EA Tremolo - No tremolo effect

[MetalUpYerEye]

Ok so i've finally finished my EA Tremolo after it sitting on the shelf for over 2 years. I'm getting a boosted signal (that sounds awesome by the way) but no tremolo effect. I read that you can use this circuit as a booster as well if you shut down Q2 so i'm kind of assuming that is what has happened here.

I used the ROG layout here...
http://www.runoffgroove.com/eatremolo.html
Its on a PCB that was made by a fellow member here, although I don't recall who, but it is nicely made.

I bypassed the volume control completely by putting a jumper in its place and used a BS170 (Q1), J201 (Q2) and a 2n5088 (Q3) for the transistors. Q1 is biased at 5v to the drain. I used a regular green LED for the pulsing LED.

When its turned on the LED stays lit solid and the circuit acts as a booster. I'm not getting any voltage on any of the pins of Q2. I get about 0.7v on the anode of the 22uf cap right before the drain of Q2. It has a sweet boost to it, but no trem! Ya think that 22uf electrolytic could be bad?

[R.G.]

Debugging - What to do when it doesn't work

[Cardboard Tube Samurai]

I had the same problem with my first EAT and it turned out that I either had the wrong FET in the trem circuit or I had it oriented the wrong way so check there

[MetalUpYerEye]

cardboard - I checked the J201 and originally had had it backwards, but it is facing the right direction now and still no sound.

RG - yeah, I need to get voltage measurements for other other two transistors... I kind of assumed that the problem lies with Q2 being that its behaving like it would if you had normally bypassed it...

[R.G.]

... I kind of assumed that the problem lies with ...

Yep. That's where I get myself into trouble. I've done it so often that I finally developed the response that when I realize I'm assuming the problem is -- here-- that I think "I'd better do something more rigorous to avoid losing a day or two chasing the wrong thing." Measuring all the voltages forces you to examine things you would not otherwise think of doing.

I didn't develop that for this forum - it's what I use.

[MetalUpYerEye]

Here's some more voltage readings...

Q1
D-5v
S-3v
G-1v

Q2
D-0v
S-0v
G-0v

Q3
C-0.6v
B-0v
E-0v

I checked all the pinouts for the transistors with the layout and with the schematic and they all look correct. I also noticed that the LED seems to 'tremolo' like it should about 3 times right when power is connected but then it goes solid.

[R.G.]

Q1
D-5v
S-3v
G-1v

Is this a typo? The MOSFET should have the gate about 2V higher than the source.

Q2
D-0v
S-0v
G-0v

That's OK for DC conditions.

Q3
C-0.6v
B-0v
E-0v

This is incorrect. However. it may be a problem with measurements. The base should be higher than 0V, but it is possible that a low-impedance meter would pull it to 0V because of the high value of the 2.2M feedback resistor. If the base was really 0V, the collector would be 9V.

Pull out that 0.47uF cap on the collector. Just open it up. Now does the LED flash more than thrice?


I checked all the pinouts for the transistors with the layout and with the schematic and they all look correct. I also noticed that the LED seems to 'tremolo' like it should about 3 times right when power is connected but then it goes solid.

[MetalUpYerEye]

I finally got a few minutes to sit down with this circuit today... Here's my results...

I tried removing that cap on the collector, but it didn't do me any good so I put it back. I took a small pick-like object and gently worked it in between all of the solder traces to make sure I didn't have any tiny bridges where they weren't supposed to be and then I used my iron to systematically (but carefully!) remelt each solder connection on the board.

I got lucky this time and it worked out for me. In part of the Debugging page it says 'mother nature doesn't lie, but she is a stickler for details,' which is my new debugging mantra.

So everything is working fine now, I just need to add a trem/booster switch for use as a booster pedal and swap my dpdt footswitch for a 3pdt to support my indicator LED.

So... Onto the next... I was thinking the MXR Phase 90 but I want to wait until I get a breadboard before I get into another really involved build. I was also looking at the 'Murder One' sub-mini pentode amp, as if I need another amplifier sitting around...

Can anyone recommend a reverb box? I've been eyeballing the Blackstar HT5 and one of the two things stopping me from buying it is that it doesn't have reverb...