When did you get involved with the design of the 5150 III?
Pretty much at the beginning. When we were first approached by Ed to do this, Fender had taken a tack of trying to provide existing platforms that we felt were close to what he was looking for. It wasn’t necessarily the path he wanted to take. He’s always chasing his tone. It’s very evolutionary, and he always wants to go to the next step. After discussing with him and realizing what he was looking for, we had some good starting points.

It’s a three-channel amplifier. For a lot of his career he has been a one-channel guy. Did you start with a core tone, and then branch off to cleaner and dirtier from that?
We did start off with some basic tones that were akin to what he had been doing in the past. But he gave us a lot of freedom on the first channel. He said, “You guys know what you do as far as a clean tone—you guys come up with it.” But we also knew he wasn’t looking for something super sparkly clean— which is why Channel 1 does clean up very nicely, but it can get down and dirty if you adjust it properly. We knew that Channel 2 had to be a killer crunch tone—something that was very articulate, but had the girth underneath to really grab you. Channel 3 has been the channel that evolved the most. Ed is somebody who looks for a lot of sustain, and that’s something he’s still driving us to perfect. So Channel 3 has become more chaotic and over-the-top from where we started on the early production models.

Channel 1 has a surprising amount of sustain for a clean channel.
It’s how we designed the gain stages to interact. There’s a heck of a lot more gain that can be had in that channel—especially on the pre side of the gain control. You can roll that off, and get it nice and clean, but if you really want to dig into it, you can get that sustain characteristic—though not the buzz-saw type of tone you can get with Channel 2. He was pretty happy with Channel 1 from the beginning, and it was like, “Yep—move on to the next channel.”

One thing that always comes up in the discussion of this amp’s design are the transformers.
The transformers are a huge key to the amp. Ed was very specific about certain companies to use, and certain materials to use. This is still something we talk about as we evolve into the next generations of amplifiers. With the power transformer, it was a matter of getting the design right in terms of what the voltages were going to be, and how it was going to react when you dug into it. On the surface, it’s a design you can find in a lot of tube amps. It’s fairly linear supply. One of the keys, though, is we didn’t put a choke in there. Instead, we use a highwattage resistor, which also changes the character. It allows the power supply to breathe, it allows it to sag, and it also allows it to come back up in a more natural way. It doesn’t make the amp as stiff.

There’s a lot of iron in the output transformer, but Ed felt really strongly about that. For the type of tones he’s getting, a lot of it is defined in the preamp, of course, but there’s a particular feel to the amplifier that the power amp provides, and we wanted it to sustain, but also compress nicely. It also keeps the harmonic content you developed in the preamp, and doesn’t degrade it in any way. Those were the basic tenets to move forward on.

What about the tube complement? Was it always 12AX7s in the front, and 6L6s in the back, or did you experiment with different power tubes?
They were always 6L6s. EL34s were discussed at one time, but we started out with the 6L6s, and they felt good to him, so there was no reason to stray. The preamp side is completely 12AX7. What did change from the production model and the current amps were the different flavors and different manufacturers of tubes. Some of it was due to getting a higher quality tube. We always looked at this amp like it was a Ferrari—a high-performance machine. So we experimented to see what were the best quality tubes we could get in there—what would make this amp perform at a different level than any other amp.

As this design was coming together, you guys performed a “crash test,” where he turned everything up all the way, put the guitar in front of it, and let it feed back for a month. Is this a recommended thing from a design standpoint?
It was definitely not something we would normally do. Ed felt very strongly that this was a way to exercise the amp and tubes to see if everything would hang on and survive. He didn’t even know me yet, and he came up to me and said, “Hey, make sure that nobody messes with that sound test. I’m performing this crash test that’s really going to prove the reliability of the amp.”

So far, we’ve been talking about the 100-watt model. What can you tell us about the new 50-watt version?
It’s a three-channel amp with a clean-but-kind-of-dirty Channel 1, a nice crunchy Channel 2, and an over-the-top lead channel on Channel 3.

The first two channels share EQ on the 50-watt. What are the challenges to making that work?
We did have to change some of the voicings, but we tried to hold true to the voicings we had done on the 100-watt. Channel 3 was translated straight from the 100-watt to the 50-watt, because that channel is very important for Ed, so we wanted to maintain that. The 50-watt has the same tube complement— though two 6L6s instead of four—and it’s completely 12AX7 across the preamp, effects loop, and phase inverter.

Is the footswitch the same design for the 50- watt as the 100?
No. We did change the circuit topology where we felt we could improve upon the design, but still keep the same channel switching speed—which Ed loves on the 100-watt. The 100-watt uses a 7-pin DIN cable, but our view was, “Wouldn’t it be better to use a regular two-conductor 1/4" cable that you can get anywhere?” So that’s what we did. Based on feedback from other artists who were using the 100-watt model, we also added a MIDI In to accommodate channel switching via external controllers, such as a Voodoo Lab Ground Control or a Boss multieffects pedal.