Newbie Here - OTL and Low Impedance HP's
Feb 22, 2021 at 12:18 PM Thread Starter Post #1 of 6

Luckyleo

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Hi All,

Been listening to headphone audio for years. However, I'm new to the science of it all.

I have an OTL headphone AMP. Feliks Audio Espressivo. Love it. It drives my DT800's terrifically well. 600 OHM. Also drives my Clears (55 OHM) and all my Grado's (about 32 OHM). None with resistance over 110. On every headphone forum I go to they say low impedance HP's don't work on OTL amps. It seems that mine do, at least for this particular amp. Can anyone help educate me on this matter? Below are the stats for this amp.

Impedance:100kohm
§ Frequencyresponse:15Hz-45Khz+/-3dB
§ Poweroutput:400mW
§ Amplificationlevel:20dB
§ THD:0.4%(300ohm,20mW)
§ Optimalheadphonesimpedance:60-600ohm
§ Headphonesoutput:Jack6.3mm
§ AC:230V/120V(powercordincluded)
§ Weight:3.5kg(7.7lbs)
§ Dimensionswithouttubes:275x220x115mm[10,8x8,7x4,5inch]

Thanks!

Leo
 
Feb 23, 2021 at 6:42 AM Post #2 of 6

Kammerat Rebekka

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The golden rule:
The output impedance of your amp should at the very least be 1/8 of your headphone’s damping factor. If not you are most likely going to experience an impedance hump in the bass plus added distortion/mud.
OTL amps generally come with a high output impedance which is why they’re most often used together with high impedance headphones (300 ohm Sennheisers fx).
Then again there are many who dig their headphones with an impedance hump in the bass. That’s basically what you get when you pair the HD600 with a Bottlehead Crack:)
For more and far better information on the subject, I highly recommend this thread:
https://www.head-fi.org/threads/headphone-amp-impedance-questions-find-the-answers-here.607282/
Best of luck👍
 
Feb 23, 2021 at 9:19 AM Post #3 of 6

Luckyleo

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The golden rule:
The output impedance of your amp should at the very least be 1/8 of your headphone’s damping factor. If not you are most likely going to experience an impedance hump in the bass plus added distortion/mud.
OTL amps generally come with a high output impedance which is why they’re most often used together with high impedance headphones (300 ohm Sennheisers fx).
Then again there are many who dig their headphones with an impedance hump in the bass. That’s basically what you get when you pair the HD600 with a Bottlehead Crack:)
For more and far better information on the subject, I highly recommend this thread:
https://www.head-fi.org/threads/headphone-amp-impedance-questions-find-the-answers-here.607282/
Best of luck👍
Thanks very much!
 
Feb 23, 2021 at 9:26 AM Post #5 of 6

Kammerat Rebekka

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^Indeed...and hid from view it (almost) sounds indestinguishable from a solid state amp except from a faint high pitched noise emanating from the left channel which can get audible during very quiet parts of some tracks... Well at least the 3 Valhallas I’ve come across that is:)
 
Feb 23, 2021 at 10:35 AM Post #6 of 6

castleofargh

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Often, an OTL design will work well with higher impedance and that scenario should be kept in mind when getting gear. Just as a general rule, if an amp suggests a certain range of loads, it's probably not a bad idea to listen. When people tell that OTL amps aren't for low impedance headphones, they don't mean that something will instantly explode if you do it. Just that gears are designed with a certain function in mind and tend to have nominal behavior when used that way. We're very lucky that most of the time, when we don't follow a manufacturer's recommendations with our headphone rigs, the worst consequence is inferior fidelity. Not all electrical appliances are as tolerant.

Beyond that, the actual consequences of using low impedance headphones may vary for each case. It could be that the amp doesn't have much current available. But just because the headphone is low impedance doesn't automatically mean you'll need a lot of current at your listening level and will fall into a worst case scenario. Sensitivity also matters, along with listening level.
You might also end up with more or less frequency response changes into some lower impedance headphone. I wouldn't suggest to do it on purpose, but if you like what you have, then you're probably good.
 

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