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:
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.
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.
HP 8903B data for above Graph.
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 ...
Can also be used as a headphone amplifier.
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.