Headphone amp gain and output

[MagR]

Hi
 
Can someone explain to me how gain operates in relation to my circumstances. I have an Epithany Acoustics EHP-O2D which incorporates the open source O2 amp and ODAC. The amp has maximum output of 7Vrms and the ODAC outputs 2Vrms. The amp is a two stage design having separate gain and output stages.
 
My lower gain setting is 2.5X. As the amp has a very low output impedance of about 0.5 ohm I believe this means maximum volume equates to 5V – within the maximum possible by 2V.
 
My higher gain is 5X which would equate to 10V at maximum volume with this source. However the amp can only output 7V. What happens here? Once the volume pot setting reaches 7V does it simply not get any louder or does it start to distort if you turn the volume pot any higher? I’ve seen some mention of input overload. If I use a gain of 5X which is impossible to achieve will I always get distortion with this source no matter what the volume because I’m trying to overload the input stage of the amp?
 
I’m pretty confused by this. I can’t really see why it doesn’t just have a fixed gain of 3.5X as 2V * 3.5 = 7V. The reason why this has now become an issue is I’m thinking of buying another set of headphones which might need over the 5V available at the low gain setting to get loud enough. My existing Sennheiser HD650’s and AKG K701’s are fine at the low gain setting.
 
Thanks in advance
 
Mag

 

[PleasantSounds]

I don't think calculations are going to tell you the whole story - sometimes numbers seem right and the sound is cr@p, or the other way round. A couple points to consider:
- if you look up the definition of gain, you'll find out that it may be relating to voltage, but it could be relating to power as well. Are you clear about which one is in the specs? If it's the latter then the gain from 2V to 7V is 12 x.
- The 2V on the input is the maximum signal, and the signal overload is related to this value. Many consumer grade devices output only 0.89V (peak-to-peak line level standard) - in that case to get to 7V you'd have 8 x gain (assuming the voltage ratio definition).
You may be better off asking for user experiences with your intended headphones and the same upstream gear - chances are someone already has tried this combination. 

 

[MagR]

Thanks for your reply. I'll ask for advice on the specific O2/ODAC thread I've just noticed.
 
Thanks again
 
Mag