Sunday, April 21, 2013

Building a Modified EA Tremolo Pedal on Veroboard

Good morning, everyone. Who wants to build a tremolo pedal today? Well I know I do.

The original EA Tremolo was published in “Electronics Australia”, an Australian (you don’t say!) electronics magazine, in November 1968 and later proved extremely popular among the DIY community. Since then, several modifications/improvements have been made.

Here’s the one I’ve decided to try:

A description of the circuit can be found here:

Helpfully, a Veroboard layout is already available. This one was laid out by Andrew Carrell, who asks that it not be reposted, so instead I will simply provide a link:

[Note that the flashing LED appears to be wired in the wrong way around in that veroboard layout, so swap its polarity. See comments below for a bit more info.]

As you may be aware, I’m a bit of a fan of Veroboard circuits, since they can be quite easy to build (assuming you choose a fairly basic circuit) and don’t require you to buy or make a specific circuit board for each project (here’s one I did earlier, for example:

I decided to try a few new techniques this time around, which I’ll mention as we go along.

Let’s start with the Veroboard itself. We need a 26 x 9 grid (26 holes x 9 strips), so we cut that out first.

Then we need to cut the tracks in 17 specified places, as shown in Andrew Carrell’s layout. Previously I’ve used a number of different tools to do this, all of which have been a little more time-consuming than I would like, so this time I decided just to drill holes through the board at those specific points:

I was hoping this would help avoid having to check each track to make sure it wasn’t touching the next one near the break, but I found I had to do just as much tidying up as with previous tools. Also, if you drill too many holes close to each other, you’re going to weaken the board (not really a problem in this case, but worth thinking about in future), so I don’t think I’ll be using this method again.

I'd previously laid out all of the components I’m going to be using on a piece of paper. I haven’t really ever done this before, but found it a great way to stay organised and reduce errors.

Note that due to a lack of local availability (story of my life) I had to substitute all three of the transistors for alternatives, as follows:

BS170 - > 2N7000
J201 -> 2N5457
2N5088 -> 2N5089

The components are soldered to the board:

And the wires are added:

Now let’s deal with the enclosure.

I decided to just mark the holes on top of the plastic protector that came on the box.
These are the hole sizes I needed (careful – you might require a different size):

Pots – 7mm
Audio jacks – 9mm
DC-in jack – 12.5mm (I drilled to 12mm then used a taper to enlarge it just a little more)
LEDs – 8mm
Switch – 12mm

Then I punch dents to centre the holes:

The holes are drilled using a stepping drill bit (of course standard drill bits will work too):

And here are the finished holes (I had to remove the back cover to finish the switch hole, since the stepping drill bit was hitting off the back cover):

You’ll notice that I haven’t drilled the LED hole(s) yet, as I wanted to check on a few things before committing to a position.

OK, now we put everything we can in place. You may notice that I’ve not put the DC-in jack in (I decided to move its position and you’ll see it making an appearance later in this post).

I’m laying everything out to get an idea how long I need to make the wires. Some are cut a bit shorter and one or two might even be replaced with a longer wire if necessary.

NOTE: If you need a hand wiring up the switch, jacks, DC-in, etc., have a look here:

Once all the wires are cut and soldered in place, we have this (note the new DC-in jack position and the LEDs):

And here’s how it looks from the top. I haven’t decided how I’m going to finish the enclosure, so it’ll stay like this for the time being.

So what about the hole left by the original DC-in jack position? Well, it turns out I had an old coin lying around (a Spanish one peseta coin) that fitted exactly in the hole. Here it is:

A couple of things I should point out before letting you hear the pedal. Firstly, in the Veroboard layout, there is a note that says: “Vol 2 goes to output”. This is basically the output of the CIRCUIT and should go to the appropriate pin on the stomp switch, not straight to the output jack.

Secondly, the value of the 100k trim pot (TR1) is critical and it must be adjusted slowly and carefully while using the pedal in order to find the sweet spot (my pedal had NO OUTPUT AT ALL until I found the right position, at which point the output was suddenly perfect). Alternatively, you can measure the voltage at Q1 drain, and adjust until it reads between 4.5v and 5v.

There's nothing else to add now, except that here is a demo. You will notice that the yellow pulsing LED (which indicates the speed/rate) is always on once the jack in plugged in. Apart from letting you know the speed/rate, this also serves as a good reminder that you are always using the battery, even though the effect isn't switched on. The steady green LED indicates that the pedal is switched on. The pots are, from left to right, Volume, Speed/Rate and Depth.



Daniel Garcia said...

NIce post, now i want to build one for me. I have just one question: HOw do i adjust the trim? do i need to read some values of the Q1?

stu said...

Hi Daniel. Thanks. There are two ways you can go about this. If you have a multimeter, you can adjust the trim pot until to have a voltage of between 4.5v and 5v at the Q1 drain (in fact it's written in very small print at the bottom of the circuit diagram - I somehow missed it myself until after I'd adjusted the trim pot my own way).

The second way you can do it, and this is a good workaround if you don't have a multimeter, or if the pedal's still not working even though you think you should have 4.5-5v at Q1 drain, is to switch the pedal on and play through it, while slowly adjusting the trim pot. While it is in the wrong position, you will get no output. Once it is in the correct place, the pedal will suddenly work perfectly, so it's pretty easy to determine if you are in the right place.

Daniel Garcia said...

Thank you Stu! i will go for the second option, i have a final question: do you have a offboard wiring diagram? wich did you use? thank you again

stu said...

Hi Daniel. Sorry, I should've added a link to that information. Done now. Let me know if you can't find it or need any more help.

Anonymous said...

Hi thanks for the post!
I tried building the ea trem to your exact specifications except for q3 where i tried using 2N3904 or BC550c instead of the 2N5089.
I get no tremolo at all, clean tone. I went over my wiring according to the vero layout and the schematics and everything seems right. I resoldered everything from scratch and still the same clean tone. Do you have any idea what i could be doing wrong? Can i send you a picture of my vero for advice? Thanks!

stu said...

Man, that must be very frustrating. Sure, send me an email on

Anonymous said...

hi stu, i have the same prob, turns on, just a clean tone coming through. no trem action, even the trem led isnt flashing, i have all the correct components.. any clues where to start looking ?
cheers mick

Anonymous said...

hey i found that taking out the flashing led, the circuit works.. now where do we hook the flashing led up to?

stu said...

Hi mick, I discussed this a bit with the previous commenter and he mentioned that the LED appeared to be wired in the wrong way around in that veroboard image that I linked to. Having had a look at it, I think that he is correct about that (the negative side goes through a resistor to 9v, which wouldn't make sense). I think I remember switching the direction of my LED when it didn't light up initially and just assumed I'd made a mistake. Maybe try wiring it in the other way? Other than that the first thing I would recommend is checking all the wires, especially to the rate pot. You might have a dodgy connection somewhere. Please let me know how you get on.

Anonymous said...

swapped the polarity of the led and kapow! she works... cheers

stu said...

Hey, thanks for reporting back, Mick. I've added a comment in the article about the reversed LED.

Anonymous said...

Hey, great post! Does it matter what kind of capacitance materials I use? What are you using here?

stu said...

I wouldn't worry too much about that. Just make sure you don't mix up the polarised and non-polarised capacitors. The yellow ones I used here were metallized polypropylene film capacitors and the green one was polyester, though you should feel no obligation to do the same.

david tranter said...

Have I missed something - I can't see the stomp switch specified anywhere?

stu said...

Hi David. Have a look here for more info on wiring up the stomp switch, etc:

david said...

Thanks Stu.

Thibaut Voirand said...

Hi Stu!

Your answer to Daniel from 2/5/2013 helped me getting my EATremolo to work, thank you 1000 times!

I built it a week ago, and thought everything was fine. I adjusted my trim pot to have btwn 4,5 and 5 volts at the Q1 drain, but I did not know that I could also switch the pedal on and play through it, while slowly adjusting the trim pot.

I had no idea that the output vanished when the trim pot is on wrong position, this should be written on the building instructions more often ;)

Cheers to you

stu said...

Hey Thibaut,

I'm glad it was of use to you. Enjoy your pedal!

Brian Dill said...

My rate stays the same... I've checked everything. Any clue as to what that could be? Great job btw... Very fun build

stu said...

Hey Brian,

Sorry, didn't notice your comment. Does the LED flashing rate change when you move the pot at all? If not, then I think you're just going to have to check your wires again, sorry. Maybe disconnect the pot and make sure it's working properly with a multimeter. Also, I assume you saw the info about the LED polarity being wrong in the veroboard layout.

stu said...

Actually another thing you might want to try is to take everything out of the box (assuming it's been boxed already) and try it out unboxed, just to rule out anything touching the enclosure and causing a short.

Chazz said...

So I seem to be having a couple problems here… :( firstly, the LED stays a solid color unless the trim POT is turned all the way down, so no flashing at all. I am also unclear of whether or not the second stud of the volume control goes to ground or output...and if it goes to ground, what goes to output? Right now, I am getting a barely audible tone with plenty of noise and no audible tremolo, although my wiring seems to be ok. My thought is I'm messing up some part of grounding or output...any advice? Thanks for posting and answering everyone's questions!!


stu said...

Hi Charlie,

Don't give up! The middle pin of the volume control becomes the circuit output, so it goes to the pin on your stomp switch that is labeled "from circuit output". See the bit about the switch here:

When you say trim pot, are you talking about TR1? If so, don't worry about the LED and concentrate on getting between 4.5v and 5v at the drain leg of Q1. If you're not sure how to measure that let me know. I suspect there may be another issue with the circuit, so just let me know how you get on with the above.

UnitedSound said...

I put one of these together last week and it sound great. Thanks for the info.

Laying out all the components on paper like you did made it a breeze to put together.

One question regarding the trim pot. I didn't measure the voltage but just put it in a spot where it worked. (this was about 11o'clock for me)
Within the small range of the trim pot where the pedal works is there any difference in performance being, for example, closer to 4.5v or closer to 5v. In other words does the value of the trim pot effect the speed (max speed or min speed) of the vibrato? Or, is it just a case of works or doesn't work?

One thing I noticed is that the rate pot seems to do almost nothing from 0 to about 12 o'clock. It's only after 12 that you start to see an increase in the rate.

Thomas Bernard said...

HI Stu, I built the tremolo that you did. With the original transistors (BS170, J201 & 2N5088) and with no battery, only DC jack.
When I switch-on for the trem effect, a big noise's comming (BZZZZ...).. even with Q1's drain (4.5 / 5V). And no trem effect but clean sound..
Do you have an idea of what it could be?
Maybe the DC jack i used is not correct? (DC 9V / 1100mA)

Thanks in advance


stu said...

Hey Thomas,

The buzz could be caused by a number of things, including coming from the power supply itself. I'd try it out with a battery just to check if that solved the problem. It could also be from a bad earth connection, or from inadvertently swapping the two wires coming in from your guitar.

Another thing to watch out for is something on your circuit board or pots/connectors maybe touching the enclosure.

Other than that you really need to go back and check every connection again.

stu said...

Oh and make sure you wired up the DC connector properly (

Seba said...

Hi, thanks for the very useful post!
I'm currently trying to build one, and was wondering if I could use just one LED both for "on/off" and for rate status. I read somewhere that I should break the connection between LED- and Q3. So shall I make it pass through the third lug (I mean: third column, first row) of the 3dpt switch? Sort of "Q3 -> 3dpt -> LED-"?

If I get it, I'll have 3 different connections in that lug of the 3dpt:
- from vol. 2 (output)
- from circuit board (Q3)
- to LED-
Is this it?
Please correct me if I'm wrong, thanks!

stu said...

Hey Seba,

You're welcome.

I think it should probably work, though I'm not sure if you might experience a "clack" noise when you switch from off to on on account of a sudden change of voltage going through the circuit. Best way to find out is to just try it.

As for how to wire up the switch, yes, break it where you said (between Q3 and the LED) and then just use the two pins that are currently being used for the on/off LED. In my case if you look at the photos, you'll see where I connected the resistor coming from the on/off LED and also a black wire to ground (the centre pin). That LED, resistor and black wire would need to be removed, by the way. There are many ways to wire up a stomp switch so I can't say for sure unless I know which way you do it, but if you look at the photo, you can see my method. The 3 different connections on one lug that you mentioned don't sound right though.

P.S. Not sure if you've already seen it already, but this link might help clarify some things:

Seba said...

Thanks for the quick reply and clear explanation Stu!
I believe I've got it, but I'll tell you as soon as I finish it... :)

Just another small doubt about pot wiring: when the scheme says "Volume n. 1" it means the third lug from the left when I'm soldering and watching from inside the pedal (could I say watching bottom-up?), doesn't it?

Thanks again

Seba said...

Hi Stu, eventually i've found some time to finish wiring the pedal but seems like I made something wrong. Could I please send you a pic of my veroboard for advice?

stu said...

Hey Seba, sure thing. My email's in the sixth comment.

Skyler C. said...

Hello Stu! I am very excited to get started on this pedal. I do not have any 250K ohm pots lying around. What would be the outcome of the sound be if the 250K ohm depth knob was replaced with a 100K ohm or 500K ohm pot? (100K and 500K are what I have in my workshop)

Thanks for the help!

Anonymous said...

My pedal only has an audible tremolo effect when the Rate pot is turned all the way up. The LED flasher works but when I turn the rate down the tremolo slows down at first (as it should) and then after about 1/8 of a turn it fades into a clean sound. As I turn the rate pot down the led pulses slower until around 1/8 of a turn and then and then turning the pot any more fades the LED into solid color and a clean sound. The full range of the knobs do not seem to be working. Also I can hear a pulsing thump sound coming out of my amp. Any ideas about what I should do? I did have to use some resistors that were slightly different from the schematic but nothing too big.

Hart C. said...

How might I increase the speed range? What could I change in order to allow the rate pot to allow much slower rates all the way to much faster ones?