EA Tremolo first build debugging

[Dinosaur_Sr]

Hi Guys,

Apologies if this is the wrong place to ask.

I recently bought an EA Trem kit and it's tying my head in knots... Here's the instructions: http://pedalparts.co.uk/wp-content/uploads/2012/06/EAtremelo.pdf
There were a few niggles as my PCB was slightly different to the one highlighted here (also the Transistors appear to be layed out backwards as compared to the other diagrams that I've seen?) and a cap was missing from the kit. Anyway, after assembling it all it didn't work at all, so I set about fiddling and eventually managed to get it to boost the clean signal but no trem or pulsing LED.

I went and ordered a crap-load of parts and I've now installed sockets for the trannies and now have the 5088 in Q3, J201 in Q2 and BS170 in Q1. Now I've got a really weird problem where the LED starts pulsing when I switch it on, but then quickly turns solid, if I short E then the LED pulses again shortly and turns solid. There is still no effect however.

Q1 (BS170)
S = 1.3V
G = 1.8V
D = 4.6V

Q2 (J201)
D = 0
S = 0
G = 0

Q3 (2n5088)
E = 5.9
B = .6V
C = 0V

I'm a completer noob and this is driving me crazy, so many hours spent on this damn thing! One of the other parts must be crapping out but I don't know where to begin and as it's a tiny circuit, and I've soldered it up, I can't go in and start removing parts easily. I'm assuming that my problem is the Q3 collector? Any help would be extremely greatly received.

[Dinosaur_Sr]

I've just been able to get an effect out of it and I noticed that if I move the rate knob then the LED turns solid and the effect stops, I think the pot may be bad so I'm going to stick in a new one and see if that fixes it

[Dinosaur_Sr]

ok, nope! Damn it... It's not the pot (B100K), it seems to work within a certain range and then stops when I go too far in either direction

[B Tremblay]

Try replacing R11 with a slightly higher value resistor, like 1k2.

[GGBB]

This is actually the same circuit as the HomeWrecker/RunOffGroove version (http://www.home-wrecker.com/eatremolo.html) which I've built.  However there is one difference - for some reason they have R8 as 2K2 whereas the ROG specifies 10K.  That's a big difference that would affect the oscillator I think.  Try changing that.  There is also a version without the pulsing LED that uses 15K there and no LED.

[B Tremblay]

Good eyes, Gord!  Yes, change that 2k2 to 10k before trying my fix.

[GGBB]

It might also be something with the 1uF caps C6, C7, C8.  Did you use polar (e.g. aluminum electrolytic or tantalum) or non-polar (e.g. film, ceramic)?  If they are polarized, they need to be oriented the right way for the oscillator to work.  But try R8 first.

[Dinosaur_Sr]

Holy momma! I tried the R8 to 10k and it just stopped the LED from lighting, then I tried R11 to 1k8 (all I had!) and that stopped it from crapping out at the highest rate and but it still died when I moved the rate knob down to 1, so I flipped R8 back to 10K aswell and that's done the business! It works great now, thank you so much guys!

[GGBB]

Holy momma! I tried the R8 to 10k and it just stopped the LED from lighting, then I tried R11 to 1k8 (all I had!) and that stopped it from crapping out at the highest rate and but it still died when I moved the rate knob down to 1, so I flipped R8 back to 10K aswell and that's done the business! It works great now, thank you so much guys!

Awesome!  I used a trimmer (2K would be ideal) instead of R11 and adjusted it by setting the rate pot to max speed and the lowering the trimmer slowly until it stopped tremoloing, then backing off a hair.  Note that I found once you go over the speed limit and it stops tremoloing, you need to back off the rate pot for a moment until its starts again.  I was actually able to get R11 under 1K a little.

[duck_arse]

erm, one thing I've noticed about your voltages is that you have 0V on the collector of q3. either the transistor or your writing down is backwards.

we love the ea tremolo, it gets more questions than any other circuit I can think of. the output of the phase shift oscillator will peak at "a" frequency, and falls off either side of same. oscillation sometimes stops at the low end of the rate pot.

if you are having trouble with the oscillator, you can short the led to see if it works, then worry about the led part.

[Dinosaur_Sr]

Well I did get it working completely and it sounded great, then I went and tried to fit it into an enclosure that was almost too small! I managed to get creative and get everything to fit inside but I managed to create myself a good few hours of trouble and debugging in the process. After a lot of ball-ache I've actually got her going again but I've come across a new issue, if I add it to my pedal board then weird things start happening. First of all it saps the pedal before it making it sound muted, the trem comes through fine but there is a little noise. Does this thing need a separate power supply? I'm using a one-spot but I could dig out another 9v plug from somewhere.

[Dinosaur_Sr]

Ok, never mind! I've just sorted that our too, I think one of my transistors was loose, it seems to be playing nice with the other pedals now... Few! Well, hopefully that's the end of my troubles with this one, on to playing with it! Cheers all