Do Super Reverbs and Vibroverbs have the same guts?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by dk123123dk, Feb 17, 2009.


  1. dk123123dk

    dk123123dk Member

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    ...and different speakers? I was looking at the Fender Amp Field Guide and the names of the circuits are the same for blackface models. AA763 and AB763. The non reverb blackface pro is a AA763. Other than the speakers are there any differences between these amps? Thanks.

    dk
     
  2. tlpruitt

    tlpruitt Member

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    Yes, there are differences. If you gaze at the schematics long enough, like many of us here have, the differences will pop out at you.

    For the reverb amps look at the mid caps on the tone controls, the ground resistor on the phase inverter, the series resistor where the reverb is mixed back in before the last gain stage, and the phase inverter's plate resistors.

    -Tim
     
  3. hasserl

    hasserl Member

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    Transformers are different as are the operating voltages.
     
  4. phsyconoodler

    phsyconoodler Member

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    A Super Reverb AB763 is basically the same as any AB763 circuit.Sure,there are minor differences but they are not really worth mentioning.
    A Vibroverb is not a TRUE vibroverb unless it's the 6G16 circuit with the bias-vary trem.
     
  5. dk123123dk

    dk123123dk Member

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    Thanks for all the replies everyone! I guess the subtle differences make up a lot of tone in the long run.

    The reason I ask is because I was thinking about building a super reverb style head, and trying it with different speaker cabs to change up the sound a bit.

    Thanks again.

    dk
     
  6. tlpruitt

    tlpruitt Member

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    Sounds like you want something like a Bandmaster Reverb TFL5005 with some blackface mods and maybe a multi-tap output transformer.
     
  7. pula58

    pula58 Silver Supporting Member

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    I looked at the schematics of the AB763 Vibroverb and AB763 Super reverb.

    There are only five circuit differences I could find:

    1) The vibrato channel in the SR has a 10k midrange pot whereas the vibroverb has a fixed 6.8K resistor.
    2) The output transformer of the super is 2 ohms output impedance, the vibroverbs is 8 ohms. The vibroverb's OT is a smaller transformer than the SR's--it'll have less bass response and will saturate sooner...less headroom, more compression...
    3) The feedback volatage divider resistor in the Vibroverb is 47 ohms, it is 100 ohms in the super reverb. So, the Vibroverb has roughly 2x more gain
    4) The vibroverb has a 0.047uF cap (connected to the mid range 6.8K resistor), the Super reverb has a 0.022uF cap.
    5) the 3.3Meg reverb mix-in resistor in the super reverb is 2.3Meg in the Vibroverb

    Everything else is 100% identical..plate voltages, choke, everything! Have I missed anything folks?

    Speakers make a big difference too....of course!

    This has got me thinking: What is the tonal difference between the 0.047 cap and the 0.022 cap in the tone stack?? And, what is the tonal doifference between the 3.3Meg and 2.3Meg reverb return resistor? Does anyone know the answers to these questions?
     
  8. phsyconoodler

    phsyconoodler Member

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    Those differences don't do very much at all.The speakers make more difference than anything in the circuit.
    The mid pot is a tonal difference,but at 10k it's not huge.A 25k pot would do more.
    The 6G16 Vibroverb is radically different.Try one some day if you have an oportunity.
     
  9. SatelliteAmps

    SatelliteAmps Member

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    The difference between the .047 and the .022 cap has to do with frequency response affected. Higher values allow more bass side of frequencies to get through. In other words, a .1 cap will sound bassier because it is letter more bass frequencies through the filter (tone stack).

    All of those small variations do make a difference to the feel of the amp. It might not look like much, but if you could play the two side by side, you would notice some differences between the two amps. Not necessarily better or worse, just different. Speakers and speaker wiring do also make a difference, but to me the big difference tonally is the output transformer.
     
  10. tlpruitt

    tlpruitt Member

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    All else being equal, in a typical Fender BF type tone stack a .022 mid cap is going to provide a bit more low end and low mids than a .047 mid cap. Check it out on the Tone Stack Calculator. http://www.duncanamps.com/tsc/

    -Tim
     
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  11. hasserl

    hasserl Member

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    The difference in resistors is to account for the different impedance of the output transformer secondaries (2 for the SR, 4 for the Vibroverb).
     
  12. soldersucker

    soldersucker Member

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    I built a Vibroclone out of a donor 74 Silverface Super.After Blackfacing it that 47 ohm feedback divider is about all i changed(OT Allen multi tap)it sounds great!
    [​IMG]
     
  13. tlpruitt

    tlpruitt Member

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    I agree. Its a shame they didn't carry that mid cap tweak over to the Vibrolux Reverb. I like a .02 mid cap in my VR...the extra low mids sound great with the 2x10" speakers.
     
  14. soldersucker

    soldersucker Member

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  15. Lammy

    Lammy Member

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    I have a 15 cabinet housing a super reverb also. Sounds great!
     
  16. PEImatrix

    PEImatrix Member

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    I had a 63 Super Reverb that ran at 2ohms. I was told it was 1 of the few Fender amps that did.
     

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