Trembling Satellite tremolo

From the vendor

Trembling Satellite tremolo

Jun 4, 2023 5 min read

The Tremulus Lune is by far the most popular DIY tremolo project, and for good reasons: it's a simple enough circuit that does all you expect from it, and more thanks to the large amount of controls. Unfortunately, the original circuit features an underwhelming input stage, and variations of it fail to address this issue properly.

I've talked about this before with the Pelota 2, which addresses the same issue in its own inspirations. In few words, resistors produce thermal "Johnson" noise, and even if a 220k resistor doesn't give the best input impedance, it still seriously compromises the noise performance. Quoting from there:

Even using 220kΩ resistors for an inverting input stage, already a big compromise in input impedance, the simple follower outperforms that by 6 or 7 times in terms of noise voltage density (the Johnson noise of the 220k resistors widely exceed the input noise of a TL072).

This is why I have modified the input stage of my Tremulus clone to a non-inverting buffer, which is simple enough to do. Mine was originally built according to the Aion version, which you'd think improves the situation by using lower value resistors and buffering the input; but the noise you save from the resistors is added back by the buffer and the result is the same.

Does this matter in practice? I think it does, because it means you can have audible "huffing" from the white noise cyclically being amplified then not, probably more annoying than just constant noise.

While I am at it, it's worth going over some "communication issues" with the Tremulus: the number of controls has sprouted multiple versions with multiple combinations of the full set of controls, with or without the separate "fine" and "coarse" rate controls, which are just an attempt in the original of getting good control from linear pots. Having built one with as many controls as possible (save for a single, rev-log "Rate" pot), I can say from experience that most people don't need these many controls on a tremolo, surely not on the "go-to" DIY tremolo.

Yes, it has two foot-switches and barely fits in a 1590B, more on that later.

It's worth giving credit to the Shoot the Moon for recognizing this issue first and picking the three controls I also consider the most useful: "Rate" and "Depth" obviously, and "Shape" being "Smooth", a continuous variation between triangle and trapezoid LFO. This could have been the end of the story if it offered an improved input stage and maybe an output pull-down resistor. Since it's not, there are a couple of other things worth going over again, such as handling different kinds of LDR and the volume going up at low "Depth" settings.

Schematic

Here's the circuit. Having some experience with its inspiration and its qualities, I didn't change what was already working and focus on the aforementioned issues.

The input stage is non-inverting and with a small amount of gain. A buffer would already be