Possible causes for sound degradation due to amplifier
Dec 23, 2016 at 3:38 AM Thread Starter Post #1 of 12

Dulalala

Headphoneus Supremus
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Recently I came across a post in which someone said that his Fiio E07K was inadequate in powering his HE400i. By quick comparison of specifications, the HE400i, which has a rating of 93 dB SPL/mW and 35 Ohm requires ~5mW of power to get 100 dB SPL. The Fiio E07K outputs a maximum of 220mW at 32 Ohm which should be adequate to power them. However the poster said this...
"At full (12db) gain and at 80% volume, its still not bleeding levels and if the music is bassy, the amp distorts with each bass kick. You can hear it so clearly. I dont care about the measurements here. Im hearing distortion and each kick pound is like an industrial slop. And anyhow, by the time i increase the volume to that level the bass has already become so dry and thin."
Now I know that impedance mismatch can cause distortions but is there another reason that could distort the sound such as lack of current or voltage?
 
Dec 23, 2016 at 4:50 AM Post #2 of 12
  Recently I came across a post in which someone said that his Fiio E07K was inadequate in powering his HE400i. By quick comparison of specifications, the HE400i, which has a rating of 93 dB SPL/mW and 35 Ohm requires ~5mW of power to get 100 dB SPL. The Fiio E07K outputs a maximum of 220mW at 32 Ohm which should be adequate to power them. However the poster said this...
"At full (12db) gain and at 80% volume, its still not bleeding levels and if the music is bassy, the amp distorts with each bass kick. You can hear it so clearly. I dont care about the measurements here. Im hearing distortion and each kick pound is like an industrial slop. And anyhow, by the time i increase the volume to that level the bass has already become so dry and thin."
Now I know that impedance mismatch can cause distortions but is there another reason that could distort the sound such as lack of current or voltage?

You already have the power spec: 220mW > 32 ohms.  So you already know voltage (2.65) and current too (83ma), for the given conditions.  You can't separate voltage, current, power and the load, it's an equation, if you know any two parameters, you can calculate the third (or fourth).   BTW, their spec is >220mW @32 ohms, and >250mW @ 16 ohms., and from that second spec we get 2V and 125ma. 
 
Impedance mismatch doesn't always cause distortion, you need to know more about the specific conditions.  Technically, for any good headphone amp you're always working with an impedance mismatch (the headphones never "match" the amp), it's really more a question of how the amp deals with the differing sensitivities and loads of various headphones.  In this case the HE400i actually measure somewhat higher impedance than stated in the specs, but are quite sensitive requiring a small fraction of the total available power. 
 
There's really not enough info in your quoted post to diagnose the problem, but on the surface it sounds like inept usage.  Looking at the HE400i test data, there's nothing that would indicate they are at all difficult to drive.  The E07K would have no trouble driving them to nearly a dangerous level.  There's something else wrong in how the user is doing his test, like perhaps a huge amount of bass boost EQ.
 
Dec 23, 2016 at 5:21 AM Post #3 of 12
I have zero knowledge of the E07K, but the question was about the possible reasons, so here are some of them:
 
One problem with the power rating is that to be meaningful, it should also state what is the level of distortions at that power. The value of max power output is not absolute and increases with our tolerance for distortions (to some point): the same amp can output 200mW at 1% THD and only 50mW at 0.05% THD. 1% THD is a value some will argue they can hear....
 
Another possible issue is that sometimes the amp can raise the output voltage pretty high, but the power supply is not capable of delivering enough current. This ends up causing massive distortions, mainly in the low frequencies which draw most of the power. A dead giveaway that the power supply may be somewhat compromised is if the output power does not increase proportionally to impedance reduction - e.g. if an amp outputs 220mW at 32 Ohm I would expect the output at 16 Ohm to be around 440 mW. But this only matters if your headphones have impedance in that non-linear range (here less than 32 Ohm), and usually at unhealthy volume levels.
 
Dec 23, 2016 at 5:26 AM Post #4 of 12
same observation as @pinnahertz. we first need to know how it was used? digital input or analog input?
I'd take a guess and say it was analog input of maybe 1V or more while set on high gain(I don't own the device but the specs seem to suggest that the gain setting is there to adapt to the source voltage, not to make the headphone louder.) 
so my wild guess would be clipping from using high gain for the wrong reason in the wrong situation. it seems like a plausible cause for the described problem.
 
 
else even with innerfidelity's pair, and counting less power into 45ohm, loudness shouldn't be an issue for anybody who cares for his ears.
 
Dec 23, 2016 at 6:27 AM Post #5 of 12
Well I don't have any other information but this...
 
"Well Im using the he400i with the e07k. At full (12db) gain and at 80% volume, its still not bleeding levels and if the music is bassy, the amp distorts with each bass kick. You can hear it so clearly. I dont care about the measurements here. Im hearing distortion and each kick pound is like an industrial slop. And anyhow, by the time i increase the volume to that level the bass has already become so dry and thin. Overall the amp is not so bad but insufficient. It gives in before it totals out. And no these are not quite ear bleeding levels. Only at at least 40% volume at high gain do the cans become comfortably audible."
 
Regardless, Thanks for the information. I think I sort of understand the reasoning behind it.
  I don't own the device but the specs seem to suggest that the gain setting is there to adapt to the source voltage, not to make the headphone louder.

I don't quite understand this though, the gain setting doesn't make the headphone louder? If I understand correctly, the gain setting is used to change the voltage supplied but wouldn't a change in voltage also affect the total power output which would change the volume? Sorry if I'm asking rather simple question.
 
Dec 23, 2016 at 9:54 AM Post #6 of 12
ok I'm explaining that as a general idea, because again I don't know that product and it's very possible that my idea is wrong or that I'm explaining something that does not apply to this specific amp. so don't assume I know what I'm talking about ^_^:
 
well let's say I make an amplifier, I know that DACs can go up to about 3.5V(some desktop DACs), I will design my amp so that we're close to the limit with an input at 3.5V, that way I can get the most out of the components I use to maximize SNR and dynamic with 3.5V inputs.
now some portable devices like my sony A15 don't come even close to sending that. the line out of that sony sends 0.25V... so of course it will still work with an amp designed for 3.5V that's no issue at all. but from 3.5 to 0.25V, that's a signal 23db quieter, with potentially the same lower limit for noise in the amp. so that's not great. not a catastrophe, but not great.  one option would be to have a gain switch, so that you can change the voltage coming in and make it closer to what's ideal for the amp section itself. that way the amp can come closer to its maximum SNR and whatever, while using a source as weak as my sony. but now of course the amp won't work with 3.5V. and if I do use such a source, the amp will clip like crazy. thus the different gain options.
 
of course increasing the gain makes the signal louder, you're right about that, but it will do so up to when the components can't do louder and clip. that's what I suggest might have happened to our fellow.  high gain on a source that wasn't so weak, and the amp clipped from receiving too much voltage and still trying to apply some gain to it.
but for all I know there are other ways to mess up, maybe with the bass boost, maybe with setting to line output instead of HO, maybe the DAC just needed a reset... I just tried to guess one most likely reason.
 
Dec 23, 2016 at 10:19 AM Post #7 of 12
  ok I'm explaining that as a general idea, because again I don't know that product and it's very possible that my idea is wrong or that I'm explaining something that does not apply to this specific amp. so don't assume I know what I'm talking about ^_^:
 
well let's say I make an amplifier, I know that DACs can go up to about 3.5V(some desktop DACs), I will design my amp so that we're close to the limit with an input at 3.5V, that way I can get the most out of the components I use to maximize SNR and dynamic with 3.5V inputs.
now some portable devices like my sony A15 don't come even close to sending that. the line out of that sony sends 0.25V... so of course it will still work with an amp designed for 3.5V that's no issue at all. but from 3.5 to 0.25V, that's a signal 23db quieter, with potentially the same lower limit for noise in the amp. so that's not great. not a catastrophe, but not great.  one option would be to have a gain switch, so that you can change the voltage coming in and make it closer to what's ideal for the amp section itself. that way the amp can come closer to its maximum SNR and whatever, while using a source as weak as my sony. but now of course the amp won't work with 3.5V. and if I do use such a source, the amp will clip like crazy. thus the different gain options.
 
of course increasing the gain makes the signal louder, you're right about that, but it will do so up to when the components can't do louder and clip. that's what I suggest might have happened to our fellow.  high gain on a source that wasn't so weak, and the amp clipped from receiving too much voltage and still trying to apply some gain to it.
but for all I know there are other ways to mess up, maybe with the bass boost, maybe with setting to line output instead of HO, maybe the DAC just needed a reset... I just tried to guess one most likely reason.

Ah ok I get the gist of it now. Thanks. I have one more question though. Does this mean in a DAC/Amp combo, the DAC section outputs the same voltage regardless of the gain setting if I understand correctly? Does this mean for different gain settings within the DAC/Amp itself that the amp section of it will be under less ideal conditions as I would assume that the DAC itself would be designed to work with the amp at 0 gain?
 
Dec 23, 2016 at 7:36 PM Post #8 of 12
  Ah ok I get the gist of it now. Thanks. I have one more question though. Does this mean in a DAC/Amp combo, the DAC section outputs the same voltage regardless of the gain setting if I understand correctly? Does this mean for different gain settings within the DAC/Amp itself that the amp section of it will be under less ideal conditions as I would assume that the DAC itself would be designed to work with the amp at 0 gain?

If your gain setting is used to accommodate different input voltages, you might add some switchable attenuation at the input stage of the amplifier to adjust the level of the signal to the level that the amp was designed to work best with. With this, your amplifier can operate with a fixed gain since you can set the input to whatever is best for the DAC you're using.
 
In a DAC/amp combo, the amp does not need to function with different input ranges, but it does need to function with different loads. A switchable gain can help in this situation as well. In this case the input will always come from the internal DAC so it will always be at the ideal range. To accommodate different loads you might instead switch the amplifier's gain stage using a feedback network.
 
If you want your amp to work with high impedance, low sensitivity headphones, you need to give it a high gain. This will not work so well with sensitive headphones and IEMs because it will raise the noise floor and reduce the usable range of your volume control. To accommodate the sensitive headphones you also need a low gain setting. You could lower the output of the DAC or attenuate the input of the amp in order to accommodate the sensitive headphones which would solve the problem of the usable volume range, but it wouldn't do anything to help the noise floor.
 
It comes down to compromise. If you know your amp is always going to be used with a specific DAC and headphone, you can design it to operate best under those specific conditions and eliminate the cost and complexity of a switchable gain, or put those savings into better components. It's not too difficult to add a switchable gain to the amp though, you don't sacrifice much to put it in there and you gain a lot of flexibility.
 
Dec 23, 2016 at 9:45 PM Post #9 of 12
hi can any body help please i was given a pioneer sx-700L the rest of the system is working good but when i plugged in my turn table into the phono and for some reason i get some distortion on that channel and it is clean and crisp sound on the aux and the radio is there a way i can get the phono fixed so i can get the clean and crisp sound so i can listen to my vinyls.
so can any body help or put me in the right path please 
 
Dec 27, 2016 at 8:09 AM Post #10 of 12
First, check your ground.  Some turntables came with a ground connector to attach to the chassis of the receiver to remove ground loops etc.   If that is right, it might have a problem in the preamp circuit.  The phono input on integrated receivers has a preamp that isn't used on any other inputs.  This is because phono output is usually a fraction of what other standard outputs are.  If you were to move the phono to the aux input, you might get clean sound but probably at much lower volume. (This is a good test by the way).   One option would be to have someone who knows electronics take a look at the board and trace the phono input to make sure it doesn't have a leaking capacitor or any other obvious problems.  The other option is to buy an external preamp and then use the aux inputs for the turntable>Preamp combination.    This would bring the signal up to the expected level for your aux input and would result in a volume similar to what you would get from the phono input with the turntable directly connected.
 
Hope that helps
 
Dec 27, 2016 at 9:42 AM Post #11 of 12
  First, check your ground.  Some turntables came with a ground connector to attach to the chassis of the receiver to remove ground loops etc.   If that is right, it might have a problem in the preamp circuit.  The phono input on integrated receivers has a preamp that isn't used on any other inputs.  This is because phono output is usually a fraction of what other standard outputs are.  If you were to move the phono to the aux input, you might get clean sound but probably at much lower volume. (This is a good test by the way).   One option would be to have someone who knows electronics take a look at the board and trace the phono input to make sure it doesn't have a leaking capacitor or any other obvious problems.  The other option is to buy an external preamp and then use the aux inputs for the turntable>Preamp combination.    This would bring the signal up to the expected level for your aux input and would result in a volume similar to what you would get from the phono input with the turntable directly connected.
 
Hope that helps

Yes, check the ground wire first.  Then I'd vote for buying the external preamp, and not spending much on it, like less than $50.  Repairing the defect, especially if there's a cost to doing so, would not make sense.  
 
BTW, a phono preamp does MUCH more than just increase the volume.  RIAA eq is not a small thing, it covers the entire audio range and has a 40+dB curve variation.  Yeah, you pretty much have to have that.
 
Dec 27, 2016 at 10:13 AM Post #12 of 12
  Yes, check the ground wire first.  Then I'd vote for buying the external preamp, and not spending much on it, like less than $50.  Repairing the defect, especially if there's a cost to doing so, would not make sense.  
 
BTW, a phono preamp does MUCH more than just increase the volume.  RIAA eq is not a small thing, it covers the entire audio range and has a 40+dB curve variation.  Yeah, you pretty much have to have that.

 
He's correct on the preamp, I oversimplified more than a little but it gets the point across.  the ART DJ preamps are well thought of in the Sub-$50 range.  I have used them in the past and my daughter's current setup still runs one.
 

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