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# O2 AMP + ODAC - Page 135

Quote:
Originally Posted by Dano91

Regarding O2 power capabilities I have one question - according to designer's site, O2 is able to produce 7.15V when powered from AC. In a same time designer states that max input voltage before clipping is 7.15 / GainValue.

Does this mean that when used with ODAC, which has 2V output and standard O2 gain options (2.5x and 6.5x) you can produce 5V on output at 2.5x gain? This will also mean if we want to reach that 7.15V limit with 2.5x gain, we have to use some other source capable of outputting cca 2.8V ?

Gain is a logarithmic value. The formula if I remember it right is 20(Log X)

X is the gain value.

To put that into O2 + ODAC perspective. If O2 is powered from an AC adapter It can supply as high as 7V to a load and if powered by battery can only go as high 4.5V.

7V(O2) / 2V (ODAC) = 3.5X

Means O2 can amplify ODACs sgnal at max 3.5X gain without clipping.

20 (Log 3.5 ) = 10.88 dB

I used this online tool to get the gain in V (http://www.sengpielaudio.com/calculator-gainloss.htm)

= 3.5V

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Quote:

Quote:
Originally Posted by Dano91

Regarding O2 power capabilities I have one question - according to designer's site, O2 is able to produce 7.15V when powered from AC. In a same time designer states that max input voltage before clipping is 7.15 / GainValue.

Does this mean that when used with ODAC, which has 2V output and standard O2 gain options (2.5x and 6.5x) you can produce 5V on output at 2.5x gain? This will also mean if we want to reach that 7.15V limit with 2.5x gain, we have to use some other source capable of outputting cca 2.8V ?

Gain is a logarithmic value. The formula if I remember it right is 20(Log X)

X is the gain value.

To put that into O2 + ODAC perspective. If O2 is powered from an AC adapter It can supply as high as 7V to a load and if powered by battery can only go as high 4.5V.

7V(O2) / 2V (ODAC) = 3.5X

Means O2 can amplify ODACs sgnal at max 3.5X gain without clipping.

20 (Log 3.5 ) = 10.88 dB

I used this online tool to get the gain in V (http://www.sengpielaudio.com/calculator-gainloss.htm)

= 3.5V

I think voltage gain is measured either in dB or as a ratio (eg. 3.5x), not in V directly, since gain is Vout/Vin, but maybe I'm wrong with this, nevertheless lets assume that I have only odac+o2 and some "voltage hungry" hp which will need 7V.

So I will have these two options - change the O2 gain internally to 3.5x so I get 2V (odac) * 3.5x (gain in o2) = 7V on output OR 2nd option to use higher default gain in o2 (6.5x) but lower the output from odac to 7/6.5 = 1.08V lets say by lowering the volume in PC?

Is this assumption correct?

Edited by Dano91 - 2/21/14 at 2:32am

What is difference in SQ between the O2 + ODAC and the C5D?  I am thinking of purchasing JDS Labs portable amp and pair it with either the HD600 or HE-4.

Bob Graham

On a very quick view I think that specs wise they're comparable.  (As I said, a very quick look, do your homework).

The HE-4 has a 86 dB sensitivity, that's less than the HE-500 which I own and the HE-500 can't be driven to its potential on the O2 so for sure this will not be the perfect combo, you'll need something morte powerful.

"Be under no illusion though that just because its 50% less magnets and has a \$450 price tag this headphone is not necessarily much easier to drive and that this level of musicality can be easily obtained under regular amping conditions. The HE4 still requires a good amp to maximize it’s potential. Tested out of a Go Vibe Vulcan+ and and headphone out of the Maverick D1 Dac/Amp it didn’t do it justice instead giving it a very thinned out experience even when tuned to the max."

This corresponds with what I think so I wouldn't advise you to do this.

Quote:
Originally Posted by Xenophon

On a very quick view I think that specs wise they're comparable.  (As I said, a very quick look, do your homework).

The HE-4 has a 86 dB sensitivity, that's less than the HE-500 which I own and the HE-500 can't be driven to its potential on the O2 so for sure this will not be the perfect combo, you'll need something morte powerful.

"Be under no illusion though that just because its 50% less magnets and has a \$450 price tag this headphone is not necessarily much easier to drive and that this level of musicality can be easily obtained under regular amping conditions. The HE4 still requires a good amp to maximize it’s potential. Tested out of a Go Vibe Vulcan+ and and headphone out of the Maverick D1 Dac/Amp it didn’t do it justice instead giving it a very thinned out experience even when tuned to the max."

This corresponds with what I think so I wouldn't advise you to do this.

OK. I guess it is the HD600. The F**o that I have broke today. Battery refuses to charge which is a common problem with products from this maker. So I will need to order the C5D today. Now, what source do you recommend? Something small at least transportable, and hopefully does not cost over \$100?

EDIT: I just ordered the C5D!

Bob Graham
Edited by r010159 - 2/21/14 at 7:15pm
Quote:
Originally Posted by r010159

What is difference in SQ between the O2 + ODAC and the C5D?  I am thinking of purchasing JDS Labs portable amp and pair it with either the HD600 or HE-4.

Bob Graham
The O2/ODAC combo sounds more transparent to me compared to the C5D; mostly a larger soundstage, better instrument separation. The overall sound signatures are about the same though, the C5D sounding a tad bit warmer and the midrange a bit more forward. If you're looking for a portable O2/ODAC unit, the C5D is great in that regards.

As for the HD600, I'm not too sure, but both the C5D and the O2/ODAC pair well with the HD650, as I just tried out yesterday. I tried the HE-4 with the O2/ODAC at a mini-meet recently, and they seem lacking in bass. I think the bass boost of the C5D can come in handy in that case.
Quote:
Originally Posted by Xenophon

On a very quick view I think that specs wise they're comparable.  (As I said, a very quick look, do your homework).

The HE-4 has a 86 dB sensitivity, that's less than the HE-500 which I own and the HE-500 can't be driven to its potential on the O2 so for sure this will not be the perfect combo, you'll need something morte powerful.

"Be under no illusion though that just because its 50% less magnets and has a \$450 price tag this headphone is not necessarily much easier to drive and that this level of musicality can be easily obtained under regular amping conditions. The HE4 still requires a good amp to maximize it’s potential. Tested out of a Go Vibe Vulcan+ and and headphone out of the Maverick D1 Dac/Amp it didn’t do it justice instead giving it a very thinned out experience even when tuned to the max."

This corresponds with what I think so I wouldn't advise you to do this.
Can you explain this? One of my friends has an Emotiva amp and although it sounds great with the HE-4, I really need to turn down the source's digital volume to get the HE-4 to sound quiet enough for my listening sessions (otherwise my ear drums would blow out).

Planar magnetics needing a speaker amp to sound their best is a myth to me. I just tried the Emotiva with the the V-MODA Crossfade M-100. The M-100 has a dynamic driver and is not a difficult load on the amp at all. The same effects I heard from the HE-4 from the O2 to the Emotiva can be heard with the M-100; so headphones don't require a powerful amp at all. Heck, the O2 gives me plenty of head-room to play with even at 1.0x gain: I was running it with the volume knob at around 12 o'clock with most of my music.
Quote:
Originally Posted by miceblue

The O2/ODAC combo sounds more transparent to me compared to the C5D; mostly a larger soundstage, better instrument separation. The overall sound signatures are about the same though, the C5D sounding a tad bit warmer and the midrange a bit more forward. If you're looking for a portable O2/ODAC unit, the C5D is great in that regards.

As for the HD600, I'm not too sure, but both the C5D and the O2/ODAC pair well with the HD650, as I just tried out yesterday. I tried the HE-4 with the O2/ODAC at a mini-meet recently, and they seem lacking in bass. I think the bass boost of the C5D can come in handy in that case.

I am looking for a portable unit for a couple of reasons. Otherwise, I would get the O2/ODAC unit. For that matter, the particular user of the C5D is not that discriminating. It is good that the HD650 pairs well with this DAC/amp.

Bob Graham
Quote:
Originally Posted by miceblue

Can you explain this? One of my friends has an Emotiva amp and although it sounds great with the HE-4, I really need to turn down the source's digital volume to get the HE-4 to sound quiet enough for my listening sessions (otherwise my ear drums would blow out).

Planar magnetics needing a speaker amp to sound their best is a myth to me. I just tried the Emotiva with the the V-MODA Crossfade M-100. The M-100 has a dynamic driver and is not a difficult load on the amp at all. The same effects I heard from the HE-4 from the O2 to the Emotiva can be heard with the M-100; so headphones don't require a powerful amp at all. Heck, the O2 gives me plenty of head-room to play with even at 1.0x gain: I was running it with the volume knob at around 12 o'clock with most of my music.

I think even though headphones can sound good without a more powerful amp, with some phones there is a better transient response, particularly with the bass. But this is just my impression. FWIW I also find the 12-o'clock volume position to be plenty loud to me at the low gain setting.

Bob Graham
Quote:
Originally Posted by miceblue

The O2/ODAC combo sounds more transparent to me compared to the C5D; mostly a larger soundstage, better instrument separation. The overall sound signatures are about the same though, the C5D sounding a tad bit warmer and the midrange a bit more forward. If you're looking for a portable O2/ODAC unit, the C5D is great in that regards.

As for the HD600, I'm not too sure, but both the C5D and the O2/ODAC pair well with the HD650, as I just tried out yesterday. I tried the HE-4 with the O2/ODAC at a mini-meet recently, and they seem lacking in bass. I think the bass boost of the C5D can come in handy in that case.

This is good to know. Right now the ODAC/O2 with some music had me looking around the room when there were spoken words in the recording. I also reached for my phone when I heard a sound that seemed to be coming from my cell phone. Yes, the O2 is transparent. :-)

Bob Graham
Edited by r010159 - 2/22/14 at 12:52am
Quote:
Originally Posted by miceblue

Can you explain this? One of my friends has an Emotiva amp and although it sounds great with the HE-4, I really need to turn down the source's digital volume to get the HE-4 to sound quiet enough for my listening sessions (otherwise my ear drums would blow out).

Planar magnetics needing a speaker amp to sound their best is a myth to me. I just tried the Emotiva with the the V-MODA Crossfade M-100. The M-100 has a dynamic driver and is not a difficult load on the amp at all. The same effects I heard from the HE-4 from the O2 to the Emotiva can be heard with the M-100; so headphones don't require a powerful amp at all. Heck, the O2 gives me plenty of head-room to play with even at 1.0x gain: I was running it with the volume knob at around 12 o'clock with most of my music.

To get the full explanation you'd have to get the input of an amp builder, which I'm not.  But I'll try paraphrasing what some people here on Head-Fi who are no fools explained and what a personal friend of mine who's a conductor and owns audiophile equipment worth a rather big house + an engineer have explained me.  But first two points in the interest of full disclosure:

1. I currently drive my HE-6 with the Violectric V-200 fed via XLR from my V800 DAC.  The V200 delivers 2750 mW into the HE-6's 50 Ohm.  Until recently I was of exactly the same opinion as you are,(headphones don't require a speaker amp) just check some previous posts of mine.  If you go by the numbers and do the math, that's a very reasonable conclusion, the Vio should drive the HE-6 without any problem at all and with headroom to spare.  Hell, even the O2 looks (marginally) doable on paper.  I've since talked to many people who presented imo good arguments to the contrary suspended judgment and ordered a FirstWatt F3 amplifier.  It's designed to drive high efficiency speakers.  It outputs 15W into 8 Ohm.  Do the calculations and you'll say that at 50 Ohm it will certainly not do better than the Vio.  Yet, people who own even less powerful FirstWatt amps and who have owned the Vio swear to me that they get superior results.  A fellow Head-Fier drives them from an F1-J model of the same brand with a 10W output in 8 Ohm.  Note:  The firstWatt amps are not your typical speaker amps, if you want to know more about the design, check www.firstwatt.com

2. I've heard the HE-6 with a couple of conventional (high powered) speaker amps and some of them sounded like crap, high noise floor, distortion...but in all likelihood that's because they had a lot of gain (as the HE-6 and HE-4 are planar magnetic designs we can largely discount impedance mismatch, certainly if we're not talking tube amplifiers).  Headphones don't require massive gain, nor do they require huge current.  What they require is sufficient power to drive them well and sufficient power reserve on tap at all times.  With designs like the 6 and to a slightly lesser extent the 4 I believe that the problem lies there:  not enough power 'on tap' to deal with dynamic range.  On modern pop records that's mostly not such an issue but with classical music for instance it is (you'll have to take my word for it or do some digging).  If you take a look at most headphone amp measurements (for the rare brands who don't outright fudge the numbers or present them in a very selective way) then you'll see that what they post as performance is typically a static picture (power output into a specific load with distortion measured at a certain frequency etc).  But they don't take dynamics and fluctuation into account.  Simple observation, look for yourself.  If you run efficient cans from a decent headphone amp then typically you won't run into a problem but with extreme cases and dynamic music, despite the static measurement data showing all's well, the amp will simply not be able to timely deliver sufficient power (the 'power reservoir' so to speak being too small).  That's where the advantage of speaker amps lies imo.

Again, I'll let you know once I received my FirstWatt and I've gained some experience + the 'new toy' syndrome has blown over.  It's an experiment but the explanations I've heard (and which I probably didn't accurately reproduce above) sound plausible to me.  Plausible enough to sink about 3000 USD into this little experiment anyway.

In short:  I'm not claiming that a speaker amp may be required let alone the best for any and all headphones, I'm not claiming that just hooking up any 100 WPC amp is a shortcut to nirvana, I'm not saying that all headphone amps are crap (I own several and with the right cans they're very good).  But I do think that it's plausible that with insensitive designs such as the HE-6, HE-4, HE-5...speaker amps can bring something to the table that most headphone amplifiers cannot due to their form factor if for nothing else:  massive power on tap and instantly available.  It's not about driving them 'loud', that's gain and comparatively easy to accomplish, it's about driving them to their max potential and getting the very best out of them.

I hope the above makes some sense but if you want the full technical explanation I'll gladly hook you up with some guys who have a more solid theoretical basis.

^ Quite a long post. But by the gist of it, I think I can sum it on one word -- "Snake oil".

People can always believe what they want to believe. I agree with amp headroom and stuff but you have to draw the line between sense and just myth.

Sure speaker amps should be fine and can be used to drive headphones, but if anyone is telling me that I need a speaker amp to drive a headphone then something is wrong. Either the headphone design is inefficient or people just buy in to the idea of bigger/powerful is better.

An O2 in itself is more than enough to drive almost all headphones. I even needed to limit my O2 to 2.5x gain so I don't run into an accident of driving my T1 to very loud volumes.

Quote:

^ Quite a long post. But by the gist of it, I think I can sum it on one word -- "Snake oil".

People can always believe what they want to believe. I agree with amp headroom and stuff but you have to draw the line between sense and just myth.

Sure speaker amps should be fine and can be used to drive headphones, but if anyone is telling me that I need a speaker amp to drive a headphone then something is wrong. Either the headphone design is inefficient or people just buy in to the idea of bigger/powerful is better.

An O2 in itself is more than enough to drive almost all headphones. I even needed to limit my O2 to 2.5x gain so I don't run into an accident of driving my T1 to very loud volumes.

I'm not trying to convince you nor anyone else but let me remark that your reaction is low on one parameter which contradicts your professed aversion to 'snake oil' and love of rationality:  I do not read a single solid argument.  I'm not proselytising, just going to give it a try and we'll see.  Believe what you want (and hone those reading skills because nowhere did I say that 'a' speaker amp is 'required' to drive 'a' headphone, I honestly couldn't care less.

Lets take an extreme example of an audiophile looking for the best transient response from their amplifier. He happens to be an engineer at JPL. He wanted the best guarateed transient response, among other things, from his amp. So he purchased this big turkey of an amp. When turned on, it actually dimmed the lights in his house, until the internal capacitors charged up. 8-O I have seen him actually turn the unit off and it still powered his speakers for up to a half an hour later. 8-O This tells you how much an emphasis he placed on this parameter of an amplifier. It is not only to have significant power available, but also how quickly that power can be delivered. I do believe this amp of his to be overkill to the extreme. I think a fraction of an amplifier compared to his wil still be a very good amplifier. And we are not trying to power a setup of power hungry speakers, just a pair of headphones,

I thought all of you would find this a little amusing. :-)

Bob Graham
Edited by r010159 - 2/22/14 at 6:37am

What all of you guys are trying to describe is slew rate: how quickly an amplifier can rack up the voltage.  An example of a top-flite headphone amplifier is AMB's B22 - it has a slew rate of 198V per micro-second.  For comparison, one of the faster opamps available - the AD8397 - has a slew rate of 53V per micro-second.  The classic OPA2134 (used in the CMoy) has a slew rate of 20V per micro-second.  Those specs for opamps are "laboratory conditions," though.  There's an awful lot of extra amplifier circuitry necessary if they are to provide that to a meaningful load.  The B22, on the other hand, meets that 198V per micro-second level while providing 49V point-to-point.

Slew rate can be shown graphically (somewhat) by square wave response, too.  Interestingly, the O2 has a slew rate of only 3.5V per micro-second.  Not surprisingly, the designer dismisses the slew rate specification by referring to an "industry rule of thumb" and by stating, "There can be ugly side effects associated with excess slew rate."  Well, yeah - if the amplifier or opamp has a ringing issue, but that would be shown in the square wave response, too.

Anyway, orthos are supposed to be very transient-responsive, somewhat similar to an electrostatic.  That means you need peak voltage and it needs to be fast.  Sometimes speaker amps can do that easier than many headphone amps.  However, I think if you look at the B22 as a headphone amp example, it's quite possible to achieve that with a headphone amp, too.

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