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First Person

Classic Mesa Boogie Tube Amp Sound Reengineered

By Nicholas Choma

Nicholas Choma with self-designed amp

Audio tech student Nicholas Choma with tube amp he designed and built

When beginning my independent study of building a tube guitar amplifier, I decided I wanted to give myself the challenge of creating something both unique and intricate in design. Rather than start off with a typical Fender or early Marshall clone, I went straight to high gain (that is, distortion). In addition to the difficulty of sourcing all parts, creating a successful design, and realizing the end result, I now took on the task of managing noise and oscillation, both of which can quickly deteriorate sound quality.

After some research—and the past experience of owning several over the years—I decided to build my take of the high gain channel on a Mesa Boogie Dual Rectifier. I’ve always enjoyed playing and hearing these amps, but each time I’ve bought one I’ve sold it relatively quickly because they simply don’t have the quick response that I find myself craving. Rather, the Rectifiers are somewhat lazy, bass-heavy amps that—although they sound great—don’t always inspire the player. I wanted to build something that would have a similar sound and similar power, but could push me as a player to the next level.

Although every part that goes into a tube amp can have a large influence on tone, my tweaking dealt with cathode bypass capacitors early in the signal chain. These capacitors are used to alter the tone coming out of each tube, and they can allow different frequencies to either go on to the next stage or to be attenuated. In the Mesa design, higher frequencies are attenuated, which accounts for the excess bass and lazy feel. For my design, I reshaped each stage to allow more mid to high frequencies. These changes increased gain and harmonic content, and they offered a more immediate and rewarding response from the amp.

After deciding on a design, sourcing parts was the next big challenge. Although the schematics tell a lot about the build, they say nothing about the actual layout. I settled on a fairly customizable circuit board on which to mount the components so that, if I needed to rearrange stages or work with parasitic oscillation issues (a type of oscillation only present while playing—it can sound like a mosquito riding on the note), I would be able to. From there, I balanced noise and component tolerances with tone; then I ordered some of the best parts being currently made: including Orange Drop signal capacitors, F&T electrolytic, and Mercury Magnetics transformers.

When it came time to building the amp, I was careful to plan everything out the best I could to avoid problems later—although some issues inevitably rose. I used the star grounding system, which ties any component’s side that needs grounding to one local spot; this is to avoid noise and oscillation issues. Throughout the build, I needed to make some small tweaks and adjustments here and there. Because I ordered a transformer that gave me more options than I initially planned, I was able to add a switch lowering the amp’s overall voltage —similar to what Eddie Van Halen did with his Marshalls on his first records. 

The build ended up taking about thirty hours after all was said and done. I had only one significant issue, where the Mesa schematics weren’t correct—including a polarity issue on the transformer tap setting how “hot” or “cold” the output tubes run. Apart from that, the amp turned on and worked! I needed to do some small revising to get rid of excess noise and oscillation if the controls were turned in a certain manner, but for an amp with so many gain stages and so much distortion on tap, things were very quiet.

As for the sound? The changes to the Mesa schematic I made were a complete success! The amp still sounds like a Rectifier, but it tracks far more quickly, the tone is much “clearer,” the lazy bass response is gone, and an added bonus I hadn’t expected was that the tonal differences between guitars is more noticeable, something I hadn’t even thought of until I tried out different guitars.

After the success with this amp, I plan to continue designing and building amps. My next goal is to package, market, and sell amplifiers like this one. After receiving quite a bit of interest and praise in the local music store and online, I’ve gained some confidence that this type of product would be a great addition to the high gain amp market. The biggest inspiration to me is in knowing that every other amp builder started off just like I have.