EA Tremolo

[jfrabat]

So, I bought this kit.  I am following these instructions.  Things that are different from the kit is using the dual color LED that the instructions call for, and not using the PCB for the stomp switch, as the connections did not match the ones on the instructions.  The odd thing is that in bypass mode, it is working fine, and when I activate the circuit, the volume works fine, but there is no tremolo effect, regardless of how much I play with the pots (only the volume is working).  Any idea what could be happening here? 

For those who do not want to read the PDF, here's a preview of the main parts that matter:





Other than that, the only real difference is using a Stereo 1/4 Jack and putting the battery ground there.  Here are some pics:

[Mark Hammer]

The essence of the circuit is that the LFO makes the drain-source resistance of a FET get higher and lower, changing the gain of another transistor as it does so.

Being able to do that requires that the LFO feed the right pin of the FET used for gain-variation.  As I like to joke, in complete defiance of mathematical laws, even though a FET only has 3 pins, there are several hundred ways to get the pin orientation "wrong".You probably need to scrounge up a datasheet for the specific 2N5457 you are using.  I certainly can NOT (edit) state unequivocally that this is the case for you, but I have found in past that manufacturer A has the pins for a given FET-number this way and manufacturer B has them different.  So verify that you have the transistors inserted with the right pins in the right sockets.

[GGBB]

Just so as to not ignore the obvious - you don't have the kill switch on do you?

[jfrabat]

I tried flipping the switch.  Notthing.

[duck_arse]

do the leds waggle? can we have some voltages?

[EBK]

 Your jumper on your stomp switch catches my eye.  Check for accidental continuity with the "jumped-over" terminal.

[robthequiet]

I know this won't be a popular suggestion, but I would disconnect  the stomp switch and make sure the circuit is working otherwise.

[cnspedalbuilder]

I know this won't be a popular suggestion, but I would disconnect  the stomp switch and make sure the circuit is working otherwise.

This is a great suggestion. I am pretty sure that Rob saved me from a seemingly hopeless problem with a Phase 45 build--turned out that the circuit worked fine but the switch was bad. To check on the circuit itself, you will need to remove the in and out wires from the PCB and then run wires directly from the PCB to in and out jacks.

[jfrabat]

I'll give it a shot and see whats up...

[Transmogrifox]

If that doesn't work, then desolder the kill switch too.  The symptoms sound a lot like the kill switch being miswired or solder bridged somewhere.  If you can at least narrow it down to that by removing it from the board then it will help you a lot in finding what causes the problem.

[jfrabat]

So just take out the wires leading to the kill switch and leaving them out?  Or do I need to jumper them?

[GGBB]

So just take out the wires leading to the kill switch and leaving them out?  Or do I need to jumper them?

Out. But if you have a meter you could just check to see that the switch actually breaks the connection between A and B (Q3 gate and ground) when off.

[jfrabat]

Well, I took all 4 cables coming out of the switch out of the PCB, and no change.  Still, only the volume pot is actually doing anything.  Ideas?

[robthequiet]

Do you have a meter? I would like to know if there are proper voltages on the transistors and LEDs.

[jfrabat]

Yeah, I do.  Took some readings, and they are WAAAAYYY off.  I do not know what they should be, but I am pretty sure the voltages at Q3 and Q4 are not what they are suppossed to be;  Here are the voltages I have:

Q1: (2N5088)
G: 4.37V
S: 5.55V
D: 9.2V

Q2 (2N5088)
C: 5.34V
B: 1.71V
E: 1.13V

Q3 (2N5088)
G: 180 to 190mV
S: 160 to 176 mV
D: 0V

Q4 (2N5088)
C: 0V
B: 0V
E: 0V

All 4 JFETs and transistors are socketed, so I can replace them (although I do not know how easy to find they will be locally).  Same for the 2 LED's.

[Fndr8875]

i bought that pcb a while ago and IMO they ar a pain in the ass. not a big fan of bi colored leds, and its jumper this and swapp that and disconnect this if you dont want to build it our way. And honestly i think the ROG trem im much easier to etch and build, He seems to use odd value components as well. And like i got a rat as well when i ordered tem, if you want to use a 1590b vs 125bu gotta mount tings on opposive side, if you choose 1590b well good luck getting ato any comonents without disassemblying who pedal as 3pdt is buil in and if you mount it on component side well all ur components and inaccessable. Im not knocking barry, i jus thinnk if im gonna pay for a pcb it should be a strealined process, such as some little know madbean guy haha. I want clear cut instructions and not ten mods all requireing different parts or switches or whatever. to each his own. After disaster tem build i emaled barry  and he gave me a full refund and said keep rat boad. So hes a stand up guy, its just a matter of preferece in wat you want out of prefabbed pcb. I personally and devoting an hour a day to diptrace, sooo tired of abuild go well then one thing @#$%s the who build, such as tow components plaved a hairs width apart. and yes my skills are improving but still have a way to go. Also i want some of those sexy oshPark boards. My main adive is to go slow, when i first started building building and electra dist bored me to death, i dived in deep end say from electa  straight to triple wreck kinda circuits.  I did make a nice euphoria, but id get all excited an 20 min in id be pulling my hair out, so im starting over. gonna use diy lc and diptrace, breadboardthe circuits and then just go with oshpark pcbs from now on. Bellows was first diy lc breadboar, im still not home so i cant test it, if anyone could veryify id love to clean it up and send it off to oshP, prob a speaker cranker 2 in one pedal,such simple circuits buy sound amazing.

[robthequiet]

Yup. Looks like a biasing problem. Before I dig in, is switch SW1B operating properly, is the LED D1 lighting up at all?

[jfrabat]

The switch is a single switch with 2 poles.  But no, the LED's are not lighting up.

[robthequiet]

Do you think that maybe the power is not getting from +9 through R12 and D1 to the collector of Q4?

[jfrabat]

Do you think that maybe the power is not getting from +9 through R12 and D1 to the collector of Q4?

I'll check tonight...  But yeah, I think the fact that Q4 has no voltage has to be the issue.  WHY it has no voltage, I have no clue...