Tube Tremolo part ?? – Light Bulb

I finally went back to this project after having a light bulb over the head.

I’m not fan of Vactrol for effect, they’re slow beasts and therefore distort a bit what you’re trying to do (triangle has a more squarish type of sound).Beside, they’re expensive (for a component point of view anyway)

On the other hand they offer a nice isolation (no bleedthrough) and are easier to use and design around (switching).

You can also take advantage of that slowness as Buchla does. This is certainly what give them that so distinctive sound. I really like buchla sound but they must be built by millionaires or composed with moon dust to cost so much.

Anyway, back to something more old and rusty : valve !

I found out that biasing the waform lower than Vcc/2 gave a better response. The LRD has more time to discharge, avoiding that “pump effect” at fast rate. Obviously more the speed is fast, less the LRD has time. As I won’t go really fast I can find a compromise. The type of vactrol is also of importance because every references is different in terms of decay and current (see datasheet). Nothing fancy but interesting, I think I finally arrived where I wanted to go.


The tremolo will be really “vintage” and won’t go into ring-modulator-fast-shape because of this very vactrol. Really fast you won’t hear a tremolo at all. I think I’ll put another tube circuit to maximise the use of the transformer. Don’t know what yet (overdrive? 2 stages phaser ? compressor?)

One triode will be used as an ouput buffer because I don’t know how that thing (if it ends up as a real gear) will be connected. And buffers are cool, yes !!!

If you’re wondering why there’s so little real (not that gimmick marketing crap consisting of putting tube in a product to fool people around) tube effects on the market. Here’s the reason why : From my point of view, so much effort and cost for a simple tremolo is a bit vain. You can have a decent tremolo for half the price of this (a Boss tr2 for instance) minus the large space, the transformer, the safety issue of such high voltages, and so on.

For an hobbyist level, it’s fun to build and when you do DIY you know that your money is wated anyway beside you don’t have the requirements that a manufacter have.

Though I’d prefer a full DC coupled circuit I think I’ll continue to play a bit with that idea and mess around, try to find a way to accomodate all these puppies together.For sure I’ll need a low power transformer, 2 relays and obviously….the boring part…a case.

Yes the usual safety rules apply, don’t try to stick your finger in it. I used to put a wood plate when the circuit is on and  no HV is going into the patch cable.

The light is dimmed because it’s bloody hot in here !




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2 responses to “Tube Tremolo part ?? – Light Bulb

  1. Gordon

    I’m not really sure why Vactrols are so expensive, maybe they’re seen as being as specialized part. It is quite easy to make your own with an led and ldr and some sort of lightproof housing. It gives you the opportunity to try different types of ldr and leds.The nsl32 vactrols are quite cheap, but I’ve never tried them in an audio context.

    • yep one can build his own optocoupler but the characteristics are unknown. Although they can be “sort of” find with experimentation.

      It exists some chinese clone of the VTL series. Never tried them but maybe I will.

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