So, the Objective2 headphone amp - designed entirely around the measurements? (PLEASE READ RULES BEFORE POSTING)
post-7681021
Post #301 of 1,042

Shike

Headphoneus Supremus
Joined
Feb 1, 2005
Messages
1,888
Reaction score
70
Joined
Feb 1, 2005
Posts
1,888
Likes
70
Quote:
Why do you choose to interpret that as an insult?
 
How should it be interpreted?  More importantly, what do YOU associate with flat earthers, since that's the term you used.
 
     Share This Post       
post-7681060
Post #302 of 1,042

kwkarth

Electronics guys... we have our plusses and minuses. With advent of digital everything, we're being phased out
Joined
Sep 30, 2001
Messages
10,307
Reaction score
95
Joined
Sep 30, 2001
Posts
10,307
Likes
95


Quote:
 
How should it be interpreted?  More importantly, what do YOU associate with flat earthers, since that's the term you used.

Read Discworld.  Wonderful series.
 
 
     Share This Post       
post-7681061
Post #303 of 1,042

JamesMcProgger

Headphoneus Supremus
Joined
Oct 8, 2010
Messages
6,552
Reaction score
185
Joined
Oct 8, 2010
Posts
6,552
Likes
185
this thread went to the crapper. shame. I enjoying reading the first 10 pages somebody drop me a shout when the final design or group buy is out plz..
 
     Share This Post       
post-7681069
Post #304 of 1,042

Shike

Headphoneus Supremus
Joined
Feb 1, 2005
Messages
1,888
Reaction score
70
Joined
Feb 1, 2005
Posts
1,888
Likes
70
Quote:
this thread went to the crapper. shame. I enjoying reading the first 10 pages somebody drop me a shout when the final design or group buy is out plz..


Agreed, I'll do my best to inform you though.  I'll be reviewing it when I have mine built with PCB.
 
     Share This Post       
post-7681074
Post #305 of 1,042

Anonanimal

100+ Head-Fier
Joined
Jun 2, 2009
Messages
397
Reaction score
11
Joined
Jun 2, 2009
Posts
397
Likes
11


Quote:
 


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. 


Thanks for the input, all.  Will revisit the questionable numbers.
 
Edit:
 
Okay I've revisited all of the numbers and corrected the sensitivities that were originally 1dB/V.  I have added a calculator to the spreadsheet to do that.
 
Nikongod- actually the gain column is using the input Vrms@0dBFS, which is set to 1.40Vrms for the gamma2 DAC.  It was performing a roundup operation to give an integer gain number with some extra headroom.  I've removed the roundup to make it more exact.  This should help shed some light on how little gain most headphones really need.
 
The Beyer T1 numbers were correct, per this datasheet: http://north-america.beyerdynamic.com/shop/media//datenblaetter/T1_DB_E_A2.pdf
 
Also, I've moved it to Google Docs-  Give this link a try: https://docs.google.com/spreadsheet/ccc?key=0ArBLkTRCqzhSdENZVW9kYTA3VUlMMV9UODIxLUpPVnc&hl=en_US#gid=0
 
I can confirm at least the T1 numbers, as my B22 has a gain of 2 (fed by gamma2) and I have not run into volume limitations on a single recording.  The spreadsheet recommends a gain of 2 for 110dB peak levels.
 
     Share This Post       
post-7681221
Post #306 of 1,042

chinesekiwi

Headphoneus Supremus
Joined
Feb 29, 2008
Messages
3,797
Reaction score
27
Joined
Feb 29, 2008
Posts
3,797
Likes
27


Quote:
what does nothing sound like?
 
The Benchmark DAC1's headphone amp. An amp and source is not supposed to 'sound' like anything...it should be as transparent as possible.
However better sound results from less distortion unless you are recreate a  speaker surrounding, in which of course, there always have more distortion than headphones, which is why a lot of people prefer 'warmth' in their music.
 
 
     Share This Post       
post-7681240
Post #307 of 1,042

Head Injury

Headphoneus Supremus
Joined
Sep 11, 2009
Messages
5,404
Reaction score
434
Joined
Sep 11, 2009
Posts
5,404
Likes
434
I browsed through the diyAudio thread and, in light of concerns about clipping with 3x gain and hot sources, NwAvGuy has dropped the default gain to 2.5x. I thought I would pass this on, to maybe elicit constructive discussion again.
 
     Share This Post       
post-7681294
Post #308 of 1,042

Beefy

Headphoneus Supremus
Joined
Mar 4, 2008
Messages
2,562
Reaction score
50
Joined
Mar 4, 2008
Posts
2,562
Likes
50
 
Quote:
I'm not so sure about folks who claim this amp sounds like "nothing," without ever having heard it.  I believe that lacks a bit, no, a lot, of substance. 

I can't believe that I agree with kwkarth on something.
 
For reference, I am a scientist and skeptical of many audiophool traditions...... but I strongly believe that anyone who thinks an amp is perfectly transparent because of a select and limited group of measurements is wrong. It shows a substantial amount of arrogance, and a strong underestimation (or misunderstanding) of the complexities of both the electronics and the human brain.
 
The amp needs to be ABX'ed, double blinded, some sort of proper listening test. Until then, both the objectivists and the subjectivists are full of it.
 
*
 
The gain issue is still not solved adequately to my mind. I cannot fathom why the designer is introducing such significant potential problems for the sake of a few dB of SNR. We all know how many noobs are going to end up with one of these, switch to a MOAR BETTAR GAINZ and wonder why it sounds bad. Seriously, even if the SNR was dropped by 30dB by moving the pot, it would still measure very well, and the problem is gone.
 
     Share This Post       
  • Like
Reactions: rroseperry
post-7681332
Post #309 of 1,042

mikeaj

Headphoneus Supremus
Joined
Jan 10, 2010
Messages
1,639
Reaction score
107
Joined
Jan 10, 2010
Posts
1,639
Likes
107
If you believe the designer, he says he did blind listening tests between his Benchmark DAC1 and the O2 and found them to sound the same.
 
From the first article:
 
"SUBJECTIVE COMPARISONS: I’m more than a little biased, so that’s why I broke out the blind testing gear. And, as near as I and a few others can tell so far, the O2 sounds so similar to the well regarded Benchmark DAC1 Pre’s headphone amp we can’t tell them apart. See The Subjectivist Pitch above. I also believe those currently listening to amps with significant problems, be it higher output impedance, high distortion, audible noise, insufficient power, etc, might be in for a real treat (unless they like those things). I’m looking forward to more blind tests with the O2!"
 
     Share This Post       
post-7681334
Post #310 of 1,042

Satellite_6

1000+ Head-Fier
Joined
Feb 12, 2009
Messages
1,205
Reaction score
25
Joined
Feb 12, 2009
Posts
1,205
Likes
25
[redundant quote removed]
 
NwAvGuy has claimed to have done a blind test already. I don't see how the designer is responsible for the user's ignorance. He even has a whole section on how to operate the O2 properly. 
 
It sounds good, but I would like to see more details and more tests of course. 
 
I hope I haven't broken any unwritten rules this time . . . 
 
 
 
     Share This Post       
post-7681335
Post #311 of 1,042

Head Injury

Headphoneus Supremus
Joined
Sep 11, 2009
Messages
5,404
Reaction score
434
Joined
Sep 11, 2009
Posts
5,404
Likes
434
Quote:
The gain issue is still not solved adequately to my mind. I cannot fathom why the designer is introducing such significant potential problems for the sake of a few dB of SNR. We all know how many noobs are going to end up with one of these, switch to a MOAR BETTAR GAINZ and wonder why it sounds bad.

At that point it's builder error, though. If you build it within spec, is there really a problem?
 
 
Seriously, even if the SNR was dropped by 30dB by moving the pot, it would still measure very well, and the problem is gone.
 
Ouch! I'll take the better SNR.
 
A stern warning to any potential builders (as a preface to the schematic perhaps) would prevent (almost) anyone from turning the gain too high, and won't lower SNR.
 
Luckily for my uses a 2.5x gain is plenty high enough without causing clipping.
 
----------
 
Note to the above posters: Blind tests really only work if the listeners expect to hear a difference. If you don't expect (or want) a difference, then even if there is one you might bias yourself into thinking there isn't. I can't speak for the others NwAvGuy tested, but his own blind test is definitely flawed.
 
     Share This Post       
post-7681348
Post #312 of 1,042

Beefy

Headphoneus Supremus
Joined
Mar 4, 2008
Messages
2,562
Reaction score
50
Joined
Mar 4, 2008
Posts
2,562
Likes
50
 
Quote:
If you believe the designer, he says he did blind listening tests between his Benchmark DAC1 and the O2 and found them to sound the same.
 

Well firstly, I don't believe that the Benchmark is a good comparison. Most people whose opinion I trust think it sounds shrill and metallic.
 
Secondly, I don't know good his hearing is. I want to see more of these in the wild.
 

Quote:
At that point it's builder error, though. If you build it within spec, is there really a problem?

Because it isn't the builder I am worried about, but the end user. Accounting for people's stupidity is a better design decision than taking SNR beyond the range of human perception.
 
     Share This Post       
post-7681447
Post #313 of 1,042

dsavitsk

MOT: ECP Audio
Joined
Aug 3, 2003
Messages
2,883
Reaction score
41
Joined
Aug 3, 2003
Posts
2,883
Likes
41
The gain issue is still not solved adequately to my mind. I cannot fathom why the designer is introducing such significant potential problems for the sake of a few dB of SNR.

I don't think this is nearly as big a deal as people are making it out to be, but, I do think there are two different issues that have been aggregated into one. The first issue is whether having an input limit is an inherently bad thing, and the second is whether the input limit of this amp is too low.

1. To address the first, all amps have an input limit. This is particularly noticeable in an amp with an input transformer where it will saturate if the signal level is too high. But, it is also true with something like a B22 where a very high level input could damage the pot (and in some cases, such as with a stepper, that level is exceedingly high, but it does exist).

So, input limits are inherent in designing a headphone amp. But, with an IPT, or the opamp before the volume control, there are concrete objective benefits to doing it such as CMRR, isolation from ground loops, and lower SNR. There are also trade-offs, such as the fact that badly behaved sources (those with too high of an output) may not be compatible. The fact that not all sources are compatible with all amps should not be a surprise to anyone, particularly in an area where there are no hard and fast standards. Indeed, I try to keep my sources at 1Vrms or lower which works well as I tend to transformer couple most amps. Further, while this amp may not be able to handle a high source level, it seems to be, with perhaps some tweaking, able handle a higher source impedance than many other amps.

2. The second issue is that this amp may have a particularly low signal input limit. OK. So, as I say, not all amps are useful in all situations. Use something else. This is a different and new-ish topology to the headphone world. Like all circuits, it has benefits and drawbacks, and will work in only limited situations. This does not make it any different than any other amplifier out there, AMB's designs included. The flaw here seems to be not in having a limit, but in the designer's contention that it is perfect and better than everything else in every situation. Clearly this is not the case, so, use it where it is appropriate. In places where it is not, use a resistor divider (or another pot) in front of the first opamp, or use a different transformer to increase the power supply.

Finally, so I can avoid posting in this thread again, for an amp with a lot of feedback, the THD numbers don't strike me as being off the chart. They are fine, but not spectacular. My soundcard does better than that, and it sounds terrible. And, that's the last issue -- contrary to what at least one poster believes, not much can be gleaned from the numbers posted in the first post. All you can say is that the amp is working within expected specs. There is a lot about audio design, how an amp reacts with a real world load (back EMF injected into a feedback loop, for instance) and human perception that is not captured in those measurements.

 
post-7681580
Post #314 of 1,042

mikeaj

Headphoneus Supremus
Joined
Jan 10, 2010
Messages
1,639
Reaction score
107
Joined
Jan 10, 2010
Posts
1,639
Likes
107
Quote:
Note to the above posters: Blind tests really only work if the listeners expect to hear a difference. If you don't expect (or want) a difference, then even if there is one you might bias yourself into thinking there isn't. I can't speak for the others NwAvGuy tested, but his own blind test is definitely flawed.

I totally agree here, and it's more than likely that the other listeners are also biased.  Blind testing is really best for determining that a difference exists, not confirming the opposite.  This is the caveat I neglected to point out.  It also depends on the kind of blind testing done and the amount of honest effort put into the testing, though we can't be sure about either.  It's a shame that this sums up all the listening we know about so far, but...time to wait for the v1.1 board to get into peoples' hands.
 
 
I also agree with the sentiment of a limited set of measurements not telling the whole story, but with the number of different THD tests, different IMD tests, square waves into different loads (including real headphones and real headpones + capacitor), blind listening with a variety of headphones, and so on, as well as all the other unpublished results, it just seems kind of unlikely that the real-world performance would be noticeably poor in some way.  Some things that humans perceive don't really map well to these standard metrics and benchmarks.  Anyway, maybe when somebody builds one they can do a line-out -> O2 -> line-in recording with the O2 driving some real headphones, and do a differencing test against the recording that was played?  You'd probably need a really really good ADC though, as well as DAC.
 
Most likely it will sound similar to the Benchmark...which in turn probably sounds like nothing really (i.e. like not much was added to the input signal).  Whether or not a high-fidelity signal sounds shrill and metallic, is up for the listener to decide.  But doesn't that depend on the music that is being played?
 
     Share This Post       
post-7681638
Post #315 of 1,042

Beefy

Headphoneus Supremus
Joined
Mar 4, 2008
Messages
2,562
Reaction score
50
Joined
Mar 4, 2008
Posts
2,562
Likes
50
 
Quote:
Finally, so I can avoid posting in this thread again.......
 
...... how an amp reacts with a real world load (back EMF injected into a feedback loop, for instance) and human perception that is not captured in those measurements.

Please stick around, because this point you have raised is something I am very interested in.
 
I've been speaking with other folk on another non-DIY forum, lamenting that the vast majority of amp testing is done with purely resistive loads which are a LONG way from real-world headphones. Do you think that testing with actual headphones connected to the amp instead of simulated loads would be beneficial? Or can you think of a better simulated load than just a resistor? Or are your ears the best decider?
 
     Share This Post       

Users Who Are Viewing This Thread (Users: 0, Guests: 1)

Top