On 8/12/2015 4:01 AM, wrote:
Update :

https://dl.dropboxusercontent.com/u/29948706/33901.jpg

Now have calibrated distortion in via a matched set of resistors and
an external generator. It measured 0.055 % on its own oscillator. I
had a 10K rom that nd a 10K from the HP generator with 600 ohm output
impedance.

I calibrated, which is to set the level so the needle goes to 100 %
and then you switch the switch.

We found that even moving around the room affected the reading when
we were reading that 0.0055 %. Also, because of my slight (only one
order of magnitude) error, we were measuring 10 KHz, not 1 KHz. Of
course all the filters were off, but I do want to try those filters.

I started to get close to the null frequency with the external
generator. I saw how the response dropped.


THD is a ratio of RMS voltages, so 1.5V vs 3V is 50% THD, not 25%.

Cheers

Phil Hobbs



--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net