[r010159]

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.

[snip]

Very interesting read! I also did not realize slew rate can vary so widely between amps. I wonder how fast a slew rate increase would stop making an audible difference? I am surprised the O2 is so slow. It is a good sounding amp. But with the right amp and headphones, I am sure I would notice a difference. What do you think?

Bob Graham

 

[miceblue]

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.  

Interesting to know. I was unaware of what the "slew rate" is despite seeing it in some op-amp specification sheets.

As mentioned, I found the speaker amp to have a similar effect on planar magnetic headphones as dynamic driver types, so the extra oomph is ruled out in that case and the difference in sound quality was characteristic of the amp, not as a result of the extra headroom or "reserve power." Whenever people talk about speaker amps and planar magnetic headphones, they never do a test with other types of headphones and they tend to come to the conclusion that the extra oomph from the speaker amp magically causes the headphones to transform in sound quality.

The amp itself sounded great compared to regular headphone amplifiers I've tried!

 

[James-uk]

Basically the O2s slew rate exceeds any possible scenario that could be thrown at it so nothing extra would make an audible difference. The O2 is transparent and will not get in the way of the recording. You will hear exactly what your HP are capable of and how they should sound. If you don't like what you hear from the O2 use eq or buy new headphones.

 

[r010159]

Basically the O2s slew rate exceeds any possible scenario that could be thrown at it so nothing extra would make an audible difference. The O2 is transparent and will not get in the way of the recording. You will hear exactly what your HP are capable of and how they should sound. If you don't like what you hear from the O2 use eq or buy new headphones.

 
My listening to the O2 tells me it is definitely a transparent amplifier. But what exactly would I get with a better quality amplifier. I do know that more power does not necessarily equate to higher fidelity. What are we talking about here? Features? Balanced line out? A better designed power supply? Better noise rejection? I am just making this stuff up trying to figure out the differences. Still, I am quite happy with the O2D.
 
Bob Graham

 

[r010159]

Interesting to know. I was unaware of what the "slew rate" is despite seeing it in some op-amp specification sheets.

As mentioned, I found the speaker amp to have a similar effect on planar magnetic headphones as dynamic driver types, so the extra oomph is ruled out in that case and the difference in sound quality was characteristic of the amp, not as a result of the extra headroom or "reserve power." Whenever people talk about speaker amps and planar magnetic headphones, they never do a test with other types of headphones and they tend to come to the conclusion that the extra oomph from the speaker amp magically causes the headphones to transform in sound quality.

The amp itself sounded great compared to regular headphone amplifiers I've tried!

 
I did notice a significant difference, including the bass response, going from an iPad headphone jack to the O2. This noticeable difference in the responsiveness of the bass I attributed to power and slew rate. Maybe it was in my specific case? I do not know.
 
Bob Graham

 

[James-uk]

My listening to the O2 tells me it is definitely a transparent amplifier. But what exactly would I get with a better quality amplifier. I do know that more power does not necessarily equate to higher fidelity. What are we talking about here? Features? Balanced line out? A better designed power supply? Better noise rejection? I am just making this stuff up trying to figure out the differences. Still, I am quite happy with the O2D.

Bob Graham

Better features and coloration is all you can get. The better features (plus it looks really nice) is the reason I brought the Sennheiser HDVD800 , I have my ps4 on optical ( I'm a sad 32 year old gamer!) plus my mac on USB . It's been designed with a 47 ohm output impedance so should add a touch of warmth the the HD800 because of its impedance curve but to be honest I think I would fail a blind test between it and the O2/odac. It cost me 6X more than the O2D so I've paid all that for optical connection and looks ( oh and I can have 4 headphones connected at once) so I have the HD650 and 800s always plugged in. Oh and they are both connected with balanced cables and that makes no difference to sound quality .

 

[James-uk]

By the way I spent an afternoon doing sighted A/B comparisons between O2 and HDVD800 (using balanced connection) with some of my favourite records . Obviously being sighted it was flawed but both sounded identical to my ears . I'm confident in saying I would fail a double blind test. It confirms to me that solid state amps / dacs really do all sound the same if certain criteria is met and exceeded.

 

[r010159]

Better features and coloration is all you can get. The better features (plus it looks really nice) is the reason I brought the Sennheiser HDVD800 , I have my ps4 on optical ( I'm a sad 32 year old gamer!) plus my mac on USB . It's been designed with a 47 ohm output impedance so should add a touch of warmth the the HD800 because of its impedance curve but to be honest I think I would fail a blind test between it and the O2/odac. It cost me 6X more than the O2D so I've paid all that for optical connection and looks ( oh and I can have 4 headphones connected at once) so I have the HD650 and 800s always plugged in. Oh and they are both connected with balanced cables and that makes no difference to sound quality .

 
I agree. The balanced outputs provide for noise isolation in a noisy environment, which has nothing to do with the quality of the amplifier. For instance, I think mics have balanced inputs because of the noisy environment that they can operate in. Still, the better amps tend to have balanced outs, probably as a marketing decision than any real difference it makes in quality.
 
Bob Graham

 

[James-uk]

I did notice a significant difference, including the bass response, going from an iPad headphone jack to the O2. This noticeable difference in the responsiveness of the bass I attributed to power and slew rate. Maybe it was in my specific case? I do not know.

Bob Graham

I pads only output 1volt so not enough power for something like a 300ohm senn which needs about 6 volts to be able to reproduce the full dynamic range of a recording. Now if you connect a sensitive , low impedance iem to an I pad it would sound identical to it connected to the O2 .

 

[Xenophon]

Basically the O2s slew rate exceeds any possible scenario that could be thrown at it so nothing extra would make an audible difference. The O2 is transparent and will not get in the way of the recording. You will hear exactly what your HP are capable of and how they should sound. If you don't like what you hear from the O2 use eq or buy new headphones.

There's such a thing as the right tool for a job.  Overall and considering the price the O2 and its clones are great, hell, I'm listening to it now (mainly because I live in 2 locations and it's a damn sight easier to move than my 30 kg tube amp).  If you use it with cans and under conditions that do not exceed its technical limitations then you'll indeed be hard pressed to hear a difference -apart from colouring which is a subjective quality- with other amplifiers and arguably it makes no sense in spending more, strictly going by objective criteria.
 
This entire discussion evolved out of a members' question if the O2 would be a good pairing to drive a HE-4.  And for those headphones and listening to certain types of music at a certain loudness level, it is NOT the right instrument and while I agree that I might not be able to hear a difference between ss amp A and B, when driven within their limits, with for instance my HE-6 I can assure you that at *any* loudness level I could easily tell apart my Vio and the O2 even if one were able to eliminate sound colouring.  That doesn't make the O2 bad, it's just not the right tool for the job with those cans.
 
My other hobby is riding motorcycles.  Here in India I ride an Enfield bullet and given local road and traffic conditions it's just perfect (19 HP, max speed 70 mph on a good day, old school carburettor, price about 1300 GBP).  I Europe I ride an Agusta Brutale 1090RR (160 HP, max speed limited to 180 mph, 18000 GBP).  What works here wouldn't work there and vice versa.
 
As a -speaker but that's irrelevant now- amp builder said:
 
"There is no such thing as a perfect amplifier. Every audiophile and his associated equipment has specific needs, but in each case there is such a thing as a best amplifier - the one that makes you happy."

 

[headwhacker]

Better features and coloration is all you can get. The better features (plus it looks really nice) is the reason I brought the Sennheiser HDVD800 , I have my ps4 on optical ( I'm a sad 32 year old gamer!) plus my mac on USB . It's been designed with a 47 ohm output impedance so should add a touch of warmth the the HD800 because of its impedance curve but to be honest I think I would fail a blind test between it and the O2/odac. It cost me 6X more than the O2D so I've paid all that for optical connection and looks ( oh and I can have 4 headphones connected at once) so I have the HD650 and 800s always plugged in. Oh and they are both connected with balanced cables and that makes no difference to sound quality .

I agree, better amp than O2 only translate to additional features, connection and more power. But if you are looking for SQ improvement, it's better to look for a better headphone or better source.

 

[tomb]

Basically the O2s slew rate exceeds any possible scenario that could be thrown at it so nothing extra would make an audible difference. The O2 is transparent and will not get in the way of the recording. You will hear exactly what your HP are capable of and how they should sound. If you don't like what you hear from the O2 use eq or buy new headphones.

Sorry, I don't mean to be critical, but this is simply an unsubstantiated rationalization in order to justify the small investment in an O2.
 
I am not at all saying that the O2 is bad - far from it.  However, when people take that ~$129 investment (a good buy, no doubt) and try to convince everyone that it's as good as it can get ... that's where rationality has left the discussion.

 

[r010159]

About an amplifier's slew rate: http://forums.audioholics.com/forums/amps-pre-pros-receivers/7278-de-mystifying-slew-rate-amplifiers.html
 
And an interesting article about an amplifier's damping factor: http://www.crownaudio.com/media/pdf/amps/damping_factor.pdf
 
It looks like current technology does make these and other parameters easily met. But then what is the actual difference between an well-designed $300 amp/DAC and a much more costly $1000 amp/DAC? Is the $1000 implementation addressing limitations of the $300 implementation? If so, what are they? Or is the difference that of features and a pleasantly colored sound? And the rest of the difference being expectation bias?
 
Bob Graham

 

[Xenophon]

  About an amplifier's slew rate: http://forums.audioholics.com/forums/amps-pre-pros-receivers/7278-de-mystifying-slew-rate-amplifiers.html
 
And an interesting article about an amplifier's damping factor: http://www.crownaudio.com/media/pdf/amps/damping_factor.pdf
 
It looks like current technology does make these and other parameters easily met. But then what is the actual difference between an well-designed $300 amp/DAC and a much more costly $1000 amp/DAC? Is the $1000 implementation addressing limitations of the $300 implementation? If so, what are they? Or is the difference that of features and a pleasantly colored sound? And the rest of the difference being expectation bias?
 
Bob Graham

All of the above and then some.  Get a good book on amplifiers or hire a consultant; I'm sure that for a couple of thousand he/she could explain in detail what it's all about and then you'll have a good basis to decide wether or not to spend more than 300 USD.  The previous remark is only half made in joking. 
 
On the one hand you have technology which comes at a cost and it's a general law in economics that beyond a certain point there's no linear relationship anymore between performance increase and cost, cost rises exponentially if you want to achieve those last couple of %.  Wether that's worth it or not depends on a) your finances and b) what you want to achieve.  Everyone has his own point of diminishing returns beyond which they stop.
 
Then there's intangibles such as personal preference, brand reputation etc which are worth more for one person vs another.  And convenience.  Example:  the amp I purchased last week costs, all said and done and delivered to me, about 3000 USD.  The builder actually published the detailed plans, and provides free advice about construction.  Depending on the material you use, it's possible to build it for around 800 to 1200 USD (the case is actually the biggest cost).  Add about 350 for shipping everything.  That would equal 1500 USD or half of what I'm paying.  Am I irrational for paying double?  No because in my own appreciation, the time, frustration and effort it would take me to build it myself carries a larger cost than the difference.
 
I fully agree that there's lots of vapourware and hype in audio (imo about cables etc) but be under no illusion:  there's no free lunch when all is said and done (cfr. my first remark about technology).  In fine the only person who can decide is yourself.

 

[r010159]

  All of the above and then some.  Get a good book on amplifiers or hire a consultant; I'm sure that for a couple of thousand he/she could explain in detail what it's all about and then you'll have a good basis to decide wether or not to spend more than 300 USD.  The previous remark is only half made in joking. 
 
[snip]
 
I fully agree that there's lots of vapourware and hype in audio (imo about cables etc) but be under no illusion:  there's no free lunch when all is said and done (cfr. my first remark about technology).  In fine the only person who can decide is yourself.

 
I agree that the $300 DAC/amp is not what some would term as the  "endgame".  You are definitely getting more value out of your expensive amplifier. And there is that law of diminishing returns that one has to justify when paying up for the amp. But I like to know in practical "everyday life" terms what are the differences. I remember in the past there was very little being written on the subject. At this point, I think the difference between what one would term as a "good" amp, and one that is "excellent" is altogether not anywhere near as much as the price difference would imply. One of these days I would like to attempt to hear the difference myself.
 
Bob Graham