Question about an EA Tremelo Clone

[diamonddogs]

Hey, I've recently finished building two EA tremolo clones by the schematic on general guitar gadgets and one of them is working strangely and its got me confused. I was hoping you could help me out.

This is the problem I'm having.  The speed pot of the tremolo is working very strangely. At the lowest and highest ends of the pot the Tremolo does nothing, not only the extremes but like 25% from the top and bottom it does nothing. The 50% in the middle at first looks like it does nothing, but if I leave it a short while it stabilizes and starts giving a nice tremolo, but only for a limited range of speeds.
If i move the pot to one of the extremes and then again to the middle it again takes awhile until the led starts flashing and the effect starts working.

I've checked all the connections and transistors and anything too obvious but I might have missed something.

I really hope you'll have ideas as to what could be that matters.
Thanks alot.

[GibsonGM]

Hi 'dogs,

1) please post a direct link to the schematic if you need help, it makes it quicker to see what circuit you're talking about!

2) offhand, I'd say something is wired wrong.  Esp. in the LFO area.  Need schem, and for you to read the "Debugging" thread at the top of the forum.    Measure your voltages, post them, and give some more info. 
Using a new battery or a power supply?
Is your speed potentiometer the right kind? (log, linear, or whatever it calls for...)
Is the circuit in the box with a stomp switch yet, or do you simply have in/out jacks at this stage?   
Does wiggling wires do anything?  Pressing on the solder pads where the pot wires connect?
You sure transistors are in correctly (check the pinout).  Same if you have any opamps in there.
Does it pass signal (unmodulated) until the LED 'kicks in', or is it dead and only make sound when the LED comes on?

Eventually you/we will figure it out!    Get some voltages posted, do some more detective work til then.

~Mike

[diamonddogs]

Hi, thanks for the replay.
Here is the link to the page on General Guitar Gadgets with the schematic:
http://www.generalguitargadgets.com/content/view/142/26/

Here are the voltages I read off the transistors: (Using a power supply at 9.3v)
Q1
collector = 6.46v
base = 1.37v
emitter = 0.8v

Q2
Drain = 0v
Source = 0v
Gate = Variable (0.02~0.8v)

Q3
Emitter = Variable (1~4V)
Base = 0.58v
Collector = 0v

Q4
Drain = 9.2v
Source = 5.2v
Gate = 3.1v

Everything seems right according to the instructions and the site, except the gate of Q4 which is supposed to be 4v and its 3.1.

About the questions you raised:
- I checked the wiring in the LFO area but couldn't find anything wrong
- I used both a log and a linear speed pot, both acted the same way. The instructions say its supposed to be a reverse log pot, but I couldn't find one, could that be a problem (though I used a linear pot for the other tremolo and it works well).
- The circuit currently has no switch, its wired for testing, with no box.
- Wiggling wires has no special effect.
- The transistors are right, I've tried switching them around.
- I can't tell if the signal passes unmodulated since I don't have a switch yet.

It seems to me as if something is wrong in the LFO area but I can't tell what. I've checked the connections and tried replacing some parts I thought were no good, but the problem persists.

I really hope you can help me out.
Thanks.

[diamonddogs]

Hey! I almost fixed it! but it now I have some more questions.

I read in some post about the EA Tremolo that sometimes the flashing LED light drains voltage from the LFO circuit. So, I removed it completely and what do you know, It works!

Problem is, I really want the flashing LED mod, and I don't understand why in one of these effects the flashing LED is problem free and in the other one it ruins the whole thing (as I said, I built two).

So two questions:
1. Could the fact that removing the LED made it work be only a symptom of a different problem?
2. If not, how should I wire the flashing led so that it doesn't ruin the LFO circuit ??

Please give it a second and try to help me out
Thanks again.

[jkokura]

If the exact same circuit worked once, and not the in the second version, then yes it's likely a symptom of another problem.

I can't help you fix the problem without more details, or comparative data, but I can tell you that if it worked once, it should work again.

Have you tried taking all the debugging info down for the two of them and then comparing?

jacob

[diamonddogs]

Hey, it just so happens that I just tested the other effect again and turns out it has the a similar problem.
Again removing the LED makes it work great.
And what makes it work even better is connecting it to a 12V power supply.

Then the questions remains, is there another way to wire the LED so it doesn't drain voltage from the LFO circuit?
(or perhaps there is some other problem?)

If you need more details tell me which I will happily post time (Theres a link the the schematic and voltage readings two posts back)

Thanks again

[ppatchmods]

http://www.generalguitargadgets.com/pdf/ggg_eat_mods.pdf

here are a couple of ways to wire it