fletcherkane Posted October 21, 2005 Share Posted October 21, 2005 Hey guys I just got home from goodwill, and I came home with a Denon Integrated Amp that I paid 5 bucks for. It certainly is a monster, and it sounds great. The front panel lists this amp as "New Optical Class A" It wasn't too long ago that I posted a similiar question about a Technics Integrated that called itself "New Class A" What does the "Optical" have to do with anything? Anyway, I am pretty happy with my purchase, and look forward to hooking it up in a two channel set up. Other than being a little dirty, it appears to be in pretty good shape. Quote Link to comment Share on other sites More sharing options...
Parrot Posted October 21, 2005 Share Posted October 21, 2005 What a steal! What's the model number? Quote Link to comment Share on other sites More sharing options...
fletcherkane Posted October 21, 2005 Author Share Posted October 21, 2005 The model number is PMA 980R The Denon website isn't very comprehensive, so I haven't found out much about its specs and such yet. It is remote control capable, so it isn't terribly old...I am guessing that it is from the late 80's, early 90's? Any Denon fans that can help me out with more info on this thing would be appreciated. Quote Link to comment Share on other sites More sharing options...
Parrot Posted October 21, 2005 Share Posted October 21, 2005 Here's one that sold on eBay for $163: http://cgi.ebay.com/Denon-PMA-980R-Integrated-Stereo-Amplifier_W0QQitemZ5813581479 I'll give you $10 for it if you want to double your money. Quote Link to comment Share on other sites More sharing options...
fletcherkane Posted October 21, 2005 Author Share Posted October 21, 2005 $10...hmmm let me think...um no. LOL Anyway, Parrot, thanks for looking that up. How do you find ended listings on ebay like that. Is there a special search function that I am unaware of? Thanks again.. Quote Link to comment Share on other sites More sharing options...
Parrot Posted October 21, 2005 Share Posted October 21, 2005 There sure is. On eBay, in the left column, under Search Options, just check the box that says Completed Auctions. It only goes back about a month though. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted October 21, 2005 Share Posted October 21, 2005 It means that you can Optically see that it says Class A on the front so it has to be good[] But really I have no clue. If you get no answer here try over at AudioKarma.org Craig Quote Link to comment Share on other sites More sharing options...
djk Posted October 22, 2005 Share Posted October 22, 2005 ( 5 of 7 ) 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. http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/srchnum.htm&r=1&f=G&l=50&s1=4,752,745.WKU.&OS=PN/4,752,745&RS=PN/4,752,745 Quote Link to comment Share on other sites More sharing options...
fletcherkane Posted October 22, 2005 Author Share Posted October 22, 2005 Thanks djk! Now, can someone else put that in english for me...[8-)] What does it mean to me as I put this amp to use? Quote Link to comment Share on other sites More sharing options...
artto Posted October 22, 2005 Share Posted October 22, 2005 A long time ago a musical instrument amplifier company named Standel used an optically activated current limiter as a means of amplifier and speaker protection from excessive amplifier power output. When the power level reached high enough, it would light up this little neon bulb which activated an optical sensor which sent the current limiter into action. <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /> I suspect this amplifier design is doing something similar, except in this case, its using the optical coupler/sensor to adjust the bias current based on the level of output of the output transistors, instead of merely limiting amplifier output. I could be wrong, (not the most electronically literate here), but thats what it sounds like to me (in plain English). So what does that mean to you? If my interpretation is correct, it means the amp, technically speaking by definition, is not a true Class A amplifier (an amp where 100% of the current flow is available 100% of the time, regardless of whether or not a signal is present), but essentially operates like a Class A amp in that the current bias is continuously monitored and adjusted by an optical sensor connected to the amplifiers output devices. When it sees more output, it adjusts the current bias so the amp remains in a Class A region of operation. When no signal is present the current bias remains low and the amp doesnt use as much idling power and runs cooler. Quote Link to comment Share on other sites More sharing options...
Marvel Posted October 22, 2005 Share Posted October 22, 2005 A long time ago a musical instrument amplifier company named Standel used an optically activated current limiter as a means of amplifier and speaker protection from excessive amplifier power output. When the power level reached high enough, it would light up this little neon bulb which activated an optical sensor which sent the current limiter into action. I guess for cost considerations they didn't want to build in a UA LA-2A. A built in optical compressor might have been pretty neat. Bruce Quote Link to comment Share on other sites More sharing options...
artto Posted October 22, 2005 Share Posted October 22, 2005 Yeah, I was kind of surprised at the tme (circa 1968) to find out that's all they had to do for current limiting. I cut the wire to the optical sensor (LOL) so the amp would "put out". On the other hand, my Standels also had aftermarket JBL D140's installed, they could take the extra abuse. At the time Standel had bought the Stephens speaker company and began making their own drivers, which, they obviously knew weren't quite up to the task at hand, hence the optical current limiter. Quote Link to comment Share on other sites More sharing options...
djk Posted October 22, 2005 Share Posted October 22, 2005 "Now, can someone else put that in english for me..." (regular bias circuits)are non-linear and can introduce distortion into the amplified signal. (the optical) isolation mechanism... eliminate(s) the distortion found in prior art. "What does it mean to me as I put this amp to use?" It should sound better than the old way of doing things. For those interested in schematics, follow the link I gave for the USPTO, and click on 'images' (you need a TIFF viewer). Quote Link to comment Share on other sites More sharing options...
fletcherkane Posted October 22, 2005 Author Share Posted October 22, 2005 Thanks DKJ! Quote Link to comment Share on other sites More sharing options...
Marvel Posted October 22, 2005 Share Posted October 22, 2005 fletcher, Nice PK album. I think one of my favorites is "Lights of Madrid." Bruce Quote Link to comment Share on other sites More sharing options...
fletcherkane Posted October 22, 2005 Author Share Posted October 22, 2005 Thanks Marvel I switched to that avatar right after I got that album. It completed my PK collection. I agree with you. Lights of Madrid is one of his all time best albums. Quote Link to comment Share on other sites More sharing options...
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