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Question about amps

post #1 of 92
Thread Starter 
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.
post #2 of 92
amps can differ in the maximum Voltage and Current they can provide - with dynamic headphone impedance and sensitivity varying by an order of magnitude or more there are simply some pairings of amps and headphones that will not reach reasonable dynamic music peak SPL without clipping

the several orders of magnitude sensitivity differences in IEM vs "Studio Monitors" means amp gains and noise levels can also cause differences that make some pairings unusable

audible frequency response can differ with some types of amps, output coupling capacitors in some single ended designs can cause low bass loss with low impedance headphones where the same amp may be fine with high Z cans

tube amps often have higher output impedance over the whole frequency range and this can interact with the headphone's impedance curve to give objectively measurable frequency response difference in the output


so there are some differences between amp/headphone pairings that are expected to be clearly audible on objective technical grounds


there is the more controversial claim that when all technical, measurable differences are accounted for then "all amps sound alike"

supporting that position is the "Carver/Stereophile Challenge"

diyAudio Forums - Blind Listening Tests & Amplifiers - Page 22
post #3 of 92
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.
post #4 of 92
Yeah, I support odiggs thinking. Plus odigg, care give me some ~<$100 amps (SS).

I only found some Samson S·Amp for ~$50. Might buy it someday...
post #5 of 92
Bullseye: I have the presonus HP4, and I purchased it for 100 dollars. It'll perform identically to the S-amp, but the HP4 has a monitor pass-through for speakers. The S-amp should suit you well.
post #6 of 92
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.
Your E-MU 0404 doesn't have a dedicated headphone out, right? If so, the line out may be able to produce sound through your headphones, but it is electrically limited (current supply), may distort and roll off the bass, as it's designed to «drive» a high-impedance load (such as >10 kΩ) instead of a headphone.

A headphone amp has an output stage specifically designed for this purpose. So it represents a better precondition than the (line) outputs of soundcards, even those with a dedicated headphone out. Extrapolating from my E-MU 1212M, I suppose that the 0404 has decent sound quality – as a source. Depending on your sonic demands, an outboard DAC would be a higher-quality option, or a DAC/amp combo (→ Meier-Audio, HeadRoom...).

There are cheap and expensive amps around. Roughly spoken, expensive amps use better parts and may have more sophisticated designs for better sound quality. It's just a rule of thumbs, and there are exceptions to the rule. People on this forum usually buy the amps after audition; so they chose the one that suits their sonic preferences best. This «best» amp isn't necessarily the most neutral and accurate amp, but maybe the most euphonic amp or the one with the best synergy with the existing gear. Some people don't care for neutrality.

From my wording you can deduce that different amps sound different. Yes, they do, at least to my ears (and I'm not alone). I wouldn't have spent ~$1000 if I could have got away with $200 to get the same sound quality. I still have some other (older, cheaper) amps around; compared to the Symphony and the Opera they just don't have the same finesse and resolution. Even between Symphony and Opera there's a difference in favor of the former. Although some recordings benefit from the slightly smoother, more forgiving presentation of the latter.

Technically the sonic differences are hard to verify. There are measuring differences, but they are very small, since 95% of modern solid-state amps have a virtually ruler-flat frequency response and very low distortion (< 0.01%). That's why the sonic differences are somewhat disputed in certain circles.

It really depends on your own demands. You may be satisfied with a $100 or $200 amp.
.
post #7 of 92
Quote:
Originally Posted by royalcrown View Post
Bullseye: I have the presonus HP4, and I purchased it for 100 dollars. It'll perform identically to the S-amp, but the HP4 has a monitor pass-through for speakers. The S-amp should suit you well.
Thanks royalcrow, I was looking for other alternatives at a nice price and you gave me one. It was what i was looking for. So I will have to decide between both, the S·Amp and HP4.
post #8 of 92
Quote:
Originally Posted by Bullseye View Post
Thanks royalcrow, I was looking for other alternatives at a nice price and you gave me one. It was what i was looking for. So I will have to decide between both, the S·Amp and HP4.
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!

Another option are the Behringer Mixers like the UB1202 or the 802. I had the UB1202 (unfortunately I did not measure it) and enjoyed the sound from a 250 ohm DT880 and Denons. Keep in mind that I did not perform a very rigorous test so I cannot make any solid claims about the sound.

There is also the Behringer AMP800 but I have not tested it.
post #9 of 92
Good point odigg, I neglected to note that his headphones are low-impedance Grados. Bullseye, if you search pro audio sites such as sweetwater or zzounds you can find a huge selection of pro headphone amps. Try the SM Pro Audio HP4 available at zzounds (SM Pro Audio HP4 Headphone Amp from zZounds.com!), it will perform identically to the other amplifiers but it has a 22 ohm output impedance - not the lowest, but it should be low enough for 32 ohm headphones. From my personal experience and observations, so long as the damping factor is a bit above 1.0 (that is, the headphone impedance is at least a bit higher than the amp's output impedance), you should be fine with headphones. Speakers need much more, but (likely due to the small size and power requirements of headphones) this doesn't seem to be the case for headphones.

The downside is that there's no pass-through for a pair of speakers. I bought the HP4 based on that, and I could've probably had the same performance for 20 bucks, but the convenience of having a quick button to switch between headphones and speakers was worth the extra cash. You can find various pro amps at many price ranges, and they all perform the same (given a proper match in terms of impedance), but they have different features.
post #10 of 92
Yeah, well. I was looking at that kind of amps because of the Fostex T50RP HP I will receive in a few days @ 50 Ohm (not really high, but I prefer SS for that) impedance and in case I buy the Beyerdynamic DT48E @ 200 Ohm (which is a bit cheaper than the 25 Ohm version).

I know low impedance HPs really don't need amplification, but I want to have something to control the volume easily (like a volume knob).

EDIT: Odigg and royalcrown: I found this in the presonuns HP4 tech info:
Output
TRS balanced: 51 ohms impedance. So maybe the Fostex do work good with it.


Whereas the Samson S·Amp has the following:
Output Impedance: 100 Ohm each output

Technically the S·Amp would perform worst with the T50RP @ 50 Ohm than the HP4.
post #11 of 92
Quote:
Originally Posted by Bullseye View Post
I know low impedance HPs really don't need amplification, but I want to have something to control the volume easily (like a volume knob).
Depending on your source/amp a low impedance can might need a separate amp. When I plug the Denons (25 ohm) into my computer's motherboard onboard sound there is slight bass rolloff. It isn't huge, but it's there.

Let's not forget that Grado has their own amp, the mighty RA1. It is the pinnacle of audio engineering, basically a cmoy in a fancy box. Hey, if the RA1 is enough for John Grado, it's certainly enough for me!
post #12 of 92
Quote:
Originally Posted by Bullseye View Post
...Fostex T50RP HP I ... 50 Ohm...
...I found this in the Presonus HP4 tech info:
Output
TRS balanced: 51 ohms impedance. So maybe the Fostex do work good with it.
50 ohm is too high an output impedance for a 51 ohm headphone. Ideally it should be around 0 ohm. Any non-linearity in the impedance curve would show up in the electrical frequency response and thus distort the acoustic frequency response. Even if the Fostex as an othodynamic design has a quite even impedance curve (don't know, but possible), you burn 50% of the produced current in the serial resistance of the amp's output.

There are only few headphones which benefit from an accentuation of the usual bass resonance around 100 Hz due to a corresponding impedance curve and the interaction with the serial resistance. 0 ohm is the best value, also in the interest of the damping factor (which OTOH doesn't have as much meaning with headphones as it has with speakers). If you think it sounds better with the bass accentuation, adding serial resistors is an easy exercise.


Quote:
Originally Posted by odigg View Post
When I plug the Denons (25 ohm) into my computer's motherboard onboard sound there is slight bass rolloff. It isn't huge, but it's there.[/i]
It's most likely a consequence of undersized buffer capacitors in the output stage. A notorious design flaw with many portable players, BTW.


Quote:
Let's not forget that Grado has their own amp, the mighty RA1. It is the pinnacle of audio engineering, basically a cmoy in a fancy box. Hey, if the RA1 is enough for John Grado, it's certainly enough for me!
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.
.
post #13 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.
I was mostly making fun of the Grado RA1 for being the epitome of what I consider ludicrously overpriced gear that is praised because people do not look at it with a critical eye.

I have compared some of the "better" desktop ($1000+) amps or amp/dac combos frequently discussed on Head-Fi with some of the "not better" stuff on Head-Fi. For a lot of reasons I'm not going to a list the exact gear. My conclusions are the same.
post #14 of 92
Quote:
Originally Posted by odigg View Post
My conclusions are the same.
Does that mean the $1000-4000 amps sound the same as Behringer, Presonus, SM Pro, Samson & the like?
.
post #15 of 92
Quote:
Originally Posted by JaZZ View Post
Your E-MU 0404 doesn't have a dedicated headphone out, right? If so, the line out may be able to produce sound through your headphones, but it is electrically limited (current supply), may distort and roll off the bass, as it's designed to «drive» a high-impedance load (such as >10 kΩ) instead of a headphone.
[/COLOR]

He mentioned an 0404 usb, which does have a headphone out capable of some volume - drives 250 ohm DT250's with a good chunk of headroom for transients.

Quote:
Originally Posted by jcx View Post

supporting that position is the "Carver/Stereophile Challenge"

diyAudio Forums - Blind Listening Tests & Amplifiers - Page 22
That is a very interesting link.


I've more or less come to a similar conclusion through a roundabout way.

I've done some single blind testing with some desktop amps (which involved kludging together a switcher from AV switch boxes that may or may not have wreaked havoc with impedance seen by the amps), and in the end couldn't justify keeping them (even though they were paid for). Especially when I could envision trading them for a shiny new 30" lcd and GTX 285

It is damn hard to put together even a single blind test, though.
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