Replacing a tube oscillator with a FET.

[Mark]

I would like to free up a triode so I can have more gain on tap to use filtering to eliminate the dreaded tremolo thump experienced by 18 watt amp users.

What are your thoughts on dropping a FET/MOSFET into.

I did post this on the 18 watt site.

http://www.18watt.com/forums/viewtopic. ... ET#p237043

[gingertube]

The Tremlo Oscillator is NOT in the audio path so whether it is tube or SS would make a Rodents Hind Quarters difference.

Some circuit changes would be required to cope with the MOSFET being an enhancement mode device rather than a depletion mode device (needs to be biased ON) but they should be reasonably trivial.

It would be possible to use a JFET/MOSFET cascode in place of the triode but probably easier to do the minor redesign required to use just a MOSFET.

Cheers,
Ian

[Leo_Gnardo]

You could also use a cookbook circuit with a 555 chip, cheap. They are made to be oscillators.

[eniam rognab]

You could also use a cookbook circuit with a 555 chip, cheap. They are made to be oscillators.

ewwww.... 555 timers only send out digital DC pulses, square wave.... LED on, LED off, repeat

i breadboarded a neato analog LFO that has four controls, two of which i think could be trimpots. its the 'upper part' of the schematic for the tremulus lune from tonepad. will make an LED ramp up to full bright, and then dim back down to off, easily incorporated with like an opto-coupler, simple LED butted up against an LDR and heat shrunk several times for stability, maybe draw some inspiration from this as i did

[Leo_Gnardo]

You could also use a cookbook circuit with a 555 chip, cheap. They are made to be oscillators.

ewwww.... 555 timers only send out digital DC pulses, square wave.... LED on, LED off, repeat

Just trying to make an LED blink on & off... and without too much trouble, 1 R and 1 C, can turn that square into a ramp or asymmetrical triangle if necessary. At the other end of the bug, photoresistors ordinarily have a bit of lag time before they change resistance too.

FWIW I've seen plenty of "modern" Fenders where the vibrato sounds weird, clicks on & off in a disconcerting way when depth dialed up past 8. And they're tube-driven, as in RI Twins, Deluxes etc. I'm guessing Fender bought photocells with fast response, oops. Well who can blame them, they must have saved a penny. Aftermarket "bugs" often have this too. That's why I build my own. Late 60's-early70's there was a "chopper" effect like this, some people liked to use. A friend's parents bought a Kimball living room organ with the chop chop feature built in. Never much did like it.

[eniam rognab]

yeah Leo, no disrespect intended, i was thinking you could do something like you described while i was posting, just hadn't experienced it as you had, my experience with 555's was in the educational realm, setting the time/duty cycle, math involved

just thought id share a little dealy that i found

[Long Distance Call]

Hello, first time poster here. Maybe this might work.

http://www.geofex.com/Article_Folders/s ... remolo.htm

[Leo_Gnardo]

yeah Leo, no disrespect intended, i was thinking you could do something like you described while i was posting, just hadn't experienced it as you had, my experience with 555's was in the educational realm, setting the time/duty cycle, math involved

No worries, have a look at your # of posts as you posted that.

Coincidence? Hmmmmmmmmmm.....................

[martin manning]

FWIW I've seen plenty of "modern" Fenders where the vibrato sounds weird, clicks on & off in a disconcerting way when depth dialed up past 8. And they're tube-driven, as in RI Twins, Deluxes etc. I'm guessing Fender bought photocells with fast response, oops. Well who can blame them, they must have saved a penny. Aftermarket "bugs" often have this too.

Could it be that ROHS has forced a change in the composition of the LDR's?

[eniam rognab]

yeah Leo, no disrespect intended, i was thinking you could do something like you described while i was posting, just hadn't experienced it as you had, my experience with 555's was in the educational realm, setting the time/duty cycle, math involved

No worries, have a look at your # of posts as you posted that.

Coincidence? Hmmmmmmmmmm.....................

woah, damn!! ancient aliens? no one said there weren't any aliens........

[ampgeek]

Welcome to the fun LDC. Great little link in a well timed thread for me. Thanks for posting that up!

Cheers,
Dave O.

[Leo_Gnardo]

FWIW I've seen plenty of "modern" Fenders where the vibrato sounds weird, clicks on & off in a disconcerting way when depth dialed up past 8. And they're tube-driven, as in RI Twins, Deluxes etc. I'm guessing Fender bought photocells with fast response, oops. Well who can blame them, they must have saved a penny. Aftermarket "bugs" often have this too.

Could it be that ROHS has forced a change in the composition of the LDR's?

Maybe possibly ROHS is their excuse but I get LDR's that act "normal" in a bug. One type from Mouser, or another from CE, meant for Morley pedals. I've used both with LED's too and no chop chop effect.

Fender bean counters chipping away at the bottom line, I expect that's the real reason. Or else they just don't care. Imagine that.

[Masco]

Here's the AC-30CC style trem circuit w/ single FET. Not sure if you want to reconfig to output style trem???

[Structo]

Hello, first time poster here. Maybe this might work.

http://www.geofex.com/Article_Folders/s ... remolo.htm

Welcome LDC, I hope you enjoy it here.

We always need new contributing members here.

[Long Distance Call]

Thanks Ampgeek and Structo for the nice welcome.

I can see this is a friendly and knowledgeable community and I'm looking forward to hopefully adding some more good stuff to the mix.

LDC