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  • Writer's pictureRyan

Inside & Analysis of a REAL John Mayer Two-Rock Signature Amplifier

Updated: Nov 30, 2021

Ah so excited to finally see the inside of one of these bad boys and learn about the features that make up the tone of John's Signature Two-Rock amps! As a reminder, I publish these insights and thoughts for educational purposes and not to undermine, destroy, or promote in any sort of way. The information is to guide someone someone to learn to build this amazing, out of production, amplifier.

On the Dumble amp clones and D-style pedals Facebook group, a generous forum member who was working on a JM Sig for a customer (it kept blowing a fuse) provided some really nice gut shots. Because of my own quest for information, as well as a few other members on My Stupid Mouth forum, these pics help with reference points. There were a few prototype and post production "signature" amps that were let out into the wild which did not flip the preamp section and did have pictures taken of the inside to help the information flow along.

Some of my notes that I cover in the YouTube video

  • The Wonderland layout as provided by Amplified Nation component values seems to be very accurate compared to the production amp.

  • The amp that Amplified Nation had included 100R resistors in the power section that is not present on the production amp

  • The power caps on the AN amp are Illinois (IC) which is different than the production units.

  • The treble pot measures ~262k Ohm and is marked with an "H" to indicate it's a high value.

Component lists

Some of this information is hard to say it's 100% accurate without seeing the components with my own eyes, but I'm fairly certain the production unit uses the following components.

  • 1/2 Watt carbon film resistors are mostly used throughout the circuit.

  • 1/2 Watt carbon film resistors are used on the local negative feedback side of things.

  • 100k Ohm Dale RN65D Military precision resistors used on plate load on the preamp board.

  • 1/2 Watt metal film resistor used for the global negative feedback resistor.

  • Vishay 1kv ceramic disc capacitors are used on the bright, mid, reverb, and other parts of the circuit where the yellow caps are used. I believe they are X5F dielectric type (yellow) and I suspect the red disc on the reverb might be a different tolerance or dielectric type

  • 715p 400v orange drop mainly except for the phase inverter (600v). I can't seem to find 1NF and 2NF in 400v so I'm assuming Two-Rock chose 600v for these values.

  • I'm pretty sure the brown local negative feedback .047uF resistors are JB 473k metalized polyester based on Two Rock using them for a while throughout their amps.

  • Belton octal and 9 pins.

  • General Cable/Carol 18 ga hookup wire C2064 series.

  • Likely General Cable/Carol coax white wire.

  • Power Transformer: ClassicTone 40-16932 (about 10% lower voltage than a standard Fender Twin Reverb PT)

  • Choke: M1529C1 (replacement p/n is 40-18003)

  • Reverb Driver: M1529A1 (replacement p/n is 40-18034)

  • Output Transformer: ClassicTone 40-16852 (replacement p/n is 40-18013)

  • 20uf 500v supply capacitors are Sprague Atom

  • 220uf 350v supply capacitors are likely Ruby since Two-Rock used Ruby around this time period.

  • Accutronics 9AB2C1B reverb pan - 3 spring medium decay

As I learn more about the amp and other parts, I'll publish findings. If YouTube videos are your style, I made one with the same info as above :-) If you have any information to add, please contact me or comment on the YouTube video and I'd love to learn more!

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