Custom Amp Build

The Beginnings

I was recently contacted by a guitarist looking far a new amp.  He first asked if I have a Texas Tone 12 with reverb but not tremolo.  He’s gigged with that amp, and was looking for something specific.  I have a reverb amp in my line but it’s a totally different circuit with different characteristics.

Because he plays slide on a Gibson SG in a duo, sometimes playing small gigs, he was looking for an amp that has those Texas Tone 12 cleans and that breaks up nicely when he pushes it a little (Princeton-esque), and that has a sweet reverb.  All the other amps he tried “sound great but the volume I have to get to push the breakup creates too much stage volume for the shows we’re playing,” and that “all my sound guys keep telling me to turn it down.”

We corresponded back and forth, with him telling me what he wanted, sonically, physically, and cosmetically.

  • Ivory/cream like a Texas Tone 12, with black grille, chrome trim
  • A shrunken down Super Reverb
  • Texas Tone 12 was a bit too much volume
  • 3-band EQ
  • Tube rectifier sag
  • Single 10″ or 12″ speaker
  • Princeton style cab
  • Fender brownface knobs, with number on the faceplate

The speaker selection process was interesting.  When browsing speaker websites and specs, they say things such as, speaker ‘A’ has “vintage American tone with punchy lows and warm, smooth, bluesy mids and highs, while speaker ‘B’ has “Fatter tone with more depth,” but the response graphs tell a different story.  Speaker ‘A’ has a much louder treble peak, while speaker ‘B’ was more balanced, with a pinch more bass.  He chose speaker ‘B’, based on the charts – balance, and presence – and I concurred.  We also chose a 10 rather than a 12, due to his choice of thick tone from the guitar.

I took his input, and went to work designing an amp that would fit his needs.

Starting with a Princeton Reverb cab and chassis, and our chosen speaker, I went with the same cosmetics as the “Honeybeard” Texas Tone 12 – Ivory Tolex, bluesbreaker style grille cloth, chrome corners and handle, and added a black faceplate with white numbers and cream colored knobs.  That was the easy part.

The Circuit

Because he wanted reverb and no tremolo in a Princeton Reverb package, I chose an AA1164 “reverb-no-trem” layout.  However, I made numerous major and minor changes and tweaks to the AA1164 circuit, all keeping in mind the desired outcome.

  • Re-voice the 1st gain stage for his Gibson SG.
  • Add a Mid-range control to the Treble and Bass tone stack, comparing calculations and frequency response.
    • Less of a mid scoop than a typical blackface amp
    • Shifting the base frequency of the mid scoop.
    • Shifting the frequency of the Bass control
  • Re-voice the split-load phase splitter for smoother breakup and less raspy distortion.
  • Changes to the output section with grid stoppers and a half-power switch to allow the power tubes to break up at lower volumes.
  • 5U4 tube rectifier.   This, of course, changes the high voltage levels, requiring requisite changes throughout.
  • Other changes non-specified.

I was pleased with the result.  The half power switch along with High and Low gain inputs, allow plenty of flexibility.  Using the Low input and half power yields plenty of warm tube breakup at low volumes, great for more intimate shows  Using the High input and full power allows for opening up the amp for more volume for larger shows with a full band.

The Result

AhmansonSpecial

The design and resulting amplifier seems to have fit the bill!  We all like the amp.  After his first gig, which was with a full band,  he commented, “Tone for days!”.  I simultaneously breathe a sigh of relief and nod a satisfied smile.

03-DontDoIt

Video of on-stage Low Volume Growl at an intimate concert at The Groove Nashville.

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