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Study: Headphone Amp Gains: Low or High?

amirm

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#1
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.
Schiit Magni 3 Headphone Amp versus JDS Labs Atom Gain Review.jpg

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:
Schiit Magni 3 Low Gain Distortion Measurement.png


Now let's switch to high gain while achieving the same 3.84 volt output:

Schiit Magni 3 High Gain Distortion Measurement.png


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:
JDS Atom Headphone Amp Low Gain Test Measurement.png


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:
JDS Atom Headphone Amp High Gain Test Measurement.png


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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RayDunzl

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#4
What are the low/high gain values?
 
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#5
Very neat, interesting to see how the noise floor rises between low and high gain.

@amirm would it be possible to plot an overlay of THD+N vs Power for each gain setting? I ask because I've seen anecdotal comments suggesting that once you are close to max volume on low gain, you should switch to using lower volume on high gain as noise and distortion will be lower, despite the gain setting (i.e Low gain 90% volume < High gain 50% volume).
 

bravomail

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#6
Cannot help but notice that voltage difference. To my uneducated guess: "Magni 3 gives twice the voltage out while only slightly worse noise than Atom". Can u elaborate?
 

wadec22

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#7

amirm

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#8
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#9
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.

----
If you like these kind of articles, please consider donating funds to support the forum using:
Patreon: https://www.patreon.com/audiosciencereview)
or upgrading your membership here though Paypal (https://audiosciencereview.com/foru...eview-and-measurements.2164/page-3#post-59054).
Thanks, I think some one here actually... poked fun at me for making a similar comment. But the rule of thumb I've always observed is to use as little gain as needed, as more gain almost always equals more noise, nice to see your finding support that at least for these two
 

Johnb

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#10
Amir, I am having a hard time understanding this. Regarding Atom, comparing levels (in review) at high gain on the THD+N Vs Power sweep, we see 0.0003% at 50mW (approx 2VRMS), on dashboard you measure 0.00088. My understanding was that dashboard would be even less than the swept, reasoning that noise, being mostly random, would cancel while averaging. Or is this because Dashboard looks at the whole spectrum, and the sweep is limited to 1khz? Someone to educate me....
 
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amirm

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#11
Excellent information, Amir! Any chance of testing the other two SOTA amps, THX 789 in particular?
I will be on the road tomorrow delivering the HP-1. So here is the test of that. I will probably post the THX in a day or two:

Neurochrome Hp-1 Headphone amplifier low gain measurement.png


Neurochrome Hp-1 Headphone amplifier medium gain measurement.png


This is all with unbalanced input so there is mains noise dominating (distortion is very low compared to it). High gain though, raises distortion:
Neurochrome Hp-1 Headphone amplifier high gain measurement.png


So the study conclusions remain: use the lowest gain setting that does the job.
 

amirm

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#12
Amir, I am having a hard time understanding this. Regarding Atom, comparing levels (in review) at high gain on the THD+N Vs Power sweep, we see 0.0003% at 50mW (approx 2VRMS), on dashboard you measure 0.00088. My understanding was that dashboard would be even less than the swept, reasoning that noise, being mostly random, would cancel while averaging. Or is this because Dashboard looks at the whole spectrum, and the sweep is limited to 1khz? Hey, maybe I answered my own question?
I am running these tests quickly and not trying to get optimal outputs. So I would not use these results for benchmarking outside of the study itself. With unbalanced connections I usually have to play to get optimal numbers.

Commenting anyway, averaging has no effect on SINAD or distortion rating. They only impact the FFT spectrums shown. What impacts SINAD is the bandwidth used.
 

pkane

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#13
I will be on the road tomorrow delivering the HP-1. So here is the test of that. I will probably post the THX in a day or two:

View attachment 18334

View attachment 18335

This is all with unbalanced input so there is mains noise dominating (distortion is very low compared to it). High gain though, raises distortion:
View attachment 18336

So the study conclusions remain: use the lowest gain setting that does the job.
This makes sense and confirms what I always knew: higher gain results in greater noise and distortions. Thanks for demonstrating this so graphically! I think I know what to expect with the THX, but still curious to see it nevertheless.
 

Johnb

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#14
I am running these tests quickly and not trying to get optimal outputs. So I would not use these results for benchmarking outside of the study itself. With unbalanced connections I usually have to play to get optimal numbers.

Commenting anyway, averaging has no effect on SINAD or distortion rating. They only impact the FFT spectrums shown. What impacts SINAD is the bandwidth used.
Thanks. I'm slowly learning.
 

Headphonaholic

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#15
This was a great study! It's nice to know the rule of thumb most of us used is actually correct.

I would also be curious to see the effect of different volumes at higher gains. What I would expect to see is performance decreasing as you increase the volume.
 

solderdude

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#16
Higher gain means less overall feedback in most designs.
Without feedback there would be incredible amounts of gain, bandwidths of only 10 to maybe 100Hz and shitloads of distortion.
Feedback 'corrects' all this. The more feedback the more correction. The lower the noise and distortion and the wider the freq. range will be.
All within certain limits of course.
There is nothing unexpected or strange about it.
It is good to see it in plots as well as manufacturers don't like to show 'worse' numbers and usually only publish the 'best measured' performance.

Lower gains are needed when efficient headphones/earphones are used so it is a good thing noise floors and distortion also drop.
In high-gain mode noise (and distortion products) can thus become audible with those type of head/ear-phones.
Using insensitive headphones (that require more gain otherwise you cannot play loud enough) a higher noise floor and distortion remains inconsequential as it remains below the audible threshold.
High output signal DAC's can also be helpful (when amp input stages aren't clipped) here as well.

As long as it stays (well) below audible thresholds (depends on the efficiency of the used speakers/headphones) I think it does not matter that much.
Blind tests with gain compensation can show how much differences there are in the audible aspects of it.
This is difficult to do or requires 2 amps.
 
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#19
This is what I always have wanted to tell those who believe that much more unused power is good sound quality or something like encouraging headphone's potential ability. I heard some guy who works at pro-studio said that they prefer low gain for convenient volume control and good SNR. Today, so many headphones and IEM tend to be sensitive(I don't think HE6 is ordinary). In my humble experience, many powerful amplifiers need attenuator like ifi's IEM match. 12V output power? I think it's ridiculous.
 
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rajapruk

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#20
Now with amps besting dacs in performance, maybe it changes this best-practice though....?
I mean it maybe might be better to use a low-gain dac with THX789 on highest gain, than using a high-gain dac with the THX789 on lowest gain. If you get what I mean, to reach a wanted total output?
The old rule of thumb would say high gain dac, and the lowest gain on the amp is best. But is this still valid now, when the amps have better performance than the dacs? :)
 
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