Denon DRA-635r - New Optical Class A

[formdissolve]

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.

 

[formdissolve]

 

[Byrdsmaniac]

About fifteen years ago I got one of those used for $65. Since then it has been playing problem free eleven hours a day, five days a week in my wife's office system. I don't know about the New Optical Class A business, but I do know it's a reliable, good sounding, low noise unit. It has an excellent tuner section as well.

 

[restorer-john]

Denon were very open to trying all sorts of interesting tweaks and developments to get better performance from their amplifiers. The 'new optical' class A designation was one and they ran with that right into the 90s. In my opinion, it wasn't anything game changing, but I'm sure they paid Nelson Pass a pretty penny to use it.

 

[formdissolve]

About fifteen years ago I got one of those used for $65. Since then it has been playing problem free eleven hours a day, five days a week in my wife's office system. I don't know about the New Optical Class A business, but I do know it's a reliable, good sounding, low noise unit. It has an excellent tuner section as well.

Yeah, I got mine for free with the purchase of another amp locally. My buddy had it for a few years and used it daily, then I got it back and used it basically daily for another five years. It's now in my back office driving some Klipsch KG1.5 and it sounds great.. The loudness knob is interesting too and works really well, especially since channel match is poor at super low volume.

I want to get active speakers or a small, more efficient amp but why spend the money? These 90s Japanese made amps seem to last forever! I'd love to get the 1035-R at some point.

@restorer-john I think I read something about a connection to Nelson Pass, I'll have to dig more into that.