At ITTSB Blog all benchmarks and testing of VFD compatible multimeter them they should be made at 50~400Hz bandwidth and at above 100V, so my results them to be close to accurate.
In order to succeed that, I am using my function generator with 7V RMS output and I was driving with it one step-up small transformer.
Due the low driving current of my AWG my experiment this was limited at 98~120V max.
Then I thought to use an small 7W sound amp so this to drive my transformer, I did get somewhat better results but this was using a TBA810S and it input this was easily saturated at about 230mV input.
Then I decide to try another solution, this is a car amplifier, this using two TDA2003 per channel, this supposed to deliver 20W.
With this I got very nice results, and I managed to get 200V output with out saturation.
This this amplifier it can handle around 700mA per channel when this working with 8 Ohm speaker.
My need is to step up voltage and make measurements with out load, but now my DIY AC voltage transformer source, it can deliver and several mA which this is great.
My step up transformer this creates an consumption at the channel of my cars amplifier equal to 40mA, it internal resistance at 50-400Hz this is at 16 Ohm.
Today I am presenting pictures of my experiments, eventually now that I am aware that this setup works well, I will combine all these items in to a single metal box.
I came down experimenting at making such a DIY setup because in the market, similar ready made products them retail over 1000EUR pricing (amp alone).
And also ACV controllable power supply, such items they also come for an exotic pricing.
Therefore I am tremendously happy about succeeding my goal by using parts that I was all ready own. Now few words about this saturation effect at sine-wave.
According to my measurements, my amplifier when this receiving 1V input, it output this is four times more.
At my tests I should drive this amp with 1.4V at 50HZ and with 1.9V at 400Hz so to avoid saturation by retaining my volts output at about 200~210V .
Saturation in the screen of one oscilloscope this is shown as slight flattening of the perfect curve (positive and negative) or peak's of one complete sine waveform.
Input Overdrive this eventually deforms sine-wave further more, and eventually at extreme overdrive this starts looking as this to be a non-perfect square wave. List of problems which occurred to me at my measurements.
My DC power supply this has connection to earth.
My AWG (generator) this has also connection to earth.
My GDS2102A Oscilloscope this has also connection to earth.
The passive probe of my GDS2102A this connected to the output of this amplifier this was causing a shot circuit.
Change of polarity at my cables this did not helped.
And I had to use my active isolated probe for this measurement.
GDS-320 portable oscilloscope this monitors the final output and it does that with out me using it active differential probe option.
If I was in need to operate both of it channels with isolation to its other, then I would be forced using it own active isolation (dual inputs) probe. Final comments
This setup works acceptably well, but output stability this improve as soon the circuitry stabilize regarding temperature and this translating to 10~20 minutes as warm up time.