Nice review video as per usual, Scott.
It was interesting to note the lack of anything that looked like a DAC. The resistors on each side of the FPGA look suspiciously like R2R ladder networks. It would be interesting to see what a full amplitude 100KHz sine wave looks like in detail at the half and quarter amplitude points.
I suspect your mains power arrangement (auto transformer and a UPS being mentioned) may be the reason why you're not seeing the full half mains live leakage on the BNC shields typical of such small class II smpsus, courtesy of the 1 or 2 nF Ycap that diverts the switching noise leakage between the HT and LV windings directly back to their origin in the direct rectified mains HT supply powering the switching chip in that 5v 3A psu board rather than let it take the scenic route and pollute the local environment. You might want to repeat that test whilst plugged directly into an ordinary mains outlet.
I thought you'd made a rather valid point over taking advantage of the use of an unearthed class II psu to eliminate undesirable earth loops via a noise polluted mains grounding circuit, complete with random DC offsets and switching noise from other smpsu powered kit accompanying the primary 50/60Hz 'hum loop noise' so hated by the audiophool types.
This was also a desirable feature of Feeltech's FY6600 and predecessor models, provided you never forget the "Ground first, unground last" connection sequence to protect susceptible DUTs from this ESD risk posed by that EMC mandated Ycap which curses all such class II smpsus. Happily, there is a simple way to have your cake and eat it in regard of this conflict of requirements and, funnily enough, the solution is a most superb example of a 'compromise' that gives more benefit than deficit. In this case it's as simple as connecting a 1 to 10 K 'static drain' resistor between the C14's PE tag circuit and the 0v rail of the main board.
Assuming a 1nF Ycap and 240v 50Hz mains supply, a 10K 'static drain' resistor will knock this 120v (circa 90vac as seen with a typical DMM) leakage voltage down to a mere 377mVac (1K reduces it to 38mVac). If we assume a BNC cord shield resistance as high as one ohm, with a 'static drain' resistance as low as 1K being used to squash the half live mains leakage down to just 38mV or so, this will still provide some 60dB of attenuation to this unwanted ground loop noise pollution. You land up a winner all round - no ESD risk and no perceivable earth loop issue to contend with.
Incidentally, it's worth pointing out that if you use a typical 5v 3A smpsu wallwart, you'll very likely have exactly the same half mains live voltage issue to contend with even if you've wired that half watt 'static drain' resistor to the PE pin on the C14 socket (unless of course, you've simply switched it off at the back and left it plugged into the mains).
For anyone looking to expand their hobby interest in electronics and unsure about spending yet another three or four hundred quid on a 'mere signal generator' to go with a recently acquired DSO, these toy generators offer remarkably good value for the money. However, it seems these recent models' improvements over Feeltech's infamous FY6600 have been more by way of show than function as exemplified here with that waste of space front rubber 'bumper' that doesn't even look the part (it looks more like a hideous stage set dressing parody rather than the real thing as seen on mainstream brands).
Whilst the improved 'haptics' are a long overdue improvement to the user interface (a keypad to directly enter parameter values), the basic electrical performance specs are none to little better that what Feeltech had been offering in their now two year old FY6600 models (and, in many cases, actually worse!
), so it's good to see these new contenders vying to displace Feeltech's products as the "Go To" cheap signal generator option being held up to close scrutiny like this.
As for myself, after tinkering with my own FY6600 'tinker toy' for the past twenty months, I'm now rather looking forward to taking delivery of a nice shiny new SDG1032X this coming Monday morning
John
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