[GRe]

"Phil Allison" wrote in message
...

"GRe"
"Phil Allison"

You need a THD meter to make sense of what matters and what does not.


Input f/V/THD Output THD (600ohm terminated)

1kHz/1.0V/0.075% 0.082%
1kHz/3.6V/0.086% 0.101%

3.6V is the max. output for the audio generator.


** You need to use a much lower frequency.

Transformer non linearity is concentrated at the low end of the audio
band.

I used the function generator HV-output(600ohm) for this test.

Input f/V/THD Output THD (600ohm terminated)

200Hz/10V/0.036% 0.049%
100Hz/10V/0.037% 0.077%
50Hz/10V/0.037% 0.170%
25Hz/10V/0.036% 0.442%

So, per "rough approximation" about 0.4% added distortion at 25Hz/10V.
Scoping the distortionmeter's output it looks like mainly 3H, but
seems quite acceptable to me for that frequency and level.

Can one simply substract THD Out/In numbers to gain THD for the
transformer only?


** To a rough approximation only.

The figures quoted above suggest the tranny is adding almost nothing.

PLUS it is crucial the source impedance be low - like 50 or 100 ohms.

In this case it does'nt seem to make a difference using the function
generator 50ohm or 600ohm output, see below, so I used the latter for
the tests as the max. Vout is about 14V vs. about 7V(unterminated).

At 25Hz/5V/600ohm output, THDout - THDin = 0.307 - 0.034 = 0.273%
At 25Hz/5V/ 50ohm output, THDout - THDin = 0.721 - 0.444 = 0.277%


Easy way is to use one channel of a good hi-fi amplifier to buffer the
output of the generator and drop the impedance to near zero.

Only handy in the living room, not on the bench.

Gio.