# Muddy Sounding Vibroverb



## Max52 (Mar 8, 2010)

I've got a 1963 Fender Vibroverb re-issue amp which I just had retubed and had the original speakers replaced with Celestion 10" Greenbacks. I was expecting it to sound much cleaner than it does.....not that I have the greatest ear. Pretty disappointing...did I chose the wrong speakers, or could it be something else that's making the amp sound "muddy"....or hopefully it's my imagination!...thanks...Mike


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## gtone (Nov 1, 2009)

Greenbacks are known for their early breakup, so are not considered "clean" speakers per se. Does the muddiness you describe increase as the gain or volume are wicked up? If so, there's a good chance it's the speaker choice for this amp that's causing your problem.


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## Max52 (Mar 8, 2010)

Thanks gtone. I guess I would say it doesn't increase with an increase in volume. Another way of describing it would be it sounds like there's a blanket over the amp. Could it be the Greenbacks are just lacking on the treble side of things?


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## faracaster (Mar 9, 2006)

There could be many things contributing to the lack of headroom. I wouldn't think that the Celestions would be one of them. They are likely of a higher wattage capacity than what ever Fender was using originally.
any time I have moved to Celestions in a Fender amp it has increased the fidelity of the amp. So new tubes or not, you may need to have a tech do some value changes in components and look at using a type of tube that does not compress as early. Tell the tech what you want out of the amp and he can help you there. Those changes should result, along with your celestions, in what you want. Failing that...... a higher power speaker like JBL/Altec 10's would be the way to go.....no possible speaker breakup with them.
I have to say I think those Vibroverbs do break up early in general. 

Cheers
pete


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## gtone (Nov 1, 2009)

Might help to know what kind of tubes were used for the re-tubing and also if the amp was rebiased at the time. This could be the key rather than the speaker issue, as certain brands/types of tubes sound different from one another (individual tubes of the same brand can sound quite a bit different from one another also). Strange as it may sound, tubes are a funny animal and can interact with each other in strange and wonderful ways in some circuits.


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## Max52 (Mar 8, 2010)

Hi gtone...The tech who did the work used Groove tubes with a 6 rating, a Mesa 12AX7 Preamp tube, and the others are JJ Electronic...it's all Greek to me, but the guy who did the work is a full time amp man.


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## Wild Bill (May 3, 2006)

Max52 said:


> I've got a 1963 Fender Vibroverb re-issue amp which I just had retubed and had the original speakers replaced with Celestion 10" Greenbacks. I was expecting it to sound much cleaner than it does.....not that I have the greatest ear. Pretty disappointing...did I chose the wrong speakers, or could it be something else that's making the amp sound "muddy"....or hopefully it's my imagination!...thanks...Mike



Mike, you are messing around with the easy things for a non-tech to do but they are also the things that LEAST affect your problem! A circuit change will do FAR more than any speaker or tube change ever could! If you want to change the horsepower rating of your car you need to do some mechanic things to your engine, not just change the tires or switch to premium gas. Many guys waste a lot of time and money 'cuz those are the only things they know HOW to do but that doesn't mean they will do any good!

There's some things you should know about the Vibro series of amps. Your VibroVerb and the Vibrolux Reverb do not use something called a "negative feedback loop". Without getting too techy, this loop is used in most guitar amps. A small voltage on the speaker side of the output transformer is fed back to the phase inverter driver for the output tubes.

This voltage is out of phase with the main signal and allows for two things. First, it can be used with a control pot to give a presence control. Second, it smooths out the amp frequency response, lowering the midrange "hump" that guitar amps are prone to have and also cancels out a bit of distortion and hiss.

As I said, most amps use this loop. In Fenders, this is your classic Blackface sound.

Your amp is more like some other amps that don't use this loop, like Vox, for instance! Without the loop you get a bit more hiss, a bit less headroom but you get a much quicker amp response to follow fast picking and you get a much smoother ramp into distortion. The BlackFace NFB loop circuit fights distortion until if really driven hard it starts to lose it on signal peaks, adding some harshness. Your amp should simply get thicker and warmer until finally it gets too distorted.

To get the sound you want, the amp must be modded. Google up "Moyer Mods" for the Custom Vibrolux Reverb and find the one about adding a negative feedback loop. This will tell you or your tech how to add this loop to your amp.

You do have an alternative. A great many players LOVE being able to switch OFF the NFB loop and pay techs like me to add this option to their amp! Try playing your amp with the guitar volume at about '8'. Crank the amp up louder if necessary. You will find that things are much cleaner and you have more headroom. If you roll the volume knob with your pinkie up to '10' for leads and such you will find the amp dirties up with a great sound, like a poor man's boost pedal! I particularly love doing this when playing some P90 humbuckers, using the bridge pickup and digging in hard with the pick! That's the snarl of rock and roll!

For this reason, you might consider having a small hole drilled in the back panel for a mini-toggle switch that will allow you to switch from "stock" to having an NFB loop.

Just some options...

WB


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## gtone (Nov 1, 2009)

Still with Pete on this one - speakers shouldn't be likely be suspect in this case. It was my first instinct as I have a 80's Brit Celestion G12L35 (fairly close to a GB) in a cab driven by a Phaez 15W head that gets wooly/muddy with volume or gain pushed past about 12 o'clock. But when you described the "blanket over the amp" muddiness and the fact that it's not dependent on gain/volume, that theory was blown away, however. I'd still wonder about the tubes, since that was the other variable in the equation. You might want to try swapping tubes in the amp, taking it back to the original tech with your concerns or go to another reputable tech/shop if you can't get any satisfaction.

FWIW, I've never had any experience with Groove Tubes or Mesa (GT?) tubes, but I've heard some people say that some can be hit/miss sometimes. JJ's I have used (though I usually prefer NOS) - I've had good experience with them so far and they do enjoy a fairly good reputation overall for modern production bottles.


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## davetcan (Feb 27, 2006)

Bill,
pretty sure his Vibroverb RI already has the NFB loop. The Moyer mod actually makes the Vibrolux more of a Vibroverb.





Wild Bill said:


> Mike, you are messing around with the easy things for a non-tech to do but they are also the things that LEAST affect your problem! A circuit change will do FAR more than any speaker or tube change ever could! If you want to change the horsepower rating of your car you need to do some mechanic things to your engine, not just change the tires or switch to premium gas. Many guys waste a lot of time and money 'cuz those are the only things they know HOW to do but that doesn't mean they will do any good!
> 
> There's some things you should know about the Vibro series of amps. Your VibroVerb and the Vibrolux Reverb do not use something called a "negative feedback loop". Without getting too techy, this loop is used in most guitar amps. A small voltage on the speaker side of the output transformer is fed back to the phase inverter driver for the output tubes.
> 
> ...


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## keeperofthegood (Apr 30, 2008)

memory is a wonky thing for me, I forget more than I remember every day.

I remember once having a speaker, I was excited and in my haste I had not realized I had put a twist torque onto the cone.

the result was simple, the paper did not move as it should have and my sound was like having my hand on the cone damping it down.


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## Wild Bill (May 3, 2006)

davetcan said:


> Bill,
> pretty sure his Vibroverb RI already has the NFB loop. The Moyer mod actually makes the Vibrolux more of a Vibroverb.


The original VibroVerb had the NFB loop Dave but the 63 RI Vibroverb did NOT! 

That amp, the VibroKing and Vibrolux are all actually modern amps that came out of Fender's Custom "skunk works" in the early 90's.

I referred to the schematics before I made my statement and the NFB is plain as day in the old BF VibroVerb but the modern 63 RI VibroVerb shows it conspicuously absent! Both the modern VibroVerb RI and the Vibrolux actually share the same printed circuit board, just having a few minor differences as to what parts are mounted and some wire connections from the tubes to the board.

This of course leads to the obvious question, why the hell is the 63 Vibroverb RI NOT the same circuit as the old amp of that name! I have absolutely no idea!9kkhhd


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## davetcan (Feb 27, 2006)

LOL, should have known you'd check the circuit. Lot of misinformation out there about that RI then, I saw a few statements to the contrary before I posted. Of course I can't read the schematic 




Wild Bill said:


> The original VibroVerb had the NFB loop Dave but the 63 RI Vibroverb did NOT!
> 
> That amp, the VibroKing and Vibrolux are all actually modern amps that came out of Fender's Custom "skunk works" in the early 90's.
> 
> ...


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## Max52 (Mar 8, 2010)

You guys are way beyond me, but I've been enjoying the comments and thank you all for your suggestions...Mike


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