vibrato speed not slow enuff

[popoahi]

awhile back I posted a question about my TR vibrato speed not being slow enuff... I think it was tom that told me what to do.
I copied his reply but lost it I was searching the past post but can't find it...

so I need to ask again; my twin reverb vibrato speed can't go any slower and I know it should be able to...
even when I have it turned down all the way it's just not slow enough..
I think tom's reply was that there is a way to check it and then how to make it slower...

it's is almost slow enough but I know it suppose to go a little bit slower and it would be how I like it..
so was there a adjustment I could make or do I need to buy a new part?

thanks, popoahi

[soundguruman]

You have to find out which twin and post the schematic. There's too many different twin circuits.
Yes there is a way to make it slower. You probably have to install a new part. It's not an adjustment...

[Enzo]

The Fender tremolo oscillators all work the same. There are three caps in series from plate to grid on the trem oscillator triode. From the plate they are 0.02uf, 0.01uf, and 0.01uf. I find it easiest to simply raise the two 0.01uf caps to 0.02uf. You can either replace then, or jut put a second 0.01uf in parallel with the existing ones.

You COULD instead raise the resistance of the two 1 meg resistors to ground, but most shops don;t have any resistors over 1 meg, but do have a selection of caps.

[Jazz P Bass]

There is a 'limiting' resistor dirrectly before the Speed control.
Lower that value.
Here is the RI schematic: http://support.fender.com/schematics..._schematic.pdf

And further reading: The Valve Wizard- Tremolo Oscillator

[Enzo]

Um, by removing that series resistor with the speed control, you lower the overall resistance there. Lower resistance means the RC circuits time out faster, which means faster trem.

[Jazz P Bass]

Ooops!

Didn't read all the way through the Valve Wizards explanation.

"The usual approach is to design the oscillator for a frequency that is midway between the highest and lowest desired frequency, then add a series limiting resistor to prevent the total shunt resistance being reduced to zero. Thus the frequency can then be varied both above and below the initial chosen frequency (increasing resistance causes decreasing frequency). It will usually be necessary to experiment with the value of this limiting resistor, in order to get the maximum range without oscillations actually stopping. The oscillator designs found in the classic amps use wildly varying component values, and were almost certainly chosen by experimentation rather than calculation."

Would raising the resistor help at all?

[Enzo]

It might, it wouldn;t hurt anything to experiment. I find on the typical fender that slow is just not slow enough that I have to double those caps in size to get where i want to be. I am not sure raising that one resistor would be enough. I fear if we enlarge it enough to be effective it will the reduce the sweep range of the speed control. If I wanted to do it in the resistors, I don;t think I'd change that one, I'd change the two 1 meg guys. Change them to maybe 2.2M or 3.3M. I have a few of those in stock for the reverb mixing resistor in Fenders.

[popoahi]

posting a schematic for a particular year may be a problem.. when trying to date my amp it was discussed that it could be from 1970 to 1980?? swaying mostly to the 1980 model...
so at this time I wouldn't be able to post the correct one.

but I think it was tom who didn't mention a year but that there could be a adjustment or modification one could do to get it a little more slower?
I cannot find his suggestion again....


thank you

[popoahi]

hi Enzo,

I don't have any schematics for my amp...and I'm not able to do these things myself since I don't know what you are talking about...
I'm not a electronics guy if it was welding then maybe but I'm too much of a novice when it comes to electronics..

so I would tell a amp tech what you suggest and have him do the work...and if you remember when trying to date my amp it was anywhere from a 1970 to a 1980's model,,,, with the 1980 year a stronger case... and I also don't know where to buy a schematics chart... can you tell me where to buy them from?

I just want to slow the vibrato down a little bit more...it just isn't slow enough and I am resisting using a box....

thanks, popoahi

[Enzo]

You or your guy can look on the fender web site for schematics for older amps. You can also look here:
Schematic Heaven. Where All Good Amp & Effect Designs Await Resurrection...

And of course you can come back here and ask.


meanwhile the Fender trem circuit has varied little in the last 50 years. The resistor numbers may change model to model, but the circuit is the same.

ANy competent tech ought to be able to slow down a trem, but if not, tell him to increase the value of the feedback caps in the oscillator stage.

[popoahi]

I have my TR amp on now for at least 20 min. just sitting all hooked up to my guitar and a chorus box.. the reverb is on 7 and the vibrato is all the way down at the slowest possible speed..

there's faint buzzing with a touch of slow vibrato (not slow enuff) but what puzzles me is this heartbeat sound??? sounds like distant indian drums or a heartbeat like- ONE,two, three, four...anyone think this might show me the way to approach slowing down the vibrato speed???

popo

[Enzo]

No, but it suggests turning the speed control on the chorus box to see if the heartbeat changes pace.

[popoahi]

thanks this info you provided is really helpful
aloha, popoahi

[popoahi]

hi Enzo,
yah I thought of the box so I took it out of the circuit.. but it didn't change the sound..
I wonder if everyones TR totally silent when ON and just sitting with the guitar hooked up or is there always a humm or sound and if so what kind of sounds do people have...
lol that would be interesting to see what everyones TR sound like fully warmed up and ON with the guitar hooked up and no effects box inline...???

thanks, popoahi

[Enzo]

Oh, some trems thump some and others might tick. it happens, and when it does we can usually cure it. lead dress being a common fix.