https://www.eevblog.com/forum/blog/eevblog-1157-transistor-zener-clamp-circuit/msg2043871/#msg2043871
https://www.eevblog.com/forum/blog/eevblog-1157-transistor-zener-clamp-circuit/msg2037994/#msg2037994
Here are Dr Franks’s posts he made just after Dave released his video discussing the advantage of the double transistor zener type clamp, and that this now would be implemented in 121gw.
Now there’s nothing wrong with Dave’s video as such, I think he does a great job presenting it. But it’s very hard to see how Dr Frank could have made it any clearer that this clamp solution would not work as transients at +/- 25V now could reach U9 the HEF4053. Although it of course depends on exactly how you implemented this new clamp, U9 would have a very hard time handling these voltages. There were also quite a few other members in that thread voicing their concerns.
Still the clamp change went ahead and new HW revision of 121gw released, and it seems it‘s this revision Joe received with the two production meters he recently bought. And anyone following Joe’s videos knows exactly how well this new clamp worked.
Anyway, I guess this also is an example of the (broken) “information age” we now live in, but still it’s things like this that's really frustrating as a 121gw owner, seeing perfectly valid and detailed feedback not really be taking into account.
In case that Dave really has implemented the FLUKE clamp as described in his videos, it's quite obvious, that this would fail.. and I also think that I have explained it reasonably well...but no feedback from Dave so far.
On the other hand, I would have expected that Joe might have re-engineered and analysed the actual protection circuit, either for confirmation or disproof of my findings .. instead he just did his brute-force / destructive tests on the 121GW.
Again, I'm no real friend of these tests, as they do not really comply to the usual test standards, therefore I also do not share his totally negative conclusions in full depth.
His findings about the faulty over-voltage / HV warning indication I fully support.
When I participated on the Kickstarter campaign, I was never expecting to get a fully professional and perfect DMM, so I'm not disappointed at this point in time at all.
I simply call it my 'Dave-O-Meter', so I have to admit that I also bought it, because it's from Dave and it's got the eevblog logo on it.
But in daily use, it's got several very practical and very well working features, like data logging via BT and on battery operation, which the other of my much higher grade DMMs don't have, so I'm really appreciating this instrument.
I've found and reported many bugs on this instrument, so please don't call me a fan-boy, like I also found many bugs as well in the past on professional equipment like the 3458A or the 344465A.
Maybe some guys here shouldn't be too super-critical, because they simply had too high expectancy upfront.
Frank