GGG EA Tremolo... Want to reduce depth.

[cdc3j]

So the sound of this trem is amazing, but I'd like to use an expression pedal to control the depth and leave the circuit on all the time. When the depth is at zero I can still hear the pulse. I tried a lower pot value but had no luck. Can I swap a resistor out for less trem? Which one? Goal is to have the expression heel down and hear no trem, then get a smooth increase to full chop, same as it has now with the depth knob dimed, as the expression pedal is rolled forward. Thanks

[thegnu]

i've been looking for the same thing, and a couple mods are available in this thread, but the schematic is no longer available.  if anyone knows where this schematic is, please tell me.

to increase depth, you have to add a constant current source to one of the transistors.  it must be either Q3 or Q2 in the ggg schematic, because those are the ones coming off the depth knob. i'm pretty sure it's Q3, because all the CCS diagrams look like they're on a BT.  here is what a simple CCS looks like.

my guess is that you (and I) need to put a resistor coming off the grounded leg of Q3, and connect a 9.1v or 12v zener diode to the inside of either R9 or C6.  i own 1N5242B's, which are 12v 0.5W available at mouser.com, and i will try these in the next week or so.  keep in mind, i don't actually know much about electronics, and i purchased these for ESD protection on a mosfet.

also, i'm going to implement the shape mod this guy uses, which he explains:

In the EA Tremolo circuit, the second transistor stage is where the tremolo effect is happening. There is a two resistor network from the emitter to ground, and the LFO connects in the middle of this network. Instead of connecting the second resistor to ground, I connect it to an A100K pot that connects to ground...that's it. In other words, the WAVE control varies the resistance of this second resistor to ground, which is why it adds some distortion as well.

he has to be talking Q1, i think.  Q1 and Q3 are BJTs and have base, collector and emitter.  Q2 and Q4 are FETS and have source, drain, and gate.

anyway, i gotta go.  and i edited this like 3 times, so if there's anything incoherent or contradicting, call me on it, and i'll correct it.  also, i can't remember where i lifted this from but:

I built this and mine's pretty subtle as well.  Mine work's best on clean tones, and distortion washes it out too.  You can make it go choppy if you want, though.  Add a switch to break the connection between Lug 1 of the depth pot and ground.  That will give it a real choppy depth.

choppy depth!

[slacker]

If you look at the schematic you'll see between the depth pot and ground is a 68k resistor, this sets the minimum depth. If you replace this with a jumper then minimum depth will give no tremolo effect.

[cdc3j]

Jumper worked great. I had to reduce the pot size to 50k to get a more gradual transition from off to on, but it's working great now. Thanks for the help. 

[thegnu]

lol, i apparently didn't read your post, because we want opposite things.  i'm glad you got it sorted out, though.