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
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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!
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.
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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!
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!
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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
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
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.
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.
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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.
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.
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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.
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
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
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.
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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Broadcom ASSR-1611 has on-resistance of 20 mOhm for DC.
It costs $4.12 ($2.40 1ku) at Digikey.
ASSR-1611-001E
It costs $4.12 ($2.40 1ku) at Digikey.
ASSR-1611-001E
So, I put together my Mouser cart, emailed agdr, and now I'm reading around the forums that he's taken a hiatus from the DIY community and selling PCBs 
If I don't hear back from him, does anyone have any extra boards? I was wanting to build the parallel version, but would totally build the single version if it was the only one available...
If I don't hear back from him, does anyone have any extra boards? I was wanting to build the parallel version, but would totally build the single version if it was the only one available...
Hello guys, I want to say something..
Both Xrkaudio and agdr are right..
Well I created my own BOM list for 1688cmoy(pocket O2). Resistor were Texas instrument tx2575 and etc etc...
Upgraded the whole circuit line.
Then blindfolded my friends, they were not knowing which amp they were listening to
Normal Pocket O2 vs Upgraded pocket O2 vs bottle head crack with speedball and mundorf silvergold solder, deulund caps etc(my dad loves snake oil massage)
All chose the upgraded pocket O2.
Actually when you are listening a song, there has to be a blackness in the background which can be achieved by properly shaped and extremely low distortion.
Properly shape distortion by a good Class amps can give instrument that smoothness and euphoria while low distortion gives a sense of imaging and neutrality.
I just got some better caps and better resistor on the audio line and that itself did the trick..
Texas instrument resistor itself change the audio perceived.
And yah, to actually get something better from a neutral objective Amp, you need a proper DAC to run it....
Normal smartphone and laptops benefit from class A or tube amps
Both Xrkaudio and agdr are right..
Well I created my own BOM list for 1688cmoy(pocket O2). Resistor were Texas instrument tx2575 and etc etc...
Upgraded the whole circuit line.
Then blindfolded my friends, they were not knowing which amp they were listening to
Normal Pocket O2 vs Upgraded pocket O2 vs bottle head crack with speedball and mundorf silvergold solder, deulund caps etc(my dad loves snake oil massage)
All chose the upgraded pocket O2.
Actually when you are listening a song, there has to be a blackness in the background which can be achieved by properly shaped and extremely low distortion.
Properly shape distortion by a good Class amps can give instrument that smoothness and euphoria while low distortion gives a sense of imaging and neutrality.
I just got some better caps and better resistor on the audio line and that itself did the trick..
Texas instrument resistor itself change the audio perceived.
And yah, to actually get something better from a neutral objective Amp, you need a proper DAC to run it....
Normal smartphone and laptops benefit from class A or tube amps
Desktop Version
Good day all.
I have a few build questions, for a desktop version that I am working on, that I am unable to find answers to in this informative thread...
AC-DC Power Supply (aka “Wall Wart”)
Besides the Voltage Output advice given in Post #84: “more than +/- 7.1Vdc (and less than +/-17Vdc)” what other parameters should one adhere to? Such as Current Output (Max) and Power (Watts).
USB 2.0/3.0 Power Supply
The few posts in this thread about USB power, especially the Isolated DC/DC Converter circuit idea that AGDR shared with us in Post #170, got me thinking… would not a USB Step-Up Voltage Converter Cable 5V to 9V or 12V work? Thus, killing two birds with one stone.
Amazon.com: Step Up Voltage Converter Qutaway USB 5V to 9V or 12V Step Up Cable Adjustable DC To Dc Transformer Converter With Switch (5V-9/12V): Home Audio & Theater
Headphone Jack Parameters
If one desired to hook up a 6.33mm (1/4”) jack (via a lead from the board) besides “switched” what other parameters must be followed for this amp design… Number of Positions/Contacts; Internal Switches; and Voltage Rating (e.g. 2 positions; 3 conductors/5 contacts; 500V)?
LED Parameters
If one desired to hook up a 3 or 5mm diameter LED what are the Forward Current (If); Forward Voltage (Vf); and Operating Voltage (VDC) parameters to keep within? For example, the BOM shows a 10 mA; 2.1 Vf; 1.8 - 3.3 VDC… would a 20 mA 6VDC LED still work in the circuit? I have a few of these Purple UV 6VD wired LEDs that I used on another project and I know the power supplied to them was well under 5V.
Also, would a series of two LEDs be at all possible?
Thank you for takling the time to read through my questions. Any and all advice or information would be sincerely appreciated. Respects.
Good day all.
I have a few build questions, for a desktop version that I am working on, that I am unable to find answers to in this informative thread...
AC-DC Power Supply (aka “Wall Wart”)
Besides the Voltage Output advice given in Post #84: “more than +/- 7.1Vdc (and less than +/-17Vdc)” what other parameters should one adhere to? Such as Current Output (Max) and Power (Watts).
USB 2.0/3.0 Power Supply
The few posts in this thread about USB power, especially the Isolated DC/DC Converter circuit idea that AGDR shared with us in Post #170, got me thinking… would not a USB Step-Up Voltage Converter Cable 5V to 9V or 12V work? Thus, killing two birds with one stone.
Amazon.com: Step Up Voltage Converter Qutaway USB 5V to 9V or 12V Step Up Cable Adjustable DC To Dc Transformer Converter With Switch (5V-9/12V): Home Audio & Theater
Headphone Jack Parameters
If one desired to hook up a 6.33mm (1/4”) jack (via a lead from the board) besides “switched” what other parameters must be followed for this amp design… Number of Positions/Contacts; Internal Switches; and Voltage Rating (e.g. 2 positions; 3 conductors/5 contacts; 500V)?
LED Parameters
If one desired to hook up a 3 or 5mm diameter LED what are the Forward Current (If); Forward Voltage (Vf); and Operating Voltage (VDC) parameters to keep within? For example, the BOM shows a 10 mA; 2.1 Vf; 1.8 - 3.3 VDC… would a 20 mA 6VDC LED still work in the circuit? I have a few of these Purple UV 6VD wired LEDs that I used on another project and I know the power supplied to them was well under 5V.
Also, would a series of two LEDs be at all possible?
Thank you for takling the time to read through my questions. Any and all advice or information would be sincerely appreciated. Respects.
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You might try dual 5v USB wallwart and dual MT3608 DC-DC step up connected in series +/-/+/- (common is GND). This can give dual rails at any voltage up to 24v. This costs the least but requires dual mains to 5v usb wallwarts. Proper dual rail DC-DC converters are isolated as a lot more expensive. For example a Traco 9v-18v +/-24v 310mA DC converter is $42 alone.
Yes, that’s it - make sure you buy a lot because they often blow up in flames (the little IC) when adjusting the voltage. Once set, it’s fine. Also, if you have large rail caps after this, it may shut down on power up due to in-rush. Then you need either a 4.7R power resistor in between or a slow ramp up cap multiplier. 220uF or under seems ok. 2200uF is too much.
So I would need a meter to know what the setting I have is correct?
Why wouldn't the above linked USB Step-Up Voltage Converter 5V to 9V Cable and/or AC-DC Power Supply (Wall Wart) work?
Please help... I am surely murdering this series and completely missing the Common GND for the board...
An externally hosted image should be here but it was not working when we last tested it.
Some light bulbs are beginning to turn on in my head in regards to the AC-DC power supply in my previous post above
So a Switching Split Power Supply is required, such as this one here which thus means that two (2) DC barrel panels jacks would be required. Correct?
So a Switching Split Power Supply is required, such as this one here which thus means that two (2) DC barrel panels jacks would be required. Correct?