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Princeton Reverb (no trem, no reverb) Micro

Discussion in 'Shock Brother's DIY Amps' started by robrob, Mar 1, 2020.

  1. robrob

    robrob Poster Extraordinaire Ad Free Member

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    This 1 watt amp is designed to mimic the Princeton Reverb with the tremolo and reverb set at minimum. This is the initial design and layout so I haven't prototyped the amp yet.

    The simplest way to build this amp is to buy a Princeton Reverb small parts kit but substitute the circuit board shown below in the layout for the kit circuit board. You'll also need a 275-0-275v power transformer such as the Classictone 40-18027. The output transformer is a common 22.5K:8 ohm output transformer such as the Hammond 125B.

    You can upload the Hoffman Circuit Board file to HoffmanAmps.com DIY File Analyzer and Doug will make an eyelet or turret board for you for a very reasonable price. He will even populate the boards for you for a nominal charge. I really like the Mojotone Princeton Reverb Small Parts Kit.

    I recommend using a blackface or silverface Princeton Reverb chassis and cab. A custom faceplate can be ordered to cover the excess control holes or you can add a Mid tone control, Presence control, master volume or other mods to fill the holes.

    If you would like to use a 12 inch speaker you can always build this circuit into a blackface/silverface Deluxe or Deluxe Reverb chassis.

    I added a 470k grid stopper to the phase inverter. It won't affect the clean tone but will prevent nasty "double frequency" phase inverter distortion when the amp is pushed hard. It will also make the amp more pedal friendly too.

    I also added power tube grid stopper resistors which form a voltage divider with the power tube grid leaks to attenuate the signal hitting the tiny power tube grids.

    I plan to add a headphone out jack option like in the Bassman Micro.

    More info here:
    https://robrobinette.com/AA1164_Princeton_Reverb.htm#Princeton_Reverb_Micro

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  2. D'tar

    D'tar Friend of Leo's

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    "RR"1164

    Love it!
     
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  3. tweedy_woodpecker

    tweedy_woodpecker Tele-Meister

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    Great stuff, Rob!
     
  4. King Fan

    King Fan Poster Extraordinaire

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    Rob, your micro amps are so cool. And they're totally catching on -- a lot of interest and many builds recently.

    Maybe you say this somewhere. How close is their sound to their octal-powered siblings? We hear so much about the sonic qualities of the various octal power tubes... and I can't start to imagine all the other factors that might be in play.
     
  5. robrob

    robrob Poster Extraordinaire Ad Free Member

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    It's hard to say because it's so subjective and then you have triode vs pentode power tube but the bottom line is they sound surprisingly like their full size siblings, just quieter. The typical reaction is, "Holy schidt! That sounds huge!" especially when plugged into a full size cab.

    I get emails from people all over the world building these little amps and haven't had anyone express any disappointment.
     
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  6. robrob

    robrob Poster Extraordinaire Ad Free Member

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  7. mjcyates

    mjcyates Tele-Meister

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    Thanks Rob! What if I want this same thing with the power section from a AA764 Champ circuit? What changes would be needed?
     
  8. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Last edited: Mar 2, 2020
  9. Mark the Moose

    Mark the Moose Tele-Holic

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    That's pretty cool. You're a national treasure, Robrob.
     
  10. tubedood

    tubedood Tele-Holic

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    Hi Rob.
    Great work here (as always!)

    I have been tagging along as you and the folks on this fine site build a few of these micro amplifiers. Would it be difficult to use a 6SN7GTB in place of the 12AU7?

    I have a few old 6SN7's and I have heards they can be quite useful in a small wattish amp... (maybe a bit more output than the 12AU7 tho?)

    Dale
     
  11. robrob

    robrob Poster Extraordinaire Ad Free Member

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    It does look like the 6SN7 could put out a little more power than the 12AU7 but I've never used one as a power tube.
     
  12. supersonicobr

    supersonicobr TDPRI Member

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    Hey Rob, you got the PI grid stopper on the description and layout but not on the schematic - thought I'd give you a heads-up.
     
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  13. scelestus

    scelestus Tele-Holic

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    So, like a Dartmouth? A Cornell?
     
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  14. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Show me a schematic please.
     
  15. alathIN

    alathIN Tele-Holic

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    Just curious: is build simplicity the main reason to delete the trem and reverb?


    Scratch that - just saw the other thread.
     
    Last edited: Mar 5, 2020
  16. scelestus

    scelestus Tele-Holic

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    Sorry, bad joke. Just a less fancy Ivy League school as a name.
     
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  17. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Yes, I would prefer to keep the Princeton Reverb just as it is but the reverb and tremolo make it a much more daunting build and troubleshooting subject.
     
  18. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Thanks for letting me know supersonicobr, I fixed the schematic.
     
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  19. cnlbb

    cnlbb Tele-Afflicted

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    Robrob! Your website is amazing, and the 'reading schematics' section would've saved me some pain from using 50s textbooks a few years ago. Keep up the great work! :D
     
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  20. FenderLover

    FenderLover Poster Extraordinaire

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    Looks like you put it on the gain stage before the PI.
     
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