Newbie Amplification Question: Understanding Impedance and Power
May 12, 2020 at 5:58 PM Thread Starter Post #1 of 3

Hoegaardener70

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Hi! I had a question on amplification and posted this to the Abyss Thread, but there are no replies (yet). So I opened up a thread here since I know of at least two other members having the same difficulty - which is determining if a particular amp would work (well) with a particular headphone. Please keep it friendly, I know that this is a very basic question for some. Equally I read in threads a lot of misconceptions as well, so my question - and your answer - might help not just me but many others. Here it is

"I must admit that I am pretty much a Noob on amp specs, output power and headphone requirements. I do know that the ab-1266 tc requires a lot of power, but I am not sure in which technical data this translates. Abyss states the following parameters:

  • Impedance: 47 ohms nominal
  • Sensitivity: 88 dB/mW
Any amp is described with output power and voltage. For example, the iCan Pro has an power output of 16 ohms, with balanced 14,000mW. Output Voltage is 600 Ohms with balanced >23 V . Could anybody explain the relationships here? My specific question is, can the ab-1266 tc be driven with an amp producing 2 x 1W @ 1kHz under 32 Ω?Thanks for your help"
 
May 13, 2020 at 3:47 AM Post #2 of 3

ProtegeManiac

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"I must admit that I am pretty much a Noob on amp specs, output power and headphone requirements. I do know that the ab-1266 tc requires a lot of power, but I am not sure in which technical data this translates. Abyss states the following parameters:

  • Impedance: 47 ohms nominal
  • Sensitivity: 88 dB/mW

88dB sensitivity indicates you'd need somewhere around 2048mW of power.

The amp you get however has to deliver that 2048mW into a 47ohm load, since the output power changes depending on load.

Think of an internal combustion engine. Torque changes with rpm, but horsepower is a function of torque X rpm, and torque increases early then begins to level off, so you can have an engine in a pick up truck that has 275hp and 350lb/ft of torque but the same engine block with other parts configured to perform at higher RPM in a Corvette will do 500hp and 480lb/ft of torque; and then you'd have a Ferrari that does even higher rpm so even if it does 550hp it's only doing about 425lb/ft of torque.


Any amp is described with output power and voltage. For example, the iCan Pro has an power output of 16 ohms, with balanced 14,000mW. Output Voltage is 600 Ohms with balanced >23 V . Could anybody explain the relationships here?

Power varies by load impedance that is presented to the amplifier. Like horsepower, power in watts or fractions thereof are from an amp is a function of current or voltage delivery. I won't go into the math as I barely remember it, but at lower impedance current matters more, so they rated it at 4800mW at 16ohms. You can still compute for power in watts at higher impedance, but for some reason they stated the voltage, as output whether you use it single ended (ie common ground) or balanced/differential drive mode (separate L- and R-).

In any case, the voltage or power output at high impedance loads doesn't matter for your specific application, since the Abyss' nominal impedance is 47ohms. A very quick way to guesstimate is to assume that power halves as impedance doubles (note: not all amps do this, regardless of what its highest wattage output is), so best case scenario, you'd have somewere around 5250mW at 48ohms. Even assuming it does not just halve the the output (unlikely, considering it's still spitting out 11.5V into 600ohms - that's only a little under what my Meier Cantate.2 can put into a lower impedance load), there's so much power at 16ohms and 47ohms isn't too far off it's unlikely to not have at least 2048mW.

And even then it's not like you're using all of that all the time, or even when delivering peaks in properly recorded music. That guesstimate for power requirement based on sensitivity has more to do with "you will absolute not distort at the peaks; go way over, andit would have to be a badly designed amp for electronic noise off the amp to be a problem."


My specific question is, can the ab-1266 tc be driven with an amp producing 2 x 1W @ 1kHz under 32 Ω?Thanks for your help"

It can get it loud.

Will it sound decent? Maybe, if the noise+distortion levels are below audibility, and you don't try to crank it up that you actually have the amp clip when there's a peak in the music.

You want to be absolutely certain, shoot for around 2000mW, but watch out for noise levels. That said this isn't as much of a problem with headphones where you mostly get Class A or good Class A/B amps, unlike speakers where you can't just pull a PA system Class H amp with 300watts and then be surprised that even the 89dB/1W speaker is hissing at sane volume levels (and could even be audible while music is playing) and your friend's 50W at 32ohms Class A dual mono push-pull KT88 amp sounds cleaner and actually has more audible low end, just that if you really crank it up you can start hearing that bottom end (and the rest of the range) start falling apart.
 
May 13, 2020 at 9:06 AM Post #3 of 3

Hoegaardener70

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88dB sensitivity ...

ProtegeManiac, thank you so much for taking the time explaining and answering my questions- I really appreciate it and I hope this is not only of use for me, but for other head-fiers as well.
 

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