Hey guys, i am trying to understand how an impedance adapter can alter the sound of headphones and i need some help with the theory behind it.
My scenario is, i have a Qucksilver amp and i hear some background noise when i plug my Focal Clear OG in it, it is almost unnoticeable but it is there, and i have a 30ohms impedance adapter i decided to try.
From what i read so far that adapter should cause differences in the frequency response, but that did not happen.
The benefits i get from using that adapter are:
- The background noise is gone;
- I can use the volume pot more easily since it is less sensitive;
- I can saturate the tubes a bit more? Not sure if i can actually hear this one…
Am i missing something? Is there a detrimental effect to using such adapter?
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It won’t into a fixed load (read resistors and planar headphones).
Impedance adapters do two things, they act as dividers dropping the and they present a specific impedance to the amp.
For none reactive loads (read pretty much all measurement gear) all that’s going to do is drop the volume. For reactive loads it will change the shape of the impedance curve of the headphone as presented to the amp, because assuming your headphones impedance curve is some function of Frequency (F) R =f(F).
With the adapter what the Amp sees is R = R1 + (f(F) || R2) which is a none linear relationship. In effect it smooths it out. That can impact the frequency response if the amp has a none zero output impedance, the lower the output impedance the less the effect (In effect this is what damping factor is).
Technically in a transformer coupled tube amp, you also move the load line and potentially not in a subtle way, which could impact tonality, but again based on my experience it’s a MUCH more subtle impact than you might expect, my working theory for this is the Voltage swings for a headphone amp are so small, you have negligible none linearities, so changes in them don’t have a big impact.
The impact IME is extremely small, I built one into my tube amp (mostly to fiddle with load impedance) and it’s extremely hard to differentiate between the volume change and any change in tonality.
Yes, a function of just scaling down the output which scales noise proportionally with the signal, and noise is often not running through the amplification, so you can in effect just turn the noise down relative to the signal.
The only downside is your running through additional resistors, those can be audible, but again it’s extremely subtle, if you want to jump down the rabbit hole you can look at pieces on amp component selection, and the differences in sound between carbon resistors and metal film resistors in a circuit.
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