Fender Vibr-O-Dee Mod

[BobW]

Thanks Smitty for posting this! I missed you the last few times visiting Nashville / Cragnackers.

[Smitty]

I miss Tuesdays at Cragnackers.

[cbass]

Cool stuff Thanks for sharing.Would be cool if it was in the fender side to.I just happened to catch this by chance.

[Phazor]

Thanks Smitty. Great contribution and sharing of ideas.

[ic-racer]

Thanks for sharing this. My Fender Super Twin Reverb project started life with a simple OD mod like that you posted. Then it morphed into a full channel switching Dumble Style mod. http://ampgarage.com/forum/viewtopic.php?t=5396&start=0

[Mainetone]

I wanted to thank Smitty for info on the vibro dee mod, I used the info and some trial and error and built a great ods channel in my DR {silverface}, this was long overdue

Anyone have any thoughts on tightening the bass up? I have experimented with tone stack caps and resistors but would like a little tighter bass response.

[Structo]

What caps on the phase inverter do you have feeding the power tubes?

If you have 0.1uF, try .05uF (borrowed from #183)

That has been the best mod for me to reduce overall bass.

If you have 10uF bypass caps, try 5uF where the bass is heavy.
IOW, if the OD is too bassy, try 5uF there on V2.

I use 5uF across the board.

[Mainetone]

Thanks structo,
Yes I have the .1's,

Ill swap them out when I get home,

I left the 25@25's in I did change the resistor value to 2k2 and 3k3 according to a dlite schematic.

I also increased the 16@450v's to 47@450 for the first two b plus supplies,

[da Geezer]

I left the 25@25's in

If the .05 PI couplers doesn't get you all the way there, I'd try reducing those 25's down to 5uf....10uf max

[Smitty]

The amp in the pictures actually has a little different cap value setup in the OD stage. Larger than normal 22nF coupling caps and really small 1uF and 2.2uF cathode bypass caps. About the same amount of bass you'd expect from an OD stage but the effect of the partially bypassed capacitor is a little more exaggerated and extends higher into the upper bass region.

That's part of the Dumble thing. Partially bypassed cathodes. A great area to experiment. I'm a custom tuner at heart so I take the whole amp and the player into consideration when I do a mod. This guy played a Les Paul with very light OD. Has the whole amp working. Old school blues. Sounded really nice.

[Mainetone]

So I ran over to radio shack and got the standard nichicons they stock, I swapped out the 25's on the 1st gain stage for 10ufs, and 4.7uf for the overdrive stage.

Significant change the bass is alot tighter,still not as tight as the tone I hear in my head but better just the same, I also changed the caps feeding the power tubes to .047 this also tightened things up.

Thanks again for the help

[da Geezer]

still not as tight as the tone I hear in my head

Then try even lower (as Smitty said)....on down to 2.2u or 1u

[jelle]

Agreed, that will compensate for the relatively (relative to the modern ODS values) bigger coupling caps. Let us know if you have a hard time locating the caps.

[Mainetone]

Tested the amp at practice last night I play in a working pop,disco, country type band.

It rocks, had a little noise possibly a tube issue or maybe a connection, noise would be there intermittently on both channels {od channel and stock fender channel} it really showed up on the low notes G# was really noisy on the sixth string but overall real nice,

Hoping to work thru this tonight, it will be nice just use a cable from my guitar to the amp and eliminate the pedals in between....lol

[Structo]

It's funny the lengths we will go to, to get the tone we want.

Usually to trim bass or treble.

But if you think about it, most recordings or live performances by pros have the guitar(s) sounding pretty bright in order for them to cut through the mix.

I don't think my clone would cut through very well but that can be easily remedied.