Fender low-end problem when using a tremolo pedal.

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Improviser, Oct 31, 2005.


  1. Improviser

    Improviser Supporting Member

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    Thanks to some of the good folks here sharing their ideas and experience with amp mods, I have been trying some of these out on my '65 Fender Vibrolux Reverb amp. The amp is in excellent original condition.

    So far I have done the following:

    * installed a pair of Weber 10F150T's (original Oxfords tucked away)

    * new filter caps

    * new TAD 6L6 short bottles / rebias amp

    * general health check-over by a very knowldgeable tech

    Mods I have experimented with so far..... :

    * change phase inverter input cap from 0.001 to 0.01 value (Mallory 150)

    * disconnect tremolo (lift wire from rear of intensity control)

    * add midrange control through ground switch hole

    * fresh reverb tank (original one still works, just too much fatigue and mechanical loss)

    The amp now sounds fantastic - really spanky and very Fendery! I've been gigging with this amp for about 10 years and it is now the best it's ever sounded.

    However with the newfound lows and low-mids added, when I use my tremolo pedal (Swamp Thang - sine wave, very deep sounding) past '2' the amp gets this low-end throb starting to pulsate through the speakers. This does not sound healthy at all. I much prefer the sound of the Swamp Thang tremolo than the Fender amp tremolo (vibrato), but the low-end throb makes it just unusable.

    Is there a way (component value changes...?) that I can remove the very low-end from the amp whilst maintaining the rest of the excellent tones? Will different tremolo pedals cause the same throbbing low-end problem?

    Thank you in advance for any advice.

    Geoff
     
  2. Wakarusa

    Wakarusa Member

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    Not sure I understand what you mean by low-end throb (gotta clip maybe?). As far as removing the low end, it depends on how low you want to go. Damned difficult to remove audible bass without ripping the low end out of the amp -- and if the amp didn't have the problem before your mods, I'd look for problems in the amp before modding further (particularly a mod that's specific to a particular pedal).
     
  3. RussB

    RussB low rent hobbyist Silver Supporting Member

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    Seems more like a pedal-compatability problem than an amp problem...

    The Weber's will give you the big bass, and disconnectiing the trem will add gain to the signal, add the mid pot, and you've just got too much signal going through the amp!


    I recommend one of Jon Bessent's "Surf Bug" replacement trem roaches. Then hook the amp's trem circuit back up. They have much less signal loss from the (old & tired) stock roaches.

    Surf Bug
     
  4. Improviser

    Improviser Supporting Member

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    Thanks guys for the replies.

    Sorry, I'm not setup for making clips at the moment.

    The mid control I've installed is a 10K linear pot which is not usually set very high, just gives me a little more control over the tone. As I'm not trying to 'push the mids' too much I wouldn't have thought that this would be adding too much additional gain. I agree though that the Webers do add some bottom-end.

    Wakarusa, the amp was in good shape to begin with but was 'too midrangey' with not enough natural bottom-end. The change from the PI input cap from 0.001uF to 0.01uF is just changing from the stock Blackface to stock Silverface value.

    RussB, I'm definitely going to look into that 'Surf Bug' - thanks.

    I have reconnected the tremolo circuit to reduce the lows and low-mids a bit, however the throbbing sound still persists just with that pedal (Swamp Thang). This throbbing is not a musical sound, it is a hard, pumping, low-end sound going on. Almost like a speaker haemorraging, yet also sounds a bit electronic....

    Is it possible that the Swamp Thang (very well built with high-quality components) pedal also pushes a particularly low frequency range that the amp can't handle?

    Thanks once again.

    Geoff
     
  5. VintageJon

    VintageJon Member

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    RussB,
    THANKS! Surf Bug on it's way to Oz...

    Best Regards and May The Tone Be With You,
    Jon
     
  6. VintageJon

    VintageJon Member

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    Geoff,
    Was a bit difficult to understand problem with the phone drop-out today.
    I have read your 1st post and now I understand.

    The "pulsing and speaker movement" is due to there be not enough decoupling in the pedal circuit.

    Having designed and built the Vibro-Stomp, declared the finest tremolo and vibrato pedal in many reviews, I think I can say this. In "developement stage" I experienced this and solved problem with massive decoupling.

    I don't know if it's possible to modify the Swamp Thing with enough decoupling.

    Once you get the Surf Bug in there you won't need the pedal anyway!

    -Jon
     
  7. Improviser

    Improviser Supporting Member

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    Hi Jon,

    Welcome to the forum!

    Thanks for your response here, and I look forward to reporting back when the Surf Bug arrives and is installed in my amp. I wasn't aware that you were the designer and builder of the Vibro-Stomp...., from all the reviews and sound clips it certainly looks like an excellent pedal.

    For the record, I do really like the tones I get from the Swamp Thang (much more than the Demeter Tremulator and Fulltone SupaTrem I compared it to), however it doesn't seem to be compatible with my main amp for live gigs.

    Kind regards

    Geoff
     
  8. VintageJon

    VintageJon Member

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    Geoff,
    Yes, it's true- I freely admit to designing and building all the Austone pedals...

    Do let us know when the Surf Bug arrives and is installed. It's the 1st in Oz, to my knowledge...

    Any questions please let me know as COMPLETE support is always gladly given.

    Cheers!
    Jon
     
  9. Scott_F

    Scott_F Gold Supporting Member

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    I just ordered a Surf Bug to put into a AB763 build for a good friend. I look forward to reporting back.
     
  10. Shea

    Shea Member

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    FWIW, I've had good success making tremolo bugs out of a neon bulb and a photoelectric cell I picked up at Radio Shack, enclosed in a piece of shrink tubing. The parts cost less than $5 (but this was about 5 years ago), and they produced a lot stronger tremolo than the stock ones that they replaced. I guess they must get worn out over time.

    Nothing wrong with buying the Surf Bug if you want to make sure it's done right, but just in case someone wants to take a stab at doing it themselves, it can be done pretty easily.

    Shea
     
  11. Shea

    Shea Member

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    Also, if Improviser doesn't like the square, on-off sound of the neon optoisolater tremolo circuit, he might prefer the bias-vary tremolo circuit that was used in the Princeton Reverb and a few other Fenders, like maybe the Vibro Champ. A good tech should be able to convert his VR to that type of tremolo. Some people think it's sweeter sounding, but when I had a Princeton Reverb I thought the tremolo was too weak.

    Shea
     
  12. slider313

    slider313 Silver Supporting Member

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    Try a new set of power tubes. The TAD tubes crunch up a bit too soon for my taste. You may be pushing the signal to a point where the power supply( your tubes) are crapping out( sag). Try a set of JJ 6L6's or Svetlana (winged C) and see if it still happens.
     
  13. VintageJon

    VintageJon Member

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    Scott,
    THANKS, it ships in the morning...

    Best Regards,
    Jon
     
  14. Improviser

    Improviser Supporting Member

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    Thanks for the suggestion Shea. I do already have a pair of original '65 Princeton Reverbs which I use on some gigs, and I definitely do still prefer the tremolo tones from this type of circuit compared to the one in the VR.

    Still, the tremolo sounds - very 3 dimensional - I was getting from the Swamp Thang on lower volumes was almost hypnotic it sounded so good, far superior to either of the original Fender trem circuit tones IMHO.

    I want to improve the inbuilt trem sounds in my amps where possible, but a single great trem pedal that I can get familiar with and can use with my Fenders, Voxes, and Marshalls is probably my ultimate aim there.

    Yeah I've thought about this, and I do have a NOS set of Philips 7851's to go in there. I've switched out all other tubes except for the power tubes so far...

    The Surf Bug arrived quickly and is now installed in my Vibrolux Reverb. The trem sounds are much improved, and there is definitely less signal loss when going from straight sounds to trem sounds in the amp. I'm sure if I like my amps trem sounds as much as some pedals I've tried, but this is definately a cost-effective and very worthwhile improvement over the original Fender part.

    I still have a few other 'bugs' to iron out here, but I have to say to everyone that Jon has been very friendly and helpful with me trying to get to the bottom of my amp's problem. I'll definitely be interested in checking out his other products and services in the future. Thank you.

    Cheers

    Geoff
     
  15. VintageJon

    VintageJon Member

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    Geoff,
    My pleasure, Sir.

    May The Tone Be With You,
    Jon
     

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