t-man Posted October 20, 2001 Share Posted October 20, 2001 I was hoping the brain trust here would educate me a bit on what it means to have a D.C. amplifier. What's the deal with these? Anything special? Please excuse the stupid question, if indeed this is stupid. I wouldn't know - hence the question T-man ------------------ KG 5.5 (mains) KG 2.2v (center) KLF-C7 (center in storage) KG 1 (rears) KSW-12 (sub) Denon AVR 681/1601 Toshiba SD-3109 DVD Kenwood LVD700 LD Sony CD changer Sony 27" Trinitron Sony PLX I Quote Link to comment Share on other sites More sharing options...
WMcD Posted October 20, 2001 Share Posted October 20, 2001 I believe this term means that the amplifer has the capability of reproducing down to zero Hertz. This implies that it has the capability of amplifying a d.c. level, and everything above. I.e. 1, 2, 3, etc. cycle per second tone. (Hertz = cycles per second) signal. If you wanted to "amplify" d.c., it is as if you applied a 1.5 volt dry cell at the input, had an amp with a gain of 10, and expected a 15 volt output. In other areas of electrical engineering, this may well be necessary. Is that true in our setting? No, in all likelyhood. There are several reasons why this is so. First, there is nothing in music or speech in the area of d.c. or even 1 to 10 Hertz. Second, the recording media such as CD's don't go that low. You see some cynical statements. Essentially they say that the amp is good from d.c. to "daylight". Daylight meaning the upper reaches of the electromagnetic spectrum. I.e. perfect in all possible ways. In truth, our hearing is limited at the low end and the high end. Audio amps work just fine if they reproduce 20 Hz to 20,000 Hz. Maybe less. That is also a reasonable limit to where speakers work. Gil Quote Link to comment Share on other sites More sharing options...
TheEAR Posted October 21, 2001 Share Posted October 21, 2001 DC to 2.4MHz! You should take a look at Spectral their amps have incredible specs.These amps are true extreme bandwith amplifiers. And they are very fast,the level of detail is out of this world,as is the price.Even when compared to PassLabs,Krell,Bryston the Spectral is fast.Only some Goldmund amps are close in speed. Again who will hear down to 1Hz or above 2MHz? TheEAR(s) Now theears Quote Link to comment Share on other sites More sharing options...
djk Posted October 21, 2001 Share Posted October 21, 2001 Since you are so impressed with speed why don't you buy my 100W amp? For only USD$31,000 it goes to 1,200Mhz.I have a two year waiting list. Quote Link to comment Share on other sites More sharing options...
TheEAR Posted October 21, 2001 Share Posted October 21, 2001 I am not impressed with mere specs,the sound quality may impress me.Not specs Its just fun to see amps like Goldmund and Spectral. What is the make of your 1.2MHz amp? Does it have to be cooled with a Swiftech MC462? Does it support SSE2 instructions? How many MIPS? And above all can I overclock? TheEAR(s) Now theears Quote Link to comment Share on other sites More sharing options...
djk Posted October 22, 2001 Share Posted October 22, 2001 1,200Mhz is 1,200,000,000hz (1.2Ghz).You slipped a few decimal places. Quote Link to comment Share on other sites More sharing options...
Ray Garrison Posted October 22, 2001 Share Posted October 22, 2001 t-man, In many cases, the "D.C amplifier" is a marketing concept, and implies that there are no coupling capacitors between the input and output. Capacitors block DC and pass AC. Specific characteristics of where the cutoff occurs and how steep the attenuation not really of concern here, in this context it's your typical marketing maven's perception that capacitor = bad, no capacitor = good, because no capacitor means bass response can, theoretically, go down to zero cycles per second with no rolloff. Note that amps that use an output transformer (Mcintosh, most tube amps) cannot pass DC whether there are capacitors in the signal path or not, as the transformer will isolate the DC component from the output. Passing DC can be a very, very bad thing depending upon the design of the amp and the nature of the upstream equipment. If you have an amp that will pass DC, and it doesn't have some kind of circuit to identify and cancel a DC component in the input, and you're feeding that amp a signal, say from a preamp, that has a small but non-zero "DC offset" (that is, with no signal present the preamp is presenting a small voltage across it's outputs, maybe a few millivolts), then the amp is going to amplify that DC signal and feed it through your speakers, which can, over time, overheat the amp's output circuits or overheat the voice coil in the speaker. ------------------ Music is art Audio is engineering Quote Link to comment Share on other sites More sharing options...
Guest BobG Posted October 22, 2001 Share Posted October 22, 2001 For amplifier bandwidth to minimize any group delay, it is common to use this rule of thumb - the -3 dB points should be three octaves below and three octaves above the signal content. Three octaves below 20 Hz is 2.5 Hz while three octaves above 20 KHz would be 160 KHz. As with all things, single spec focus is very misleading. Quote Link to comment Share on other sites More sharing options...
Marvel Posted October 22, 2001 Share Posted October 22, 2001 djk, I would like to place an order. Can you up that to 2.4 GHz for me while you're at it. My microwave is on its last legs, and I could use it for double duty as a satellite uplink. I could probably cook a whole cow on the hoof with that too. Marvel Quote Link to comment Share on other sites More sharing options...
sunnysal Posted October 23, 2001 Share Posted October 23, 2001 gentlemen, I have seen some Marantz amplifiers that have "DC" in the model designation...on the back panel they have a switch near the inputs that read "AC coupled" and "DC coupled" ... I have no idea what this means or what it does BUT this could be what t-man meant by a "DC" amp...anyone have light to shed? Quote Link to comment Share on other sites More sharing options...
djk Posted October 23, 2001 Share Posted October 23, 2001 Marvel, I make an HPA version (high power amplifier) that will cook a whole cow. Rated at 800W it will typically put out 1.2KW . For double duty it will talk to the E3 AWACS. I might have to ask NATO if I can sell you one though.sunnysal, that switch just shorts out the input coupling cap.I'll bet there is still a cap in the feedback loop somewhere. Quote Link to comment Share on other sites More sharing options...
Ray Garrison Posted October 23, 2001 Share Posted October 23, 2001 Sunnysal, "AC coupled" = input signal path has a coupling capacitor someplace. "DC coupled" = input signal path does not have a coupling capacitor someplace. Whether they sound any different or not will depend upon how the circuits are designed and built - my guess is any difference that may exist would be miniscule, if at all detectable. ------------------ Music is art Audio is engineering Quote Link to comment Share on other sites More sharing options...
sunnysal Posted October 23, 2001 Share Posted October 23, 2001 thanks ray...Marantz had half a dozen models with that input option, they must have thought it made some sort of difference in sound...perhaps this is an important issue in matching preamps to amps? Regards, tony This message has been edited by sunnysal on 10-23-2001 at 04:50 PM Quote Link to comment Share on other sites More sharing options...
WMcD Posted October 23, 2001 Share Posted October 23, 2001 I'm not disagreeing with any of the above. However, please condsider that if "group delay" is the issue, we'd better look at the whole system. Unfortunately, we typically know little about the extent to which the recording end of our chain has, or has not, group delay in any area of the audio spectrum. Also, speakers themselves have filters in the cross overs, they have physical offset, and their own group delay as a consequence of their band pass nature (they are not full range individually). The bottom line is that having a near perfect amp does not mean the "group delay" problem is cured by any means. There are many other sources along the way, and they may add up errors, or maybe not. It may well be a good long term goal. That is a big maybe. We'd have to determine just how much group delay the human ear can detect in any given circumstance. Gil Quote Link to comment Share on other sites More sharing options...
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