I suggest you try the BYV28-150 diode instead. mouser.com link
And if you send me one of your AC18V 500mA wall warts, I'll optimize a super snubber for it that completely damps any and all oscillations, even when the MOSFET body diode is used as a rectifier. Wall wart AC transformers typically have enormously more leakage inductance than PCB-mounted or chassis-mounted transformers, so they ring a lot more. Thus they benefit a lot more from a snubber.
How about this idea: I'll buy a wall wart from you and pay the shipping too. You send it to me and I'll test it and optimize the snubber. When I'm done I'll publish the before-and-after results. If you decide you like what you see, you can buy back the wall wart for the same price. I'll ship it back to you. Notice that the cost to you is zero and the financial risk is also zero.
Send me a PM for mailing address etc.
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What value did you use?
Are you using any current mirrors?
As mentioned in an earlier post, small signal cascodes also have a tendency to oscillate at high freqs (50 MHz and above). Ditto Hawksford VAS.
EF3's - See Cordell for a very good expose on how to cure oscillation. I had serious problems on my original Ovation 250 amplifier - you have to use the appropriate techniques to stop the problems.
The cascode uses DN2540s and I added 100R gate stoppers to them. The BF862 gates aren't very accessible but I added 150R in series with the phase lead cap which is 1.5cm or so away over a ground plane and is the only inductive path to that point. The input is decoupled with a tunable RC, but there is still the capacitance of the input wires which presumably could form part of a VHF oscillator.
What's a clam more or less between friends, I always say.
But I do see your point, think I prefer to embark on shell exploration in other exotic locations.
If you are not changing the amplitude of the "noise" noticeably by touching things (just use your finger unless it is high voltage) it is not likely an oscillation. Perhaps it is external interference.
No, yard work is what the Brits do before they plant the roses, Camelias and Magnolias. They just call it 'gardening'.
I've seen several examples of oscillation and demodulation while adjusting this amp already, and the mysterious noise does not resemble that. It doesn't change when I use the 20MHz filter on my scope. It's still possible it could be demodulation, but I've messed with anything that could be acting an an antenna already. The feedback resistor was the last thing I messed with before the noise changed, so if I can't find a problem with my scope, I'll try that.
Can you trigger on it? Is it anything approaching coherent?
Does it go away with the power off?
I can trigger on it, but everything after the trigger point is a big blur. I don't think it's present with the power off but I will check that again.
Well entirely off any topic. Here is a quick snap of my long weekend project. 16 filler panels rough cut, planed, carved ,painted and sanded. Those plus three top rails, three bottom rails. All started as rough cut white oak planks.
Shown is the shortest of the rails for my front porch.
Shown is the shortest of the rails for my front porch.
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When rain gets into the groove on the bottom rail, how does it get out?
My "Good Neighbor Fence" collects water there, and suffers premature dry rot.
My "Good Neighbor Fence" collects water there, and suffers premature dry rot.
When finished there are filler strips and the top surface of the bottom rail is tapered to allow water to run off. The top rail also has a curved top for the same reason. Also has filler strips even on the inside bottom to keep insects out. The glue is epoxy and the clear finish should seal everything. Also is on the east side of the house. The weather comes from the west side. Then it is white oak which is what they used to use to build sailing ships.
Good question though. (Back porch on the west side used Home Depot wood posts. Even painted totally rotted out in 4 years!)
Yes as long as I like the music they can practice here, as they cleaned up quite nicely. (Meaning a bit of the mess more than what was theirs.) I own lots of hearing protectors.
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