Zeus Line Driver

Front End for Zeus Power Stage - 600 / 150 Ohm

Please see my Audiophonics website for the most recent information on these projects. These pages remain as I transfer and update the contents and will be consolidated to link across to my Audiophonics website.

After further development the final version of the Push-Pull line driver uses VMOS fets and a large gapped core transformer for optimum performance. See:

http://www.audiophonics.com/audiophonics-zeus-line-driver-vmos-pp-1.html


Fig 1. General Line Driver Schematic.


This same transformers (T1 & T2) are used for both the NMOS Line Driver as described here, and the VMOS version. The VMOS Line Driver has the advantage of being auto biased as is possible with a triode implementation.

These transformers are now available direct from Sowter to order online, see Parts for DIY page on my Audiophonics website.


Test Setup

  • Q1, Q2: STP55NE06 mosfets

  • V+ approx 24 volt supply

  • T1 Input Transformer: Gardners 1:2+2

  • T2 Output Transformer: 1+1+1+1 Quad-filar wound, 0.71 mm magnet wire.

  • Rterm: 10K

  • R1, R2: 330R

  • Z1, Z2: 12V

  • 250 mA bias per mosfet.

  • Output configuration to drive: 600 ohm series, 150 ohm parallel.

  • Vbias: STP55NE06 + 2 x Schottky diodes + 10K pot + LM317 current source.

1 kHz THD+N at 2 V rms into 600 ohms = 0.007%


Line Drive Amplifier with Output Transformer

600 ohm balanced input, balanced XLR output to power amplifier.

Potentiometer to adjust Vbias.

Line Driver - 1 kHz FFT (-12dB) - 0.007% THD+N

However note that the actual test system, although at a lower level, has the same THD+N.

 

Soundcard loop-back - 1 kHz FFT - 0.007% THD+N

(Both tests 192 kHz sampling, 1 million point transforms.)


PP v SE THD% Comparison

Zeus Line Driver with same transformers as push-pull but configured as single ended.

Fig 2. General Single Ended Amplifier Schematic.

  • Q1: STP55NE06 mosfet

  • V+ approx 24 volt supply

  • T1 Input Transformer: Gardners 1:2+2

  • T2 Output Transformer: 1+1+1+1 Quad-filar wound.

  • Rterm: 10K

  • R1: 390R

  • Z1: 12V

  • 250 mA mosfet bias.

  • Output configuration to drive: 600 ohm series, 150 ohm parallel.

  • Vbias: STP55NE06 + 2 x Schottky diodes + 10K pot + LM317 current source.

Comparison Graph.

Frequency - Hz SE - THD% PP - THD%
20 0.773 0.4910
25 0.482 0.3240
31.5 0.310 0.2236
40 0.202 0.1505
50 0.136 0.1041
63 0.092 0.0671
80 0.062 0.0438
100 0.045 0.0294
125 0.036 0.0187
160 0.032 0.0141
200 0.029 0.0124
250 0.028 0.0122
315 0.027 0.0110
400 0.026 0.0105
500 0.026 0.0092
630 0.026 0.0079
800 0.026 0.0065
1000 0.027 0.0053
1250 0.029 0.0045
1600 0.031 0.0042
2000 0.036 0.0037
2500 0.040 0.0036
3150 0.048 0.0036
4000 0.057 0.0036
5000 0.069 0.0037
6300 0.086 0.0039
8000 0.108 0.0041
10000 0.133 0.0044
12500 0.167 0.0046
16000 0.235 0.0049
20000 0.320 0.0105
25000 0.410 0.0333
31500 0.500 0.0789
40000 0.590 0.1418
50000 0.703 0.1587

HP 8903B data for above Graph.


Toroid Test

Line Drive Amplifier with 15VA Toroid Transformer as Inductor

A toroid transformer's secondaries can be used, optimal for 600 ohm line drive, for testing purposes.

Note: A larger, circa 120 VA (use 120+120 primary windings), toroid transformer is required for single ended use.

When using standard mains power toroidal transformers the performance is not as good as with the specifically designed EI lamination transformers but provides a useful introduction to the principles of operation.


Zeus Pre-Amp with TX102 Magnetic Volume Control

Pre-amp / Line Drive Amplifier Basic Schematic - 600 ohm input.

Replaces the 1:4 Gardners input transformer with 2 off TX-102 magnetic volume controls.

Note: At time of writing the schematic for the TX-102 shown on the S&B TX-102 webpage is for their Mk II design (which I used for the above schematic), whereas the current part is a Mk III which features 2dB steps descending from the 0dB position, not 3dB as shown. I.e. Attenuation is: 0 db, 2 db, 4 db, 6 db, 8 db, 10 db ...

PDF Schematic here.

Can also be used as a headphone amplifier.


Back to Zeus Main Page


Design by: Susan Parker, MIEE.

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

N.B. Personal liability disclaimer applies.


This page last modified on: 11th November 2006

All information, drawings and images Copyright 1995 - 2006 Susan Parker unless otherwise credited.