[Head Injury]

Quote:

kwkarth, if you're not going to provide any objective concerns, I don't think this is the thread for you.
 
Anonanimal, very handy table. Could you add LCD-2 rev.2 to the list for me? Audeze increased impedance to 60 ohms. Thanks 

(I suppose I could just use the K701 and rev.1 as approximations)

 

[Anonanimal]

Quote:

 
Anonanimal, very handy table. Could you add LCD-2 rev.2 to the list for me? Audeze increased impedance to 60 ohms. Thanks 

(I suppose I could just use the K701 and rev.1 as approximations)

Sure.  I've upped the dB requirement to 115 for some additional headroom for quieter recordings.  In practice I've found this to be enough, but again YMMV.
 
I'd attach the .xls file instead of posting screenshots but I seem to have been denied that ability.  Sorry!
 

 

[kwkarth]

Quote:

Where is your data showing that the amp does not, by spec, have enough output to properly drive the quoted headphones?
 
Actual power specs:
6.25 volts RMS on AC power at < 1% THD into 150 ohms
4.5 volts RMS on DC power at < 1% THD into 150 ohms
 
Compare to this calculations chart using actual headphone specifications.  This is using a Gamma2 as the reference DAC.  YMMV but this should give you an idea.
 

Nice chart!  To answer your question, one word...  headroom.
 

 

[limpidglitch]

Quote:

 
I'd attach the .xls file instead of posting screenshots but I seem to have been denied that ability.  Sorry!
 

Why not uploading the file to mediafire, Google Docs or similar, and post a link?

 

[Anonanimal]

Quote:

Why not uploading the file to mediafire, Google Docs or similar, and post a link?

I can do that if there's interest.  It's a series of pretty simple calculations but I've got them packed in a table for quick reference.

 

[kwkarth]

Quote:

I can do that if there's interest.  It's a series of pretty simple calculations but I've got them packed in a table for quick reference.

I think it's potentially very useful!
 

 

[digger945]

Indeed, Google Docs integrates seemlessly for me and works great with Excel, whether uploading or downloading to or from Google Docs.

 

[nikongod]

 
Quote:

Sure.  I've upped the dB requirement to 115 for some additional headroom for quieter recordings.  In practice I've found this to be enough, but again YMMV.
 
I'd attach the .xls file instead of posting screenshots but I seem to have been denied that ability.  Sorry!
 

Nice chart!
 
Your numbers for Beyer and Sennhesier are off. These companies declare efficiency in "db@1v", except for the HD600 whose efficiency is declared in db/mw. 
 
Im not sure about the AKG K701. it "looks and feels" like the declared efficiency (also given by AKG in db@1vrms) has been converted but Id double check by setting the "target spl" to whatever AKG says the K702 has@1v, and seeing what you get for voltage required
 
The gain you give in the far right column assumes that you have a 1v input signal. If you have quiet music you may only have a 0.25v signal or maybe even less with that same DAC. To achieve 115db with Hd800, and a quiet recording it could require boatloads of gain... If you want the amp to play LOUD there is no way around including the gain switch. 

 

[Armaegis]

Can anyone provide the formula that converts from sensitivity in V to mW?

 

[The Monkey]

I'm a bit confused why there's a de facto assumption that this is designed to be a portable amp. From what I can glean from the designer's comments, the amp in its initial iteration is small, and therefore portable, but the designer also indicates that the amp also is suitable as a desktop amp (with bigger enclosure if wanted and other options). Regardless of whether the amp is used as a desktop or portable, it does not appear that there are any substantive differences in configuration. In other words, the amp designer appears to suggest that this amp is equally suited to desktop duties as it is to portable. So until someone offers a compelling reason to the contrary, I think limiting assumptions about the types of sources used to portables is inappropriate. Did the designer not use the Benchmark's amp as a comparator?

 

[kwkarth]

Quote:

Can anyone provide the formula that converts from sensitivity in V to mW?

Watts (W) or milliwatts (W/1000) are the product of Voltage (V) and Current (I) and  R=V(2)/I .  therefore...
 
A sensitivity of 105dB / V is what is published for the AKG K702.  It has a published impedance of 62 ohms, so, our knowns are Voltage and resistance.  Since W=V(2)/R, then 1/62=0.01613, or roughly 16mW required for 105dB output from the AKG K702.
 

 

[fishski13]

Quote:

I'm a bit confused why there's a de facto assumption that this is designed to be a portable amp. From what I can glean from the designer's comments, the amp in its initial iteration is small, and therefore portable, but the designer also indicates that the amp also is suitable as a desktop amp (with bigger enclosure if wanted and other options). Regardless of whether the amp is used as a desktop or portable, it does not appear that there are any substantive differences in configuration. In other words, the amp designer appears to suggest that this amp is equally to desktop duties as it is to portable. So until someone offers a compelling reason to the contrary, I think limiting assumptions about the types of sources used to portables is inappropriate. Did the designer not use the Benchmark's amp as a comparator?

the performance goal posts keep moving to suit a particular line of argument.
 
i generally recommend keeping the gain as reasonably low as possible for improved noise and giving you more play/adjustment with the volume.  also, a lower gain will give you better distortion numbers with increased negative feedback.  while the above table re: HP power requirements is handy, i would caution and reiterate that the source recording may not output enough V to achieve modest volumes, much less silly 115dB, under what i consider to be 'real world'/common playback situations.  choose your source and HPs carefully.
 
 
 

 

[Armaegis]

Quote:

Watts (W) or milliwatts (W/1000) are the product of Voltage (V) and Current (I) and  R=V(2)/I .  therefore...
 
A sensitivity of 105dB / V is what is published for the AKG K702.  It has a published impedance of 62 ohms, so, our knowns are Voltage and resistance.  Since W=V(2)/R, then 1/62=0.01613, or roughly 16mW required for 105dB output from the AKG K702.
 

That part I know. I was wondering about the conversion from 1db/V to 1db/mW, which I'm pretty sure has a log or two in there. I could probably do it, but I'm a little too sleep deprived to crunch numbers right now. 
 
... doubling power... roughly 6dB... 2^x... equals P... zzzzzz

 

[The Monkey]

the performance goal posts keep moving to suit a particular line of argument..
 
 
 

Spot on.

 

[bcg27]

Quote:

That part I know. I was wondering about the conversion from 1db/V to 1db/mW, which I'm pretty sure has a log or two in there. I could probably do it, but I'm a little too sleep deprived to crunch numbers right now. 
 
... doubling power... roughly 6dB... 2^x... equals P... zzzzzz

 
Someone should double check this to make sure I didn't make a mistake but:
 
Sensitivity @1mW=sensitivity @1V - 10*log(P(1V in mW))
 
if you want to substitute in the formula to get power from 1 volt you get
Sensitivity @1mW=sensitivity @1V - 10*log(1/R*1000) = sensitivity @1V - (10*log(1/R)+30)
 
logs are base 10 logarithm