Custom Vibrolux - could normal chan be moded to match the bright?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by jrbanjo, Feb 17, 2012.

  1. jrbanjo

    jrbanjo Member

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    hello - I am a guitar player only, not an amp tech so please forgive.

    But, how different circuitwise are the bright and normal channels on a Custom Vibrolux, and how hard would it be (or even possible) to mod the normal channel to match the sound of the bright channel?

    Let me add that this would be done by a qualified tech and not me. ;-) I'm just wondering if it could be done.
     
    Last edited: Feb 17, 2012
  2. jrbanjo

    jrbanjo Member

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    also don't spare the tech talk since I'm just a guitar player. I can follow along. ;-)
     
  3. LarryN

    LarryN Member

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    The schematic shows a 47pf cap jumpering the volume pot on the bright channel, same as a Deluxe Reverb. I don't know what they look like inside but it shouldn't take much to do it.
     
  4. guitarcapo

    guitarcapo Senior Member

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    There's a simple mod you can do to blackface Fender amps to get the Normal channel to run through the same circuit as the Vibrato channel exactly. It involve adding a simple jumper wire. Not only does it allow the normal channel to have reverb and sound more like the vibrato channel, but it puts the two channels in phase so that you can jumper the two channels like Fender amps without reverb. You can also add effects in the jumper between the two channels as an effects loop. I did it on my Super Reverb and it works great....Maybe a tech can remind me how it's done?
     
  5. Jerry Glass

    Jerry Glass Member

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    All of that is done in this amp from the factory...except the effects part.

    The only difference is the 47pF cap across the bright channel volume pot. It's actually located on the pot board but the normal channel can have one added to the volume pot's terminals.

    Backup question...why do you want two identically voiced channels? Both are already run through the same circuit after the preamp and both have reverb and trem.
     
  6. phsyconoodler

    phsyconoodler Member

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    The CUSTOM VIBROLUX already has reverb and tremolo in both channels stock.
    The only difference is the reverb channel has extra gain for the reverb and tremolo.
    That and the 47pf cap on the volume control.
    The channels were made to sound different by Fender in the old days and making them sound the same is what Fender had in mind with the new 'Custom Vibrolux'.
    The mods guitarcapo is talking about do not apply to your amp as it's a different circuit and is on a PC board.
    Most people want to undo Fender's poorly executed 'Custom' mods and return the amp to when they actually sounded great.
    So,no,you can't make the normal channel sound exactly like the bright channel.
     
  7. guitarcapo

    guitarcapo Senior Member

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    well if it's just a bright cap, then I guess another question would be why would you need 2 channels when a brightness cap switch would suffice?

    I mean are there any people who actually plug two guitars into one amp anymore to justify having a tube burning away unused in there most of the time?
     
  8. jrbanjo

    jrbanjo Member

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    I have a weekly gig, same room, same set up. After much experimentation the sound that works for me is the Bright channel on about 3.3, TS9 with the level almost full, using volume knob on the tele.

    I want to also have a non TS9 clean sound at the same level. Only problem with this is that I can't just turn off the TS9 because then the volume would drop out.

    I know that i could just run the TS9 at equal volume to be able to turn it on and off. But, I swear that hitting the front of the amp hard with the TS on almost full just really gets that thing singing.

    So I was thinking about running an AB switch so that I could click over to a straight clean sound - with that matched up volume wise as close as i could get it (and i do realize that there would be a little break up happening at that point too).

    To my ears the Normal channel is too dark/dull. I really like the bright channel. As I said with the TS9 runnng hot I can't just click it off. So, just want to basically have two choices.

    Maybe through the tone stack I could get close to the brighter channel...
     
    Last edited: Feb 17, 2012
  9. Jerry Glass

    Jerry Glass Member

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    Try a brighter 12AX7 in V1 (normal channel preamp) like a 5th gen Chinese 12AX7 (example: Ruby 12AX7AC5) before you resort to circuit changes. It will save you some $$$ and everyone needs a spare tube or two anyway.
     
  10. phsyconoodler

    phsyconoodler Member

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    What most people don't seem to do is use the normal channel on a two channel Fender amp,for an effects loop.Simply plug into the reverb channel,then use a patch cable from the low input to the delay or echo effect,then into the normal channel.Voila! You have a buffered effects loop with controls to boot.
     
  11. guitarcapo

    guitarcapo Senior Member

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    don't they phase cancel? at least the ones wit reverb I mean
     
  12. Jerry Glass

    Jerry Glass Member

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    They are out of phase in the typical SF/BF Fender but that can be a useful tone (the Custom Vibrolux isn't though). Plus, if it is an issue, many chorus pedals have both an inverting and non-inverting output...problem solved.
     
  13. phsyconoodler

    phsyconoodler Member

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    In a Black or silver face Fender you can separate the shared cathode resistor/cap on V1/V2 and give them their own resistor/caqp and it helps immensely with the out of phase issue.And it gives a better,more detailed tone as well,as long as you don't bias too hot.Don't use less than 1.5k as a cathode resistor unless you want lots more gain.
     
  14. pdf64

    pdf64 Member

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    No, the only difference is the 47pF bright cap; the 'bright' channel has one, the 'normal' channel doesn't.
    Unless you are competent working on a PCB amp, consider getting a tech to do it. It should be a pretty quick simple job, minimum bench fee.
    Regards post #13 above, your amp already has a seperate cathode resistor / bypass cap on the 1st stage of each channel.
    Pete.
     
  15. jrbanjo

    jrbanjo Member

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    i picked up a live wire ABY box and it POPS like a mofo when changes. I must have a defect.

    Question, I'm switching between two channels on the same amp - could that be a source of the pop? Something to do with the fact that I want to toggle between a normal and bright channel?

    Otherwise I may have a defect because I couldn't believe that anyone would release and ABY with this much noise....
     
  16. jrbanjo

    jrbanjo Member

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    also I think I can balance out the tones and making the normal channel closer to the bright by really turning up the treble....
     

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