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Headphone & Amp Impedance Questions? Find the answers here!

Discussion in 'Sound Science' started by proton007, Apr 25, 2012.
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  1. MrMateoHead

    Sometimes the best way to learn is to just buy the best (or worst or just cheapest) tube amp you can find and see if you can figure out its contribution (or distortion) to the music you like. Then spend more money on different tubes seeing if you can hear a difference between them.
    You can try to be an electrical engineer and decide, based on facts and theory, ahead of time, how things should sound. Or you can just go straight to the "play" phase. I suggest you do. Just understand that planers are less reactive to output impedance than dynamic headphones. They may not "color" as obviously via high-impedance outputs. A cheaper way to color the sound would be to just pick some random EQ curves and apply them. You won't get the even-order distortion of tube amps, but you will familiarize yourself with how different "shapes" sound.
    Recently I got tired of reading reviews of speakers and trying to understand measurement techniques since they vary. So I bought a $15 measurement mic, an Android App, and wasted hours of my life seeing how my measurements stood up to published data. It has been rewarding as I am coming to understand the process better, and interpret the results. To make a long story short, it isn't THAT hard to get the basic profile of a speaker nailed down. But any measurement I do will be a lot "noisier" than an anechoic chamber. Period. Turns out one hsa to be pretty creative even when they are trying to be "objective"!
  2. bigshot
    The room is as much of a factor to sound quality as the speaker is, in both good and bad ways. It isn't just a matter of trying to eliminate the sound of the room. If you did that, you'd have an anechoic chamber and no one wants to listen to music in that. The trick is using the sound of the room to its strengths. How the speakers and room relate directly controls how the soundstage and sound location within it work.

    An easier way to experiment with the sound of tubes is to just use a regular transparent solid state amp and use a tube emulator DSP. That way you can fine tune exactly the degree and type of coloration you're looking for. There is a good thread on that in this forum.
    Last edited: Sep 6, 2018
    WoodyLuvr likes this.
  3. Steve999
    This thread has been dormant for too long! And so much of it is waaaaaaaaaaaaaaay over my head. So let me bring things back down to earth.

    I have this portable headphone amp. I think it cost me $245. It was some number of years ago. I don't think for a moment it's worth its value in parts. They told me they put some of the stuff from the XM6 in it because the delivery time took a little longer than was stated.

    They actually answered the phone when I called and told me that there was no audible difference between their XM4, XM5 and XM6! As there are considerable price differences between the three, I thought that was very cool. If it was a sales tactic they bamboozled me for sure.

    But the XM5 ticked ALL of the boxes for me--impedance switch, so I could drive low impedance or high impedance headphones; bass boost and treble boost buttons for when I am listening at low volumes or to anemic headphones; variable crossfeed so I don't get freaked out when I listen to Sgt. Peppers; a +10db gain button for when headphones are particularly hard to drive; and the ability to use it as a DAC with a computer or as an analog amp. Portable, rechargeable or works on mains power or normal batteries. I am using it as a DAC with my computer plus as a headphone amp right now. I've snipped the specifications and the purported measurements below. So I am just asking a generalist question, what does anyone see here? Good, bad, unusual, preposterous? Are the internal components pretty cool? Is there anything to be learned here?

    I can tell you it works and you can drop it on the floor a few times and it still works.

    Sometimes I want something, and I know it's not worth it's price in parts, but it's exactly what I wanted. So that's what this was.

    I am doing snips instead of links so you don't have to click to review the information and so I'm not being a shill for the manufacturer. I won't even show you a picture. I'll just say I got the slicker looking black version for no extra cost for some reason or other. It was a few years back at least.


    upload_2018-11-17_15-55-18.png upload_2018-11-17_15-54-9.png

    Last edited: Nov 17, 2018
  4. bigshot
    Features, build quality, and convenience are the best reasons to choose one home audio component over another. Sound quality isn't a good reason because any DAC designed to perform to spec should be audibly transparent. Sound quality is a big issue with transducers.
    Last edited: Nov 20, 2018
    Steve999 likes this.
  5. JustASnack
    This may seem a bit silly, but I'm not really sure if using my high-gain switch is affecting the way my music sounds (aside from obviously making the signal louder). Unfortunately blind AB testing is very impractical, since using the switch instantly increases/lowers the volume, without giving me time to volume-match the high and low settings. I'm using a Burson Soloist SL MKII

    According to the amplifier's manual on page 5, switching from low to high gain increases the headphone amp output from 0.18W to 2W. My question is, does switching from low to high gain affect the way my music will sound if I listen to it at the same volume on both gain settings? When I switch to high gain for example, it always feels like there is better treble and bass response, though obviously it's not a fair judgement, since the music gets noticeably louder when switching, before I have enough time to adjust the volume knob accordingly.
    If it helps, my daily drivers are currently the DT 1990 Pro, which have an impedance of 250Ohms and a sensitivity of 102 db SPL (1mW / 500Hz). Also the amplifier is rated at 2.5W @ 16Ohms, with an output impedance of 3Ohms @ 1W. I'm not sure if these specs matter to my question. Truth be told I've tried to understand how this stuff works so many times, but I just can't wrap my head around this kind of stuff. Physics was never my strong point :frowning2:
  6. 71 dB
    The setting should not affect the sound. The trick is to have equal levels. There is a 10.5 dB level difference and if you don't correct that precisely, the louder setting is likely to sound better. The setting doesn't affect the power, just how loud the sound is for given volume knob setting. So, with very low sensitivity headphones you may want to use high gain setting to avoif having to crank the volume to "eleven."
  7. JustASnack
    Thanks for your reply! With what you've said in mind, is the reason some people describe certain headphones as sounding better when driven balanced because balanced can drive headphones louder? Or can balanced outputs drive certain headphones "to their fullest potential" when single ended can't, given we're driving the same headphones at the same volume from both outputs?
  8. StandsOnFeet
    Some people will claim that the system sounds better when they replace their volume knob with an expensive one made of rare wood. Being skeptical of any claim that isn't supported by blind testing seems like a sound plan.
  9. castleofargh Contributor
    balanced outputs, not always but very commonly have double the impedance and voltage. the difference in listening level alone is enough to invalidate any impressions they get. then you add the delay caused by having to switch the cables so users usually won't have the ability to rapidly switch between the 2 options. that's another red flag as far as listening tests are concerned. and as cherry on the cake, I'd say that the effort to get a balanced amp, and often purchase balanced cables for our headphone, is already the action of somebody who wishes and expects the balanced setup to sound different/better. so if it wasn't already obvious, people's impressions about this shouldn't be taken at face value.

    as for the old question of SE vs balanced. until I see decisive evidence of the contrary, I'm of the opinion that it's a false dichotomy. good amps do not happen to all be SE or all be balanced. amps designed to nominally drive your headphone load at your desired level aren't all SE or all BA. some amps will do the job, some amps are crap or simply designed for a different range of loads and gains. those are relevant variables, along maybe with some concerns for basic fidelity.
    Last edited: Apr 23, 2019
    BobG55 and Krutsch like this.
  10. E1DA
    I have two HPAs, one with 1.5ohm output impedance, second with 50 mOhm, and I easily hear the difference in bass there. 1.5ohm has a bit less control but noticeable more punch vs 50mOhm. It is quite normal for the 4-8ohm speakers if less damping induces some hump on the frequency response but I use a planar headphone with perfectly flat impedance vs frequency. That's a bit confusing to me..
  11. bigshot
    You should make sure your impedance is matched properly. Then everything will sound correct and you won't run into imbalances like that.
  12. castleofargh Contributor
    with such a small impedance variation on a planar, I really doubt that it's the cause for what you feel in the low end. with impedance we always have as you mention some typical bass hump where the impedance rises most on the headphone/speaker(common for dynamic drivers). we have some usually inconsequential low freq roll off with low impedance loads(could become audible at some point, or really obvious when caps at the output join the headphone to form a high pass filter). when the damping ratio is horrendous, we end up hearing what's IMO just bad mechanical damping after the electrical damping has become bad enough. it's something we can also experience with big speaker drivers, but with headphones my personal experience is that it's pretty hard to create such circumstance because headphones tend to be pretty tight on their own. plus the typical impedance is much higher than that of speakers.
    so I would suspect other reasons due to design for audible difference in the low end in your case, and the difference in output impedance to be mostly or completely unrelated to how they sound.
  13. bigshot
    Which one is transparent and which one isn't then?
  14. E1DA
    castleofargh, you could be right again. These two design is completely different for topology reason, first is open loop Power DAC(PowerDAC V2 = TAS5558 I2S->PWM and lots of LVC logic gates in parallel as a PWM power stage + passive LC demodulation), the second one is conventional DAC+AMP(#9038S = ES9038Q2M+ AD8397 power stage). Both using a USB 5V as a power rail without extra regulation, just as is, with lots of capacitors with few milliohms ESR. For sure in the first case, just due to the system has no feedback at all, all 5V regulation dynamics goes directly to the output, of course, it is smoothed by 5000uF 5mOhm solid-polymer caps but not up to the bottom end, simply no room for 20000uF, actually, USB will fail to start with >5000uF. In the case of AD8397 output stage, the system has a lot of loop gain targeted to correct 5V rail disturbances, and finally, THD+N vs frequency is perfectly flat. The PowerDAC has higher THD+N in low freqs, with about 100-200Hz corner, depends on the load impedance. BTW, 1 year ago I worked with proto of Power DAC amp 125W*2ch 4ohm, where I can bypass a noise-shaper in one single click i.e. the system could operate in the one of modes 1-open loop(no feedback)/2-closed loop(tonnes of feedback). And the situation is reproduced in the same manner as I have with headphones PowerDAC V2 and #9038S:
    1) Open loop mode sounds more punchy in bass and kinda softer, bass less controlled but pleasantly
    2) Closed loop mode has a lot less THD+N and much better SNR, bass sounds tight and a bit dry vs Open loop mode
    1 year ago I explained that phenomenon by damping factor difference and complex speaker impedance nature but today I have the same with planar headphones :wink:
    In my opinion, the open loop system sounds more pleasant(kind of more freely) but a bit less accurate in basses. In highs, both PowerDAC V2 and #9038S, sounds razor-detailed with no any smoothy unlike cheap HPA on TI chips like TPA6130(THD 6kHz is 10x times higher than 1kHz i.e. the different amount of loop gain applied withing audio-band. As claimed B. Putzeys this is the common reason for coloration in highs. It sounds like treble knob tuned down for -3-6db).
    archdawg and NotKunvinced like this.
  15. castleofargh Contributor
    you're suggesting that I've had good ideas twice in 2019 already. now I know this is my year!!!!! ^_^
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