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post #46 of 83
6/4/11 at 2:39am
Thread Starter 
Quote:
Originally Posted by High_Q View Post

No, we recommend for accuracy and precision(simply for the right values) as an EE.  So, we don't say measure offset using dmm if it's not measuring offset.  We recommend a tool that measures offset.basshead.gif

 

Wrong, DC measurments, when input is DC.  Audio signal is AC+ offset(there will be some offset).  explain to me how offset is being measure by the dmm with the DC setting.rolleyes.gif
 

RMS what? Duhh. Voltage.. what is this thread about again, you should know by now..wink.gif

 

FYI

 

 

The RMS value of a set of values (or a continuous-time waveform) is the square root of the arithmetic mean (average) of the squares of the original values (or the square of the function that defines the continuous waveform).

In the case of a set of n values \{x_1,x_2,\dots,x_n\}, the RMS value is given by:

x_{\mathrm{rms}} =\sqrt {{{x_1}^2 + {x_2}^2 + \cdots + {x_n}^2} \over n}.

The corresponding formula for a continuous function (or waveform) f(t) defined over the interval T_1 \le t \le T_2 is

f_{\mathrm{rms}} = \sqrt {{1 \over {T_2-T_1}} {\int_{T_1}^{T_2} {[f(t)]}^2\, dt}},

and the RMS for a function over all time is

f_\mathrm{rms} = \lim_{T\rightarrow \infty} \sqrt {{1 \over {2T}} {\int_{-T}^{T} {[f(t)]}^2\, dt}}.

The RMS over all time of a periodic function is equal to the RMS of one period of the function. The RMS value of a continuous function or signal can be approximated by taking the RMS of a series of equally spaced samples. Additionally, the RMS value of various waveforms can also be determined without calculus, as shown by Cartwright.[1]

In the case of the RMS statistic of a random process, the expected value is used instead of the mean.



 


all of the above aside, if the DAC does not mute the output with no signal and the offset is constant at any volume (it is for the two devices I measured), then you're just measuring vanilla DC voltage on the outputs and a DMM is more than adequate
Edited by svyr - 6/4/11 at 2:43am
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post #47 of 83
6/4/11 at 5:39am
Quote:
Originally Posted by High_Q View Post

Wrong, DC measurments, when input is DC.  Audio signal is AC+ offset(there will be some offset).  explain to me how offset is being measure by the dmm with the DC setting.rolleyes.gif


I had a reply typed but came to the conclusion that this is better: LOLWUT?
 

 

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post #48 of 83
6/4/11 at 5:43am

There a bit you have to take into consideration.  It's not a easy as, get a dmm, find DC(if it does measure DC and do you know how?)

 

If you are concerned about offset damaging your phones.  

 

First look up mtf power rating of lowest rated headphones, it could think of a good one, ibuds.

 

If you are absolutely sure your offset is 150mV?  You have to take into consideration offset across the headphones(when load is applied).

 

Since there is output impedance, the load offset will be lower.

 

Find the lowest rating

 

apply the formula:

 

P=V^2/Z  , where Z=effective impedance of the headphone, and V=offset voltage across the heaphones

 

If the offset value alone is not at damaging level, to find out with audio signal applied:

 

1. Measure the peak at max voltage(O-scope required)

 

Find the output impedance of the headphone out, and minimum impedance of the headphones.

 

Either figure out the via voltage divider, headphone load voltage at max voltage swing outputted by the headphone out.

 

P=V^2/Z

 

2.  Measure load(across the headphones) voltage

 

P=V^2/Z

 

Z=lowest effective headphone impedance

 

measurement tools must have necessary precision.

 

 

Finally, if is way beyond mft recommendation, dig lower if you are curious where it would tear apart your headphones.biggrin.gif

 

It makes no sense to measure offset and think it would damage the headphones without taking into consideration max voltage deviation from the offset(worst cas scenario)

 

 

 


Edited by High_Q - 6/4/11 at 5:53am
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post #49 of 83
6/4/11 at 5:57am

hahahahahahaha. how do you ever get ANYTHING done??

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post #50 of 83
6/4/11 at 6:00am

It's not about getting it done, it's about getting it done precisely(so you have the crucial measurements) so you don't damage anything(or make it sound like crap) in the process.wink.gif  Understanding what is going on helps exponentially.  Stuff I mentioned is pretty elementary and should be quick, from the your reply it seems like it would take you a long time to figure it out?
 

Quote:
Originally Posted by qusp View Post

hahahahahahaha. how do you ever get ANYTHING done??



 


Edited by High_Q - 6/4/11 at 6:09am
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post #51 of 83
6/4/11 at 6:13am

is that so, and your method is precisely how useful for someone who doesnt have a scope? and i speak of the vast majority of people on this forum that you are 'advising'. its also bull, measuring how much dc offset at the output to a safe level is easily within the usefulness of a regular 2 dollar dmm

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post #52 of 83
6/4/11 at 6:16am
Quote:
Originally Posted by svyr View Post




all of the above aside, if the DAC does not mute the output with no signal and the offset is constant at any volume (it is for the two devices I measured), then you're just measuring vanilla DC voltage on the outputs and a DMM is more than adequate


this

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post #53 of 83
6/4/11 at 6:18am
Thread Starter 
>If you are absolutely sure your offset is 150mV? You have to take into consideration offset across the headphones(when load is applied).

Surprisingly, at the driver terminals of DT48e it's still the same lol - about 145mV. (we've been over it about a page or two ago biggrin.gif )


>http://www.head-fi.org/forum/thread/550811/how-much-dc-offset-would-you-consider-harmful-to-hp-and-after-which-point-would-you-throw-the-commercial-amp-out/45#post_7517967

I don't understand the purpose of that post at all. We've been discussing DC offset on balanced line out, not for driving HP, and a very specific situation where the grnd to + and neutral and an offset and but not + to neutral.
The discussion about how much DC is harmful to your HP has been concluded on the prev page where it seemed to reach a consensus of - a) DC offset = bad, if enough may overheat the driver for low impedance/high sens IEMs b) the driver will possibly die from the quoted max power stated on the box, if the signal + dc offset manage to exceed that rating.


>1. Measure the peak at max voltage(O-scope required)

Not really, have a look at the manual for a good RMS meter. Most have have a min/max mode (don't really need it if applying a pure tone anyway), and you can get the V by applying a pure tone? Then adding the DC offset. (If I understand correctly AC is measured as a change so whatever the DMM will display will just be the AC amplitude....

any regular meter will measure the DC offset just fine lol. For AC signal measurement (accurate ones), maybe you'd want a true RMS meter, but IDK, a ballpark figure/accuracy of the meter for AC should all be in the DMM manual biggrin.gif
Edited by svyr - 6/4/11 at 6:23am
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post #54 of 83
6/4/11 at 6:27am
Quote:
Originally Posted by svyr View Post

>If you are absolutely sure your offset is 150mV? You have to take into consideration offset across the headphones(when load is applied).

Surprisingly, at the driver terminals of DT48e it's still the same lol - about 145mV.
I question the value because you have said you measure it with dmm

>http://www.head-fi.org/forum/thread/550811/how-much-dc-offset-would-you-consider-harmful-to-hp-and-after-which-point-would-you-throw-the-commercial-amp-out/45#post_7517967

I don't understand the purpose of that post at all. We've been discussing DC offset on balanced line out, not for driving HP, and a very specific situation where the grnd to + and neutral and an offset and but not + to neutral.
The discussion about how much DC is harmful to your HP has been concluded on the prev page where it seemed to reach a consensus of - a) DC offset = bad, if enough may overheat the driver for low impedance/high sens IEMs b) the driver will possibly die from the quoted max power stated on the box, if the signal + dc offset manage to exceed that rating.

The title of the thead? You asked?
>1. Measure the peak at max voltage(O-scope required)

Not really, have a look at the manual for a good RMS meter. Most have have a min/max mode (don't really need it if applying a pure tone anyway), and you can get the V by applying a pure tone? Then adding the DC offset. (If I understand correctly AC is measured as a change so whatever the DMM will display will just be the AC amplitude....
You can send a tone signal to the DAC, but must be digital.  It's a DAC? You will know the real V analog at the output.  You will need to measure that.  And figure out the offset?confused.gif
any regular meter will measure the DC offset just fine lol. For AC signal measurement (accurate ones), maybe you'd want a true RMS meter, but IDK, a ballpark figure/accuracy of the meter for AC should all be in the DMM manual biggrin.gif
My point is that dmm does not meaure offset, it measure RMS.  It all depends on what dmm is used, some dmm have more functionality and precision vs the $2 dmm qusp mentioned.
 
 


 


Edited by High_Q - 6/4/11 at 6:31am
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post #55 of 83
6/4/11 at 6:34am

i say the words in the previous post also because i dont see how you can find time to be an engineering student and still spend sooo much time in all areas of this forum carrying on utterly pointless arguments that are of no consequence whatsoever

 

so i'll leave you to it again. someone linked me to the particularly humorous content in the last couple of pages, only reason i'm here.


Edited by qusp - 6/4/11 at 6:36am
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post #56 of 83
6/4/11 at 6:41am

And your last few posts have any points?rolleyes.gif  I see that you have much greater amount of time to burn than I do base off of your 6,564 post since 6/2008biggrin.gif  I can see that forum count is not proportional to how much expertise you have in the area.  And you DIY. And you are on other forums with more forum counts.basshead.gif  Where do you find time to do... stuff... ?confused.gif I don't DIY(unless is worth my time), I have a job.  I don't sit on my ass looking for places to swap out for V-caps.  Is your job posting in forums all day?

 

I'm actually on the forum looking for good equipment, and try to contribute to posts by adding feedbacks based on what I know.

 

Quote:
Originally Posted by qusp View Post

i say the words in the previous post also because i dont see how you can find time to be an engineering student and still spend sooo much time in all areas of this forum carrying on utterly pointless arguments that are of no consequence whatsoever

 

so i'll leave you to it again. someone linked me to the particularly humorous content in the last couple of pages, only reason i'm here.



 


Edited by High_Q - 6/4/11 at 6:54am
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post #57 of 83
6/4/11 at 7:11am
Thread Starter 
>You can send a tone signal to the DAC, but must be digital. It's a DAC? You will know the real V analog at the output. You will need to measure that. And figure out the offset?

Tone to DAC obviously. and obviously you need to measure it (signal and offset). and That's what the post above says lol...


>It all depends on what dmm is used, some dmm have more functionality and precision vs the $2 dmm qusp mentioned.

You'd be pretty hard pressed to find an electronics multimeter without DC/mV mode. Sure the cheaper ones will have less precision and accuracy, but for a ballpark figure it'll do. qusp was meaning to say $5 smily_headphones1.gif (could be $2 at production biggrin.gif )


>My point is that dmm does not meaure offset, it measure RMS.

I have no idea what you're trying to say there, RMS and DC in the same sentence don't make sense to me...For measuring just the offset, http://www.head-fi.org/forum/thread/550811/how-much-dc-offset-would-you-consider-harmful-to-hp-and-after-which-point-would-you-throw-the-commercial-amp-out/45#post_7517798 that seems like an adequate way.


PS, guys please remain civil and don't flame each other. I've had enough flaming in the burson thread for one day biggrin.gif. High_Q please explain yourself clearly, so people who are currently going 'lolwut' can actually solidify where they think you're wrong and correct you, or change their mind.
Edited by svyr - 6/4/11 at 7:15am
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post #58 of 83
6/4/11 at 7:14am

Since this is bound to be locked soon I may as well get in...

 

All you seem to be doing is copy and pasting whatever you read on wikipedia in a thinly veiled attempt to appear intelligent.

Why do you feel the need to drag these threads into "I'm smarter at this than you are" pissing contests?

 


Edited by nattonrice - 6/4/11 at 7:17am
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post #59 of 83
6/4/11 at 7:22am
Quote:
Originally Posted by svyr View Post

>You can send a tone signal to the DAC, but must be digital. It's a DAC? You will know the real V analog at the output. You will need to measure that. And figure out the offset?

Tone to DAC obviously. and obviously you need to measure it (signal and offset). and That's what the post above says lol...


>It all depends on what dmm is used, some dmm have more functionality and precision vs the $2 dmm qusp mentioned.

You'd be pretty hard pressed to find an electronics multimeter without DC/mV mode. Sure the cheaper ones will have less precision and accuracy, but for a ballpark figure it'll do. qusp was meaning to say $5 smily_headphones1.gif (could be $2 at production biggrin.gif )


>My point is that dmm does not meaure offset, it measure RMS.

I have no idea what you're trying to say there, RMS and DC in the same sentence don't make sense to me...For measuring just the offset, http://www.head-fi.org/forum/thread/550811/how-much-dc-offset-would-you-consider-harmful-to-hp-and-after-which-point-would-you-throw-the-commercial-amp-out/45#post_7517798 that seems like an adequate way.
When I say RMS, I mean RMS of the signal put in.  If the signal is an audio signal, it will be alternating signal with a offset.  The dmm is measuring the RMS of the signal when switch to DC setting, unless pure DC is fed to the dmm, how does dmm measure offset if alternating signal is also involved?

PS, guys please remain civil and don't flame each other. I've had enough flaming in the burson thread for one day biggrin.gif. High_Q please explain yourself clearly, so people who are currently going 'lolwut' can actually solidify where they think you're wrong and correct you, or change their mind.
I aways try, thats why I include equations.  It doesn't get more clear than equations, they tell the truth.  Also, qusp has been very rude in other posts, so I really don't have great history with him or nikon.  Also nikon has responded to my post in a very rude manner, don't have much respect for him either.


 


Edited by High_Q - 6/4/11 at 7:27am
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post #60 of 83
6/4/11 at 7:23am

No, I copy and paste because I'm too lazy to type in latex??smile.gif  I would not paste it, if I didn't understand it in the first place because they go with my explainations.wink.gif  Want me to derive Maxwell's equations infront of you?  I can get to the point to find the c constant.
 

Quote:
Originally Posted by nattonrice View Post

Since this is bound to be locked soon I may as well get in...

 

All you seem to be doing is copy and pasting whatever you read on wikipedia in a thinly veiled attempt to appear intelligent.

Why do you feel the need to drag these threads into "I'm smarter at this than you are" pissing contests?

 



 


Edited by High_Q - 6/4/11 at 7:24am
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