Van Halen (Van Halen), and Stevie Ray Vaughn
The official THD website includes a much more comprehensive “THD Artist List”.
References
^ a b c d e f g h i j k l Guppy, Nick. ure Gold. uitarist. March 2004: p. 85.
^ Guppy, Nick. ure Gold. uitarist. March 2004: p. 82.
^ Buddingh, Terry. he Flexi-50 uitar Player. December 2004: p. 169.
^ Schuchard, Monica. he Secrets of Success. xperience Hendrix. July/August 1998.
^ Schuchard, Monica. he Secrets of Success. xperience Hendrix. July/August 1998.
^ Guppy, Nick. ure Gold. uitarist March 2004: p. 85
^ Schuchard, Monica. he Secrets of Success. xperience Hendrix. July/August 1998.
^ Gill, Chris, and Art Thompson ew Gear 94 All Stripped Down! uitar Player. May 1994.
^ Cotey, Stan. ead to Head, Comparing 14 All-Tube Combo Amps. uitar Player. March 1992.
^ Thompson, Art. ne Tube Wonder. uitar Player. February 2002.
^ Taylor, Mick. exi Coology. uitar Buyer August 2004. p. 86.]
^ Buddingh, Terry. he Flexi-50 uitar Player. December 2004: p. 170.
^ Buddingh, Terry. he Flexi-50 uitar Player. December 2004: p. 170.
^ Buddingh, Terry. he Flexi-50 uitar Player. December 2004: p. 169.
^ Ellis, Andy. 13 Amp Shootout. uitar Player. December 1992.
^ Taylor, Mick. exi Coology. uitar Buyer August 2004. p. 84.]
^ Molenda, Michael. he Better Late Than Never 2005 Reader Choice Awards. uitar Player. April 2006.
^ a b THD Electronics. HD Hot Plate Power Attenuator. HD Electronics, Ltd. February 2004.
^ Gill, Chris. ittle Yellow Thrills. uitar World. May 1996: p. 170
^ Thompson, Art. ne Tube Wonder. uitar Player. February 2002.
^ Guppy, Nick. he UniValve Head. uitarist. December 2001: p. 61.
^ Guppy, Nick. ure Gold. uitarist. March 2004: p. 83.
^ Guppy, Nick. HD UniValve Head. uitarist. December 2001: p. 60.
^ Guppy, Nick. HD BiValve-30 Head. uitarist. 2002.
^ Guppy, Nick. HD BiValve-30 Head. uitarist. 2002.
^ Guppy, Nick. HD Flexi-50 Head. uitarist. April 2004: p. 144
^ Guppy, Nick. HD Flexi-50 Head. uitarist. April 2004: p. 144
^ Guppy, Nick. HD Flexi-50 Head. uitarist. April 2004: p. 144
^ Buddingh, Terry. he Flexi-50 uitar Player. December 2004: p. 169.
^ Schuchard, Monica. he Secrets of Success. xperience Hendrix. July/August 1998.
^ Blackett, Matt. aul Gilbert. uitar Player. September 2008: p. 66
^ THD Artist List
External links
The THD Official Website
Categories: Guitar amplifier manufacturers | Privately held companies of the United States
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