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OPA1688 Super CMOY, 2x 9V with real ground and headphone relay - PCBs
OPA1688 Super CMOY, 2x 9V with real ground and headphone relay - PCBs
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Old 19th February 2017, 04:40 AM   #241
agdr is offline agdr  United States
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OPA1688 Super CMOY, 2x 9V with real ground and headphone relay - PCBs
Quote:
Originally Posted by stellarelephant View Post

Agdr, you probably have a better grasp of the sound signature of your amp than anybody else. Are you able to pick out the Super CMOY in the comparison?
It will be interesting to see what results he gets! I haven't really been following that thread though because I'm having trouble wrapping my arms around the validity of a test like that. A big part of what happens with headphone amplifiers is the interaction of the amplifier itself with the headphones. How the output stage of a given headphone amplifier deals with the reactance of specific headphones and their cables. And what happens to damping if the headphone amplifier has significant output resistance. A virtual listening comparison might have some validity with line-level things, like comparing eq settings on the same piece of music, where no heavy load (like headpones) is being driven.

The only valid type of test I'm aware of for headphone amplifiers is what NwAvGuy used and discussed, fully blind A/B testing, to eliminate "sighted bias", with actual amplifiers and headphones. His blog posts on the subject are really good and worth a re-read:

NwAvGuy: What We Hear

NwAvGuy: Subjective vs Objective Debate

Last edited by agdr; 19th February 2017 at 04:43 AM.
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Old 19th February 2017, 05:34 AM   #242
stellarelephant is offline stellarelephant  United States
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Quote:
Originally Posted by agdr View Post
It will be interesting to see what results he gets! I haven't really been following that thread though because I'm having trouble wrapping my arms around the validity of a test like that. A big part of what happens with headphone amplifiers is the interaction of the amplifier itself with the headphones. How the output stage of a given headphone amplifier deals with the reactance of specific headphones and their cables. And what happens to damping if the headphone amplifier has significant output resistance. A virtual listening comparison might have some validity with line-level things, like comparing eq settings on the same piece of music, where no heavy load (like headpones) is being driven.

The only valid type of test I'm aware of for headphone amplifiers is what NwAvGuy used and discussed, fully blind A/B testing, to eliminate "sighted bias", with actual amplifiers and headphones. His blog posts on the subject are really good and worth a re-read:

NwAvGuy: What We Hear

NwAvGuy: Subjective vs Objective Debate
You aren't the only person to question the methodology. I'll agree it it has some issues, but I will say that I can hear significant differences between the recordings, for whatever reason. I have read several of NwAvGuys blog posts before and will check out the ones you sent, thanks. Your Super CMOY looks very cool. I can't believe some folks have made favorable comparisons of such a tiny amp to the much-respected O2!
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Old 19th February 2017, 02:33 PM   #243
xrk971 is offline xrk971  United States
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OPA1688 Super CMOY, 2x 9V with real ground and headphone relay - PCBs
Quote:
A big part of what happens with headphone amplifiers is the interaction of the amplifier itself with the headphones. How the output stage of a given headphone amplifier deals with the reactance of specific headphones and their cables. And what happens to dampin
I think a little too much concern from folks about headphone transducer interaction with the amp had been expressed. I think most high quality dynamic driver loads will be driven just fine. But if that were an issue, you would think a discrete low impedance MOSFET or big BJT would have he advantage over a tiny transistor inside an IC opamp. As Aksa said regarding this concern: these are tiny low mass drivers, not big speakers with reactive crossovers and large masses and suspensions and speaker box interactions. The influence of headphone driver reactivenload is a loss less than say, a 2-way or 3-way speaker with an 8in woofer.

For those reasons when testing power amps, Inuse a real 2-way speaks as a load and record with a mic, the sound actually produced by the speaker for listening to sound clips.

Having said this, I want to reiterate that the Super CMOY in this thread is an outstanding amp. I don't have an O2 to compare but I have compared it with a top of the line Fiio A5 that packs some heavy hardware (Muses02 and LME49600 drivers) and can say that the Super CMOY holds it own both from sound quality and even measurements of THD, SNR, noise floor, IMD, response etc. I think in a shootout with O2, it would be tough to tell the difference - except for fact one fits in your pocket and other doesn't. But compared to my best SE Class A amps - none of the opamp based amps sound as good, IMO. But we will soon see other people's opinions too.

Last edited by xrk971; 19th February 2017 at 02:42 PM.
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Old 23rd February 2017, 04:40 PM   #244
agdr is offline agdr  United States
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OPA1688 Super CMOY, 2x 9V with real ground and headphone relay - PCBs
I would agree that headphones are getting easier to drive. Seems like most of what has come out over the past few years have been around 32R and high sensitivity, set up for plugging into cell phones and ipods. Some of those high sensitivity headphones really don't even need an amplifier. I had a pair of AKGs that were blasting loud at just 90mV(rms)! They were around 32R as I recall, so just 3mA(rms).

xrk971 - what I would love to see are results of some non-virtual blind A/B tests with your amp and others. If your amp wins subjectively with those - and it may! - you would have something indisputable. A lot of folks are building your amp and all of us have a bunch of different headamps (lol!), maybe a couple of folks will step up to the challenge. I just received my board, BTW, thanks!

Last edited by agdr; 23rd February 2017 at 04:47 PM.
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Old 23rd February 2017, 06:22 PM   #245
adydula is offline adydula  United States
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Hey guys,

I was one of those guys that did and still do not think that just listening to material over different headphone amps without any "controls" is not that great of an idea from an objective viewpoint.

I do have several O2's and three of AGDR's Super Cmoy's as well as his ODA and his inverting version O2 plus a Bottlehead Crack....

And I have done extensive blind testing with myself and friends.

As soon as you start twisting that volume knob to get the headphone to "play" to your subjective liking.....its all over.

Set the levels accurately, play the same material and it gets much harder to hear real world differences.

That said its an interesting excercise, but I hope people dont make buying decisions from this excercise.

I totally agree with: "The only valid type of test I'm aware of for headphone amplifiers is what NwAvGuy used and discussed, fully blind A/B testing, to eliminate "sighted bias", with actual amplifiers and headphones. His blog posts on the subject are really good and worth a re-read......."

The real differences are the actual headphones themselves by far..

Alex
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Old 23rd February 2017, 08:46 PM   #246
xrk971 is offline xrk971  United States
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OPA1688 Super CMOY, 2x 9V with real ground and headphone relay - PCBs
Quote:
Originally Posted by agdr View Post
I would agree that headphones are getting easier to drive. Seems like most of what has come out over the past few years have been around 32R and high sensitivity, set up for plugging into cell phones and ipods. Some of those high sensitivity headphones really don't even need an amplifier. I had a pair of AKGs that were blasting loud at just 90mV(rms)! They were around 32R as I recall, so just 3mA(rms).

xrk971 - what I would love to see are results of some non-virtual blind A/B tests with your amp and others. If your amp wins subjectively with those - and it may! - you would have something indisputable. A lot of folks are building your amp and all of us have a bunch of different headamps (lol!), maybe a couple of folks will step up to the challenge. I just received my board, BTW, thanks!
Hope you build yours soon. You certainly won't have any issues finding a tin with holes already cut out for it. I am curious what your subjective impressions are compared to the Suoer CMOY.

Last edited by xrk971; 23rd February 2017 at 08:49 PM.
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Old 24th February 2017, 06:11 AM   #247
agdr is offline agdr  United States
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OPA1688 Super CMOY, 2x 9V with real ground and headphone relay - PCBs
Hey Alex! You are the first person I thought about when it comes to blind A/B testing. I know you have gone to some extensive efforts there to make your tests truly blind, having other people chose the amps who are out of sight and having it all level matched.

Very good point about the various headphones having bigger audible differences than the amps! I would agree with that, at least for the amps and headphones I've tried. That comes down to some NwAvGuy philosophy too, that the amp should ideally be perfectly neutral and shouldn't mess with the sound in any way, just make the amplitude bigger or smaller. Any other processing is to be done further back in the signal chain with EQ or other effects. There are several amps here with that philosophy, like opc's "Wire". The name comes from the amp being "a wire with gain", not altering the signal in any way other than voltage gain.

But having said that, in the real world all amps will alter the signal to some extent of course. In the case of tube amps - your Crack - maybe a large extent. Sounds like xrk971 is shooting for that goal, having the amp add harmonics in a similar fashion to what the tube amps do. A lot of people do like the tube sound, but one has to realize that isn't the exact signal that went into the amp's input, for better or worse.

Lol, it comes down to the big objective vs. subjective debate, too. I think there is a 50-or-so page thread in one of the forums here about that. NwAvGuy was purely objective. If an amp measured well then it would sound good, period. Hence the name O2, objective 2. I'm only 50% on the objective thing. I do think that in the end how the amp sounds is the most important, although I certainly agree that well-measuring amps are a good place to start looking. I would tend to agree with a comment I saw attributed to Nelson Pass once that "an amp can measure well but sound bad". Technically that probably means there are other parameters that matter to the sound, other than what has been measured. He listed one, in fact, in a thread 10 years ago. Op amps on the verge of oscillation at 1x closed-loop gain vs. having a higher closed-loop gain and throwing some of it away.

Last edited by agdr; 24th February 2017 at 06:22 AM.
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Old 24th February 2017, 06:20 AM   #248
xrk971 is offline xrk971  United States
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OPA1688 Super CMOY, 2x 9V with real ground and headphone relay - PCBs
I think what he meant was an amp that measures with lower THD can sound worse than an amp with a higher THD figure. You can have lower THD but if the harmonic profile has a lot of energy in the higher orders or odd orders - even though very low levels, we can pick up on it. Some amps actually have higher third order vs second order and that's all wrong for me. I don't like that sound even if it's absolute THD is less than an amp that's predominantly second order.
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Old 24th February 2017, 01:09 PM   #249
adydula is offline adydula  United States
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Hey Good Morning!

I agree that amps do sound different, but now-a-days with so many "good" amps side by side its not as easy to tell these differences without some controls IMO.

Many folks upgrade their amps, especially the Crack crowd and there is the usual "hey its now audio nirvana"...lol and then comes the comments about well i dont really know, or its hard to tell, or maybe it sounds better.

I think its funny to read about the fellow that replaced his caps in his crack with jumbo gazillion micofarad, gazillion volts mundorfs and then states he thinks its better...again lol.

If you have to closely listen, play music over and over and over to try to hear things subjectively that should tell us something...and yes I do this as well!!

The hard thing in blind testing is being able to quickly switch from one listening setup before your "mind" starts playing subjective tricks on you.
Its hard to setup stuff, it takes time and effort, to keep things the same and to be objective in the actual listening part.

I do indeed like getting friends over and have them tell me whats better or different..the results are always amazing to me...

Alex
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Old 2nd December 2017, 12:45 AM   #250
xrk971 is offline xrk971  United States
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OPA1688 Super CMOY, 2x 9V with real ground and headphone relay - PCBs
Quote:
Originally Posted by agdr View Post
I would agree that headphones are getting easier to drive. Seems like most of what has come out over the past few years have been around 32R and high sensitivity, set up for plugging into cell phones and ipods. Some of those high sensitivity headphones really don't even need an amplifier. I had a pair of AKGs that were blasting loud at just 90mV(rms)! They were around 32R as I recall, so just 3mA(rms).

xrk971 - what I would love to see are results of some non-virtual blind A/B tests with your amp and others. If your amp wins subjectively with those - and it may! - you would have something indisputable. A lot of folks are building your amp and all of us have a bunch of different headamps (lol!), maybe a couple of folks will step up to the challenge. I just received my board, BTW, thanks!
Hi AGDR,
This thread has not been getting enough attention - I just dusted off my 1688 Super Cmoy last night - it was sitting as a bare amp in a anti static bag. I cleaned it up, removed the flux on the board, trimmed some leads, installed a professional 4pin JST jack and 9v wires for the batteries and cut a new tin. I have been listening to my SE Class A amp which uses your board’s footprint (thanks for that). Anyhow, thought I would give Class AB a try again for a change. So your 1698 Super CMOY (I think a more appropriate name is “Pocket O2”) paired your amp with a Cayin N3 as source, and KZ ZS5v1 (5ohm) quad driver IEM’s. The rig sounds quite nice and the 1688 drives those 5ohm IEM’s just fine.

In case you haven’t seen, the virtual headphone amp comparison thread’s results ended up with people preferring Aksa’s 2SA1837 CFP SE Class A amp first, then my Pocket Class A second. Yours did ok too. In a blind test I think SE Class A generally wins.

Blind Virtual Audition of Several Headamps

I have built many more headphone amps since that test, and will probably
run Round 2 in coming months with a few more commercial offering plus my DIY stuff. One amp that really surprised me was the Wayne Kirkwood THAT1646 Class A zero global feedback push pull. Very transparent.

Have you had a chance to build my Pocket Amp
Yet?

Cheers,
X
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Last edited by xrk971; 2nd December 2017 at 12:48 AM.
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