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Gold Member Username: NuckParkhill, Ontario Canada Post Number: 1479 Registered: Dec-04 | Fairly simple q, I suppose. The amplifier simply ups the signal that it is fed. What is the maximun input signal, or voltage to achieve the maximum output from the amplifier? If the amp is fed from a pre-amp or receiver via pre-outs, how will I know if the pre-outs are delivering the appropriate signal strength to the amp? I havn't seen, or didn't understand these values for my equipment. Thanks. |
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Gold Member Username: Jan_b_vigneDallas, TX Post Number: 7704 Registered: May-04 | In consumer audio there are no maximum nor minimum input sensitivities and no standard output voltages. There are generally agreed upon values which represent logical extremes for both numbers. Generally two volts out will work OK for a pre amp though some digital sources output as much as five volts and the pre amp does not step these down. Additionally, some low output phono cartridges might not drive the phono section to its full output voltage and would then require a step up device to achieve enough gain so the circuit isn't swamped by its own residual noise. You will often see a spec for a power amp which indicates full power with 1 volt input. This is by no means standardized in consumer audio and the number can vary from the typical pro sound spec of 0.75 volts input to what ever the designer feels works best for a particular component. The higher the input voltage, the more likely the SN spec will go down assuming the output voltage doesn't distort the inputs. But the spec for reaching full power is usually no more than 2 volts. You need to pay more attention to overload capability than input sensitivity. There is no spec typically provided for "overload" in consumer audio but if your pre amp outputs five volts and your power amp only requires 0.75 volts to reach full power, there is the chance of overdriving the front end of the amplifier. If nothing else, the additional sensitivity of the amplifier will mean you will be running the volume pot of the pre amp in a low position at which point most pots don't track well. Gain controls on the power amp can help somewhat in this situation but then you are usually altering the input impedance measurement. How much voltage the input of any piece of equipment can tolerate before distorting is a function of the design. A pre amp meant to operate with a 5 volt output from its mated pre amp might not care about high input voltages while a power amp designed for 0.75 volts might be driven into distortion at the inputs. If you choose poorly when combining equipment and the input/output impedances are mismatched, this will also affect the gain of the subsequent stages and have an effect on the sound. Normally a pre amp should have a very low output impedance under 600 Ohms. However to get this low, the designer will usually have to include additonal buffering stages (cathode followers) to the outputs. More circuitry means more chances for the signal to pick up additional noise and distortion and loose signal along the way. The power amp should have a desired input impedance ten times, or more, higher that the pre amp's output impedance. (500 Ohms out to 50 kOhms in.) Anything higher than ten times will give the system some stability while anything lower could contribute to system instability and will typically not have the dynamic drive of the higher impedance input nor the same frequency response. 250 kOhms is typical for a (classic) tube power amp input. Beyond that point, there is little benefit to be had in raising the input impedance as it will need to be stepped down again to operate the subsequent stages of gain devices. |
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Gold Member Username: Jan_b_vigneDallas, TX Post Number: 7705 Registered: May-04 | Sorry, you'll know if the output voltage of the pre amp relative to the input sensivity of the power amp is high enough, when you can drive the amplifier into distortion. If the volume pot is set to maximum clockwise rotation and the signal is loud enough without distortion, then, for all practical purposes, you have sufficient voltage and adequate sensitivity. |
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Gold Member Username: NuckParkhill, Ontario Canada Post Number: 1482 Registered: Dec-04 | Absolutely lovely...thanks Jan. Q2..will the pre/receiver run into distortion itself with the clockwise rotation? Unit in question is H/K avr55(10 yrs old). Gracias |
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Gold Member Username: Jan_b_vigneDallas, TX Post Number: 7710 Registered: May-04 | As I stated, you can run the inputs into saturation or overdrive which will result in distortion. Turning the vc all the way clockwise will essentially just remove it from the circuit. At full "volume", if you measure the resistance of the vc across to ground, you should get a 0 Ohms reading. "Turning down the volume" does nothing more than increase the resistance of the potentiometer. If you have a 100 kOhm pot as a vc, you should read 100 kOhms at the "rest" position. Decreaseing the resistance wil increase the volume/voltage until the vc is finally out of the circuit. At this point there should be no clipping of the pre amp's waveform as it is simply running as if the vc were not in the signal path, which, for all intents, it is not. The vc has become nothing more (or so we would like to think) than a high priced jumper. So think of the pre amp as constantly running at full gain and the vc simply adjusting the input voltage from the sources to adjust the output voltage of the pre amp. In essence this is how a pre to power amp connection works also. The power amp's circuits are running at full gain but the output voltage of the amplifier is determined by the pre amp's output voltage (input voltage to the power amp) and the sensitivity of the power amp's input circuitry. (There's a bit more to it than that, but this is a good place to begin thinking about how the system works.) So the relationship between input voltage to the pre amp to output voltage of the pre amp (which than becomes the input voltage of the power amp) determines where (on the vc) the power amplifier will "clip". That brings us full circle to the higher the source's output voltage, the lower on the vc's position will the power amp run out of steam. Now, of course, that is all on a bench and doesn't take into account the varying current demands of the speaker on the amplifier's ability to remain undistorted. The sources and pre amp have it fairly easy since they are primarily concerned with passing voltage from one unit to the next, and the next unit really doesn't fight back. Unfortunately, the power amp has to face a speaker/transducer which converts one form of energy (electrical) into another form of energy (acousitc) and the transducer would really rather not do that task. So, where the pre amp merely drives another gain stage circuit, the power amp has to drive a motor which resists all attempts to control its motion. |
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Bronze Member Username: Dan_the_manLondon, Ontario Canada Post Number: 71 Registered: Jun-04 | were you looking for a tweak Nuck? Good information btw, i asked that question to myself a little while ago when thinking of getting a two channel system (seperates) for music listening. I personally was hoping that by stepping up input signal voltage that i would achieve either more detail or at least greater amplifier output at the same volume. With the above being said i'm going to guess for most of us that its not going to make a difference, but perhaps with some equipment it might?? And with some equipment it may cause harm or distortion with too high of a input voltage from the preamp to the power amplifier? Is that right? Jan.. in regards to your last paragraph are you basically referring to EMF/ induced magnetism and its related interference with nomimal speaker impedance? If so i i think i actually get it. |
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Gold Member Username: NuckParkhill, Ontario Canada Post Number: 1491 Registered: Dec-04 | Thanks, Jan. The results of overpowering speakers, and over tasking amps I am all too familiar with! I am rather interested in the capacity of pre amps to deliver in a variety of loads, and how (if any) each can deliver. If I missed specifics in your post...sorry. I appreciate your info. Nuck |
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Gold Member Username: NuckParkhill, Ontario Canada Post Number: 1492 Registered: Dec-04 | Hi Dan! The bad factor, as I remember from dc physics is CEMF Counter Electromotive Force. Produced by the breaking down of fields produced by primary fields, in that case, by 12vdc starter motors. But electricity never studied law. And speakers never studied either |
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Bronze Member Username: Dan_the_manLondon, Ontario Canada Post Number: 73 Registered: Jun-04 | well i am an automotive tech, and mostly only deal with DC i just wondered if it was the same..... i GUESS not, lol. speakers i only know what sounds good. No idea how to make it happen. cheers |
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Gold Member Username: NuckParkhill, Ontario Canada Post Number: 1493 Registered: Dec-04 | Sorry Dan, wrong post there. A seperate power amp really opens things up a lot, if it fits your system. Beyond the power for volume, which in fact I didn't need, the power amp has added a lot of speed and treble space, for whatever reason, to for me. And more power just can't be wrong, right? |
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Gold Member Username: NuckParkhill, Ontario Canada Post Number: 1494 Registered: Dec-04 | Fanshawe? Motive Power? I was there 1983-85 |
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Bronze Member Username: Dan_the_manLondon, Ontario Canada Post Number: 74 Registered: Jun-04 | lol i was there 1996, after a falling out in sept of that year for mechanical engineering |
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Gold Member Username: NuckParkhill, Ontario Canada Post Number: 1495 Registered: Dec-04 | Dan, shoot me a mail. |
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Gold Member Username: Jan_b_vigneDallas, TX Post Number: 7714 Registered: May-04 | Your second paragraph is essentially correct. You aren't going to gain anymore detail by increasing the overall voltage unless the signal had been so low in level that its detail was swamped by circuit noise. The better alternative to this situation, however, is to lower the circuit noise rather than raise the signal voltage. Sooner or later you'll realize you cannot continue to raise the signal level but you can always try to lower the noise floor. The last praragraph in my post refers to the many things that can go wrong when an amplifier tries to drive a speaker. The speaker is a transducer as I stated, so it has to perform the conversion of energy which is not a simple task nor one that assures fidelity. The impedance of the speaker is constantly changing with frequency and the heat generated by the operation of the driver and voltage/current passing through the crossover components. As the impedance dips, the amplifier must deliver more current. As the impedance rises, the amplifier must deliver more voltage. The passive components create phase shift in the signal. As the speaker's voice coil heats, it, being a coil (inductor) with voltage running through it, changes its relative impedance forcing the amplifier to constantly deliver more current to the voice coil. The speaker's voice coil is a motor, though a very inefficient one at often less than 5% efficiency, and when it is excited by incoming voltage the movement of the coil in a magnetic field generates out going voltage and current. That current has to go somewhere and eventually ends up back at the amplifier's outputs for the amplifier to deal with. The speaker cones do not want to be moved and once they are, they want to return to rest or they want to continue with the momentum they have developed. All this time, the amplifier is trying to block any of the DC voltage which courses through its circuits from escaping its outputs to the speaker. All in all, the job of the amplifier is rather amazing to me that it gets it right most of the time. Just to clarify something in my post; "So think of the pre amp as constantly running at full gain ... ". Think not of the pre amp running at full "clip", if you will; but, rather, if a gain stage in the pre amp is designed with 25dB of gain in the circuit (or 5db of gain), it is always operating at the full 25dB (or 5db) of gain. To do otherwise would result in pandemonium. The amount of input voltage to the gain stage circuit will be determined by what the vc passes, and this incoming votage will then be stepped up by 25dB (or 5db) in that gain stage. So, the net result is each gain stage operates at all times at its designed step up level. It is up to the designer to lay out the circuit so the preceding stage cannot overdrive the following stage. |
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Bronze Member Username: Dan_the_manLondon, Ontario Canada Post Number: 75 Registered: Jun-04 | how do you think my marantz sr-6300 would pair up with a power amp? I also was looking at a pair of paladium mono's, any ideas? I think they daisy chain, only one set of pre outs on the marantz..... |
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Gold Member Username: NuckParkhill, Ontario Canada Post Number: 1498 Registered: Dec-04 | I gotta check the inputs on those, if you wanna chain, the Outlaw 200's are made for that...and more |
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Bronze Member Username: Dan_the_manLondon, Ontario Canada Post Number: 76 Registered: Jun-04 | thanks jan |
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Gold Member Username: NuckParkhill, Ontario Canada Post Number: 1503 Registered: Dec-04 | Jan, I've seen you post before that it is rather amazing that this stuff works at all. Being the first Saturday of the month, I shall raise a toast to all the loons and geniuses(Wile E comes to mind), who have been able to give us all so much pleasure. And toast the diabolical morons who have caused us all so much consternation. |
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Gold Member Username: Jan_b_vigneDallas, TX Post Number: 7724 Registered: May-04 | Yes, I am still in awe of all those who figured this stuff out. After about the third glass of Glenmorangie or Chivas I sit in the darkened room, listening and imaging all those tiny, little guys swiftly carrying positive and negative electrons back and forth from the CD player to the speakers. Amazing stuff! |
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Gold Member Username: NuckParkhill, Ontario Canada Post Number: 1519 Registered: Dec-04 | Indeed. I have opened up combustion engines and marvelled that anything could work so well, when physics say that the thing should blow to pieces at any given moment. The electronics end of things are equally as finite as a micro-polished camshaft, but given to non-moving parts. The ability to co-ordinate the little bits to do one's bidding(mostly) and to persue the perfection of electron management may expose one's desire for control(often a male domain) and for gratification(also typically male). Is it Alan Alda in here or is it just me? |
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Gold Member Username: John_aLondonU.K. Post Number: 3965 Registered: Dec-03 | Awesome grasp of the technology here, except the bit about positive electrons! I always thought "It's a miracle you hear anything at all" about LP. Let alone actual music coming out of these things. |
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Gold Member Username: Jan_b_vigneDallas, TX Post Number: 7750 Registered: May-04 | John - For the record, I am just as fascinated by the negative electrons. Mostly, I am fascinated by the people who figured all this stuff out with nothing more than a slide rule. |
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Silver Member Username: PraetorianCanada Post Number: 110 Registered: Dec-05 | Becareful Jan! Only John Wagner's cables can contain both matter and anti-matter! |
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Gold Member Username: John_aLondonU.K. Post Number: 3967 Registered: Dec-03 | Somewhere there is a universe of antimatter with people remembering to wire up the interconnects with the arrows pointing towards the source. |
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Bronze Member Username: Dan_the_manLondon, Ontario Canada Post Number: 79 Registered: Jun-04 | lol i guess no one has read about the "hole" theory of amperage flow..... no one really knows how it all works there are only "theories" |
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Silver Member Username: My_rantzAustralia Post Number: 336 Registered: Nov-05 | John, when you get some directional cable, just go ahead and connect them in reverse to the arrow - go on - I dare you. Just be sure to have a fire extinguisher nearby. Some people have called an excorcist in when inadvertantly connecting directional cables the wrong way. They thought the devil had possessed their audio systems when the music played backwards. Believe it or not :-) http://stereos.about.com/od/homestereotechnologies/a/cables_tech_3.htm |
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Bronze Member Username: Dan_the_manLondon, Ontario Canada Post Number: 80 Registered: Jun-04 | http://www.phys.ualberta.ca/~gingrich/phys512/latex2html/node63.html haha that was just for sh*t's and giggles |
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Gold Member Username: John_aLondonU.K. Post Number: 3976 Registered: Dec-03 | Question: will the cables burn-in just as well with the arrows pointing towards the source.....? Sorry if everyone already knows the answer to this. |
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Gold Member Username: Jan_b_vigneDallas, TX Post Number: 7795 Registered: May-04 | What if the arrows are in a foreign language? |
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Gold Member Username: NuckParkhill, Ontario Canada Post Number: 1575 Registered: Dec-04 | If I could spell heilogryphics, I would insert it here. Really. |
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Gold Member Username: John_aLondonU.K. Post Number: 3978 Registered: Dec-03 | Jan, They already are. Nuck, You could, and did. |