Bold, Spongy, and Rectifier Selection

Posted: February 16, 2016 in Amp Settings, Mesa Boogie Dual Rectifier, Tube Amps
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On the back of every Mesa Engineering Dual Rectifier, there are 2 switches to select options for the power supply.  One of these is to select Bold and Spongy and affect overall voltage to the amplifier, with Bold being full power and Spongy reducing power by about 20%.  The other switch is used to select the rectification: Silicon or Tube.  Selecting Tube reduces power by nearly 10%, since the tube has losses when it conducts.  There are 4 options for running the power supply:

  • Bold and Silicon
  • Bold and Tube
  • Spongy and Silicon
  • Spongy and Tube

Before I get to decisions for selecting power supply options, we should cover some facts and history.  Along the way, we’ll learn basic information about the differences between these options.

Good Old Days

When amplifiers were first being mass marketed, tubes were state-of-the-art technology.  Solid state devices and integrated circuits (chips) were not yet developed.  All amplification involved using a tube to increase the size of a signal.  To convert AC to DC, which is rectification, a tube diode was used.

Once solid state diodes were developed, they began to replace tube diodes.  Germanium was an early material, but was not very consistent.  Silicon was the more successful material and became the standard for solid state materials used in guitar technology.

A tube rectifier loses a significant amount of voltage across it when a large demand is made.  This causes the amp to reduce in total power and then ramps up to its full voltage potential.  This causes some compression, or sag, and makes the decaying signal increase in volume before it fades away.  Low notes are harder to reproduce, since the frequency is slower and generates a larger signal, because of the ellipsis made by the string.  A tube diode lends a bouncy, soft feel to the notes.

Silicon has less voltage lost across it when it rectifies the signal, .7 to 1.5 volts is normal, depending on the diode.  This enables it to very quickly supply power to the amplifier.  There is much less sag, a tighter, more defined, bottom end, and a firmer feel.

Beyond amplifiers, listening to music made in studios with tube consoles vs solid state consoles will illustrate differences between the two technologies (Led Zeppelin III vs Presence, The Beatles The Beatles vs Abbey Road).

I Have The Power

In the late-1970s a hotshot guitarist came along and reinvigorated popular guitar music.  His name is Eddie Van Halen.  One of the things he claimed to use for his sound was a device called a Variac.  It reduces the mains voltage going to an amplifier; the amp is plugged into it and it is plugged into the power source.  By reducing the overall voltage, it makes the sound become darker, less firm, and enables the amp to breakup at a slightly lower level of volume.

Van Halen had an enormous impact on guitar playing.  People began shredding like him and copying parts of his setup to get a similar sound.  This impact on popular culture lasted until the mid-1990s, but still continues to this day in a less overt way.

In Comes The Diamond Plate

The Dual Rectifier calls back to the Golden Age of guitar playing in many ways by giving a user these power options, though it also hot rods the preamp so a person can dial in distortion at lower levels than amps from that era (and way more distortion).  When I look at the schematic, I sense that Mesa was producing a “What If?” amp.  To me, the question seems to be: “What if Fender had competed with Marshall’s designs and turned the tables on them copying the Bassman?”  They took a modified Soldano SLO 100 preamp married to a hot-rodded Mesa version of a Fender power amp, threw in some Vox for Modern and Clean, and gave users the choice of rectifier for Bassman/JTM45 (Tube) or Marshall-ish/Modern (Silicon), and also a built in voltage reduction (Spongy) for the people who worship at the alter of Van Halen.

So Many Options

Rather than just describe the differences, I’m going to name bands, genres, or songs that illustrate my personal choices for selecting the 4 power settings:

  • Bold/Silicon: Metallica Reload (or any Metallica), Alice In Chains Facelift, Soundgarden Badmotorfinger, Slayer God Hates Us All, any music with extremely fast tempo or massive lows.
  • Bold/Tube: Soundgarden Superunknown, Early Led Zeppelin, Black Sabbath Master Of Reality, Alice In Chains Alice In Chains, Sludge Metal, hard rock or any music with slow to moderate tempo, Late 1960s English Blues-Rock.
  • Spongy/Silicon: Classic Rock, Van Halen 1984, Alice In Chains Dirt, Grunge, Alt Rock, Modern Rock, thick and firm sounds, Doom Metal, Pearl Jam Vitalogy.
  • Spongy/Tube: The Beatles, The Rolling Stones, Classic Rock, Jazz Fusion, Blues, early Rock-n-Roll, really loose and bouncing music with early breakup which lacks extreme distortion.

These examples aren’t hard rules and a person can often get away with playing styles with any power setting, but the above puts the feel and sound into the right ballpark for the differences between styles, sound, or feel.  One thing I can say about the tube rectifier is that it helps create a feel that is like old amps being recorded on, and overdriving, tube consoles.  I really like that.


On the Reborn Rectifiers, there is an option to reduce the power to 50W, by taking two tubes out of the power amp circuit.  This does a similar thing to the sound and feel as Spongy does, but darkens it to a greater extent.  Since the Recto is voiced for Bold/Tube (Normal) at 100W, the 50W setting with Spongy will be incredibly dark, loose, and the easiest to achieve breakup , but it loses definition as the distortion increases.

Thanks for reading.

  1. kennyxxl says:

    I like the idea of bands as examples for sound settings. Are you familiar with Living Colour´s album Stain? The guitar sounds on “Ignorance is bliss”, “Wall” and “Leave it alone” are kind of my holy tone grail. There is something in these sounds that I think could be the tube sag which made me lust for a recto for ages. Can you comment on these sounds and what settings would be appropriate (knowing Vernon Reid not only used rectos on that record…)? Thanks!


    • Warpedpig#1 says:

      I only listened to Vivid back in the day. Listening to Wall and Leave It Alone right now, it’s difficult for me to discern, because Vernon is mixed really low and an effect is on. The vocals and drums are way too loud and I’d almost bet the mixing engineer had trouble with the lower guitar sound. That said, his mids are prominent on the recorded version of Leave It Alone as well as the live MTV version. He’s also getting some sick harmonics and the lows aren’t dominating. I think a small-to-moderate amount of OD or boost into Modern is a good start. The tube rectifier will remove punch from the bottom. It seems Vernon likes a lot of presence and mids. Put all of the EQ at Noon and adjust the presence and mids until it sounds right.


  2. Mirja says:

    Thank you, I never thought about the option of adding boost/slight OD… And yes, the mix is a little weird indeed. 🙂


    • Warpedpig#1 says:

      His Marshall JCM tone was definitely boosted and he loves pedals like I love my kids. I bet there’s a Guitar World or Guitar Player article from the time about his gear.


  3. tim says:

    The absolute best explanation of the 4 power settings I’ve read, including Mesas Owners Manual. You should be writing their technical manuals!

    I just bought the ‘90’s dual rectifier tremoverb and your explanation totally demystified the mind boggling owners manual


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