# US 10,320,343 B1 · Amplifier output stage using toroidal transformer

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- Number: US 10,320,343 B1
- Document ID: US10320343B1
- Status: Granted
- Kind: B1
- Application number: 15/915,832
- Filed: 2018-03-08
- Granted: 2019-06-11
- Earliest claimed: 2018-03-08
- Assignees: Real Analog, LLC
- Applicants: Real Analog, LLC
- Inventors: Rudolph J. Liedtke
- Web page: https://patentgrep.com/patent/US10320343B1

## CPC

- H03F 3/181: Low-frequency amplifiers, e.g. audio preamplifiers
- H03F 1/32: Modifications of amplifiers to reduce non-linear distortion (by negative feedback H03F1/34)
- H03F 3/22: with tubes only (H03F3/24 takes precedence)
- H03F 2200/03: the amplifier being designed for audio applications
- H03F 2200/534: Transformer coupled at the input of an amplifier
- H03F 2201/3215: To increase the output power or efficiency
- H03F: AMPLIFIERS

## Abstract

An audio amplifier includes an output stage including a first toroidal transformer with a first pair of secondary windings that are coupled in parallel across an output terminal. The output stage further includes a second toroidal transformer with a second pair of secondary windings that are connected in a series combination that is coupled across the output terminal.

## Claims

### Claim 1

An audio amplifier comprising:
first and second amplifying elements driven by associated control signals that are 180 degrees out of phase with each other;
a first toroidal transformer with first and second primary windings coupled together at center terminals to a common voltage source and coupled in push-pull configuration to the first and second amplifying elements, and with first and second secondary windings that are coupled in parallel across output terminals; and
a second toroidal transformer with first and second primary windings coupled at center terminals to corresponding constant current sources and coupled in push-pull configuration to the first and second amplifying elements, and with first and second secondary windings that are coupled in series across the output terminals.

### Claim 2 (depends on 1)

The audio amplifier of claim 1 wherein the first and second amplifying elements are vacuum tube devices.

### Claim 3 (depends on 2)

The audio amplifier of claim 2 wherein the first toroidal transformer and the second toroidal transformer are 60 Hertz power transformers having a pair of 120 Volt primary windings and a pair of 12 Volt secondary windings.

### Claim 4 (depends on 1)

The audio amplifier of claim 1 wherein the first and second amplifying elements are solid-state transistor devices.

### Claim 5 (depends on 1)

The audio amplifier of claim 1 wherein magnitudes of current supplied by the constant current sources are balanced to prevent magnetic saturation of the first and second toroidal transformers over a predetermined frequency range.

### Claim 6 (depends on 1)

The audio amplifier of claim 1 further comprising a non-polarized capacitor coupled between center terminals of the first and second primary windings of the second toroidal transformer.

### Claim 7 (depends on 1)

The audio amplifier of claim 1 wherein a magnitude of current supplied by each of the constant current sources is selected to enable operation of the first and second amplifying elements in a Class A mode and the first and second amplifying elements are operated in the Class A mode of operation.

### Claim 8

An output stage for an audio amplifier comprising:
a first toroidal transformer with a first pair of primary windings coupled together at center terminals to a common voltage source and coupled in push-pull configuration to first and second amplifying elements, and with a first pair of secondary windings that are coupled in parallel across output terminals; and
a second toroidal transformer with a second pair of primary windings coupled at center terminals to separate constant current sources and coupled in push-pull configuration to the first and second amplifying elements, and with a second pair of secondary windings that are coupled in series across the output terminals.

### Claim 9 (depends on 8)

The output stage of claim 8 wherein the first and second amplifying elements are driven by associated controls signals that are 180 degrees out of phase from each other.

### Claim 10 (depends on 8)

The output stage of claim 8 wherein the first and second amplifying elements are vacuum tube devices, and the first toroidal transformer and the second toroidal transformer are 60 Hertz power transformers having a pair of 120 Volt primary windings and a pair of 12 Volt secondary windings.

### Claim 11 (depends on 8)

The output stage of claim 8 wherein magnitudes of current supplied by the constant current sources are balanced to prevent magnetic saturation of the first and second toroidal transformers over a predetermined frequency range.

### Claim 12 (depends on 8)

The output stage of claim 8 wherein the first and second amplifying elements are operated in a Class A mode of operation.

### Claim 13 (depends on 8)

The output stage of claim 8 further comprising a non-polarized capacitor that is coupled between the center terminals of the second pair of primary windings.