Different headphone sound on two outputs.

[iv0]

Hello, I need help to develop the vocabulary to describe my issue.

I have a digital source and a/b naim amplifier.
When I plug my headphones in the source directly everything is punchy and aggressive. There is real kick to the bass. When I plugin in the ab amplifier with class a headphone amp it feels like I put a rug on the base. Its very bloomy and kinda slow. What am I experiencing?

When I restart the amp, things seem to better.

 

[DVDdoug]

first, make sure you are listening at the same volume. Our ears are not linear and when you turn-up the volume it sounds like you've turned-up the bass even more. And our brains can trick us in other ways.

A good headphone amp will give you the "real" frequency response of the headphones but a couple of things can happen -

If the headphone amp has an output capacitor it combines with the load (headphones) to make a high-pass filter. The lower the headphone impedance (and the lower the capacitance) the higher the cutoff frequency so you can lose bass with lower impedance headphones.

Or, headphone impedance varies with frequency response. If the headphone amplifier's output impedance isn't low compared to the headphone impedance you'll get variations in frequency response. It's not uncommon for headphones to have a resonance bump in the bid-bass range and with some headphone amps that makes a (relative) bump in the mid-bass and it might "sound better" with an inferior headphone amp.

Higher impedance headphones (or an amp with low output impedance) minimizes both of these effects. But usually you don't get an actual output impedance spec for the headphone amp... Usually they are giving you the minimum recommended headphone impedance.

with class a headphone amp

It's not related to the amplifier class. The amplifier class has more to do with energy efficiency and wasted heat in the amplifier (not much of an issue with headphone amp). But a class-A amplifier is likely to have an output capacitor.