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Why do amplifiers with a high output impedance have trouble delivering power/current to low impedance speakers/headphones?

Music707

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Hi everyone,

I've read about damping factor, and how it relates to the control of drivers, and the corresponding changes that it can make to a frequency response based on the impedance curves of the amp and drivers.

However, I've always noticed that amplifiers which have a high output impedance and corresponding low damping factor were never able to deliver much power/current to low impedance speakers/headphones. Is this at all related to damping factor, or is there other variables involved here? What causes this to happen? I feel like this is a really simple question but I haven't really found a simple answer to it yet.

Also, beyond this, I've found examples such as the SPL Phonitor X, which despite having an output impedance less than 0.4ohm (measured by Amir) was still unable to provide enough power/current to low impedances. This especially made me question things, this to me looked similar to the characteristics I've commonly found high output impedance amplifiers to have. Is this to do with a lack of current able to be supplied by the power supply?

Thanks,
Virtua

For headphones the video below should provide a satisfactory explanation (which BTW is common for Julian Krauses's videos):

 

SSS

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For headphones the video below should provide a satisfactory explanation (which BTW is common for Julian Krauses's videos):

What is demonstrated in the video is of course right when the headphone intentionally is built for a voltage source with low impedance. I guess that in reality it is this way. In electronics the other way is also used, high impedance source which delivers a constant or modulated current. For example, a transistor is controlled mostly by base current, the base voltage is around 0.7 Volt for silicon.
 

DonH56

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sarumbear

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That's what they say.
If they are wrong so am I :)

View attachment 270639

(it's the one inside Peachtree that Amir tested )
38A at 4ohms means 5776Watts.

If you don’t even understand Ohms law I suggest you not to worry about these things and just enjoy the music.
 

Sokel

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38A at 4ohms means 5776Watts.

If you don’t even understand Ohms law I suggest you not to worry about these things and just enjoy the music.
Oh,I do!
(It's only 2x600 - 1x1200,take your pick,that what's Amir measured but don't correct me,correct the Ice Power people,I posted their pdf,I'm more suspicious than anyone in here,don't worry)

They will add a 5000 watt one in the line in time,they have announced that as well.
 

fpitas

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I doubt you'll see that 38A unless the output is almost shorted. I recall it starting as a trendy spec to sell amps to people with bizarre speakers that dip below an ohm.
 

sarumbear

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Oh,I do!
(It's only 2x600 - 1x1200,take your pick,that what's Amir measured but don't correct me,correct the Ice Power people,I posted their pdf,I'm more suspicious than anyone in here,don't worry)

They will add a 5000 watt one in the line in time,they have announced that as well.
If you do then you should know when you see a silly spec and ignore it. It’s not nice to refer to that saying if they are wrong then you are.
 

sarumbear

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I doubt you'll see that 38A unless the output is almost shorted. I recall it starting as a trendy spec to sell amps to people with bizarre speakers that dip below an ohm.
In other words it’s a lie
 

fpitas

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Sokel

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In other words it’s a lie
Then again...


ohm's.PNG


(2.7 Ohms is it's rated minimum spec)
 

sarumbear

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fpitas

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I would suspect less than momentarily :).
It seems like it, if they guarantee it works into that 2.7 ohms continuously.
 

sarumbear

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I only put two of them,if the calc is wrong so am I (²).
As I said earlier. If you don’t understand basic electricity you are better of enjoying the music.

PS. Naturally, nothing is stopping you to learn it.
 

restorer-john

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I would suspect less than momentarily

The 'high current delivery' crowd have been touting absolutely ridiculous current numbers for many decades. Basically, you take an incredibly low resitance 0.1R (like the emitter resistors) and drive the amplifier with a single cycle (yes, one cycle only) and measure the peak voltage drop. Convert that to a peak current.

The output stage will survive (hopefully) and the marketing department gets a stupid high current number that bears no relationship to anything the amplifier will ever see in the real world except under a fault condition.
 

Sokel

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The 'high current delivery' crowd have been touting absolutely ridiculous current numbers for many decades. Basically, you take an incredibly low resitance 0.1R (like the emitter resistors) and drive the amplifier with a single cycle (yes, one cycle only) and measure the peak voltage drop. Convert that to a peak current.

The output stage will survive (hopefully) and the marketing department gets a stupid high current number that bears no relationship to anything the amplifier will ever see in the real world except under a fault condition.
They have tons of papers in their extranet section (for professionals only I think,I can't get in it,I only saw some of them in diyaudio about their full bridge stulf,blah,blah),you electrical guys could helps us all pointing out the BS stuff cause all we rest of us have is the (very detailed,ok) public pdf.


Edit:Hypex states similar numbers :facepalm:
I think they need the stick too!:)

Hypex.PNG
 
Last edited:

sarumbear

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They have tons of papers in their extranet section (for professionals only I think,I can't get in it,I only saw some of them in diyaudio about their full bridge stulf,blah,blah),you electrical guys could helps us all pointing out the BS stuff cause all we rest of us have is the (very detailed,ok) public pdf.


Edit:Hypex states similar numbers :facepalm:
I think they need the stick too!:)

View attachment 270745
Ha! Hiccup mode. Creative… :p
 
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