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Note:
The Toshiba 2SK1529 Audio FETs are vertical not lateral MOSFETs,
although VGS is much lower than with other types (e.g. IR and ST) I have
been using which has caused some confusion.
Gate−Source cutoff voltage VGS (OFF) at VDS = 10 V, ID = 0.1 A:
2SK1529 VGS min-max of 0.8 — 2.8 V
compared to:
IRFP150N VGS min-max of 2.0 — 4.0 V, and
STW34NB20 VGS min-max of 3.0 — 5.0 V
A true lateral MOSFET such as the
Exicon ECW20N20
has a VGS min-max of 0.1 — 1.5 V
The distinction is "Gate threshold
voltage is less than 1 volt for lateral parts and over 2 volts for vertical
parts."
(I now have some Exicon 20N16s to test, and will put the results up on
a separate page.)
My thanks to those who have brought this matter to my attention.
P.S. Subsequent testing with the Exicon 20N16s were very disappointing.
They were very prone to parasitic oscillation and even when "tamed" did not
give as good results as the STW34NB20s!
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4:1 Output Transformer Tests
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Test setup
-
Signal generation: E-mu 1212M > TPA6120
-
Amplifier: 1+1:10 Sowter > 2SK1529 > 4:1 75W
Tx
-
Load: 8 ohm
-
Soundcard: E-mu 1212M, balanced XLR cable to
1/4" balanced input.
-
Amplifier Output Impedance = 0.25 ohms @ 1
kHz
Distortion Test at 1kHz into 8 ohms
| V ac |
% THD+N |
Watts |
| 1.52 |
0.0141 |
0.3 |
| 1.92 |
0.0115 |
0.46 |
| 2.00 |
0.0098 |
0.5 |
| 2.28 |
0.0089 |
0.65 |
| 2.56 |
0.0082 |
0.8 |
| 2.71 |
0.0073 |
0.9 |
| 2.87 |
0.0070 |
1.0 |
| 3.04 |
0.0067 |
1.2 |
| 3.41 |
0.0062 |
1.5 |
| 3.61 |
0.0058 |
1.6 |
| 3.83 |
0.0056 |
1.8 |
| 4.05 |
0.0058 |
2.0 |
| 4.29 |
0.0058 |
2.3 |
| 4.55 |
0.0059 |
2.6 |
| 4.82 |
0.0058 |
2.9 |
| 5.01 |
0.0059 |
3.1 |
| 5.41 |
0.0061 |
3.7 |
| 5.72 |
0.0063 |
4.1 |
| 6.06 |
0.0066 |
4.5 |
N.B. 6 V ac is this test setup maximum limit.
Tests: 43 Hz to 96 kHz FFT
1 kHz sine (see TPA graph for comparison of harmonic
structures).
THD+N at 2 watts into 8 ohms = 0.0058%
19 kHz + 20 kHz Intermodulation.
Residual noise for above tests (signal = mute).
TPA6120 Line Driver Comparison Tests
1 kHz sine (see amplifier graph for comparison of
harmonic structures).
TPA6120 THD+N = 0.005%
19 kHz + 20 kHz Intermodulation.
TPA6120 Residual noise for above tests (signal =
mute).
Notes:
These tests were performed "open" on the bench.
It is interesting to compare the harmonic structure of the
TPA6120 Line Driver loop-back only tests with that of the amplifier.
In these and the other tests on this page and elsewhere is
is apparent that the signal source has an appreciable effect on the test
results, for example with the relative levels of the second and third
harmonics.
A valve based source should therefore maintain the valve
quality of the sound, and a solid state source should also retain it's own
signature.
The FFTs results are all produced on scales which are +10 to
-180 dB. The signal floor is discernable below 140 dB and whilst "noisy"
still shows effects and structure. For example in the three amplifier test
graphs the wavy undulation is a function of the FFT sampling aliasing with
50 Hz pickup in the transformers.
2:1
Op Tx:
Intermodulation - 19 kHz + 20 kHz
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80 Hz to 96 kHz FFT
-
Signal generation: E-mu 1212M > TPA6120
-
Amplifier: 1+1:10 Sowter > 2SK1529 > 2:1 75W
Tx
-
Load: 8 ohm
-
Soundcard: E-mu 1212M, balanced XLR cable to
1/4" balanced input.
Test setup
-
Signal generation: HP 8903B > SSM2015 >
Attenuator > OP275 > TPA6120
-
Amplifier: 1+1:10 Sowter > 2SK1529 > 2:1 75W
Tx
-
Load: 8 ohm
-
Soundcard: E-mu 1212M, balanced XLR cable to
1/4" balanced input.
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Test Conditions
- 1.45A Quiescent i.e. 750 mA per 2SK1529 FET
- 3.116 Volts Bias
- Q1 = 832 mV
- Q2 = 836 mV
- Gate resistor = 330R
- -3 dB Bandwidth = 60 kHz
- Load = 8 ohms
- Output impedance = 0.99 ohms @ 1 kHz, 0.95 ohms @ 120 Hz.
- 2 Watt THD+N @ 1 kHz = 0.027%, -71.3 dB
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First FFT results.
1 kHz sine wave, 800 Hz to 96 kHz, 4.11 Vac, 2 Watts into
8 ohms.
-
1kHz peak is at -6db on the graph = 4.11 Vac RMS .
-
1 kHz signal, 4.11 Vac RMS into 8 ohm load = 2 Watts.
-
75 W transformer, 2:1.
-
8 ohm load @ 1 kHz = 8.024 ohms, 3.6 uH on 12 foot
cable.
A series of tests to confirm basic operation of the test setup and put
the above results into context.
E-mu 1212M residual input noise with XLR cable - open
circuit.
Amplifier ON, Input Open Circuit, 8 ohm load.
I guess the stuff up above 30 kHz is the switching power
supplies in the computer and monitor.
Apart for the interference pickup the residual noise is about
the same as the soundcard.
Amplifier OFF, Input Open Circuit, 8 ohm load.
As previous test but with the amplifier power off for
comparison. That pickup above 30 kHz still there.
TPA6120 Line driver output.
This is the output from the TPA6120 headphone amp chip (with
OP275 and SSM2015), source HP 8903B 1 kHz sine wave (peak is at -6 dB on the
graph = 4.11 Vac), direct to the 1212M input.
Amplifier ON, input from TPA6120 nominally zero signal, 8
ohm load..
This is the output from the TPA6120 headphone amp chip, source
HP 8903B 1 kHz sine wave, with attenuator set to minimum. Theoretically no
signal to the amplifier.
PRO EX Version +
64-bit ultra high precision
FFT;
192kHz/24 Bit ASIO support.
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