Zeus35 Power Amplifier

My Original Pair of IRFP150 MOSFET Monoblock Amps - Built in 1995


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 needs to be a lot bigger for high bias implementations e.g. 300 x 250 x 40 mm or 300 x 200 x 84 mm.

  • The heatsink is mounted away from the rear panel with spacers to reduce thermal heating of the inside of the enclosure (M4 washers are sufficient).

  • I use the amps in 4:1 mode for most speakers. 2:1 mode is only suitable for LS3/5As or other "high" impedance speakers.

  • Yes, these amps are still working (without any modifications, updates or adjustments). The only time the top has come off is to take these pictures.

 

Input Transformer Specification

35W Output Transformer Specification


Testing

Test setup

  • Signal generation: HP 8903B > 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 4:1 = 0.25 ohms @ 1 kHz, 0.29 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

Zeus35 2:1 and 4:1 distortion figures

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 Tests (2008)

4:1 Op Tx - 1 kHz sine wave, 8 ohm load.

4 Watt THD @ 1 kHz = 0.0353%

2 Watt THD @ 1 kHz = 0.0254%

1 Watt THD @ 1 kHz = 0.0148%

0.5 Watt THD @ 1 kHz = 0.0154%

Amplifier ON, residual noise and pickup, 8 ohm load.

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


4:1 Op Tx - 2 Watt (nominal), 8 ohm load.

2 Watt THD @ 20 Hz = 0.2594%

2 Watt THD @  50 Hz = 0.0532%

2 Watt THD @ 100 Hz = 0.0295%

2 Watt THD @ 200 Hz = 0.0183%

2 Watt THD @ 500 Hz = 0.0149%

2 Watt THD @ 1 kHz = 0.0185%

2 Watt THD @ 2 kHz = 0.0284%

2 Watt THD @ 5 kHz = 0.0642%

2 Watt THD @ 10 kHz = 0.1358%

2 Watt THD @ 20 kHz = 0.2460%

2 Watt THD @ 50 kHz = 1.735% (HP8903B measurement)

 

FFT Analysis by WINaudioMLS software

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


Design by: Susan Parker, MIET.

The information contained here may be used to construct one system specifically for personal NON commercial use only.

N.B. Personal liability disclaimer applies.


Email: susan@audiophonics.com

All design and other information, drawings and images on this website are
Copyright 1992-2010 Susan Parker MIET (unless otherwise credited).

These designs and other information may be used to construct systems specifically for personal NON commercial use only.

N.B. Personal liability disclaimer applies - see T&C.