For the gain, unity gain is the way to go. Less than unity will cause worse SNR. If the gain is before the pot, the snr is what counts. If the gain is after the volume pot, the noise floor itself is what counts.
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Study: Headphone Amp Gains: Low or High?
- Thread starter amirm
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CerealKiller
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This is an analysis of whether you are better off using low or high gain mode in a headphone amplifier in their overlapped region. Traditional rule of electronic design says there is no free lunch: higher gain means higher noise. While this has become the "conventional wisdom" and one that I routinely state myself, forum member asked if there is any hard data to back this. So I decided to test the theory on two headphone amplifiers: the Schiit Magni 3 and JDS Labs Atom.
The test matrix here is infinite in scope. What volume does one choose for each gain to test? After pondering for a second or two, I decided to go the defensible route of setting low gain to max and then matching the same in high gain. Both of these amplifiers have analog volume controls and in high gain, they can be touchy as far as getting accurate levels out of them but I managed to get close enough.
Let's see what the measurements say.
Measurements
For these tests, I chose to use 300 ohm test load as that is in my analyzer and hence, higher fidelity than my external dummy load.
Here is the dashboard view of Schiit Magni 3 in low gain at its maximum value:
View attachment 18330
Now let's switch to high gain while achieving the same 3.84 volt output:
View attachment 18331
We take a 3 dB hit. The impact on SINAD is not as large as one expects because the performance of Magni 3 is distortion limited. If you look at the noise floor in FFT in top right, you can see the large increase in noise floor (about 20 dB).
Note also that channel matching suffered a bit in high gain. Slight inaccuracies in the volume potentiate translates into larger errors in high gain mode although obviously this is situation specific.
In low gain mode, the JDS Labs output is much lower:
View attachment 18332
Performance is so amazing that the noise floor falls off the bottom of the FFT produces superlative SINAD of 115.
Let's switch to high gain and match levels:
View attachment 18333
We take a considerable hit to the tune of 13 to 14 dB. As with Schiit Magni 3, our noise floor rises by good bit (around 10 dB).
So I think we have our answer.
Conclusions
Given a choice, use the low-gain setting of the headphone amplifier unless actual measurements stipulate otherwise. In the case of both Schiit Magni 3 and JDS Labs Atom, this is indeed the wise strategy.
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Amir, thank you for this comparative, does dx3pro exibits the same behaveour? I always play this little game "by ear" on all my amps with gain switches and dx3 sounds to me just a hair more noisy in high gain, but of course Is not an AIB test... Presing the gain button an level matching takes couple of seconds and its far from acurate.
This is much more prominent since dx3pro uses digital volume. The gain is after the attenuation. So all the noise will be directly go to the output.
CerealKiller
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I'm not a very aducated person regarding amplifier topology,
Is this a standart? Ateunation of input signal is to be made befor the input gain when digital atenuators is used? If thats so, when picking analog atenuation, is it common to place it after the input gain ? And last, if the amp has a gain switch, does that meas that there are to gain stages in that particular design? first one would be input gain (wich will be switchable between two fixed values) and last one will be the amp gain itself?
Hope, thats clear enough for a question so I can learn a thing. =) cheers.
DX3Pro has built-into the DAC chip a digital (32-bit) volume control, so it's not a dedicated external volume control like PGA2310, so it will not have an actual gain stage inside the digital control (DAC chip). The amplifier itself has a gain stage...something around 3X.
I guess John was referring to the fact that internal headphones amplifier's noise will get injected into the headphones because there's no analogue potentiometer and no analogue gain adjust switch between amplifier's input stage and the output stage. I guess that output stage noise might be heard with extremely sensitive headphones (IEM's >100dB/mW SPL), so not quite an issue.
I guess John was referring to the fact that internal headphones amplifier's noise will get injected into the headphones because there's no analogue potentiometer and no analogue gain adjust switch between amplifier's input stage and the output stage. I guess that output stage noise might be heard with extremely sensitive headphones (IEM's >100dB/mW SPL), so not quite an issue.
As long as you don't hear it at low gain that's good enough. If you want to "fix it" the only way is to use an external amp. But I don't think that's necessary.
The way they did on dx3pro has both benefits and disadvantages. Big advantage is that the
volume is balanced from the minimum to maximum. Disadvantage of course is to sacrifice snr at low volume.
The more effective way to implement is like trl said.
DAC - Gain stage - potentiometer - output buffer. This way snr will mostly saved and the noise will be only dominated by output buffer's residue noise.
CerealKiller
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Interesting, got one more, in that last ideal snr case you are pointing, the gain stage is the total amp gain ?
Actually i got two, can someone recomend some good literatury?
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Talking about gain, could @amirm please publish the voltage gains (Vo/Vi) for the tested amps.
This is an important figure. As I mentioned in another thread, I was initially sure lo gain was unity on all amps.
This is not the case. For example, the Schiit Magni 3 as a lo gain of x1.4 (3dB), whilst the Atom has a lo gain of x1 (unity indeed).
So a fair comparison would be to read the Atom's output voltage just before clipping, and adjust the Magni's input voltage to obtain the same output.
FYI, Magni's high gain is x7, and Atom's x4.5. Difficult to make comparisons.
This is an important figure. As I mentioned in another thread, I was initially sure lo gain was unity on all amps.
This is not the case. For example, the Schiit Magni 3 as a lo gain of x1.4 (3dB), whilst the Atom has a lo gain of x1 (unity indeed).
So a fair comparison would be to read the Atom's output voltage just before clipping, and adjust the Magni's input voltage to obtain the same output.
FYI, Magni's high gain is x7, and Atom's x4.5. Difficult to make comparisons.
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Gain difference between amps might help the lower gain amp to have a lower background noise, but all the other measurements will remain unchanged. Although, a difference between 1X and 1.4X shouldn't change the background noise much anyway.
A good example is changing the internal gain in Objective2 (or another gain adjustable headamps) while inputs are shorted to ground (basically, no music playing). With very sensitive cans or IEMs it's easy to notice the noise difference between 1X and 3.5X or 6X.
A good example is changing the internal gain in Objective2 (or another gain adjustable headamps) while inputs are shorted to ground (basically, no music playing). With very sensitive cans or IEMs it's easy to notice the noise difference between 1X and 3.5X or 6X.
I do agree, but I think it's important to compare apples with apples, which means using the same output voltage ie the same power in the same load.
The amp with the lowest efficiency should be driven to its maximum output before clipping, and the input voltage of the higher efficiency one set accordingly.
Mind you, this will probably not make any difference with respect to the ranking of the amps (eg Massdrop THX > JDS Atom > Schiit Magni 3)
The amp with the lowest efficiency should be driven to its maximum output before clipping, and the input voltage of the higher efficiency one set accordingly.
Mind you, this will probably not make any difference with respect to the ranking of the amps (eg Massdrop THX > JDS Atom > Schiit Magni 3)
OP
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Sure. I have been doing that for power amps. I usually put in the input voltage level so you can compute it yourself.
Yes, if you also quote the output voltage.
I am using HD600 with Atom.
I understand that these tests show that with low gain there is less noise than with high gain.
However, when I listen to music it sounds to me that with the gain knob on "High" the sound is more "open" than with low gain, for the same volume level (as far as I can tell).
Could it be that with low gain there is not enough power to drive well the headphones through all the frequencies? Could it be for example, that the bass or soundstage suffer?
On low gain, I listen with the volume knob from 9:00 to 2:00 approximately, depending on the music.
Forgive me if that is a naive quesiton.
I understand that these tests show that with low gain there is less noise than with high gain.
However, when I listen to music it sounds to me that with the gain knob on "High" the sound is more "open" than with low gain, for the same volume level (as far as I can tell).
Could it be that with low gain there is not enough power to drive well the headphones through all the frequencies? Could it be for example, that the bass or soundstage suffer?
On low gain, I listen with the volume knob from 9:00 to 2:00 approximately, depending on the music.
Forgive me if that is a naive quesiton.
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There is no difference in power when using low or high gain. That's the common misconception. If you can give high enough input signal low gain will reach the same level as high gain. The gain stage does not affect the output stage in any way. They are separated.
OP
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That happens to me every time I switch to high-gain. The reason is that it is much louder. If you equalize the levels with low-gain, that difference vanishes.
PenguinMusic
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Hi,
No intention to dig out an old post.
But I recently got into listening to music with headphones.
I have 2 DAC/amp combos to use : ASUS Xonar Essence STU and Oppo HA2-SE.
Both have "hi-gain" setting...
Used headphone is Sennheiser HD700.
Well, on both DAC/amp combos, the statement is the same.
If I use "low-gain" I have to turn up the volume to a point where I distinctly hear a "hum" or "hiss" in the background.
If I use "hi gain" I can keep the amp to really low levels and do not hear that "hum" or "hiss" background anymore.
So I tink will keep using "hi gain" with low volume level instead of "low gain" with high volume levels.
Am I doing something wrong ?
No intention to dig out an old post.
But I recently got into listening to music with headphones.
I have 2 DAC/amp combos to use : ASUS Xonar Essence STU and Oppo HA2-SE.
Both have "hi-gain" setting...
Used headphone is Sennheiser HD700.
Well, on both DAC/amp combos, the statement is the same.
If I use "low-gain" I have to turn up the volume to a point where I distinctly hear a "hum" or "hiss" in the background.
If I use "hi gain" I can keep the amp to really low levels and do not hear that "hum" or "hiss" background anymore.
So I tink will keep using "hi gain" with low volume level instead of "low gain" with high volume levels.
Am I doing something wrong ?
HD700 has 150 ohm impedance. It’s preferred to use high gain on such impedance characteristic. In IEMs it’s a different story where low gain is preferred due to their sensitivity to hissing
Probably not, but from a hearing safety I would stick to the lowest gain.
First of all i don't see why you hear hiss but there can be some explanation with the hum.
One possible cause of this can be that the high gain allows you to use the volume pot at lower position which has less equivalent resistance. Hence the source impedance seeing from the amp itself(more possibly output stage) is smaller. In this case the input of the output stage has very small impedance to the ground, this way the hum will be reduced.
The hum can have several causes. As it's single ended this is very possible. Now the ha2 is battery powered (if you are not charging while listening, if you are, try without charging), the hum can come from the grounding design of asus essence. It's actually difficult to have the transformer inside the chassis and not getting interference. You can try plugin your ha2 to a dongle like meizu, apple, musiland anything like that, with your phone of course. And see if the hum is gone.
Hope this helps.
EDIT: I wasn't reading carefully enough to see you use two devices individually. So I would suggest to try plug each device independent to each other and to a laptop running on battery.
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