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Thread: How do I mod my custom vibrolux reverb to reduce the harsh treble sound ?

  1. #1
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    How do I mod my custom vibrolux reverb to reduce the harsh treble sound ?

    Are there any tips out there to help me get rid of the way too trebly sound of this amp. I'm think that the 15 inch speaker would help but I'd like to try something else first that doesn't require major surgery

  2. #2
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    It's treble control has a wider range than regular BF amps, as it can actually cut treble. http://bmamps.com/Schematics/fender/...lux_manual.pdf
    If it's still too trebly, maybe there's something wrong with the amp, eg bad tube, bias too cold?
    Has it always been this way?
    If so, then yes, a different speaker type may significantly change the tone, but there's no need to go to the hassle of changing it from 2x10 to 1x15.

  3. #3
    Senior Member robrob's Avatar
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    Is the speaker broken in? If not you may want to wait on mods until it is.

    First mod I would recommend is clipping the bright cap on the Bright channel volume circuit. This is a very common AB763 mod.

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    Last edited by robrob; 01-23-2017 at 07:05 PM.
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  4. #4
    Supporting Member Chuck H's Avatar
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    What they said^^^^^^^^^^^^^^^

    But I guess I need to ask, what is too bright? If adjusting the treble control isn't sufficient then I need to ask why. That's not a cut, it's an inquiry. If, for example, you're clipping the amp then you need the treble up a little for good harmonic response and less farty bass. So in that case you can't just turn the treble down. So, is it harsh sounding when clipping? Is it just too bright clean? Does the amp lack bottom end? Do you want the treble, but it's to tippy and glassy sounding? There are a lot of versions of too bright.

    I can sure back what Rob said about breaking in the speaker. A lot of guys aren't crazy about the V30 speaker. I've always liked their upper mid character, but a little hashy on the top end. It took me a year to break one in for a 20W combo. Sounds great now. Best possible speaker for this amp. I hope I never need to break in another one But the point is just that it does make a big difference. Impatience ending in replacing your speaker can lead to a speaker that's too dark once it's broken in. That also happened to me.
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  5. #5
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    Quote Originally Posted by robrob View Post
    ...You can also clip the 10pF bright cap that's across the 3.3M reverb mix resistor...
    Rob, these amps have a rather different mixer circuit, and don't feature that nasty 10pF peaking cap (or anything similar).
    The normal channel is the exact same as the bright channel, except that it doesn't have the 47pF bright cap on its volume control.

  6. #6
    Supporting Member Chuck H's Avatar
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    Ah, Right! They have it set up like the a vintage Vibroverb. I always wondered why Fender got away from that design, which was their first on board reverb and favored the 3.3M to 4.7M resistor with the 10pf cap instead.?.
    "The man is an incompetent waste of human flesh. He should donate his organs now to someone who might actually make good use of them." The Dude re: maybe I shouldn't say, but his name rhymes with Trump

    "...less ear-friendly but handy for jazz." Leo_Gnardo

  7. #7
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    Question:

    Is this the 90s Custom Vibrolux Reverb from the Pro Tube Series (Twin-Amp, Prosonic, etc.) or is it the newer "68 Custom Vibrilux Reverb" w. SF & drip edge? These are two quite different beasts, methinks... might make a difference which one we're looking at. I am thinking it's the 90s one with BF & white barrel knobs... but neither will be am AB763. Schematic?

    Justin
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  8. #8
    Senior Member robrob's Avatar
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    I looked at the service manual you posted, there are lots of differences from the AB763. I edited my earlier post.

  9. #9
    Old Timer olddawg's Avatar
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    What type of guitar/pickups are you using? If the amp is operating properly you might just want to invest in a stompbox eq? Or roll off your tone control? What genre are you playing? It's all very subjective. I prefer a slightly darker amp. I read the other day that Johnny Winter played a Firebird through a Twin with no Reverb on, the bass control on ZERO, and the channel, middle, treble and master all on 10! Would be an icepick to the head for me but sounded great for him!

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