Zeus Power Amplifier

35 Watt 8 ohm Output Transformer.

For completeness I include information on the original Zeus35 amplifier's output transformer. This is only recommended for small listening rooms with sensitive speakers or for systems which will use separate amplification for the low bass.

Close up showing the four sets of winding terminations.

Electrical

Inductance of each winding = 155 mH @ 1 kHz, 191 mH @ 120 Hz.

Impedance of each winding = 3.2 KΩ @ 1 kHz, 1.2 KΩ @ 120 Hz.

Inter-winding capacitance between input and output windings (wired for use) = 11.6 nF

Output impedance in circuit when powered = 2.78 Ω @ 1 kHz.

Mechanical

Laminations:

Material = Orthosil M6 (Optional: SuPer Orthosil) grain oriented transformer steel.
Size = EI-1.1/4" (Standard dimensions = 15.9, 15.9, 31.8, 47.6, 5.6, 104.8, 8.7 mm )
Thickness = 0.35 mm
Frame Mounting (has bolt holes in the corners).

Single chamber bobbin, EI 96 x 45.7mm
Quad Filar wound, 0.80mm insulated copper wire.
No insulation between layers.
Terminations: to tags on bobbin.

Version 1 Windings

This transformer version is for standard 8 ohm impedance (or greater) speakers.

2 x Primary:
12 full layers ( approx. 144 turns each).
Start and finish at same side of bobbin

2 x Secondary:
12 full layers ( approx. 144 turns each).
Start and finish at same side of bobbin

Starting from same bobbin end, wind all four for 12 layers.

Tag Sequence (left to right) [ 1S 1F 2S 2F 3S 3F 4S 4F ] - see picture.

N.B. The 4 simultaneous windings must be even without crossings over the width of the winding. Cross-overs allowed at ends when changing direction.

Version 2 Windings

This version of the transformer has a split secondary to allow the amplifier to drive low impedance speakers including paralleled line array drivers; for normal operation use in series.

2 x Primary:
12 full layers ( approx. 144 turns each).
Start and finish at same side of bobbin

2 x Secondary:
6 + 6 full layers ( approx. 72 + 72 turns each).
Start and finish at same side of bobbin ( opposite side from primary).

Primary: Start Finish
Winding 1: 22 24
Winding 2: 25 27

Secondary: Start Finish Start Finish
Winding 3: 13 15 17 19
Winding 4: 14 16 18 20

Starting from same bobbin end, wind all four for 6 layers, loop out the secondaries to the tags, wind remaining six layers.

The 4 simultaneous windings must be even without crossings over the width of the winding. Cross-overs allowed at ends when changing direction.

Finish

Vacuum impregnated varnish.

(The transformer is equivalent to a 200 VA mains transformer and may be constructed from commercially available mains transformer kits. Remove the mains primary windings and the centre divider from the supplied bobbin. Also ensure that the laminations are made of M6 material.)

Note: Orthosil (M6) Transformer Laminations

Orthosil is a grain oriented electrical transformer steel available in .004", .006" and .014" thicknesses.

Orthosil is a squared hysteresis loop iron-silicon alloy expressly developed to provide lower core loss with higher permeability in the rolling direction. The elementary patterns of crystals in the material are "oriented", or so arranged that the axis of easiest magnetization is nearly parallel and aligned in the direction of rolling. The alignment is accomplished by special cold-rolling and annealing processes.

There are several advantages to using Orthosil .004", .006" and .014" laminations:

Lower core losses
Higher initial permeability
Higher permeability at higher inductions
Controlled gauge uniformity

See Thomas and Skinner website for further information.