Tremolo-matic X by stompboxology

Tremolo-matic X by stompboxology

This circuit is based on a type of tremolo that some Fender amp models. Its operation is very interesting. It splits the signal path into a low pass and high pass routes and alternates crossfading between each. It has a sweet subtle flavor of tremolo.

I had built this circuit years ago making a PCB from scratch with ferric chloride and the drill press. I remember it sounding good. This time I put the circuit into Eagle PCB. Then designed a layout for the box and used this to help position parts before doing the board layout.

The circuit uses four controls: Rate, Depth, Low Pass, and High Pass. I need four knobs along with the switch and LED. Seemed a little much to get into a 1590B enclosure so opted for 1590BB. Here are my were the ideas.

In the end, I went with this design. It was the simplest and easiest to work with. I did really like the design with the larger knobs, I may have to revisit these in the future.

Last I sent the design out to PCBWay.com and had some boards made. Here’s what the final product looked like. If you’re using PCBWay.com keep your boards under 100mm and the price is cheaper! The first design I did for this board was just over and the price jumped. I did a redesign and nudged the pots inward to bring the width of the board down to just under 100mm and the price was $5, such a deal! 

The boards were great quality, as always PCBWay.com does an excellent job.

I did make one mistake that needed a jumper to fix. You can see it in the last image in the group above. I’ll fix this in an update after some more tests.

I milled an enclosure. Along the way, the low pass and high got moved to the right side of the box.

I decided to use some colored knobs for the high pass and low pass controls to make these stand out.

The sound is subtle and sweet. That said there isn’t a wide range of sounds available. I think I will experiment with the filter values and test some more to see about getting more from this design.

The circuit is built around NE571 compander. This is sort of a dual VCA on a 14 pin DIP. This chip was out of production for some time. I bought some years ago and have about 8 or so in my parts bin. Luckily these chips have been put back into production. You can get them in several places. If you’re in Europe the Electric Druid has some here. If you’re in the states they are available at Stompboxparts.com.

If you’re interested in reading the original Stompboxology newsletter check it out here.

Here is a schematic of the circuit.

After some testing and comparison between the original and the new version. I notice the original build has a better sound. Seems the low pass and high, especially, has less range than the first build. This will need some research. There may be another error in my PCB 😱!

The sound of the original gets a very deep tremolo of the bass signal, adding some high pass starts to give a sort of phase shift to the sound. It sounds super sweet!

The new PCB makes for a much nicer build. With all of the pots, and LED mounted to the board, and the off board connections organized at the top and bottom of the PCB makes for a clean build.

Just thinking out loud here, I like the format of the first build but using the landscape arrangement allows for some larger knobs as an option. What do you think?


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