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Old 5th June 2011, 09:32 PM   #41
gpapag is offline gpapag  Greece
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Quote:
Hi George, I'm still digesting this information (I'm a bit thick sometimes when it comes to electrical circuit theory)
Me too (I mean that I am digesting the information too AND that I am thick too when it comes to electrical circuit theory)

There are two hypotheses made, remaining to be substantiated later by further measurements.
One is that the LF roll off is affected by the (reflected to the) primary impedance and the other is that the 50Hz main’s noise is picked up by the x-formers themselves and not from the interconnects.

For now, some more data
It is from two x-formers that I have salvaged from some recording desk modules I found on the street by the garbage container.
The x-formers are made in 1968 by AUSO. (may be a subsidiary of Siemens in Italy?)
They are shielded externally and incorporate an electrostatic shield btn primary and secondary.
Attached Images
File Type: jpg Picture 013.jpg (389.7 KB, 59 views)
File Type: jpg Picture 002.jpg (363.7 KB, 54 views)
File Type: jpg Picture 003.jpg (403.7 KB, 52 views)
File Type: jpg Picture 009.jpg (407.9 KB, 53 views)
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Old 5th June 2011, 09:57 PM   #42
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Hi George by the reflected impedance, do you mean the inherent impedance of the secondary winding or the impedance of the load attached to that winding?

Tony.
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Old 6th June 2011, 01:09 AM   #43
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Quote:
Originally Posted by wintermute View Post
Hi George by the reflected impedance, do you mean the inherent impedance of the secondary winding or the impedance of the load attached to that winding?

Tony.
Quote:
Tony
Reflected voltage, current, and impedance across a transformer - Semiconductor Technical Support at Texas Instruments

The voltage from the secondary side multiplied by the turns ratio is equal to the reflected voltage on the primary side. The current on the secondary side divided by the turns ratio is equal to the reflected current on the primary side. The impedance on the secondary side divided by the square of the turns ratio is equal to the reflected impedance on the primary side. The turns ratio is equal to the number of primary turns divided by the number of secondary turns of the transformer.
reflected impedance: Definition from Answers.com

I hope that these help. If not, ask again

Sorry for the delay.I was distracted.
Radio was transmitting Enrico Caruso in il Pagliacci . Live recording from 1904 !
Listening to such a tenor, turns the quest for Hi Fidelity sound into a meaningless wandering.

Here is data for AUSO ELA 75-12/8 x-former
Attached Images
File Type: jpg Ch1-H-L.JPG (44.7 KB, 42 views)
File Type: jpg Ch1-L-H.JPG (44.6 KB, 6 views)
File Type: jpg ela 75-12-8 h-l overlays.jpg (156.9 KB, 8 views)
File Type: jpg ela 75-12-8 l-h overlays.jpg (155.2 KB, 7 views)
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Old 6th June 2011, 01:12 AM   #44
gpapag is offline gpapag  Greece
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And here is data for AUSO ELA 75-03/218 x-former
Attached Images
File Type: jpg Ch1-H-L.JPG (44.7 KB, 5 views)
File Type: jpg Ch1-L-H.JPG (44.6 KB, 2 views)
File Type: jpg ela 75-03-218 h-l overlays.jpg (153.5 KB, 6 views)
File Type: jpg ela 75-03-218 l-h overlays.jpg (156.0 KB, 6 views)
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Old 6th June 2011, 01:24 AM   #45
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Oops
I forgot to normalise the numbering on the dB vertical axis.
Here are the same diagrams with the dB axis starting from 0dB on top.

Regards
George
Attached Images
File Type: jpg ela 75-12-8 h-l overlays.jpg (156.4 KB, 8 views)
File Type: jpg ela 75-12-8 l-h overlays.jpg (154.6 KB, 7 views)
File Type: jpg ela 75-03-218 h-l overlays.jpg (153.5 KB, 7 views)
File Type: jpg ela 75-03-218 l-h overlays.jpg (156.0 KB, 9 views)
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Old 6th June 2011, 03:20 AM   #46
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Hi George, very impressive results with the ELA 75-03/218! I think this confirms your suspicion about the transformers themselves picking up the 50Hz as well

Do you know the specs of each of the ELA transformers?? Nice find!!

I understand the reflected impedance now (I think) with a turns ratio of 1:1 the primary should see the same impedance as the secondary, ie the input impedance of the sound card... So I'm still at a bit of a loss as to how this causes the freq response to vary with drive level

Tony.
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Old 10th June 2011, 02:23 PM   #47
gpapag is offline gpapag  Greece
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Quote:
Hi George, very impressive results with the ELA 75-03/218! I think this confirms your suspicion about the transformers themselves picking up the 50Hz as well
Tony, both of these AUSOs perform excellent in terms of main’s noise immunity.
And yes, this confirms my suspicion.

All plots shown are with the inner electrostatic shield and the outer metal screen floating, that is, not connected to Sound card’s common (call it “ground”).
Here you’ll see (att.1) a magnified view of the lowest signal curve. The difference btn. the 3 different configurations is I would say minimal.
I suspected that the good main’s rejection with everything floating was due to some symmetric physical construction of the x-formers innards.

I can not visibly see what’s the internal construction on these x-formers but the capacitance measurements (att.2) can provide some hints.
They are not torroidal. C2=C3 and C4=C5 (on each x-former) if they were .
They are not C-core with bobbins on opposite core legs. There wouldn’t be a need for inner electrostatic shield and C1 would be quite smaller.
The remaining case is that the two coils are wound over the same core leg.
Core may be either E-I or E-E shape.
They are not wound bifilar. C1 is low.
C2 is not equal to C3. Thus the two coils may be not wound on two side by side bobbins on the same leg but on one bobbin. C2 is larger than C3, which shows that H coil is closer to the outer metal screen and L coil is the inner one (this may not be so, if magnetic core is in electrical contact with the outer metal screen.)
[C2-C3] is not large, indicating that coil thickness is small (few wire layers)
C4 is larger than C5, suggesting that inner electrostatic shield is physically closer to H coil (primary) than to L coil (secondary).

Quote:
Do you know the specs of each of the ELA transformers??
In att.3 you will see some measurements for these, tabulated with my other x-formers for comparison.

From these measurements, the leakage inductance measured from the primary side is very different from the leakage inductance measured from the secondary side. This suggests that L (secondary) is wound over the H(primary) on the same bobbin.

A brief look at the Inductance/DC Resistance measurements, leads to the hypothesis that the core material of these x-formers should have a much higher permeability than mine’s.

This is good at first sight but I’ve observed with the scope highly distorted waveforms at frequencies at and below 50Hz, something that does not show in the previously attached curves (they were not meant to show distortion, only Freq.Resp).

Therefore their superiority in LF response compared to the experimental ones is under the lup.
The experimentals do "down slope" earlier, but start distorting lower and more gracefully (with the same 1Vrms applied on all primaries)

Attached are some bad quality screenshots.

Att.4&5 are Primary current waveforms (50R series resistor).
Att. 6&7 are resulting Secondary (//10k) voltage waveforms.

All are at freq. of 20Hz. The distorted ones are from one of AUSOs, the almost sinusoidal are from the bifilar. Sorry for not being precise on this, but now I can’t find my notes with the specific details.

Anyway, this behaviour will be investigated further later on, as it seems to me that this too is one of the reflected impedance effects, which is not such a simple animal as I initially ***umed. I have gathered some data but they need to be organized to be shown. So, this for now

Regards
George
Attached Images
File Type: jpg 1 magn view for shielding effectiveness.jpg (108.5 KB, 7 views)
File Type: jpg 2 ELA Capacitances.JPG (39.8 KB, 10 views)
File Type: jpg 3 Manual Measurements.JPG (79.1 KB, 9 views)
File Type: jpg 4 Picture 014.jpg (417.7 KB, 8 views)
File Type: jpg 5 Picture 022.jpg (446.5 KB, 6 views)
File Type: jpg 6 Picture 011.jpg (384.5 KB, 8 views)
File Type: jpg 7 Picture 008.jpg (354.9 KB, 7 views)
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Last edited by gpapag; 10th June 2011 at 02:37 PM.
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Old 10th June 2011, 07:15 PM   #48
gpapag is offline gpapag  Greece
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Quote:
Anyway, this behaviour will be investigated further later on, as it seems to me that this too is one of the reflected impedance effects, which is not such a simple animal as I initially ***umed.
I noticed the 3 asterisks being placed by the site’s robot that automatically censors the text.

What happened?
I wrote the word “assumed” and no asterisks but I marked the 3 first letters as bold text.
It seems thus that the censoring algorithm interpreted these 3 letters as a separate forbidden word and marked it as such.

Why do I follow-up on this?

Because the “dump” algorithm unintentionally managed to transmit exactly the same message that once in my ex professional career, a wise British auditor had warned me of:

“If you ever allow yourself to assume something without overseeing it or testing it yourself , you become what the 3 first letters of this verb mean”

Although I "got" this harsh message immediately, it took me 2-3 incidents to make me adopt it as a SOP *

Regards
George

*SOP="Standard Operating Procedure" , thanks to Scott Wurser
http://www.diyaudio.com/forums/analo...ml#post2600371
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Last edited by gpapag; 10th June 2011 at 07:21 PM.
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Old 14th June 2011, 10:03 AM   #49
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Hi George, I am starting to understand why it is that "audio quality" transformers are so expensive! It looks like there are many tradeoffs, and you have to pick your tradeoffs wisely. Perhaps there is a holy grail, but I suspect that it is quite a quest to find it

An old boss of mine once told me. " Never assume, if you do it makes an *** out of u and me"

Tony.
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Last edited by wintermute; 14th June 2011 at 10:07 AM.
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Old 14th June 2011, 11:59 AM   #50
gpapag is offline gpapag  Greece
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Hi Tony.
I saw your post just now that I was trying to post mine.
I hope you are doing well.
Now my post

This thread was started in an attempt to help Tony with his noise measurements on PSU.
I started with the idea of using a x-former as an easy implementation of a “differential to single ended” adaptor for bringing out to a sound card what one can probe with an oscilloscope.
I think that it is better to halt the long masochistic investigation on (not so easy as found out implementation of) x-former solution for a while, in order to show to frustrated Tony a not so difficult alternative.

It is an implementation of the classic 3 op.amp. instrumentation amplifier (att.1).

After some basic level simulation trials, I built it using a quad op.amp TL074.
The 6db/oct LF roll-off is due to the combination of Input cap and input shunt resistor.
The cap is needed to block the DC at the input. The input shunt resistor is for referencing each input to system ground. Increasing this resistor’s value I can lower the LF roll-off freq. without increasing the cap value (and size), but I think that I will increase the noise as well. So, 1uF and 47k seems a good compromise.

The HF roll-off is due to gain-bandwidth product of the 2 gain blocks. It goes up as the gain goes down.
R2 to R7 are 10k 5% hand matched to +/-2 Ohm.
R1 sets the gain.

In att.2, you’ll see a table with R1 value/Gain/HF –3db roll off freq.
These are results from simulation using a virtual op. amp model.

After I built it, I tested it with 3 different R1. Results:

R1=200 Ohm
Gain=38.9dB
Bandwidth (-6dB): 2.5Hz-58kHz
Overload (with +/- 15Vdc PSU and 10k output load)
Output: 9.781Vrms
Input: 104.9mVrms

R1=2k166
Gain=20.1dB
Bandwidth (-6dB): 2.5Hz-660kHz
Output: 9.48Vrms
Input: 920mVrms

R1=7k332
Gain=10.74dB
Bandwidth (-6dB): 2.5Hz->2MHz (~2.1MHz)
Output: 7Vrms
Input: 2.5Vrms



The 4th unused op. amp of TL074 can be used as a voltage comparator lighting up a LED when the output reaches 1Vrms (limit of most sound card input). I will figure out how to do it later.
Attached Images
File Type: jpg 1 Basic Diff amp.JPG (34.1 KB, 12 views)
File Type: jpg 2 Actual Diff Amp.JPG (163.7 KB, 17 views)
File Type: jpg 3 Picture 003.jpg (422.0 KB, 21 views)
File Type: jpg 4 Picture 007.jpg (403.7 KB, 19 views)
File Type: jpg 5 Picture 009.jpg (380.1 KB, 14 views)
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Last edited by gpapag; 14th June 2011 at 12:03 PM.
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