I'm having some trouble with R.G. Keene's Quick N Dirty Test Oscillator

[RedHouse]

R.G. Says:
There are several conventions about drawing schematics and which wires connect when they cross. I've had to use several of them, so sometimes I get them mixed up.

Indeed there are- but right wrong or otherwise i suppose it is my fault for misinterpreting or misreading the schematic.  After all, you are one of the long-bearded wise elders seated atop the misty mountain, and I am but the humble neophyte votary.

A brilliant man, but (with all due respect) his schematics are often less than.

IMHO, a connection should ALWAYS have a dot, no matter what a non-connection has. When I first saw that schem I thought "bloody hell man, what are you thinkin?" (in a respectful kind of way, of course)

Years ago when I first found RG's geofex site, most anything I was interested in, I had to download and redraw/edit the schems to make them easily readable according to normal standards.

[phaeton]

Simpler to use an LC oscillator, like Thomas did in the US Vox amplifiers. LC oscillators are what was used in organs before digital generation. That's better and will do OK over moderate periods of time, like years.

Cool... LC Oscillators... something else to read up on.  I *do* fantasize occasionally about building various musical instruments out of oscillators.  You probably just saved me a ton of frustration, R.G.... 

I'll have to double check that Forrest Mimms III book i've got buried in the closet.  It has some cheezy 12-note organ in it that might be LC oscillators.  (it's got a few oscillator circuits, but I didn't feel like digging around in my closet to find it, and I like R.G. a bunch)....

Buying up a ton of crystals might be overkill.

[phaeton]

Don't put a whole lot of effort into using this thing as a tuner. It will probably drift too much, a problem common to all RC oscillators.

Do you mean drift around while you're using it as a result of temperature, or do you mean that all things kept the same (incl. temp) a 440 oscillator might do 684 after a few years?  What changes to cause the drift?

LC Oscillators-  capacitors and coils of wire.... can you still buy inductors, and what sets the pitch- capacitor, inductor, or both?

[R.G.]

Yes, both. Resistors typically drift around in value with temperature and age more than caps and inductors, plus there's the sharpness of the resonance that is a problem.

Imagine this: you're trying to point to a place on a line. That line represents the frequency you're going to oscillate at. If the line is ten miles long, pointing with a pencil eraser is pretty good. Although the eraser is not even nearly as small as a true point, the relative smallness of the eraser to the entire line is so good that using a true needle point for the selection wouldn't make much difference. However, if the line is only two inches long, a pencil eraser is a terribly clumsy and inaccurate tool for marking a place on it.

A resistor/capacitor resonance "points" to a frequency. So does an inductor/capacitor resonance. However, the RC resonance has a low Q; that means it's not a very sharp point. Tiny, tiny differences in things can easily pull the resonance around in the uncertainty region. An LC resonance can be much sharper, like using a needle instead of a pencil eraser. So for the same disturbance, the uncertainty region of the needle point is much smaller. The more the L and C are pure reactances, no resistances involved, the sharper the point and the less wandering that the frequency does.

A crystal is literally a crystal of some piezoelectric material. Piezoelectric crystals change shape with applied voltage, and generate voltage when changing shape. They are also have very poor mechanical damping, so they ring when when vibrated. Frequency determining crystals have machined shapes that resonate at highly specific frequencies. The mass/compliance of the crystal itself is a mechanical inductor/capacitor. Such crystals have incredibly high Q (sharpness) and so the frequency inaccuracy is tiny. Since the mass and compliance of the crystal changes very little, they are also quite temperatur stable. And that's why we use crystals.

The frequency of an LC pair is set by both L and C. It's proportional to 1/ the square root of the product of L and C.

[phaeton]

Excellent, excellent advice and descriptions (as always) R.G....

I warned that I would ask this, but how would i situate (filter?) capacitors to remove the ripple that this oscillator puts onto the power rails of the circuit?  Breadboarded, i hear the oscillation coming through the amplifier (albeit faintly) even with no direct input from the oscillator itself, so I assume that the power circuits are doing the transferring. A suggestion of the value of the filter caps would be helpful.   If "filter caps" aren't what I'm after, I'd appreciate some direction.

Also...

Haven't upped the capacitors of the oscillator yet to change frequency.  I have few hours in the day to do what I want to do with myself and "playing with electronics" hasn't come around yet.  I will do that, and I will post my results.

Thanks again...

[Paul Perry (Frostwave)]

Maybe run the power supply via a 220 ohm resistor, and put a 100mF electrolytic from the oscilator end of the resistor to ground.