Designing the “Hot Strings” Guitar for Chet Atkins
by Ron Tipton
(Published in the May/June issue of Multi Media Manufacturing magazine.)
This is the story of an electric guitar and the musician who created it: Chet Atkins .
The story begins in the mid 1970s. I was taking a break from working on missile tracking systems to pursue what I preferred: working in audio electronics as a designer and consultant. My late wife, Virginia, and I found ourselves in Prairie Grove, Arkansas, working for GMS, Inc., a contractor to the Baldwin Piano and Organ Company. John Goss, the president of GMS, had hired us to design a line of guitar amplifiers for the Gretsch Division of Baldwin . And for other audio designs that might come up.
Another design did come up: Baldwin needed a piano tuning device for their grand piano manufacturing plant in Conway, Arkansas. This is another story but it’s relevant because I used two epoxy potted modules in the design to make it all fit inside the box they wanted to use. Chet heard about the modules and came to the GMS plant to talk to me about a project he had in mind. This was in October or November 1975.
A HOLLOW IDEA
The project Chet had in mind was incorporating some special effects modules into the guitar body. There were a number of companies making special effects units: Electro-Harmonix, Oberheim and MXR to name just a few. Most were designed to set on the floor and be turned on and off with a foot switch. Some enterprising guitarists built a wire framework to hang a module from the guitar body so he (or she) could also turn the control knob or knobs. There isn’t much space inside a guitar body but potted modules could , even then, be made rather small and could be easily shielded against hum and noise pickup without the concern about shorting out the components. Chet wanted three modules: a compressor, a phaser and a “fuzz” circuit. He told me I could buy whatever commercial units I wanted, tear them apart and then design something smaller and (hopefully) better. And any RCA semiconductors I wanted appeared on my desk within a few days.
We started on the compressor first, then the fuzz and then the phaser. Chet would visit the GMS plant about every 6 to 8 weeks to listen to the circuits individually. He wasn’t sure at that time how he wanted them interconnected. By June or July (1976) he decided to eliminate the fuzz circuit. As in any large company, and Baldwin was a very large company, other people wanted to get into the project. As an example, Figure 1 is a copy of an RCA memo to Chet dated August 17, 1976 with a proposed circuit diagram. We were already well down another path so this memo was not taken seriously but it took up some of his time to talk to the writer and explain why we were taking another direction. It also required a large amount of patience to get a couple of hollowed-out solidbody guitars from Gretsch so that I could work on the assembly. I don’t know which Gretsch model we used. I didn’t write it down as it didn’t seem important at the time.
In the photos 1 - 3, the control panel looks to be shiny aluminum. It wasn’t. It was 1/16 inch thick white plastic with a shiny black front surface and an aluminum backing for shielding. The modules and battery holder were fastened to an 1/16 inch thick aluminum plate and then covered with aluminum tape for shielding. The mounting plate and control panel shield were connected to circuit common.
By the end of August I had an assembled guitar ready for trial. Chet came to Prairie Grove about mid September to give it a try. The photos were taken inside the GMS plant and across the street in Battlefield Park (the site of a Civil War battle). We carried the equipment across the street to have enough space for all the GMS employees to listen and soon an impromptu concert developed with many of the local residents showing up. Randall Goss, who was 15 or 16 at the time and the son of the GMS president, was the only one of us with enough foresight to bring a camera. I have him to thank, and I do, for having a set of 8x10 inch photos to mark the occasion.
After the concert, Chet and I walked back to the GMS plant discussing his impressions. He was generally pleased with the performance of the modules but he wanted to make some changes in the arrangement on the control panel and he thought the phaser volume was too low at the “full on” (CW) end of the blend control. Figure 2 is a control panel drawing with his hand written changes. This is also when he came up with a name for the guitar: “Hot Strings.” If you look closely, maybe you can see where he wrote it near the bottom of the figure. I apologize for its quality, it’s a nearly 30 year old “Thermofax” copy.
Those of you with sharp eyes will notice that one the changes he made was to eliminate the toggle switch in the center that selected either the front, rear or both (in parallel) pickups. He decided that both in parallel were sufficient.
The phaser module output decreased when the load resistance decreased because the module’s output impedance was too high. I added an emitter follower to lower the output impedance and bumped up the version number to 2B. This made some more work for Virginia as she had to revise the circuit board layout once again.
ON THE ROAD AGAIN
Figure 3 shows the final circuit diagram of the compressor, COMP-1 (we didn’t change this circuit much as it sill had the original version number – “1"). It was packaged as a 2 x 2 x 0.75 inch module with a set of six right-angle pins coming out of the top surface to mate with a female Molex connector. The Phaser, FAZE-2B, circuit is in Figure 4. This one went through several revisions: 1, 2, 2A and finally 2B. It was housed in a 2 x 3 x 0.75 inch module with six right-angle pins for another female Molex connector. Figure 5 shows the module interconnection. My drawing copy is dated January 19, 1977 and shows all the wire lengths. I redrew these because they too are Thermofax copies and are showing their age.
The rear cover of RCA Records LP APL1-2786 (1978), Chet Atkins & Les Paul: Guitar Monsters shows twelve photos of Chet and Les. This guitar can be clearly seen in five of them. I also understand that Chet used this guitar in a TV special in 1977 or ‘78 but, unfortunately I didn’t see it.
Chet was innovative in other ways too. For example, he and Jimmie Webster developed the “Octabass Guitar” in the mid 1960s by replacing the two bass strings with a bass-guitar A and E strings. This extends the frequency range down by one octave and sounds like a guitar and bass duet. A fine example is the RCA LP: Chet Atkins, Solo Flights. (LSP-3922 stereo or LPM-3922 mono.)
1. In this article, I’m referring to Mr. Atkins as Chet because he preferred it. He was as unpretentious and easy going in real life as he appeared to be on stage. I truly enjoyed working with him.
2. In the late 1960s, the Gretsch company was sold to Baldwin. Under the leadership of Fred Gretsch III, it returned to the Gretsch family in 1985.
The “Official” Chet Atkins web site is:
http://misterguitar.com and it contains a lot of information about the musician and his career. You can order a two CD set of unreleased solo guitar recordings made in his home studio over a ten year period starting in 1982.
Garrison Keillor (Prairie Home Companion) is a big fan of Chet Atkins and has all of the radio broadcasts that Chet appeared on archived on the PHC web site at:
When we’re looking for design information these days we just do a Google search. But that wasn’t possible in 1975 and finding design resources was much more difficult. Bernie Hutchins, a professor at Cornell University, started publishing his ElectroNotes newsletter in 1972. And his Musical Engineers Handbook was published in 1975. Although it’s rather dated, I still use my collection of ElectroNotes and the Handbook for reference. ElectroNotes are still being published and all the back issues and the Handbook are available. You can’t order them online but you can print an order form and mail it to the address on the form with your check or money order.
The Handbook contains a chapter on the CA3080 and its “big brother,” the CA3094. The OTA (Operational Transconductance Amplifier) was a popular way to implement a resistors whose value changed with the control current. These OTAs are still available from Harris Semiconductors. My designs for both modules were based on ideas from the Handbook and various ElectroNotes issues.