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		Technical Notes

PAT 4134-ES

Wide Bandwidth Toroidal Step-up Transformer for Electrostatic Loudspeakers

RATINGS

Step-up Ratio (Np:Ns)	1:75
Nominal Power; Pnom (note 1)	80 watts
Input, Nominal Power; Zout (note1)	4 ohms
Secondary Inductance, maximum; Ls (note 2)	1600 H
Effective Secondary Leakage Inductance; Lss	22 mH
Primary DC Resistance; Rip	0.1 ohm
Secondary DC Resistance; Ris	273 ohms
Secondary Internal Capacitance; Cis	800 pF
Low Frequency Ratings
-3 dB Power Low Frequency Bandwidth; fu (note 3)	35 Hz
Tuning Resistor in Series with Primary; Rep (note 4, 8)	0.82 ohms
-3 dB Low Freq. Bandwidth with Tuning Resistor; f3L (note 5)	0.52 Hz
Primary Impedance at 10 kHz with Tuning Resistor; Z10 (note 6)	18 ohms
High Frequency Ratings
Capacitance of Electrostatic Loudspeaker; Ces	1 nF
Resonance Frequency, 2nd Order; Fo (note 7)	25 kHz
Q Factor, 2nd Order HF Filter Section; Q (note 8)	0.642
-3dB High Frequency Bandwidth; f3H (note 8)	23 kHz
Primary Impedance at 20 kHz; Z20k	1.0 ohms

Notes

A step-up transformer transforms voltages. The maximum primary voltage equals (80*4).5 = 17.9 V at 35*2.5 = 50 Hz
Maximum value; Ls is not constant. See Glass Audio 5/97; M. Vanderveen: "Measuring Output Transformer Performance".
�3dB means: 40 Watt at 35 Hz; 80 Watt at 35*2.5 = 50 Hz; 160 Watt at 50*2.5 = 71 Hz; etc.
Rep in series with the primary stops ringing of the loudspeaker. Rep is an important tuning device; see note (8).
This lower �3dB frequency is calculated with the maximum value of Ls (see note (2)).
This primary impedance is calculated with the maximum value of Ls combined with the primary series resistor Rep. When measuring this impedance at small input voltages, its value will be smaller, because Ls is not constant.
This fundamental frequency is determined mainly by the leakage inductance, Rep and (Cis + Ces).
Rep influences Q and f3H. Select Rep for 0.5 < Q < 0.74 for optimal high frequency response without ringing.

Response Curves

Schematics

Mechanical

Leads

Primary (1,2) leads are 16 AWG stranded. Stripped 6 mm.

Secondard Leads are 22 AWG stranded. Stripped 6 mm.