[High_Q]

I have stated this question on another thread, but it has gotten locked, and hopefully I can get a good explanation this time.  I'll try to be clearer with my question this time.  
 
I was curious why my tube amp(Elekit TU882) would cause hiss even at it's lowest impedance setting( 4-32ohm), but my Audinst HUD-mx1(DAC/SS amp) would not.  In addition, my JDS labs CMOY would output hiss at null volume.  Hiss is outputted on what I believe to be very sensitive IEMs such as UM3X, 1964-T customs, or ER4P.  My Sony X1051 outputs hiss at null volume, but my Sony NWZ S636F does not, even with sensitive IEMs.  
 
All are audio sources so I assume the parts used are audio grade.  So far, what I believe has to do with hiss is output impedance being much greater than the impedance of the headphones.  Another poster have stated that too much current going through the transducer(probably because the low impedance of the IEM), but I don't think that makes much sense.  What doesn't make sense is adding a impedance adaptor for ER4P supresses hiss(which adds to output impedance), but output impedance close to 0 is ideal.  It contradicts the theory that high output impedance causing hiss, although the adaptor is resistive.  I know sensitivity has to do with hiss because obviously all the IEMs that I have listed have high sensitivity, but I really don't know the relationship with the different signal sources. I know that thermal noise is picked up by the conductors and resistors in the circuit(my CMOY hisses even with metal shield, it's just not picking up RFI or other nearby noises), but what I am trying to get an understanding of is is what type of circuit configuration will create hiss with sensitive IEMs.  My amps and CMOY have audio grade parts.  I'm looking for an explanation on this so that I would be more knowledgable in what kind of specs to look for when I pick out my sources for sensitive IEMs.  

 

[xnor]

Since you're an EE you shouldn't have troubles looking at the opa2227 (used in the cmoybb) datasheet, and take a closer at the noise performance in particular. That cmoy seems to use 100k ohm resistors for source impedance (which is kinda high), and 10.2k + 2.05k resistors for a default gain of 6. (!)

That's why you get audible noise (with sensitive headphones) at the output and not because of some weird guesses about output impedance. If you don't understand what I'm talking about I suggest you to do some research before throwing around with insults.

 

[High_Q]

Actually my question is related to sensitive IEMs and it's relationship to equipment supplying audio signal if you read my title and what I have written above.  The data sheet doesn't cover how audible hiss is caused at the transducer's output for certain headphones. I know the theory behind noise, it's dependency on temperature, resistance, and how it get amplified depending on resistance values(which sets the gain). Basic stuff.

 

[xnor]

The datasheet doesn't mention hiss per se but the noise characteristics which can be used to calculate the output noise. Since you seem to be clueless simply search for op-amp noise calculators. Combine the result with the sensitivity of your headphones and you're set.

But since you already know this basic stuff we can also close this thread.

 

[High_Q]

Ok, that makes sense since the equation calculates the noise voltage at the output, and with IEM at the load, audibility of the hiss will be determined by the headphone impedance(V^2/Z) and therefore the power which determine the loudness of the noise.  But, I still don't understand how an impedance adaptor would decrease hiss though.  It reduces the sensitivity from what I saw on ER4 website.  How the impedance adaptor reduces the sensitivity I don't know, since it is in series with the transducer.

 

[High_Q]

I think I got it, the combination of the adaptor and the transducer as load should be a voltage divider of the noise voltage.  Therefore the noise voltage is divided between the resistor(taking chunk of the noise voltage) and the transducer, therefore the output noise is less.  But still don't understand why the sensitivity goes down with P to S adaptor.
 
If the mW is output power of the adaptor and transducer combo for it's sensitivity, then the P to S adaptor's sensitivity dropping makes sense.  

 

[The Monkey]

Perhaps we can make a thread in which you can only reply to yourself.

 

[nikongod]

I read a couple weeks ago that sensitivity is power dependent.


Quote:

 
Adding impedance inline effectively reduces the VOLTAGE sensitivity of the headphone. 
 
This reduces apparent hiss in many systems because random noise voltage is constant without any significant dependence on volume/voltage output. If you have a noisy source, ahead of a quiet amp, which causes random noise to increase and decrease with the output signal level that sucks as much as your source.
 
Anyways, use Kirchoffs voltage law on a 100ohm resistor in series with a 100ohm headphone VS just the 100ohm headphone. Lets say that the headphones need 1vrms to play at the desired level, and that the random noise is constant at 1mvrms. Although the noise and signal become inseparable once they are combined consider them as separate components for this problem. Label your schematic for noise and signal voltage separately and it should be very easy to see.
 

 
Quote:

Sensitivity is power dependent.  Condtradiction is:
 
one would say, it's high current and resistor reduces the current.  Then you hear about having the output impedance to 0, and adding resistor is adding a real impedance to the output to get rid of hiss.

  
 
Resistor does not equate to impedance.  its a real device, that decipates energy, not reactive device(which changes the phase, but yes there are some dicipation of energy).  But still don't know, how that factors in.
 

 

 

[High_Q]

I'm just trying to get some answers, no need to get offensive.  You need to chill the f out with your sarcasms.  And you're wondering why insults were thrown around.

  
 
Quote:

The datasheet doesn't mention hiss per se but the noise characteristics which can be used to calculate the output noise. Since you seem to be clueless simply search for op-amp noise calculators. Combine the result with the sensitivity of your headphones and you're set.

But since you already know this basic stuff we can also close this thread.

 

 

[nikongod]

 
Quote:

I'm just trying to get some answers, no need to get offensive.  You need to chill the f out with your sarcasm.  And you're wondering why insults were thrown around.

 

Its interesting how many threads you post in that turn into a fight between you and someone else. 
 
I like the monkey's idea.

 

[High_Q]

dB/mW, it is power dependent.  it is not dB/V.  loudness is caused by current applied to an impeding element, which is power.  you can have voltage without power applied, it's called open voltage. 
 
@Nikon.  It's usually with you, and I can solve that problem with the ignore feature.
 
Quote:

I read a couple weeks ago that sensitivity is power dependent.




 
 

 

 

[nikongod]

 
Quote:

dB/mW, it is power dependent.  it is not dB/V.  loudness is caused by current applied to an impeding element, which is power.
 

Sennheiser states the efficiency of their high end headphones in db@1v
It looks like AKG does too on the K701 at least (there is no way they are 105db/mw)

 

[High_Q]

We're getting off topic here, but was referring to various loads.  Well, the specs can state that for a specific headphone.  But I was referring to headphone as load in general(for all headphones), headphones varies in impedance therefore in general, power.  I really don't think V causes dB of power without the load.  You can have V at the output without a load. I don't know what the point of coming into a thread to bring up something that's not constructive to the topic at hand.

  Anyway I got my answer, probably will not help me much though because I don't know the circuit layout of the devices that I have.  I was hoping there would be something obvious to determine how my IEMs react with my equipment, but I guess not.  
 
@Monkey, looks like it worked out like that here.  I was hoping for someone to explain it for me to get a good understanding, but figuring it out myself would have been much better in this case.

 

[xnor]

@Nikon.  It's usually with you, and I can solve that problem with the ignore feature.

Yeah please make use of the ignore feature and effectively turn this thread into a soliloquy.

You should be glad that head-fi is such a friendly place and that you got your answer despite your attitude.