fletcherkane Posted April 18, 2005 Share Posted April 18, 2005 Got a quick question... I recently purchased a Technics Integrated Amp at a thrift store. The amp states that it contains "New Class A" circuitry. Do any of you know the difference between Class A and New Class A? Or was New Class A just a gimicky thing that never caught on and wasn't better than class A. I must say that this amp doesn't feel nearly heavy duty enough to be true Class A. The amp is from the late 80's. Model SU-V78. The amp provides 175 watts of clean power per channel, but just am wondering about the "New Class A" Label...any thoughts out there? Quote Link to comment Share on other sites More sharing options...
nicholtl Posted April 18, 2005 Share Posted April 18, 2005 Just a shot in the dark (didn't bother to research this online or anything), but since this is a vintage amp from the 80's, perhaps this "new class A" is simply class A, only it was considered "new" technology back then. Quote Link to comment Share on other sites More sharing options...
michael hurd Posted April 18, 2005 Share Posted April 18, 2005 Just a marketing gimmick, used by technics? ( sp ), or panasonic, I forget which now. Quote Link to comment Share on other sites More sharing options...
minn_male42 Posted April 18, 2005 Share Posted April 18, 2005 ---------------- On 4/18/2005 2:22:13 PM nicholtl wrote: Just a shot in the dark (didn't bother to research this online or anything), but since this is a vintage amp from the 80's, perhaps this "new class A" is simply class A, only it was considered "new" technology back then. ---------------- much older technology.... ...Mr. Stanley primarily showed the development of audio amplifiers through patent documents highlighting inventions such as the first class-A push-pull amplifier in 1916 and the patenting of negative feedback in the late 1920s and 1930s..... the above taken from the following site: http://www.aes.org/sections/chicago/apr02review.html Quote Link to comment Share on other sites More sharing options...
Duke Spinner Posted April 18, 2005 Share Posted April 18, 2005 Adevertising ... is the difference ... Quote Link to comment Share on other sites More sharing options...
Trooper Posted April 19, 2005 Share Posted April 19, 2005 That's likely just a marketing term that made an engineer cringe. A Technics amp from the late 80's being any kind of real Class-A is certainly unlikely. And if it's not heavy and doesn't get very hot that will pretty much guarantee its not Class-A. Enjoy your find just don't brag to your audiophile friends about your new class-A amp. Quote Link to comment Share on other sites More sharing options...
fletcherkane Posted April 19, 2005 Author Share Posted April 19, 2005 It isn't beastly heavy, but it does have a cooling fan that only operates when you push the volume and the amp gets warm...whatever that's worth... Quote Link to comment Share on other sites More sharing options...
sunnysal Posted April 19, 2005 Share Posted April 19, 2005 cooling fan indicates at least the strong possiblitiy of class A operation. a few quotes I found on the web; "I recall the biasing circuity is designed so that neither output transistor turns off (as class A) although the biasing is not the same as class A. When the output swings from positive to negative for instance the transistor does not switch off, but stays at a preset DC bias point. The same is true for the other transistor when the output swings from negative to positive. This way neither transistor passes through the nasty <~0.7V Vbe region. The transition between following the input and staying at the bias point is non-linear, if memory serves, so as to reduce switching-like harmonics." "new class A is an innovative bias circuit that keeps the output transistors in the ready state, eliminating crossover distortion, though keeping idling current low in order for more efficiency" so it is a modification of traditional class a operation, which eliminates crossover distortion. regards, tony Quote Link to comment Share on other sites More sharing options...
Trooper Posted April 19, 2005 Share Posted April 19, 2005 So then its what most people call class-AB. It's biased just past true class-B (as most amps are, BTW) so that maybe 1/2W to a few watts are class-A. This greatly reduces distortion at higher frequency which is where a true class-B design causes problems. Quote Link to comment Share on other sites More sharing options...
sunnysal Posted April 19, 2005 Share Posted April 19, 2005 no it is not simply class a/b, it runs current through the transistors at all times, so there is no crossover distortion like you get in class a/b circuits...tony Quote Link to comment Share on other sites More sharing options...
Trooper Posted April 19, 2005 Share Posted April 19, 2005 ---------------- On 4/19/2005 12:01:47 PM sunnysal wrote: no it is not simply class a/b, it runs current through the transistors at all times, so there is no crossover distortion like you get in class a/b circuits...tony ---------------- Yes, that's exactly what turning the bias up from class-B to class-AB does - keeps the transistors on just a little bit all the time thus eliminating the transistor turn on/turn off that creates the crossover distortion. Quote Link to comment Share on other sites More sharing options...
sunnysal Posted April 20, 2005 Share Posted April 20, 2005 trooper, let´s review, Let's have a quick look at some of the power amp "classes", so we have all the info: Class-A Output device(s) conduct through 360 degrees of input cycle (never switch off) - A single output device is possible. The device conducts for the entire waveform Class-B Output devices conduct for 180 degrees (1/2 of input cycle) - for audio, two output devices in "push-pull" must be used (see Class-AB) Class-AB Halfway (or partway) between the above two examples (181 to 200 degrees typical) - also requires push-pull operation for audio. AFAIK, the technics amp´s output transistors NEVER stop conducting throughout the 360 degree cycle, one output transistor just drops to a preset current. is that not different then class a/b? I am new to this stuff but it seems to be to be somewhat different. regards, tony regards, tony Quote Link to comment Share on other sites More sharing options...
sunnysal Posted April 21, 2005 Share Posted April 21, 2005 thanks mark, that is exactly what the amp does, it drops the DC bias point down when there is no signal...you helped clairfy this for us. warm regards, tony Quote Link to comment Share on other sites More sharing options...
pauln Posted April 21, 2005 Share Posted April 21, 2005 I think a point is being missed, here. The crossover distortion is caused by the misalignment of the signal value as it is passed between the transistors across the zero line. This misalignment is fairly constant so that at high signal levels it contributes less to the distortion, but at low signal levels it can be a larger contribution. Just because the transistors don't go down to 0 does'nt mean the crossover distortion does not occur. Also, crossover distortion is not harmonic because the crossing of the zero line is not periodically related to the signal waveform. This makes it real harsh and grainy sounding. Quote Link to comment Share on other sites More sharing options...
sunnysal Posted April 21, 2005 Share Posted April 21, 2005 Paul, you may very well be right, it is hard with the limited information we have to know if this implementation is a good one or not. I just wanted to make sure that this circuit was not confused with a class a/b amp as trooper had suggested, it is a different operating topology. regards, tony Quote Link to comment Share on other sites More sharing options...
fletcherkane Posted April 21, 2005 Author Share Posted April 21, 2005 Wow everyone! thanks for the insights. It is what I love about this forum. I've learned more about audio in my six months hanging out here than the rest of my life combined. This thread has gone from a few guys telling me that "New Class A" is nothing more than an advertising gimmick to some very enlightening discussion on how an amp really works. Thanks as always. I currently have this amp hooked up to my Forte's, and the sound is clean and punchy, if not a little harsher than my Pioneer HT amp that is normally plugged in to my Forte's. Dan Quote Link to comment Share on other sites More sharing options...
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