Output Transformer Testing
 
 
  The results of Transformer testing underline herewith are performed under following scenario:

Associated Test Equipments:
Hameg HM-504 50MHz 2CH Oscilloscope
Escort EFG-3210 2MHz Sweep/Function Generator
Tenma 72-960 LCR Meter
Fluke 19 Digital Multi Meter
8 ohms Dummy Load

We take great care to provide the most accurate numbers/figures according to the tolerance of the test equipments.
1) Primary Inductance (Tested at 1KHz and 120Hz) in Henry indicates transformer capability of producing low distortion at low frequency. Higher figure means the better bass response with less distortion.
2) Leakage Inductance causes roll off at high frequency. The lesser figures represent better quality output transformer.
3) Quality Factor figures derive from Total Primary Inductance divided by Leakage Inductance. The higher figures represent high inductance with low leakage. (better quality)
4) Primary Capacitance causes the transformer to resonate at certain frequency and also cause the anomaly frequency response. The lesser figures are better.

 

Fig.1
 

The Frequency Response Testing according to Fig.1 represents the ability of each transformer to perform under real working condition with 70mA unbalanced DC at relatively high power level (18Vp-p output or 5 Watts RMS to 8 ohms load).

 
 

Fig.2
 

The Pulse Behavior (square wave) Testing according to Fig.2 represents the ability of each transformer to response to perfect square waveform. Since square waveform composes of fundamental frequency plus indefinite number of harmonic 2nd, 3rd, 4th, 5th and so on. This test puts transformer to its extreme condition. Output Transformer must handle high number of harmonics at one pulse cycle and will show out its unique characteristic. Good transformers could be observed by smooth waveform with minimal raise/fall time. Good transformers also exhibit less ringing behavior even at high power level.

 
 
*See Frequency Response Graph Click here
 
Model Picture
Brand
Silk Transformer
Model
S-325
Description
3K/20Watts output transformer with EI (M6) Lamination. Although S-325 can not go as high as Tango XE-20S but comparable to U-808. It has smooth waveform response. (No peak, No dip) With its high inductance, S-325 also performs very well in bass region. (see 40Hz waveform that tilt less than U-808)
Primary Impedance (ohm)
3.0K
Secondary Impedance (ohm)
8
Primary DCR (ohm)
197
Primary Inductance (H)
19.6H/16.5H
Leakage Inductance (mH)
2.8mH/7.5mH
Quality Factor (Pi/Li)
7000/2200
Primary Capacitance (nF)
1.15nF/102.9nF
Frequency Response
See Graph Click here
Square Wave Picture
40 Hz
1 KHz
10 KHz
20 KHz
 
Model Picture
Brand
Tango
Model
XE-20S
Description
Universal output transformer with oriented hi-B cut core. With hi-B core, the transformer has lower primary turn (Less copper loss) than U-808 but also lower primary inductance. Excellent High Frequency response that could go above 100KHz but be observed the small ringing waveform.
Primary Impedance (ohm)
3.5K
Secondary Impedance (ohm)
8
Primary DCR (ohm)
114
Primary Inductance (H)
12.2H/10.7H
Leakage Inductance (mH)
6.3mH/13.4mH
Quality Factor (Pi/Li)
1936/798
Primary Capacitance (nF)
1.9nF/154nF
Frequency Response
See Graph Click here
Square Wave Picture
40 Hz
1 KHz
10 KHZ
20KHZ
 
Model Picture
Brand
Tango
Model
U-808
Description
Universal output transformer with EI core. The transformer processes very linear frequency response with smooth waveform. Due to its small core size, it has limited primary inductance compare to other big irons.
Primary Impedance (ohm)
3.5K
Secondary Impedance (ohm)
8
Primary DCR (ohm)
210
Primary Inductance (H)
17.1H/14.8H
Leakage Inductance (mH)
5.7mH/117.8mH
Quality Factor (Pi/Li)
3000/125
Primary Capacitance (nF)
1.4nF/116nF
Frequency Response
See Graph Click here
Square Wave Picture
40 Hz
1 KHz
10 KHz
20 KHz
 
Model Picture
Brand
Audio Note
Model
Trans-152
Description
2.5K non-potted output transformer with M6 EI core. Although it has small primary turn (around 1,800T-1,900T) due to its large core size, TRANS-152 has moderate primary inductance. A dip in frequency response presents at 40KHz. Waveform is on par.
Primary Impedance (ohm)
2.5K
Secondary Impedance (ohm)
4, 8
Primary DCR (ohm)
157
Primary Inductance (H)
13.5H/14.13H
Leakage Inductance (mH)
11.33mH/15.41mH
Quality Factor (Pi/Li)
1,015/916
Primary Capacitance (nF)
1.88nF/133nF
Frequency Response
See Graph Click here
Square Wave Picture
40 Hz
1 KHz
10 KHZ
20KHZ
 
Model Picture
Brand
Golden Tube
Model
SE-40
Description
1.9K SE parallel output transformer extracted from Golden Tube Audio model SE-40. Perform well considering it was mass product in mid range price.
Primary Impedance (ohm)
1.9K
Secondary Impedance (ohm)
8
Primary DCR (ohm)
120
Primary Inductance (H)
8H/10H
Leakage Inductance (mH)
NA
Quality Factor (Pi/Li)
NA
Primary Capacitance (nF)
NA
Frequency Response
See Graph Click here
Square Wave Picture
40 Hz
1 KHz
10 KHz
20 KHz
 
Model Picture
Brand
James
Model
JS-6123HS
Description
Universal output transformer with EI core that performs far behind Tango U-808. Observe the big -12.0dB dip at around 80KHz and bounce up to resonant up to 2.0MHz!
Primary Impedance (ohm)
3.5K
Secondary Impedance (ohm)
8
Primary DCR (ohm)
181
Primary Inductance (H)
12.6H/13.9H
Leakage Inductance (mH)
167mH/NA
Quality Factor (Pi/Li)
75.4/NA
Primary Capacitance (nF)
2.0nF/124nF
Frequency Response
See Graph Click here
Square Wave Picture
40 Hz
1 KHz
10 KHz
20 KHz
 
Model Picture
Brand
Hammond
Model
1628SE
Description
5K output transformer with EI (M6) lamination. It has highest inductance in the group but also has excessive primary DCR of over 400 ohms! (A lot of copper loss) Hammond has 10 to 15KHz frequency dip of -4.0dB! The waveform is anomaly beyond 5.0KHz.
Primary Impedance (ohm)
5K
Secondary Impedance (ohm)
8
Primary DCR (ohm)
439
Primary Inductance (H)
64.5H/40.78H
Leakage Inductance (mH)
28.7mH/40.5mH
Quality Factor (Pi/Li)
2247/1006
Primary Capacitance (nF)
374pF/43.05nF
Frequency Response
Square Wave Picture
40 Hz
1 KHz
10 KHz
20 KHz