Zeus Power Amplifier

Original IRFP150 MOSFET Amp - 1995


4:1 Output, 1 Watt THD+N @ 1 kHz = 0.020%
2:1 Output, 1 Watt THD+N @ 1 kHz = 0.114%
2:1 Output, 2 Watt THD+N @ 1 kHz = 0.231%


Amplifier Schematic (a reminder of the circuit complexity).


Monoblock Amplifier Front View

Top Inside View

Rear View - Note 2:1/4:1 Tx switch (RH side).

General Internal Layout

Audio Path Transformers

Heatsink Mounting on Rear Panel

Notes:

  • The heatsink will need to be at least twice this size for high bias implementations
    i.e. 300 x 150 x 40 mm.

  • The heatsink is mounted away from the rear panel with spacers to reduce thermal heating of the inside of the enclosure.


Testing

Test setup

  • Signal generation: HP 8903B > SSM2015 > Attenuator > OP275 > TPA6120

  • Amplifier: 1+1:10 Sowter > IRFP150 > 4:1 and 2:1 35W Tx

  • Load: 8 ohm

  • Soundcard: E-mu 1212M, balanced XLR cable to 1/4" balanced input.

  • Distortion v. Power = Audio Analyser: HP 8903B

Test Conditions

  • Load = 8 ohms
  • Output impedance = x ohms @ 1 kHz, x ohms @ 120 Hz.

THD+N % Distortion v. Power - 8 ohms

Vac RMS 2:1 Tx - THD+N % 4:1 Tx - THD+N %
1.00 0.123 0.094
1.25 0.109 0.070
1.50 0.096 0.057
1.75 0.089 0.049
2.00 0.088 0.040
2.50 0.099 0.032
2.84 0.118 0.031
3.00 0.128 0.030
4.00 0.224 0.029
5.00 0.369 0.033
6.00 0.512 0.043
7.00 0.598 0.060
8.00 0.646 0.086
9.00 0.665 0.116
10.0 0.669 0.161
11.0 0.664 0.542
12.0 0.652  
13.0 0.637  
14.0 0.620  
15.0 0.605  
16.0 0.588  
17.0 0.620  
18.0 0.744  
19.0 0.944 PSU Supply Limit

 

Note the much lower figures for the 4:1 setting - the trade off is the lower power output.

N.B. These results are similar to but not quite the same as the FFT derived figures.


FFT results


4:1 Tx - 1 kHz sine wave, 800 Hz to 96 kHz, 1 Watt into 8 ohms.

4:1 Output, 1 Watt THD+N @ 1 kHz = 0.020%

1kHz peak is at -9.2db on the graph = 2.84 Vac RMS .

N.B. Compare with TPA6120 Line driver graph.


2:1 Tx - 1 kHz sine wave, 800 Hz to 96 kHz, 1 Watt into 8 ohms.

2:1 Output, 1 Watt THD+N @ 1 kHz = 0.114%

1kHz peak is at -9.2db on the graph = 2.84 Vac RMS .


2:1 Tx - 1 kHz sine wave, 800 Hz to 96 kHz, 2 Watts into 8 ohms.

2:1 Output, 2 Watt THD+N @ 1 kHz = 0.231%

1kHz peak is at -6db on the graph = 4.11 Vac RMS .


Amplifier ON, Input Short Circuit, 8 ohm load.

The noise above 20 kHz is the switching power supplies in the computer and monitor.

Apart for the interference pickup the residual noise is lower than the soundcard o/c (10K input).


E-mu 1212M residual input noise with XLR cable - open circuit (10K imp).


TPA6120 Line driver output.

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.


FFT Analysis by WINaudioMLS software

PRO EX Version + 64-bit ultra high precision FFT; 192kHz/24 Bit ASIO support.


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This page last modified on: 26th November 2004

All information, drawings and images Copyright 1995 - 2004 Susan Parker unless otherwise credited.