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: http://www.home-wrecker.com/eatremolo.html

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:

http://www.aronnelson.com/gallery/main.php/v/DRAGONFLY-LAYOUTS_0/album19/album145/EA_TREMOLO_VERO.gif.html

[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: http://diystrat.blogspot.com/2011/05/building-quick-brian-may-style-treble.html).

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: http://diystrat.blogspot.com/2009/06/how-to-wire-up-stomp-box-effects-pedal.html

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.

Enjoy!