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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