There appears to be very little to stabilise the output of this osc, similar osc designs have a lamp or other variable R device ( or sloped knee zener ) to provide a feedback effect to keep the output at a definite magnitude - this is not very well done for this ckt ...
It is quite logical, if you show a signal on trace A and another signal on trace B then select ADD mode, it shows the waveform A+B.
If you do the same with one channel inverted (lets say channel B), you get A+(-B) which is A-B.
Think about what you measure normally with a ground and tip probe, its the voltage difference between them. If instead you use two (ideally x10) probes and only connect the tips, it will also show the voltage difference between them but now your scope is isolated through the probe divider networks.
There is a good explanation here: https://www.youtube.com/watch?v=BHY4o7Iknes
It uses Tek scopes but yours will I'm sure have the same functions.
Brian.
It is more commonly called "add & invert" which are two functions you combine but maybe your scope calls it something different. The only way to be sure is to check in its manual.So I actually need to use the DIFF function of my scope (which is like combining the ADD and INVERT) which measures the difference between the two probes right?
Increasing the transformer voltage or using a low drop-out voltage regulator will give better results than both those circuits.
The output of the two schematics will be identical and yes, a small capacitor across the diodes will help. The interference they create is very unpredictable and may vary even from one diode to the next in the same batch.
Your can get approx 0.3V DC more if you use Schottky rectifiers because of their lower Vf.
An IC LDO will still work better but you can use the capacitor 'multiplier' circuit. It is only an emitter follower current amplifier with the input held 'clean' by the capacitor. You don't need the 1N4007 in the base circuit or the 47K in the emitter if it will be permanently connected to the oscillator, it is only there to drain any leakage in the transistor but the oscillator will do that just as well.
Brian.
Amplitude variation over frequency is normal operation, I think. The ALC loop has little gain, respectively the input voltage will rise when the oscillator current has to be increased to compensate for Q drop.
An additional control amplifier, with proper frequency compensation to keep the loop stable.
The output of the two schematics will be identical and yes, a small capacitor across the diodes will help. The interference they create is very unpredictable and may vary even from one diode to the next in the same batch.
Your can get approx 0.3V DC more if you use Schottky rectifiers because of their lower Vf.
An IC LDO will still work better but you can use the capacitor 'multiplier' circuit. It is only an emitter follower current amplifier with the input held 'clean' by the capacitor. You don't need the 1N4007 in the base circuit or the 47K in the emitter if it will be permanently connected to the oscillator, it is only there to drain any leakage in the transistor but the oscillator will do that just as well.
Brian.
The resistors in some old power supplies were to distribute the voltage more equally when several low PIV diodes were joined in series. If you add them to the present supply it will make matter worse by increasing the 'backward' current from the capacitor to the opposite polarity from the transformer.
You can try the noise reduction shunt but I wouldn't guarantee it will make any difference. All it does is sink a little current through the shunt to drop the peaks of voltage but of course ideally you wouldn't produce peaks in the first place. A more pragmatic solution would be to wire the power source so it's output impedance is a low as possible. Basically, you make the lowest impedance point the ground and wire all the current sources and loads to it. The best place is almost certainly the negative side of the 4700uF capacitor so you would need to move all the connections (in the PSU) so they physically meet at that point. It's called a 'star' ground because all the wires radiate from a central place. Make sure the output negative wire also goes to the same point.
Brian.
Remember that all the current flowing into the capacitor is pulsed, the diodes only conduct when the transformer secondary voltage is higher than the capacitor voltage plus Vf of the diodes, that means it is likely to be anything but a clean sine wave. All the current causes voltage drops in the wiring, even if it only has a few milli-Ohms of resistance so the PSU is 'alive' with signals and voltages everywhere. It follows that where you think there is a clean DC voltage, it probably has several mV of strange waveforms on it. Keeping the ground tied together helps to minimize the voltage drop between them. In particular, consider that a voltage regulator tries to maintain a constant voltage between its output and ground pins so if the ground has signal on it, so will it's output.
The length of wires to the oscillator isn't too important but do remember to add some extra filtering at the oscillator end, at least one large (>10uF) and one ceramic (100nF) in parallel and close to where the power wires arrive.
Brian.
I found what the problem was. You won't believe it. It was a digital clock I had near by. It was causing interference. When I switched this off, the tone was clean even with no capacitors parallel to the rectifier diodes. I also placed the inductor a bit further away from metals.
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