Quote:
If the first amp can't maintain the signal into any kind of load, then double amplification would presumably make the signal worse, since you are essentially amplifying the signal + error the second time around. However, most amplifier inputs present a higher impedance load than headphones, so unless the first amp is severely underpowered, the second amp could act as a sort of "buffer" for the tougher load the headphones present.
In some cases if the headphones are REALLY difficult to drive this might be advantageous; you could use the first amplifier to drive the more benign load of the second amplifier's input, and the second amplifier would take the load of the headphones.
IMO, you are probably better off using one amp for most loads, since it will probably be able to handle most loads fine, and you won't be getting any additional error added onto the signal (however small it probably is.)
good point.
there are different circuits for outputs that go into a preamp compared to outputs that are for driving a speaker.
and usually these circuits are designed to meet the needs of the impedance curve of whatever is being plugged into the output.
for instance.. speakers usually have a high impedance at the lower frequencies and then a sudden drop that gradually rises.
a quality amplifier would know this bit of information and would take some steps to 'match' the two pieces of equipment for a much better end-result.
the input of the second amp might have an entirely different impedance curve.. or simply the same shape but substantially higher in impedance.
and what the quote mentioned is that the first amplifier might try its hardest to push voltage into the impedance of the second amplifier but the situation is the same as the example below.
* you are trying to bench press more than what you can actually lift.. so instead of pushing the bar all the way up to the top, you get halfway up and start to struggle as you slowly lower the bar until it is resting on your chest or neck *
the first amplifier will try to 'lift' more impedance than it is capable of lifting.. so instead of reaching full power (or full audio detail) the voltage is very weak for some frequencies, which makes some 'tones' or 'notes' hard to hear.
presumably worse situations would be when the second amp doesnt get enough voltage to amplify a signal at all.. which is a total loss of audio.
in car audio you here things like an amplifier that has power at 2 ohms and even 1 ohms.
usually as the ohms gets lower the wattage increases.
but what if you went the other way?
eventually the ohms would get so high that the wattage reaches zero !
so speaking specifically..
if the first amplifier is only sending a few 'watts' at the impedance of 5 khz.. then 5 khz will be difficult to hear with your ear and 10 khz wont have enough 'watts' for the second amp to pick-up and amplify.
its like watching a very bright bulb start to die out.. but instead of going totally dead, the thing turns orange and red with the very low voltage applied.
THAT is the error being mentioned.
and i suppose two amplifiers might be made to specifically work together with eachother as a 'match' to offer an end-result that applies the same amount of voltage throughout the frequency spectrum.
you have to understand that speakers do not receive the same amount of power for every note that they play.. IDEALLY they should get the same amount of power because the voice coil is thermally capable of handling the power.
but realistically the impedance curve dictates that more power is required here at this low frequency compared to somewhere else on the impedance chart.
car audio is an easy example.
the lowest impedance of a speaker might be 3.9 ohms.. so you look at the amp and see 100 watts.
but the highest impedance of that speaker is 50 ohms.. so look again at your amp and see how many watts does your amp put out at 50 ohms !!
an honest way to match 'audiophile' pieces of hardware would be to find an amp that gives you 100 watts at the 50 ohms and then use an equalizer to remove excess power as you go down the impedance curve towards 3.9 ohms
(this is usually the trick they use to make those giant paper stage-woofers sound so loud and good)
to say things once again much more simple.. the speaker output might be designed completely backwards compared to the pre-amp output.
