LFO Help...

[swinginguitar]

I'm breadboarding the EA Tremolo.

The preamp part of the circuit works fine. Last nite I added the LFO side, and it's not working. I've cross checked the schematic 3 times and everything seems OK. Any ideas?

I have an LED in place to flash in time with the LFO, but it is not flashing, only (very) dimly lit. When I first power up the circuit, it's brighter (and maybe flashes a couple of times) but very quickly dims down to barely visible (and not flashing). The speed and depth knobs do nothing (slight volume boost at one end of the depth knob).

Any help would be welcomed!

[daverdave]

It's hard to hake any kind of guess to what could be wrong, I'd start by checking the pinouts are correctly orientated for the transistors and that the wiring is right. Then make sure you've hooked up the led correctly.

[R.G.]

I have an LED in place to flash in time with the LFO, but it is not flashing, only (very) dimly lit. When I first power up the circuit, it's brighter (and maybe flashes a couple of times) but very quickly dims down to barely visible (and not flashing). The speed and depth knobs do nothing (slight volume boost at one end of the depth knob).

The problem you're describing is that the LFO has too little gain to sustain oscillation.

This may possibly be caused by it having to drive an LED as well as oscillate. Additional loads like an LED can lower gain. There is no way to tell without looking at exactly what you did.

This is one reason the "Debugging: what to do when it doesn't work" thread that's permanently affixed to the top of the threads list tells you to give us links to the schematic you're working from and to describe in detail any mods or substitutions you made. You might want to read that stickie. It would help us help you. It's much better than us tossing out guesses.

[swinginguitar]

OK - I'll read the sticky again and comply.

It's the GGG Schematic, and the flashing LED mod is published as part of it...a resistor gets changed to accomodate the extra load.

I printed out the published voltages and will check those tonite as well.

Also not sure I have my pot lugs oriented right - guess if they are wrong it would just bne backwards, right? Which lug corresponds to the schematic?


...and I don't have a reverse taper pot for speed and used what I had on hand....does that have a big effect on it?

[newfish]

Reverse taper can be easily got-round.

Use an audio taper pot ("A") - but wire it backwards so that the more you turn, the slower your tremolo effect happens.

If a Reverse Taper can't be found, this is about the easiest way I know of to get the smooth change you want - albeit in the wrong direction.