The compliment referred to Bob's Distortion Magnifier.
I wanted to thank him for his clever idea that enables sub PPM measurements with reasonably priced equipment rather that multi kilo$ specialized equipment.
I am disappointed that you took it for self praise, that was not the context at all, why did you think so?
The phrase occurs between two sentences about Bob's distortion Magnifier, not even in the section where I mention my planned implementation.
Best wishes
David
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It surely wasn't my intention to use it for self praise; I didn't think much at all. My apologies if that was somehow offensive?
Samuel
Hi David,
Thanks for the clarification. So now if I understand, you will cover 3 or 4 decades with one switch in a 1, 2, 5 sequence. If I'm right this time, sounds like a good plan.
My analyzer tests amps to less than 0.001% to 20kHz and that is THD+N, not just THD. BTW, that is one reason I get concerned about oscillator noise. My 0.0007% residual on THD+N includes distortion from both the oscillator and the analyzer. Also, my 20kHz THD+N is in a 200kHz bandwidth (sometimes commercial analyzers have an 80kHz or so measurement bandwidth when measuring a 20kHz fundamental).
Nevertheless, it is completely understandable that you would like to have the oscillator distortion well below you measurement goal of <0.001%.
Spot frequency THD measurements have always been fine with me for 90% of my amplifier testing. My most-used frequencies are 25Hz, 1kHz and 20kHz.
BTW, depending on how good the phase and amplitude match are over frequency, the DM also can make the oscillator less of a source of system distortion, since with an ideal phase and frequency match the harmonics of the oscillator also get largely canceled out.
Cheers,
Bob
Probably an improvement over two multi-pole switches.
But I doubt it's a problem, as I pointed out, it's basically what old CROs used to do and they are OK at least into the MHz.
I considered this, Glen Kleinschimdt has a reed relay implementation that's looks fine.
But I want to keep this really simple because I think the DIY fraternity would appreciate an economical, uncomplicated but low distortion variable oscillator.
Viktor's oscillator is such value at $52 that any alternative needs to work hard on cost/performance.
Best wishes
David
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You fail to consider that I save a switch and quality rotary switches are one of the most expensive components in the project.
Plus it simplifies the mechanical layout, one less knob, less holes to drill and more compact, simpler front panel.
Not dramatic improvements but should save money and problems, the rotary switches seem to have been the most difficult part of Bob's unit.
And I didn't say I would "use trimmers", I said I would "trim" it, maybe just selected values if I need them in the top decade.
The point is that the one-switch version does have the flexibility to deal with non-idealities optimally, if necessary, and the matrix method does not.
So one-switch is pretty much win-win I think.
Seems unnecessary complexity to me, For one-knob operation I just use one knob.
Best wishes
David
If you use a jfet for the agc, which Victor has demonstrated works really well, you need to trim it for different frequencies as well as the frequency setting components. I think thats 3 wafers at least. Or a lot of relays which get expensive.
You will also need an attenuator and to decide on output impedance. 50 is good because it reduces input nonlinearities but 600 or higher highlights them.
If one switch its close to the little generator from Germany. Taht is still a real value for its cost.
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You will also need an attenuator and to decide on output impedance. 50 is good because it reduces input nonlinearities but 600 or higher highlights them.
If one switch its close to the little generator from Germany. Taht is still a real value for its cost.
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10kHz boards are sensitive to the load. Usually measured 10kHz spectrum without load (only twin T) now looks that:
http://content32-foto.inbox.lv/albums/e/elterra/10kHz/10k310516.jpg
(Scale is properly adjusted at 30kHz)
Regards,
Victor.
Wel I did build Bob's analyzer at the time using a set of his boards. There must have been enough wiring in it to run a nuclear power plant. OK, a small one.
Worked flawlessly of course.
If uncomplicated diy is the target, it's hard to beat a rotary encoder and a flatcable to a PCB. Of course someone has to sell the programmed controller.
Jan
Jan, you are a bit unfair, much of the complexity is because the switches also have to control the analyser.
For just an oscillator it's much simpler and, as I noted above, I think the elimination of a decade multiplier switch will help even more.
And I prefer to avoid a uController, I would hope if anyone does copy my circuit then it should be maintainable indefinitely, no parts that become unobtainable.
One possibility is to provide switch position data lines, then an analyser with relay control could be added as an option, with minimal complication of the basic oscillator.
I was quite pleased to have had this idea, until I realized I had re-invented the Tektronix TM500 series audio analyser.😉
Best wishes
David
Yeah that's true, it added significantly to the complexity.
You can post a uC program code file online for free download. How long do you want to assure spares - 10 years, 20 years? That should be no problem. Where to draw the line?
I am working on an autoranger to put in front of a soundcard analyzer. It has three switchable inputs, over- and under-range indication, auto ranging from -40 to +16dB, range HOLD button, three preset ranges and a display showing levels and att settings.
All that goes from the front panel to the autoranging board is a DIP08 flatcable. My mind shudders by the thought to do that all hard wired - and then the display would be even impossible.
Jan
If you mean trimming the amount of nominally 50% feedback of signal from drain to gate in the JFET agc, I did find that trimming this value to something slightly different than 50% helped in some cases. However, I saw little if any sensitivity of the trim to operating frequency. I don't recall what any frequency-dependent mechanism there is and whether such a mechanism depends on the specifics of the agc-JFET arrangement.
Cheers,
Bob
Richard Marsh pointed out some sensitivity with different settings at 10K and 1k but that was 1000 posts ago or more. It may be more of a function of loop gain and component tolerance.
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For me, a human lifetime, I dislike planned obsolescence😉
Aren't you sick of products or software that don't work because they are not supported by the latest OS version, or the drivers are incompatible, or the company is out of business, or whatever?
I will spare you the rant, suffice to say that my favorite piece of equipment is a Hewlett Packard 11c calculator. 40 years since purchase and it's still perfect... well not quite, it needs new batteries once a decade.
If that's the best solution for your problem then code away.
But a rotary switch does not have to mean lots of wires.
Why not just a PC mounted switch like this?
Best wishes
David
Attachments
I am constantly struck by the number of choices to make in every little detail.
Just on the switches there was that mini-debate on one or two,
PCB mount or wire connections?
If wire connections then capacitors mounted on the switch itself?
What switch circuit for minimum parasitics and noise pick-up?
How to switch with minimum perturbation of the oscillator?
etc, etc.
No wonder Samuel has taken 7 or 8 years and still not quite finished AFAIK.
Best wishes
David
That's the curse of the diy-er. There's no spec other than 'the best I can'. The upshot is it never gets finished - there's always something to improve.
And anything can be improved if you throw enough time at it.😉
Jan
And anything can be improved if you throw enough time at it.😉
Jan