Implementing a “Y Out” on an Oscilloscope

[gpapag]

Hi all

This thread is an offspring from these two posts.
LM317 experiments and measurements

LM317 experiments and measurements

I don’t find appropriate to divert the discussion away from the LM317 there.

I should have responded to Tony a few days back, but I was carried away the last 4 days by many manual–some unnecessary-, semi and fully automatic measurements from two X-Former (self made) implementations of the Symmetric to single ended idea for the oscilloscope “Y Out”.

I have some very small (30mmx25mmx21mm plus 6mm for connection pins) 220Vac/7.5Vac E-I power (core is 12.5x10mm) transformers bought for experimentation.
The first one was built just to see what comes out by unwinding the 7.5Vac secondary (outer winding) and keeping the primary as is. I name this X-former as “Old”
Then, I built a second one, this time with as many secondary turns as the coil window allowed (primary kept again intact). I name this X-former as “New”
After measuring both, it was found that that the two primaries were not identical.

Measuring apparatus used:
Inductance digital meter: Honeytek H623
Capacitance & Inductance digital meter: Mastech MY6243
Function Generator: Hameg HM8030-3
Bench Multimeter Keithley 175 (with 150MHz (X1) probe
Resistanse Decay Box: General Radio 1434-N plus a single 10X10K General Radio Cylinder.

Attached is the result of manual measurements.
I hope to continue tomorrow.

Regards
George

[wintermute]

Hi George, take as much time as you want, the main thing is that you are enjoying it! Thanks for going to the trouble to do this as well. I'm sure it can be a useful addition to many peoples testing kit, not just mine.

It looks like you have quite a bit of test gear at your disposal!

Tony.

PS. I'm very slow to get things done The PS prototype I'm taking measurements on I first posted the design for over 12 months ago, and only just got around to building

[gpapag]

Now, here is one form of “Case 1” implementation of the “diy Y Out”.

This is implemented by using the diy x-former as the “differential to single ended converter” by connecting one coil of the x-former to the output of oscilloscope’s Ch1 Preamplifier Out and the other coil used as the single ended “diy Y Out”.

My oscilloscope (Hameg HM203-7) has already a “Y Out” . This, although I installed myself, it was actually per manufacturer’s specs and drawings (the pcb had the tracks ready, only the components were missing). It is not a great lie to say (for the economy of the discussion) that this “Y Out” is “manufacturer’s implementation”.

[gpapag]

Having this “Y Out”, it is quite convenient to check how this x-former idea performs and if it degrades the performance of the oscilloscope when it is connected to the Ch1 Preamplifier Out.

So I opened up my oscilloscope and started testing.
The first set of tests had to test for possible degradation of the oscilloscope performance, when the x-former is connected to the Ch1 Preamplifier Out.

In the attached figures you’ll see what configurations were tested.

[gpapag]

These are with the "old" x-former.

First att.:frequency response
Second att.:Intermodulation distortion (60Hz & 7kHz)
Third att.: Noise
Forth att.: Total harmonic distortion

[gpapag]

I forgot to post these figures two post above

[gpapag]

And these are with the "new" x-former.

First att.:frequency response
Second att.:Intermodulation distortion (60Hz & 7kHz)
Third att.: Noise
Forth att.: Total harmonic distortion

It is really late. I hope I'll be here tomorrow.

Regards
George

[wintermute]

Hmmm big difference with the "new" transformer George, at least on the H - L orientation! It looks like it has minimal impact on the performance.

I'm not 100% clear on what you did with the old and new... old you reduced the number of turns on the secondary, and new you increased the number of turns on the secondary? Looking at how fine the wires are it must have taken a while!!

Tony.

[gpapag]

Tony, yes the “new” x-former has more turns on the secondary.
It takes time to wind the coils when I have to count the turns or when I have to wind overlapping sections and take out the leads. This was not the case with these two x-formers. It was an easy job.

The “new” x-former seems to perform better. You will notice this on the following measurements.

[gpapag]

Now, the x-formers are used to feed the R In of the soundcard. Their output is compared again to the original “Y Out”.

Edit: My Sound card is an external "M-Audio Audiophile USB"
All recordings here are 16 bit, 192kHz