EA Tremolo problem

[PurpleTheory]

Hey guys,

I took a shot at building ROG's ea tremolo, and I'm not quite sure what I'm am doing wrong. When I plug it in, the signal comes through, but without tremolo. Also, the led seems to be working properly and changes with the rate pot. Here are a few pictures, one of the resistors isn't visible in the pics due to the enormous caps  :lol: Any help at all would be greatly appreciated.

thanks

matt

[Ge_Whiz]

Check thoroughly that you have the JFET the right way round - pinouts vary. Also search this forum for other similar queries.

[Processaurus]

Hi, since your oscillator is working, I would check its path to the jfet (Q2)by putting one of your multimeter (if there's one around) leads on the gate of the jfet and the other on ground.  Turn the rate pot to its slowest, and try the depth knobs at different positions.  If the gate voltage changes over a couple volts along with the LEDs brightness, then problem is either the JFET or  a connection between it and Q1 (the mosfet).  If there's no change in the gate voltage, then the problem is likely in between there and the collector of Q3.  You also might double check the pinout of the jfet and that its oriented correctly.  

The circuit works by the JFET acting as a voltage controlled resistor to change the gain of the amplifier made with Q1, so if its amplifying, and the oscillator is oscillating, then its 90% working, theres just a problem somewhere between the two.  

If this doesn't help, you can better help debugging your tremolo if you take the voltages of the transistors as is described in the sticky at the top of the topics list, "what to do when it doesn't work"

May your trem wobble soon.

[mat]

Hi  

Same problem that I had also. I think the Pablos PCB layout isnt correct on the Q2. Its different than the perfboard layout. Change the source and gate on Q2 and You should be ok  

Great pedal btw      

cheers,
mat

Hey guys,

I took a shot at building ROG's ea tremolo, and I'm not quite sure what I'm am doing wrong. When I plug it in, the signal comes through, but without tremolo. Also, the led seems to be working properly and changes with the rate pot. Here are a few pictures, one of the resistors isn't visible in the pics due to the enormous caps  :lol: Any help at all would be greatly appreciated.

thanks

matt

[PurpleTheory]

I switched the source and gate on Q2 and now it works great!  

Thanks!

matt

[mat]

I switched the source and gate on Q2 and now it works great!  

Thanks!

matt

You are welcome   I'm glad that newbie like me can sometime help other DIYers too  

cheers,
mat

[george79]

another one help please here!!!!!!!!!!!!!!!!!!!!
build this tremolo a and have the following voltages q1 =4.90 3.20 1.32  q2 zero at all  q3 3.45 0.60  0.0

led continous illuminates.and clean sound from the exit without volume working.

any help please???i'm going to hit my head!!!!

this is http://tagboardeffects.blogspot.gr/2012/02/ea-tremolo-modified-rog.html the tremolo.

Thanks

[antonis]

Your Q3 is always ON so something is going wrong with 3 x 1μF caps and/or Rate pot..

This results in Q2 continuosly OFF so there is no tremollo effect..

Mosfet (Q1) seems to be OK (I've never get familarized with all these "nasty" threashold and pinch-off voltages and transconductances e.t.c.) so if you get clean outpout sound without volume control the problem shoud be on your volume pot..

[george79]

thanks for the fast reply Antonis.I will check this and will inform 

[george79]

c7 one of the 1mf caps was in the wrong hole.Now when i turn it on led blinks for 2-3 secs and then steady light!!!

[GGBB]

What happens when you adjust the speed? Turn the speed down to minimum and wait a few seconds.

[george79]

ok!!!everything fine!!!bad capacitor 1mf  

now one last question.rate and depth works great.
with the volume control.counterclockwise it is supposed to decrease all the volume (mute).now its acting little strange like a tone control.turn left and cuts high freq turn right adds mid-high freq.what to do with that?any help please???
Thanks
George

[george79]

bad pot!!!!!!!!!!
solved!!!!!!!!!!!!!!!
i've got tremolooooooooooooooooooooo 

[antonis]

So, you had 3 defective points for 2 malfunctioning stages...

(not really a bad statistic result..)

[Mark Hammer]

A simple and useful mod to the circuit (now that you have it working) is to insert a back-to-back pair of LEDs between the Depth pot and the resistor leading to the input lug of the Depth pot.  This prevents the LFO signal from passing until it reaches the threshold set by the LED.  This changes the shape of the waveform from a purer triangle, to something closer to the outline of a house: walls pointing straight up, sloped roof.  The audible result is a slightly choppier-sounding tremolo.  It is NOT as pronounced a change as some tremolos have when the wave form is changed from triangle to square, but you can hear the difference, and it sounds decent.

Note that, in most instances, these added LEDs will not light up.  Not enough current for that.

[george79]

I will try that.and i want to ask how can i add more speed??change the 1mf caps with something smaller or something else??Thanks everyone for the help!

[Mark Hammer]

Depends how much faster.  Most versions will have a resistor in series with the speed pot to set min resistance (I gather connecting two of those 1uf caps directly to ground is contra-indicated).  If the version you built uses the 2k2 + 25k pot arrangement, then simply drop that resistor down to 1k, if you just want a modest bump in speed.  If you built the 1k+100k pot version, then you don't have much wiggle room.

If you want something more radical than that small resistance adjustment can provide, then yes, I suppose you'll need to drop the value of the three caps.

[george79]

I have the second version.so i have to change the caps from 1mf to 0.47.i need around 15% faster.

[duck_arse]

you can also vary the value of the fixed leg resistor to range adjust. this may prove easier, as you can just tack another across, but check you still get oscillations across the whole rate pot travel.

[george79]

you mean the 10K resistor for the led?yes thats easier i will make some experiments.much easier.
thats the tremolo that i build  http://tagboardeffects.blogspot.gr/2012/02/ea-tremolo-modified-rog.html