So, the Objective2 headphone amp - designed entirely around the measurements? (PLEASE READ RULES BEFORE POSTING)
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chinesekiwi

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Quote:
I do not understand this thread.
 
Just give me a link to where to order this thing, for once I'm going to do an impulse buy without any researching ^^

Just look up Nwavguy's blog for everything you need. Funny how some people bagging it haven't even read the posts on his website. As direct linking is banned, I'm sure you can look it up.
 
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b0ck3n

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What audible factors, besides volume without distortion, do you suggest exists?
 
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deadlylover

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It's also funny how some people seem to know exactly how it sounds despite never having heard the amp before.
 
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post-7679856
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kwkarth

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Quote:
What audible factors, besides volume without distortion, do you suggest exists?
If nothing else occurs to you, then this is not the place to discuss it.  You will probably have to discover this for yourself.  I certainly would not expect you to take my word for it.
 
 
 
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Anaxilus

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Quote:  
Well put.  Reading the design intent definitely raised an eyebrow.  
  But hey, I'm willing to see if a jack of all trades actually can be a master some.  Rarely the case but I'm not an EE.
 
Quote:
@ Nikongod

"Looking around at meets, and a quick survey on teh forums will show you that many people only use the section of the potentiometer just above mute (the -60 to -40db range). There is so much fail in this, but it is a case where it takes a deliberate and conscious effort to break the mold. What REALLY sucks is that when you do, people get visibly nervous about spinning the knob up past half way and then complain it lacks power despite not topping it out."

Absolutely true. I see this all the time. I for one don't subscribe to this and put the volume knob wherever the hell I please. If I need it past halfway that's where it goes.

x3.  I thought I was alone.  I figured everyone else had bat hearing even though my ears test fine.
 
Quote:
Well, I know this will bother many of you, but even though a couple of the cans will make noise, will the quality of that noise properly showcase what those cans are capable of?
 
No.  It all depends upon one's level of experience and expectation, quality of source, quality of program material, etc.  SPL alone does not even come close to being the whole story.

Agreed.  How many times do we run into, "my cans are loud, they don't need an amp."  Yeah, well they don't 'need' anything do they.
 
 
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Beftus

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Quote:
 Ti Kan's example of running the 114 dB/V, 32 Ohm PX100 headphones with 5x gain is anything but "real world".


That's exactly what I do: iPod Classic line out into a Mini³ (5x gain) into a pair of PX100's. Works like a charm. Could easily blow your eardrums, I think.
 
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b0ck3n

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Except Ti uses a higher voltage source than the Classic, talk about blowing your ear drums.
 
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Beftus

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GrubDAC output into Mini³ into PX100's gets really loud past 11 o'clock using recent source material. Go beyond that and your eardrums start clipping violently, but not the Mini³...
 
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b0ck3n

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Quote:
 
By spec, it doesn't have adequate output to properly drive those cans regardless of gain structure.
 
 

 
khaos974 already provided the math that proves you wrong.


Quote:
 
If nothing else occurs to you, then this is not the place to discuss it.  You will probably have to discover this for yourself.  I certainly would not expect you to take my word for it.
 
 


I have discovered for myself that alot of people are influenced by placebo and expectation bias, and mistake the difference in human perception for a difference to the signal. The O2 is about busting myths, not perpetuating them - the designer has provided exhaustive measurements showing that the O2 can drive a variety of loads admirably, including loads that relate to the T1, HD800 and LCD2 (much louder than most portable amps including the Mini3 before clipping, mind you - granted that you've matched O2 gain to your source, and that source doesn't put out more than 7v). If you propose that there's something at work here which can't be measured then I'm not sure I'm up for discussing it anywhere.
 
 
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amb

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Quote:
Originally Posted by b0ck3n
 
Ti Kan's example of running the 114 dB/V, 32 Ohm PX100 headphones with 5x gain is anything but "real world".
 
It's as real as it gets, my friend.
 
The PX100's quoted "114dB" sensitivity is for 1Vrms (according to the PX100 manual and other web sources).  This is a little unusual.  The typical convention for headphone sensitivity specification is dB/mW, not dB/Vrms.  So the PX100's sensitivity figure is not directly comparable to most other headphone specs.  In fact on the same amp, at the same volume knob position, the PX100 is only a little louder than the HD600.
 
For 1Vrms into 32 ohms, the power being delivered is a bit over 31mW.  To get 1mW into 32 ohms, you need only 0.18Vrms. Doing a conversion from one to the other. the PX100's sensitivity becomes 99dB/mW.  I mention all this to show that it's not the most efficient portable headphones compared to many others.  Yet it is an immensely popular model so it's appropriate to use as an example.
 
How much gain is needed?  You must take into consideration the sensitivity of the headphones, the output level of the source, and add enough headroom to account for recordings that are low in volume so that you don't run out of volume pot travel.  Many recordings are almost constantly pegged near the 0dBFS line and dynamically compressed.  These recordings will sound very loud (and bad).  But there are also recordings that are recorded very low in level (some from the late 70s and 80s for example), maybe 10-15dB below 0dBFS.  Thus, it is prudent to select an amp gain level above and beyond what's needed to amplify a 0dBFS signal to compensate.
 
Let's say we want to have 15dB of additional headroom.  And we assume we want to be able to have unclipped peaks of 114dB (just take Sennheiser's spec as an example because it's a reasonable number and happens to require a nice clean 1Vrms).  To add 15dB extra headroom we need to swing 5.6Vrms.  Note that we're not actually going to run 5.6Vrms into the headphones, we would set the volume control to whatever listening level we want.  Let's then assume a y2 DAC as the source with 1.4Vrms output @0dBFS.  The gain we want is then 5.6V/1.4V = 4x.  If we increase the peak dB SPL requirement to 120dB then we need a gain of 8x.
 
This illustrates that a "Mini³ with gain of 5x driving the PX100" case I mentioned is not outside "real world" usage, and is in fact quite a nice setting.  On average recordings (not too loud, not too soft), my volume pot position is usually a little over half way, but on really soft recordings I can turn it up to satisfactory levels without running out of pot travel.
 
 
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fishski13

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Quote:
 
khaos974 already provided the math that proves you wrong.




I have discovered for myself that alot of people are influenced by placebo and expectation bias, and mistake the difference in human perception for a difference to the signal. The O2 is about busting myths, not perpetuating them - the designer has provided exhaustive measurements showing that the O2 can drive a variety of loads admirably, including loads that relate to the T1, HD800 and LCD2 (much louder than most portable amps including the Mini3 before clipping, mind you - granted that you've matched O2 gain to your source, and that source doesn't put out more than 7v). If you propose that there's something at work here which can't be measured then I'm not sure I'm up for discussing it anywhere.
 


i would echo the above response from Ti and heed the concerns about having a very limited input source V and gain to drive multiple headphones.  having some headroom for differences in recording volume is not about placebo or expectation bias.  it's real.
 
this amp at 2Vrms/3.1x gain would not be able to drive my AKG 88dB/600 with any of my older Steely Dan albums to an adequate volume - 80-85dB.  also, 2Vrms is not a hot source.
 
 
 
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Shike

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2v RMS is a "normal" source.
 
2.5v RMS is a "hot" source
 
2.25v RMS is roughly the limit when using a 3.1x gain.
 
 
The Audio-GD is the hottest listed so far.
 
DacMagic: 2.1
EMU: 2.2
HRT Streamer: 2.25
Audio-GD Dac 19: 2.5 (2.7 measured)
 
One of these isn't like the others no matter how you look at it.
 
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agdr

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Quote:
I'll adjust it and report back later,
 
 
Yeah I get something like 2.7v, thanks.
 

A gain of around 2.3x for the low setting would fix it.  That would be a max input of around 7/2.3 = 3.0v. The gain equations in his write-up look like they haven't been updated yet since he added the gain switch.  It should be:
 
gain = 1 + R16 / R17   for one channel and gain = 1 + R22 / R21  for the other.  He states its is best to leave the feedback resistors R16 and R22 at 1.5k, so solving the equations gives:
 
R17 = R21 = 1500R / (2.3 - 1) = 1153R.  Closest standard 1% value then would be 1.15k,  For 5% values 1.2k would be just fine, giving a gain of 2.36.  Best to actually measure the resistor first though - some can be way off.
 
 
 
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kwkarth

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Quote:
khaos974 already provided the math that proves you wrong.

I have discovered for myself that alot of people are influenced by placebo and expectation bias, and mistake the difference in human perception for a difference to the signal. The O2 is about busting myths, not perpetuating them - the designer has provided exhaustive measurements showing that the O2 can drive a variety of loads admirably, including loads that relate to the T1, HD800 and LCD2 (much louder than most portable amps including the Mini3 before clipping, mind you - granted that you've matched O2 gain to your source, and that source doesn't put out more than 7v). If you propose that there's something at work here which can't be measured then I'm not sure I'm up for discussing it anywhere
 
 
 
Sure, the math proves me wrong.  Happy listening!
 
I've been an audio professional since the early 1970's.  I'm sure you've got me pegged.  I must be influenced by placebo effect.
 
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Anonanimal

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Quote:
If you're using a standard AC dac source, do you need a higher gain than 3 to listen to T-1s, LCDs, or 800s at decent volume levels?
 


 


Quote:
By spec, it doesn't have adequate output to properly drive those cans regardless of gain structure.
 
 


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.
 

 
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