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Question about amps - Page 2

post #16 of 92
Quote:
Originally Posted by JaZZ View Post
Does that mean the $1000-4000 amps sound the same as Behringer, Presonus, SM Pro, Samson & the like?
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With high impedance headphones (250 ohms+) I'm indifferent to plugging it into pro audio gear or a special headphone amp. Speaker amps are a different story because some of them have headphone output impedance of higher than 150 ohms!

With low impedance headphones I'm slightly more finicky because I'd like the output jack to have an impedance near 0. No fancy amp is needed for this. Even a CMOY will do. However, I typically plug 25 ohm Denons into my Nokia 5800. There is a slight (I believe it is less than 1db) bass hump at ~50 hz without any rolloff. However, during a volume matched comparison with "better" gear, I concluded the bass hump was practically irrelevant.

Quote:
Originally Posted by ph0rk View Post
It is damn hard to put together even a single blind test, though.
It is a pain in the butt to do a proper blind test. I've built myself a switching box using a toggle switch. It's such a simple design that I doubt impedance problems could be an issue. Of course I suppose somebody could point out that I'm not using expensive cable and claim that is affecting my results.
post #17 of 92
Quote:
Originally Posted by odigg View Post
With high impedance headphones (250 ohms+) I'm indifferent to plugging it into pro audio gear or a special headphone amp. Speaker amps are a different story because some of them have headphone output impedance of higher than 150 ohms!
Does that mean all of them sound the same?


Quote:
With low impedance headphones I'm slightly more finicky because I'd like the output jack to have an impedance near 0. No fancy amp is needed for this. Even a CMOY will do.
Have you ever compared a CMoy with pro amps or audiophile amps? What's the sonic difference, if there's any?


Quote:
However, I typically plug 25 ohm Denons into my Nokia 5800. There is a slight (I believe it is less than 1db) bass hump at ~50 hz without any rolloff. However, during a volume matched comparison with "better" gear, I concluded the bass hump was practically irrelevant.
How about the rest of the sonic spectrum and other criteria than frequency response? Is there a difference to an audiophile source and a high-quality headphone amp? Can the Nokia play lossless, or did you play low-bitrate MP3s?
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post #18 of 92
Jazz, I feel you are baiting me into something. I'm not interested because I know where this is going to go as most arguments usually go in this direction and ultimately DBT supporters cannot win with anti-DBT people because you cannot prove the null hypothesis meaning you cannot 100% prove there is no difference. If that is a reason to throw out my comments then by all means throw them out.

Let me leave it at this. From my testing I have concluded amps with a high input impedance, a flat frequency response when loaded, an output impedance of close to 0, a low enough noise floor you cannot hear noise when music is playing (this becomes an issue with IEMS), when not driven to clipping, sound the same.

If the impedance of the headphone is high (250+ ohms) then the 0 ohm output impedance specification can be relaxed.

And yes, sound the same with FLAC, "good" sources (mostly Computer+DACs), etc.
post #19 of 92
Quote:
Originally Posted by odigg View Post
Jazz, I feel you are baiting me into something...
Yes, I felt a bit challenged by your unclear answers, so I tried to sound things out. Your last post now is clear enough to me, thanks!

You may not be too surprised to find me a bit baffled about your experiences which contradict mine diametrically. I'm not interested in spending more money than necessary for amps and audio gear generally, and I don't strive for the most beautiful or spectacular sound, so a wire with gain would do it for me. But that's in fact so hard to find, and the cheaper amps I've tried so far are farther away from this ideal than the majority of the more expensive amps.
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post #20 of 92
Quote:
Originally Posted by JaZZ View Post
You may not be too surprised to find me a bit baffled about your experiences which contradict mine diametrally.
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Assuming the amps have met the specifications I stated above, have you tried volume matched blind testing to see if you can still hear the difference?

One additional point. The 9V Cmoy has audible distortion at high volumes with the DT880. It also has some line noise but I've found this is not an issue when music is playing.
post #21 of 92
Quote:
Originally Posted by odigg View Post
Assuming the amps have met the specifications I stated above, have you tried volume matched blind testing to see if you can still hear the difference?
No, I never tried it. But actually I don't really A/B test amps, it's usually a longer-term comparison. So the volume level doesn't really matter.
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post #22 of 92
^Oh it does. Then what you are doing is not a comparison, hence you can't say amplifier A or amplifier B sounds better. They just sound DIFFERENT to you, and most likely the same if they are properly volume matched.
post #23 of 92
Quote:
Originally Posted by Bullseye View Post
^Oh it does. Then what you are doing is not a comparison, hence you can't say amplifier A or amplifier B sounds better.
Yes, I can.

Quote:
They just sound DIFFERENT to you...
You're correct.

Quote:
...and most likely the same if they are properly volume matched.
Maybe to you? What's your own experience with different amps? Have you compared cheap amps with so-called high-end amps? (Don't worry, I don't need DBT protocols!)
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post #24 of 92
Since the OP was left in the dust, I'll try.
Quote:
Originally Posted by cfull View Post
If all an amp does is boost the power that is being output, how can that possibly change the sound (all these comments about improved bass/midrange/soundstage/etc)? I am genuinely curious, because it seems to me an amp built cheaply can fulfill the same output criteria as these 400 dollar and up jobs people spend money on. Is there any sort of science behind the notion that SQ is somehow improved, other than it makes the can louder? I don't want to start a flamewar or anything, and I'm sure this question has been debated before in some way or another on this forum, but I genuinely want to know. I just got a pair of DT880s and my emu0404 usb struggles to drive them, and i'm looking at options.
An amp doesn't, "boost power." It can provide two basic goodies:
1. Voltage gain.
2. Current reservoir.

Voltage gain gives you higher volume. End of story (well, usually).

The buffer section, however, sits there as a means to power the drivers. When signal goes up or down, and causes the driver to move, the driver then pulls current, and voltage drops (and exactly how much it does this is not the same for all frequencies!). If it's pulling more than your amp can provide (sink, usually) at any instant, or more total than your amp can provide over time, then you get distorted sound. If a big drum hit comes in, and the drivers go from ~2mA to ~50mA right then, and in no time flat go back to needing ~2mA, that can give a weak little amp some hell. With most typical consumer products being made with cost savings having priority over quality, things like this suffer.
post #25 of 92
Quote:
Originally Posted by odigg View Post
The HP4 suffers from one problem. It has a high output impedance. I've tested and measured it with everything from a 25 ohm Denon to a 600 ohm AKG. I've concluded that, ideally, the amp should be used with a headphone that is 80 ohms or higher. 62 ohms (AKG 701) should be fine as well but not ideal. Of course, it doesn't take very much to drive the 25 ohm Denons with a flat frequency response - any decently built portable amp can do it. Even a CMOY can!
Would you be able to explain how the higher output impedance effects low Z cans? Is there any advantage to having a higher output impedance with high Z headphones? I've always found this a tad unclear and any clarification on this would be great.
post #26 of 92
Quote:
Originally Posted by Jingo Lingo View Post
Would you be able to explain how the higher output impedance effects low Z cans? Is there any advantage to having a higher output impedance with high Z headphones? I've always found this a tad unclear and any clarification on this would be great.
There was a recent thread looking at this. Donald North has explained it well, or so I think because I know what a voltage divider from electronics as a hobby.

http://www.head-fi.org/forums/f4/add...minent-430035/.

As a general rule of thumb the ideal headphone amp will have an output impedance that is close to 0. Many solid state headphone amps probably (I have not measured them personally) have output impedances close to zero. The Presnous HP4 is solid state, uses an Opamp, and still has a hi-z out. I looked inside and I think they are using a resistor and capacitor at the output to prevent DC current at the output jack.

There is one "advantage" to a hi-z output, but it's "advantage" come in a counterintuitive(assuming neutrality is your goal) way. A hi-z output may adjust the frequency response of the sound. You may like this adjustment, and I suspect this recently occurred with one person who purchased a flagship headphone and found he (she?) did not like it until they plugged it into a hi-z (120 ohms?) output. My guess is that there was a noticeable increase in bass.

There is also the question of Dampning Factor. The general rule of thumb is that a higher dampning factor is better, but I have never found a proper answer to what dampning factor is "good enough" in the sense that human being will not be able to discern an increase in dampning factor after that point.
post #27 of 92
Quote:
Originally Posted by odigg View Post
After volume matched testing and playing with a ton of gear I am of the opinion that all decently engineered solid state amps sound the same or the differences are so small to be irrelevant. There are some exceptions that jcx has stated, but these are relatively easy to detect. Bass rolloff is measurable, clipping and noise are audible. Note that I support blind testing in audio.

Tube amps tell a different story.

There are a number of Pro Audio amps that are inexpensive ($100 and below) and IMHO sound the same as any number of the amps on this forum that are priced much higher. The only problem with pro audio amps is that many of them are not appropriate for low impedance cans due to a much higher than 0 output impedance. This should not be an issue with your DT880s as they are typically 250 ohms.

Why don't you try plugging your DT880 into your computer's sound card, even if it's built into the motherboard. You don't want to know my opinion on DACs.
Would love to hear your opinion on DACs.

Please pop over to my "Conundrum" thread and post your opinions.

Unexpectedly, and quite by accident I've discovered that the BenchMark DAC 1 sounds like my Stello DA100 which sounds like the Neko D100 I just auditioned. Would like to know what you think.

Thanks

USG
post #28 of 92
Quote:
Originally Posted by JaZZ View Post
Has any of you guys compared your «dream amps» you're talking about here – which all are in the lowest price category (from $50 to $200...) – with some of the high-end and über-amps recommended on this forum? Just curious.
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I personally have. I find that discussing blind test results here is pointless, because people will dismiss them as merely a product of my poor hearing (despite all audiologists I've seen telling me otherwise). I've measured and blind tested the presonus HP4 against several quadruple-digit amplifiers and have noticed no difference whatsoever - although I did hear differences when doing an unsighted comparison, which leads me to believe that most of this is placebo. If you want me to list the amps, either look through my older posts (I've listed them several times) or, if you're actually interested, PM me or otherwise notify me. I've gotten tired of listing the equipment I've used only to have people call me a liar (olblueyez) or having tin ears (too many to count).

I have adopted the position that solid-state amplifiers, after meeting certain requirements that are a breeze to meet, don't make an audible difference. I adopted this because I have a theory (that differences are largely placebo effect), data to back it up (plenty of studies, measurements, etc.) and personal experience that matches the data, which matches the theory.
post #29 of 92
Quote:
Originally Posted by odigg View Post

As a general rule of thumb the ideal headphone amp will have an output impedance that is close to 0. Many solid state headphone amps probably (I have not measured them personally) have output impedances close to zero. The Presnous HP4 is solid state, uses an Opamp, and still has a hi-z out. I looked inside and I think they are using a resistor and capacitor at the output to prevent DC current at the output jack.

There is one "advantage" to a hi-z output, but it's "advantage" come in a counterintuitive(assuming neutrality is your goal) way. A hi-z output may adjust the frequency response of the sound. You may like this adjustment, and I suspect this recently occurred with one person who purchased a flagship headphone and found he (she?) did not like it until they plugged it into a hi-z (120 ohms?) output. My guess is that there was a noticeable increase in bass.

There is also the question of Dampning Factor. The general rule of thumb is that a higher dampning factor is better, but I have never found a proper answer to what dampning factor is "good enough" in the sense that human being will not be able to discern an increase in dampning factor after that point.
A zero output impedance is not necessarily the ideal for a headphone amp. It depends on how a particular headphone is designed. There is an international standard IEC 61938 which specifies 5V with 120 ohm output impedance for headphones of the range 8 - 600 ohm. From my experience, many of the higher end European headphones are designed and tuned to mate with this specification. When I listen to the 250 and 600 ohm beyerdynamics, 300 ohm Sennheisers, and higher impedance AKGs, they all sound better to me when fed from 120 ohm output impedance. I don't believe this is coincidental.

At the same time, some headphones are designed to be fed from a low output impedance. From my experience these are usually lower impedance headphones, but not exclusive.

Damping factor isn't a hard and fast rule. For example: If a headphone were designed to be powered per the IEC spec, it would be intentionally overdamped when tested via voltage driven, so that when fed from the 120 ohm output impedance, the damping would be reduced to the amount which the headphone designer intended. This is like current driving (instead of voltage driving) your headphones. The same is true with single driver, wide range, high efficiency loudspeakers from Lowther and Fostex. They have very low moving mass, very high BL, and very low Qts (meaning they are significantly over damped). When driven with a voltage source (amplifier with near zero output impedance), they have very little bass. Power them instead with a current source amplifier (like the Pass Labs First Watt) and now you get a significant increase in bass making it similar level to the midrange and treble. The only downside to high output impedance is power wasted in the amplifier. Fortunately since headphones need such little power, the energy dissipated though the amplifier's internal impedance is low, so you won't need to stress about your electricity bill

I see some posts where people measure the frequency response on the headphone amplifier output while powering different headphones. If the amp has 0 output impedance, the frequency response should be flat with any headphone connected. Amps that have a higher output impedance will have a contoured frequency response across the headphone which depends on the impedance characteristics of the headphone. Many people quickly view this is as bad. This is not necessarily so: If the headphone were designed to be powered from a higher output impedance, say the 120 ohm IEC standard, then this is expected and part of the design towards the total sound quality and tonal balance produced by the headphone. If this same headphone were powered by a 0 ohm output impedance amplifier, this condition would in fact be producing coloration because it is deviating from the intended contour

See my post:
http://www.head-fi.org/forums/f4/wha...ml#post5749154

As with most things in life, there are no absolute rules and multiple paths to a goal. When powering headphones, it's all about system synergy. I first like to know and listen to them powered with the boundary conditions (low or high output impedance) as their designers intended. However in the end, it all comes down to personal preference and why I like to see amplifiers with selectable, specified output impedance. I commend Meier Audio for including dual outputs on some of their models.
post #30 of 92
Since I can only find that IEC doc for sale: is it equivalent to taking a near-0 Ohm source and adding an inline resistor? As in out->120 Ohms -> Driver -> Gnd per channel. I liked what 75 Ohms did for the K240S, and like what it does for my K271 mkII (tones down the treble hump). I've wondered if it was made to be run off a typical speaker->resistor output.
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