weak fender 'vibrato'...

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by opus, Aug 23, 2006.

  1. opus

    opus Member

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    i've got a SF Bandmaster with a particularly weak 'vibrato' anyone suggestions on how to make it stronger? thanks!
     
  2. brad347

    brad347 Member

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    new vibrato tube or if that doesn't work, a new opto "roach"
     
  3. opus

    opus Member

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    thanks! just did a full retube so... tell me more about this opto 'roach'

    as you may or may not be able to tell i'm not going to be doing the work... :rolleyes:
     
  4. brad347

    brad347 Member

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    was it weak before you did the re-tube? If not, that would be the first place I would start. "Infant mortality" of new tubes is NOT by any means unheard of. I'd swap it with another in the amp or if you have an extra just to be sure.

    The optoisolator "roach" is a component consisting of a neon bulb and a light-dependent resistor (LDR) packaged together in heat-shrink tubing or other such black stuff. You can look at the circuit board and see it... it is the only such component of its type and has four leads coming out of it. Looks kind of 'bug-like,' hence the name.

    Sometimes, they do wear out and start getting weak. I've had to replace two in my amps... generally they seem to have a lifespan of 35-40 years.

    Four solder joints. Easy job. The part itself is getting a little harder to find... Hoffman used to sell them. I think mojo might have them. A lil on the expensive side (like 20-ish bucks). Good luck!
     
  5. opus

    opus Member

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    after taking a look at the tubes, i remembered that only v1, v2, v3 and the power tubes were replaced... that leaves v4 as a possible culprit, which is the phase inverter (?), so v3 should be tremelo? trem was weak before the tube swap, and had also started 'ticking' when it was engaged...
     
  6. brad347

    brad347 Member

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    to a certain degree the ticking is normal. If you're getting a strong ticking then the tube is strong.

    FWIW, I'd recommend putting your cheapest, most microphonic, oldest, and most generally crappy tube in v3. The vibrato tube is for oscillation only and is not in the signal path. You can save your good tubes for v1 v2 and v4 which are the critical positions. This also cuts down on the ticking which is an inherent flaw in the design unfortunately.

    The ticking also indicates that the neon lamp in the opto is pulsing, and therefore it's probably the LDR that is bad. Generally you just replace the whole module.
     
  7. doctorx

    doctorx Member

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    Replace the trem roach. I had to do this on my Quad Reverb and Bandmaster and it fixed it.
     
  8. Blue Strat

    Blue Strat Member

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    Use a "surf bug" trem roach. Vintage Jon on the Fender Forum has these.

    These are much more consistent than stock trem bugs and every one I've tried give deeper trem. They also have less insertion loss so your normal tone is better as well.
     
  9. opus

    opus Member

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    hey, thanks for the advice!
     
  10. doctorx

    doctorx Member

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    I don't want to hurt anyones feelings, but $25 is way too damn much to pay for a lightbulb, a photo resistor, and a 1 inch piece of heatshrink. For that kind of money it would have to be hand delivered by college girls in bikinis.

    Ted Weber has one for $7, it's OPT-1 near the bottom of the page.
     
  11. Blue Strat

    Blue Strat Member

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    Is it too much if it far exceeds the crappy ones out there? Jeez:jo
     
  12. WailinGuy

    WailinGuy Member

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    I've heard of these before. I'm having some trouble understanding how they can have "less insertion loss" though. I assume you mean that, when the bulb is not lit, the photocell has a higher resistance than the ones normally found in Fender trem opto-isololators. So maybe the resistance (with no light) is, say, 20 Megohm instead of 10 Megohm. But the real tone sucker in this type of trem circuit is the 50K-RA intensity pot. This pot is wired so that it presents a 50K load to ground directly on the preamp signal. Even at high or maximum settings of the intensity knob (the wiper is connected to one side of the photocell, the other side of the photocell is grounded) the 10 Meg+ parallel resistance of the dark photocell will hardly matter.

    Or am I missing something here?
     
  13. doctorx

    doctorx Member

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    Agreed, and if you replace that pot with one with a switch you can remove it and the tone sucking with a click, then back in again when you need it. Install that and Teds seven dollar so called "crappy" trem roach (Sorry Mike) and yer in bizness. You can get the pot w/switch from ted for a couple of dollars too.

    Regarding trem roaches, not trying to start a flame war, but do you think Leo paid $25 a pop or its sixties equivalent for trem roaches back in the day? I don't think so. How many thousands, or tens of thousands of Fender amps from the sixties and seventies are out there right now with great sounding tremolos?
     
  14. DGG

    DGG Member

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    I mean VJon actually builds them by hand, tests them under HIGH voltage (typical operating conditions) and makes sure they are up to his standards for thick modulation.

    But, someone who takes the time research, build and test EACH unit isn't worth being paid $25?! You build a superior, high-quality product and yet the public wants it for free? It's an American researched and hand-made product by someone having to pay incredible dues to get that product to the masses and it's still not cheap enough @$25.

    Vintage Jon ought to charge $50 IMO. That's really what those "Surf Bugs" are worth. I've used them myself in my personal amps and installed them in other's amps and they never thought they were getting ripped off for $25 for the part. The smile on their face when they use theat trem lasts for years.
     
  15. DGG

    DGG Member

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    Uh, I've serviced some with lowsy stock trems. It's a reality they do go bad.
     
  16. mbratch

    mbratch Member

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    So, opus, did replacing the opto-coupler fix the weak vibrato?
     
  17. Angle Loss

    Angle Loss Supporting Member

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    I installed one on a friend's BF Bandmaster. It was kinda expensive for a small part, but what an incredible difference it made. The tremelo afterwards sound good and was able to get very deep. I'm considering purchasing one for my '66 Super Reverb. I'd love to hear more discussion of the technical aspects of the classic opto tremelo. I'm enjoying this thread.
     
  18. opus

    opus Member

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    ah, i've just got my amp back from my tech so i've been reluctant to give it up again (i think i just found out what is sounds like when a speaker has broken in :D)

    i'm going to be out of town next week so hopefully he can get it done while i'm gone. i'll post a report when it's done, thanks again for the suggestions!

    i'd like to be doing this stuff myself at some point, i've only soldered speaker leads up to this point. i need a good starter project...
     
  19. brad347

    brad347 Member

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    Build a fuzz face clone! Check out www.generalguitargadgets.com

    Good luck with that tremolo.
     

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