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Old 20th Apr 2021, 12:39 pm   #19
David G4EBT
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Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 5,737
Default Re: Buffer Amplifier for Digital Frequency Counter

Quote:
Originally Posted by ortek_service View Post
I wonder if anyone's tried simulating the circuit in the free LTspice ?
- Or maybe the Micro-Cap Simulator software (made available free > 1yr ago for apparently a limited time, but still there), as mentioned recently here: https://www.vintage-radio.net/forum/...56#post1364956 (Where this Preamp circuit also appears)

And you could then try a variety of different loads on it.
A good point - I posted both the information about my long-winded way of using MS PAINT to draw circuits and create PCB artwork and UV masks (post #47), and the link to Micro-Cap in post #49. But there is a steep learning curve in all these things, and with only limited hobby time, the 'law of diminishing returns' soon sets in. That's why I've yet to master KiCad or Micro-Cap, and is what's happening with this little amplifier project. I had all the components to hand, and at first sight it looked a simple little circuit to build, and useful to have, albeit it would be little used.

As to the ground plane, looking back, I don't know what possessed me.

As Lawrence remarked, it's the equivalent of adding capacitors all over the non-grounded pads of the PCB. (I've checked the capacitance per sq cm of the FR4 laminate that I used, and it's 3 pF/sq cm). That said, the second version performs better than the first (maybe because the PCB is smaller?), but as I said earlier, neither of them work above 15 mHz.

The plain fact is that the 'opportunity cost' of spending much more time on this project is the other things that I could otherwise be using my scarce hobby time on, such as restoring a radio. And I mustn't overlook taking up the scarce hobby time of other forum members who have been kind enough to read the thread and to offer their advice and suggestions.

I guess that the 'Dunning Kruger Effect' has set in. I've passed the peak of 'Mount Stupid', not really descended into the 'Valley of Despair, but I'm at the bottom of the 'Slope of Enlightenment' which is long, and has a shallow gradient! As Einstein famously said, 'The more I know, the more I realise how much I don't know". Even a dimwit like me can concur with that observation. I call it 'delusions of adequacy'.

I think the reality is that this little buffer-amp isn't a good design and there's little point in developing it further.

I'm most grateful as ever, for the advice, suggestions and encouragement from everyone.
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