Hello all - I have an old early 90s Denon DRA-635r that sounds great for its age. On the front it says "New Optical Class A" - found on another forum that has the patent below. Anyone know what this means? Is it basically a class AB?
United States Patent
4,752,745
Pass
June 21, 1988
Opto-isolated bias circuit for operating push-pull amplifiers in class A and class AB modes
Abstract
A high fidelity audio amplifier of the push-pull complementary symmetry type, featuring a feedback circuit with a bias sensing element connected to the output terminals of the output transistors. The feedback circuit includes a photoemitting element in optical communication with a photoconductive element which determines the relative voltage difference of the input terminals of the complementary symmetry output transistors.
Inventors:
Pass; Nelson S. (Auburn, CA)
Assignee:
Threshold Corporation (Auburn, CA)
Appl. No.:
086932
Filed:
August 18, 1987
(regular bias circuits)are non-linear and can introduce distortion into the amplified signal.
It is an object of the present invention to devise an amplifier using a bias circuit incorporating a feedback connection to the output nodes of subsequent gain transistors for the purpose of controlling the bias of these transistors, but with an isolation mechanism to eliminate the distortion found in prior art.
SUMMARY OF THE INVENTION
The above object has been achieved in an audio amplifier having emitter follower, complementary symmetry output transistors utilizing feedback from the output stage. It has been found that use of optical coupling in a feedback loop for biasing the output transistors reduces distortion by isolating the bias circuit from the output nodes and preventing saturation in transistors forming the bias circuit. Sufficient feedback is provided to maintain Class A or Class AB operation, yet input current is not drawn off to the output node through the feedback circuit, thereby preventing distortion.
United States Patent
4,752,745
Pass
June 21, 1988
Opto-isolated bias circuit for operating push-pull amplifiers in class A and class AB modes
Abstract
A high fidelity audio amplifier of the push-pull complementary symmetry type, featuring a feedback circuit with a bias sensing element connected to the output terminals of the output transistors. The feedback circuit includes a photoemitting element in optical communication with a photoconductive element which determines the relative voltage difference of the input terminals of the complementary symmetry output transistors.
Inventors:
Pass; Nelson S. (Auburn, CA)
Assignee:
Threshold Corporation (Auburn, CA)
Appl. No.:
086932
Filed:
August 18, 1987
(regular bias circuits)are non-linear and can introduce distortion into the amplified signal.
It is an object of the present invention to devise an amplifier using a bias circuit incorporating a feedback connection to the output nodes of subsequent gain transistors for the purpose of controlling the bias of these transistors, but with an isolation mechanism to eliminate the distortion found in prior art.
SUMMARY OF THE INVENTION
The above object has been achieved in an audio amplifier having emitter follower, complementary symmetry output transistors utilizing feedback from the output stage. It has been found that use of optical coupling in a feedback loop for biasing the output transistors reduces distortion by isolating the bias circuit from the output nodes and preventing saturation in transistors forming the bias circuit. Sufficient feedback is provided to maintain Class A or Class AB operation, yet input current is not drawn off to the output node through the feedback circuit, thereby preventing distortion.
