R2-D2 mk2, DAC/MC transformer test results

[abbey road d enfer]

Sure, it's made using 0.1 and 0.08mm enamel wire spread on 14 sections summing about 5k turns, all around a permalloy 80 core of about 0.82sqcm.

So a primary would be ca.100 turns and a full sec 2200 turns? I suspect each chamber has about 150 turns of secondary and only about 7 turns of primary?
What's the DC resistance of the secondary?

 

[Dorin Bodea]

What's the DC resistance of the secondary?

It says in the first picture, 630Ω

 

[abbey road d enfer]

View attachment 107933

What equipment do you use to produce these graphs?

 

[Dorin Bodea]

What equipment do you use to produce these graphs?

Analog Discovery from Digilent.

 

[volker]

Sure, it's made using 0.1 and 0.08mm enamel wire spread on 14 sections summing about 5k turns, all around a permalloy 80 core of about 0.82sqcm. I hope this helps and I'm also glad that someone finds my xfmr interesting enough to copy it.

Thanks for sharing. No I'm not going to build one, I have no current need for such a thing. But it's always interesting to study other designs, it's not like there is an abundance of audio transformer concepts online. If it wasn't for CJ and his generous posts it would be a wasteland.

 

[Dorin Bodea]

Thanks for sharing. No I'm not going to build one, I have no current need for such a thing. But it's always interesting to study other designs, it's not like there is an abundance of audio transformer concepts online. If it wasn't for CJ and his generous posts it would be a wasteland.

I thought so...

It is a fascinating domain and it is my belief things can be improved by design and technology, given classic materials like GOSS and permalloy, no need for fancy "metallurgic" snake oil. My approach is based on a couple of decades of experience and perhaps some mixed winding methods and I like a challenge every now and then.

 

[Dorin Bodea]

Just discovered that my Scarlett 2i2 has this behavior in "hard loopback" mode (external cable from OUT to IN), when I measure "THD vs frequency", so the previous measurement of the xfmr gets a lot better

Can anyone confirm this is how 2i2 acts in loopback (I checked, no big difference between Left and Right channel) ? Any workaround?

 

[abbey road d enfer]

Just discovered that my Scarlett 2i2 has this behavior in "hard loopback" mode (external cable from OUT to IN), when I measure "THD vs frequency", so the previous measurement of the xfmr gets a lot better

Can anyone confirm this is how 2i2 acts in loopback (I checked, no big difference between Left and Right channel) ? Any workaround?

How is it level-dependant?
Is it the same if you use a polarity inverter cable?
I had a similar problem with an interface that has a hidden ans un-bypassable analog input limiter.

 

[Dorin Bodea]

How is it level-dependant?
Is it the same if you use a polarity inverter cable?

Level-wise the values change of course but the form of the curve is the same, with that "knee" starting at 2.5kHz
Same with an inverting cable, balanced all 'till now.
Switching to unbalanced, same knee...

 

[Dorin Bodea]

... same "character" in REW

 

[Dorin Bodea]

Switching to a more realistic "Thd+N vs frequency" and using C-message weighting, here is the comparison and the results in direct loop mode and through balanced R2-D2 1:10 xfmr, input adjusted for the same level about 0dBu.
... now, this is just for show, otherwise I know they are very low Thd at any utile frequency

(Tired of fiddling with settings in simple "Thd vs frequency" mode, postponed for now )