Super simple vactrol construction

12 thoughts on “Super simple vactrol construction”

1. Don H~sig_jam says:

   December 20th, 2007 at 9:39 pm

   Using a 555 as a square wave oscillator is about as aesthetic as flirting with one’s wife at table, to channel Oscar Wilde.
   One alternative is to use an op-amp or comparator. As a starting point, take three equal-valued medium-large resistors, say, 10K for concreteness. Make them into a T-network (I know, I know, a delta network can be topologically equivalent, but bear with me) Connect the common node to the non-inverting input, and attach the three free nodes to, respectively, the top of the supply, the bottom of the supply, and the amplifier output. Construct a timing network out of a series pair RC. Connect the common node to the inverting input, the free C end to supply bottom, and the free R end to amp out. Voila! we are oscillating! This basic configuration lends itself to all kinds of interesting modifications. We can de-symmetrize the output by using steering diodes on one of the timing components. We can FM our new friend by jiggling one of the cross-over thresholds. Et Cetera. This is way more fun, trust me!

2. Collin Mel says:

   December 21st, 2007 at 7:12 am

   Huh, relative to the subject at hand, that sounds a little bit complex, no?

3. Zigs says:

   December 22nd, 2007 at 6:13 pm

   Hah, for real.

4. Don says:

   December 24th, 2007 at 5:25 pm

   Well, yeah, in terms of parts count, maybe. There is a triple string of resistors on a fivefiftyfive, a flipflop and a pair of comparators. It works fine, my point may not even be my own, but an evolution in the ee community. The advantage of an op-amp circuit is that in stocking an op amp, as opposed to a 555, one is carrying a more general part. There is little practical advantage here. The conceit is that every ee should have a unique 555 circuit performing a function undreamt of by the designers of the 555 and use anything but a 555 for an astable, monostable or unistable. The virtue of the circuit I described is that, should one draw it our and simulate it, is that it is really didactic. If one just ‘follows the recipe,’ is he really learning? If one wants to construct an oscillator that is topologically similar to the one I have described, he can use an inverting ‘Schmidt trigger’ circuit and just the timing components. Here’s a link: http://www.fairchildsemi.com/an/AN/AN-118.pdf
   ‘figure 6’ is the relevant circuit.
   A cool thing about the oscillator that I originally described is that if one can figure a way to substitute a current source/sink, he can generate a Zen-like linear ramping triangle wave as opposed to a garden-variety exponential ramp. With this toy, one can make a linear F->V, V->F and its allies.
   Now I am giving away my age! Merry Christmas!
   And remember, THE OP-AMP IS YOUR FRIEND!
   The 555 is just a chip.

5. STEIM Residency 2008 | The Burning Harpsichord says:

   November 9th, 2012 at 11:52 am

   […] to each other. After much experimentation I ended up connecting them via a series of handmade vactrol circuits. These basically consist of an LED taped to a light dependent resistor. When one toy makes […]

6. johny radio says:

   June 10th, 2013 at 7:12 am

   Don on December 24th, 2007 at 5:25 pm said:
   “With this toy, one can make a linear F->V, V->F and its allies.”

   –How!?

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