Leo Fender

Alan Alvaraz & Peter Janis

Click to enlarge

Two amps with opposing phase.
Speakers move in opposite directions

Second amp inverted to match first.
Speakers move in the same direction.

AC/DC Marshall stack on stage

AC/DC JD7 split for stage amps

AC/DC Marshall stack under the stage

JD7 Injector™ Development

Radial is an instrument interface company. Our products enable guitars, basses and keyboards to connect to pro-audio gear. This is what we do and the JD7 is at the very heart of it all. In fact, the Radial JD7 was one of the first products we ever developed. And from the original design, many other products have come to market including the Radial X-Amp Reamper™, the SGI™ Studio Guitar Interface, the Switchbone™, the BigShot PB1 power booster and the Radial JX44 Air Control™.

Radial President Peter Janis tells the story: I had this idea of producing a guitar signal splitter that would enable the player to drive a number of amps. As a former stage musician, I remember having three amps on stage and I was always fighting hum and buzz problems. I also knew that there were some custom made splitters that were very expensive but limited in scope. I figured we could come up with a design that would work for live players and be valuable in the studio for recording. Little did we know that the JD7 would be such a long standing success…

The basic design criterion was simple: Plug in a guitar and drive a bunch of amps at the same time. No fuss, no noise… how hard could that be?

Blame it all on Leo Fender!

We started with a basic layout: a 19" rack frame with six guitar amp outputs on the front panel plus a 7th on the back panel for a tuner. When the first JD7 prototype arrived, I took it home. Next morning, at about 7 AM I started to listen to it using a set of headphones. I remember calling the design engineer, and I told him 'it did not sound right'. He said 'that was impossible - it has a 1 meg-ohm input, is 100% discrete, equipped with class-A buffers and Jensen Transformers'. In his words: 'I tested it and it is perfect'. I told him that although it may be 'electronically' perfect, as a guitarist it did not sound right. The feel was wrong. Before I started Radial, I served 10 years as Product Director for Fender in Canada. Believe me - I know what my Stratocaster sounds like. Something was not right. He thought about it and a few days later, he found a solution.

Fact is, most guitarists hate the sound of buffers and solid state amps. And there is good reason! Most sound terrible! Here's the deal: When you connect a guitar to an amp, the pickup reacts with the amp and becomes part of the circuit just like a light bulb when connected to a battery. The amp's circuit affects the tone. Well, way back when Leo designed his first tube amps, he decided that a 1meg-ohm input impedance would be best. Everyone has been using a 1 meg-ohm input ever since.

  • But no one ever considered that tube circuits react differently than solid state ones. This is what I heard and what he figured out. A tube amp loads the pickup differently than a solid state amp and when you introduce a buffer, in this case the JD7 in between the guitar and the amp, the load changes. By varying the load on the pickup we can replicate the way that the guitar reacts to the amp and the sound regains the natural feel. The term 'drag' comes from a fishing rod: you adjust the tension on the reel using the drag. This is how we ended up calling it Drag Control.

    How 'real' does it feel? Believe me, if you can fool Carlos Santana, Joe Perry, Steve Vai or John Petrucci into thinking they are connected directly to their amps, you know that you have it right.

    Establishing the feature set

    Once we got the sound right, the next step was working out the feature set. We decided to recess the Drag control for 'set & forget' simplicity. The 6 output channels on the front and a 7th on the rear for a rack-mount tuner seem to provide more than enough connectivity. We then set about working through the challenges of using various amplifiers together.

    The first challenge was solving grounding problems. If you have ever Y-jacked the input a couple of old vintage amps together, you are likely aware of the dangers. Without a safety ground, you can become the ground rod and get shocked with hundreds of volts!

    Grounding issues also introduce noise problems commonly known as ground loops. A ground loop is created when the electrical ground and the audio ground share a circuit. This creates a loop. In the JD7, we eliminate the ground loop by transformer isolating all of the outputs except output 1 which is the ground path. In order to preserve the most natural sound, we of course use the world's best Jensen transformers. These deliver exceptionally linear performance without artefact or distortion.

    The next challenge is mixing one brand with another. Guitarists are often miffed when they discover their Fender may be out of phase with their Marshall. To solve this problem, the Radial JD7 is equipped with a series of polarity reverse switches that toggle the electrical phase so that the amps play in phase. It may be worth noting that most guitar pedals can also reverse the phase…

    Finally, we decided that since pedals may be brought into the signal chain but may need to be temporarily removed to compare wet and dry signal paths, we chose to add separate effects loops on output channels 5 and 6. This way, you can bring pedals in and out by simply pushing a switch.

    To Reamp is to Create!
    Probably the most exciting recording processes used today is Reamping. Reamping is a process whereby you 'quietly' capture a dry track while the guitarist is recording his wet track. In other words, you record the performance while the guitarist is fresh. The guitarist does not have to sit through hours of repetition waiting for the engineer and producer to work out the sonic details. Once you have captured the magic you send him to the beach with his girlfriend. Then, you send the dry track back out to the guitar amps, add pedals and start adjusting the tone and moving the mics around until you get the sound you are looking for. Best of all, you can go back and Reamp the track later should the tone need to be tweaked.



    Recording the dry track.


    Reamping the dry track.

    The Radial JD7 is designed for Reamping. You plug in the guitar and connect output-1 to the guitar amp. While the guitarist is having fun with his fuzz tones and flangers, you connect the direct box output from the JD7 to your recording system. You will be amazed! The dry track will not only send the notes, but you will also capture the sustaining feedback of the string. To Reamp, simply send the dry track back into the JD7 line level input, set the level and you can not fire up as many as 7 amps at the same time!

    This is how many bands such as Steely Dan have recorded for years. The track sounds fresh and the tone can be adjusted at any time to fit the production. Once you start Reamping, you will never record any other way.

    Dream Theater Records w/Radial JD7

    Photo of John Petrucci
    John Petrucci, Guitarist - Dream Theater

    "On our latest CD, "Black Clouds and Silver Linings", I used a secret weapon for the first time in Dream Theaters 25 years together. Peter Janis at Radial lent me a JD7 in the studio and it turned out to be a really important recording tool. At times I wasn't sure which Boogie amp would be the best one for the job, so by going into the JD7 and recording the direct guitar sound at the same time as the mic'd amp sound, our engineer Paul Northfield and I were able to go back at our leisure and re-amp my performance through various rigs. That way, we were able to choose one sound or the other, or a combination of the two, or alternate between amps through the song without me having to replay the guitar parts. I even added wah-wah performances to some of the tracks while recorded track was replaying through the amp! The Radial JD7 proved to be a real asset during the recording process and the best part was that my tone and guitar's response remained true when plugging into the box. I purchased the JD7 from

    Today, the Radial JD7 is used in thousands of recording studios and live stages around the world and is without a doubt the most successful guitar signal distribution system ever. In fact many magazines including Guitar Player have gone as far as calling it a studio standard. We are truly honoured.