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I have a headphone amp that has a slight hum which does not increase with changes in volume. I am using 32 ohm impedance headphones. The manufacturer recommends using a higher impedance headphone >100 ohm. Why would this make a difference? any recommendations for closed back phones < $175?
Follow Ups:
A quick solution is increasing the effective impedance of the headphones with an adapter. There are a number on the market both as plugs and pigtails. When I use low impedance headphones on the phone jack of my preamp (Anthem Pre2L, 4x6922) there is a bit of hum and hiss. I have a pigtail adapter from Ultimate Ears that I think adds another 125 Ohm effective load (https://pro.ultimateears.com/adjustable-ambient-filters-248.html).The result is that the noise is eliminated. I also use it for computer listening through an AudioEngine D1 as it gives the volume control a much greater range of adjustment.
Edits: 12/26/18
The impedance is very unlikely to be the issue you are experiencing.
A lot of 32 Ohm headphones are very sensitive (like Grados) and will be noisier than a proper high impedance headphone on something like an OTL amp (the Bottlehead Crack for example).
An impedance mismatch between headphone and amp will lead to elevated distortion from the amp and boomy/loose bass response. Such an amp may also have a coupling capacitor properly sized for 100+ ohm headphones but not well sized for lower impedance headphones.
Makes a difference because the output impedance of your amp is probably 10 ohms or higher.
The impedance of the headphones being too low makes the amp work harder due to too much of the load being taken up by the amps output impedance itself. If the amps output impedance is 10 ohms, one quarter of the amps output is being wasted on the amps output load itself.
In this case the total load being seen by the amps output would be 42 ohms (10 ohms for the amps output impedance and 32 ohms for the headphones).
Your headphone amp's power is wasted because too much is being absorbed by the amps load. If the headphone impedance was higher then a much larger portion of the amp's output would be applied to the headphones.
Also, if the amp had a lower output impedance, 1 ohms or lower, a much larger portion of the amps output would be applied to the headphone. In this second case, the total impedance being seen by the amp would be 33 ohms with 32 ohms being the headphones and 1 ohm for the output impedance of the amp.
There are way too many devices on the market that call themselves headphone amps when they are barely amps in the strict sense. If you chose a better quality amp, then you could more easily drive your headphones.
You need a better headphone amp if you want decent performance.
Ed
We don't shush around here!
Life is analog...digital is just samples thereof
Thank you Ed. Makes sense.
sam
I forgot the hum thing you mentioned when I posted. What kind of headphone amp are you using?UPDATED: FYI..a closed back headphone I used were a pair of Sennheiser HD280Pro's. They were very good for the money and were rated as a best buy quite some time ago. It looks like you can still buy them but Sennheiser has some newer models that you may consider. The HD380 headphones look interesting for the money. They are listed for about $150. I would look into the HD280Pros and the HD380s if I were in your place.
FWIW, I owned the HD280Pros for over 10 years and used them daily for a few years. I would still have them but I gave them to my son who is still using them. The HD280Pros have a 64 ohm impedance and 102db sensitivity. The HD280Pro is known for being tough and lasting. They also have good sound quality. Surprising for the money.
Ed
We don't shush around here!
Life is analog...digital is just samples thereof
Edits: 08/28/18 08/28/18
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