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(Theory) Why don't all amplifiers supply the same voltage into different loads (impedances)??

post #1 of 10
Thread Starter 

Could you please explain me (simply, if possible, as I don't have much knowledge in electonics) why some of the amplifiers have

  • the same voltage output into different loads (eg. 100W in 8 Ohm, 200 into 4, 400 into 2, with V=const, same about headphone amplifiers)

whereas other amplifiers supply

  • the same power into different impedances (eg. 100W into 8, 4 and 2 Ohms - voltage decreases linearly with impedance decreasing)
  • or even non-linear voltage supply (eg. 250mW in 16 Ohm, 220 into 32, 160 into 600)

 

Hope I didn't make it sound too complicated :)

 

Happy New Year!

U6astik

post #2 of 10
Thread Starter 

Em, up?

post #3 of 10

The more resistance you conect to amplifier the less power it can deliver to it.

 

It's impossible deliver the same power changing the headphones or speaker you conect for the same quantity of volume gain you set on amplifier, because their resistance to electricity isn't the same.

 

Low impedance headphones improve with amplifiers deliver a good amount of current (Hifiman's for example).

High impedance headphones improve with amplifiers tat deliver a good amount of voltaje (Sennheiser's for example).

post #4 of 10
Thread Starter 
Quote:
Originally Posted by Remior View Post
 

The more resistance you conect to amplifier the less power it can deliver to it.

 

It's impossible deliver the same power changing the headphones or speaker you conect for the same quantity of volume gain you set on amplifier, because their resistance to electricity isn't the same.

 

Low impedance headphones improve with amplifiers deliver a good amount of current (Hifiman's for example).

High impedance headphones improve with amplifiers tat deliver a good amount of voltaje (Sennheiser's for example).

 

Remior,

 

You have converted my first example (eg. 100W in 8 Ohm, 200 into 4, 400 into 2, with V=const, same about headphone amplifiers) into words :)

 

In reality, I am not able to tell how much power can be supplied to the driver (apart from the power into 1KHz), as the impedance of driver is dependent on the frequency. So, at each frequency there will be different amount of power supplied.

 

Anyway, we are not talking about speakers, but amplifiers.

 

For example, if we take Lamm amplifiers, there are ML models, which output power is the same into 8/4/2 Ohms (see their site for proof), which tells us that they supply the same power into any impedance between 2 and 8 Ohms (or even wider impedance brandwich).

But there are also M models, which can supply the same voltage into 8 or 4 Ohms (again, can be seen on their webpage), so we can assume that the voltage across the 4- to 8 Ohm load is constant.

 

WHY do they differ?

 

Obviously, to have “uncoloured” sound it is better to have a constant voltage. (Because if you have 10 V going into 20 Hz and, say, 20 V into 200 Hz, 200 Hz will sound 6dB louder, if I am not mistaken. So even if your driver’s frequency response is perfectly flat, your amp will add its own colour, which isn't what we're into ;)

 

But there are a lot of amplifiers (I would say most of them), which are not able to give us constant voltage.

 

Why?

 

P.S. I doubt that only high impedance headphones need high voltage, but I agree about current (due to Ohm’s law)

post #5 of 10
Quote:
Originally Posted by U6astik View Post

 

Obviously, to have “uncoloured” sound it is better to have a constant voltage. (Because if you have 10 V going into 20 Hz and, say, 20 V into 200 Hz, 200 Hz will sound 6dB louder, if I am not mistaken. So even if your driver’s frequency response is perfectly flat, your amp will add its own colour, which isn't what we're into ;)

 

But there are a lot of amplifiers (I would say most of them), which are not able to give us constant voltage.

 

Why?

 

P.S. I doubt that only high impedance headphones need high voltage, but I agree about current (due to Ohm’s law)

 

I won't try to give you a simple explanation because I don't have all the necessary knowledge, but I know for a fact that you can't use little school DC formulas to understand amplifiers. Most dynamic drivers are complex loads (not purely resistive) and non-linear as you said, so the math is quite a bit different and the power variables to achieve a certain SPL at a given frequency change across the spectrum. Let's just say that different amplifiers have different behaviours with different loads because they have different designs, with different topology. Now if you want to understand those circuit designs, you might need some more fundamental electronic knowledge, which you won't find here.

post #6 of 10
Thread Starter 
Quote:
Originally Posted by Rem0o View Post
 

 

I won't try to give you a simple explanation because I don't have all the necessary knowledge, but I know for a fact that you can't use little school DC formulas to understand amplifiers. Most dynamic drivers are complex loads (not purely resistive) and non-linear as you said, so the math is quite a bit different and the power variables to achieve a certain SPL at a given frequency change across the spectrum. Let's just say that different amplifiers have different behaviours with different loads because they have different designs, with different topology. Now if you want to understand those circuit designs, you might need some more fundamental electronic knowledge, which you won't find here.

 

Rem0o,

 

Thank you for your reply.

I am quite sorry to hear that there is nobody to explain me some basic electronic things, as I would't like to start learning electonic science..

 

But do you personally agree with my thoughts about the constant voltage advantages?

post #7 of 10

Most voltage problems come from high impedance sources. Using a simple voltage divider, you should understand.

Let say I have a SET OTL tube amp with 50 ohm output impedance. If I plug a 50 ohm headphone in, the source is going to see a 50+50 ohm load, so 100 ohm. If the source is a perfect voltage source (constant volts) and outputs 10 Vrms , only half the voltage (50 / 50+50) is going to the wanted load, the heapdhones, so 5 V rms, which translate into 500 mW rms. Now if we plug a 600 ohm headphones in, the source is going to see a 600+50 ohm load and the headphones will get (600/650)*10, so 9.2 V rms, which gives 140 mW rms. As you can see, depending on the load, the source won't be able to output the same voltage to the given load, thus the non-linear pattern.


Edited by Rem0o - 1/2/14 at 4:10pm
post #8 of 10
Thread Starter 
Quote:
Originally Posted by Rem0o View Post
 

Most voltage problems come from high impedance sources. Using a simple voltage divider, you should understand.

Let say I have a SET OTL tube amp with 50 ohm output impedance. If I plug a 50 ohm headphone in, the source is going to see a 50+50 ohm load, so 100 ohm. If the source is a perfect voltage source (constant volts) and outputs 10 Vrms , only half the voltage (50 / 50+50) is going to the wanted load, the heapdhones, so 5 V rms, which translate into 500 mW rms. Now if we plug a 600 ohm headphones in, the source is going to see a 600+50 ohm load and the headphones will get (600/650)*10, so 9.2 V rms, which gives 140 mW rms. As you can see, depending on the load, the source won't be able to output the same voltage to the given load, thus the non-linear pattern.

 

Rem0o,

 

God, I didn't even think about that.. Now, it's starting to get more complicated than I though before.

Thank you!

post #9 of 10
Quote:
Originally Posted by U6astik View Post
 

 

Rem0o,

 

God, I didn't even think about that.. Now, it's starting to get more complicated than I though before.

Thank you!

 

heheh now I think you get my point, i'm not native english speaker and it's hard to me explain myself this way but remo has put the idea on your head. But it's even mor complicated because the Ohm aren't costant in all the frequencys.... look at the Senn HD800 for example:

 

You can see the peak at 600 ohm of impedance on 100Hz... 

post #10 of 10

And don't forget that the 600 ohm peak is purely resistive (0 deg phase) while the rest is also part reactive (inductive or capacitive), which is harder to drive, even if the ohm rating is lower.

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