Low-distortion Audio-range Oscillator

[dirkwright]

Originally Posted by dennismiller55

I have found on difficult solder that I get good results if I pre-wet my wick with flux. Even if the wick already has flux in it (the flux dries out).

OK. I don't have any flux so I suffered through a painful removal of some parts off of his board. What a mess! I guess I'd better go buy some. I was using Chem-wick, but it may be old.

[dirkwright]

I put Victor's oscillator into Tina just in case I need to make one myself. I'm not sure it's oscillating. I looked up the parts he's using and used something else that's similar, like a high gain PNP transistor BC560C, and the J111 jfet. I don't really understand this circuit, so I am unable to fine tune it. Any help is appreciated.

[davada]

Originally Posted by dirkwright

I put Victor's oscillator into Tina just in case I need to make one myself. I'm not sure it's oscillating. I looked up the parts he's using and used something else that's similar, like a high gain PNP transistor BC560C, and the J111 jfet. I don't really understand this circuit, so I am unable to fine tune it. Any help is appreciated.

If you know how to install parts into LTspice I can send you Jfet models.
I don't use Tina so I can comment on that.

Your loop gain is too low.

David.

[dirkwright]

Originally Posted by davada

If you know how to install parts into LTspice I can send you Jfet models.
I don't use Tina so I can comment on that.

Your loop gain is too low.

David.

Hmmm, thanks. I did notice that I had the power supply set to +/-5V, so I changed that. The J111 jfet is supposed to be the same as the one Victor used. I also copied all of his resistor and capacitor values. How do I increase the loop gain?

[vicnic]

Originally Posted by dirkwright

I put Victor's oscillator into Tina just in case I need to make one myself. I'm not sure it's oscillating. I looked up the parts he's using and used something else that's similar, like a high gain PNP transistor BC560C, and the J111 jfet. I don't really understand this circuit, so I am unable to fine tune it. Any help is appreciated.

Dirk,
1) I see two mistakes in schematic:
R17 must be 120k.
R10 must be 10k + 100ohm.
2) Settling time after swich on is tens of seconds. Simulator must be configured for this, if it possible.
3) Power supply voltage must be +/-15V. With lower voltage, you may not drive JFET properly.

[davada]

Originally Posted by dirkwright

Hmmm, thanks. I did notice that I had the power supply set to +/-5V, so I changed that. The J111 jfet is supposed to be the same as the one Victor used. I also copied all of his resistor and capacitor values. How do I increase the loop gain?

The RDs on matches and that about it.
The Idss is much higher and the capacitance is lower for the 4391.
I'm not sure the the gate is ceter on the j111 as it is with the 4391.

I have the model if you want it.

You can try decreasing R7's value. It's tight for gain adjustment with this oscillator.
Any attempt to increase gain at the output drive will upset the filter.

David.

[dirkwright]

Originally Posted by vicnic

Dirk,
1) I see two mistakes in schematic:
R17 must be 120k.
R10 must be 10k + 100ohm.
2) Settling time after swich on is tens of seconds. Simulator must be configured for this, if it possible.
3) Power supply voltage must be +/-15V. With lower voltage, you may not drive JFET properly.

Thanks!

I have trouble using my software to look at this circuit. I tried the software 'scope but didn't see any output. Since it doesn't have a signal source, I'm at a loss right now to figure out if it's working correctly.

[dirkwright]

Originally Posted by davada

The RDs on matches and that about it.
The Idss is much higher and the capacitance is lower for the 4391.
I'm not sure the the gate is ceter on the j111 as it is with the 4391.

I have the model if you want it.

You can try decreasing R7's value. It's tight for gain adjustment with this oscillator.
Any attempt to increase gain at the output drive will upset the filter.

David.

Thanks for your help.

I'm getting basically no voltage across the jfet. I can't figure out why. There's a tiny negative DC voltage from drain to source, and the gate is at 170mV or thereabouts.

I just need the *.lib file for the jfet, thanks.

[EssB]

You'll have to run a transient analysis for a long time.
When simulating oscillators, I use a current source to inject a few cycles right at start up. this can get it running a lot quicker.

[dirkwright]

Originally Posted by EssB

You'll have to run a transient analysis for a long time.
When simulating oscillators, I use a current source to inject a few cycles right at start up. this can get it running a lot quicker.

Ah! so that's what I do.

Ok, tried that. I got a really ugly looking oscillation. I ran it for both 10 and 20 seconds. Sump'in ain't right.