[StephenGareth]

Hello

I’m experiencing some distortion with my Shure 1840 cans when driven from a SPL Crimson DAC/amp interface.

The SPL headphone output impedance is 33 ohms which is apparently pretty high. The Shure 1840s are 65 ohm 96 dB/mW sensitivity. When driving a pair of old K240M 600 ohm headphones I get plenty of loud clean signal so it isn’t the amp outright.

With a 50-100Hz sine wave test tone the problem is pretty severe IMO. Raise the volume to an average listening level and the output starts to sound saturated, soft clipped, distorted or whatever you might call it. Something similar happens with my Shure SRH 840 closed back cans too (44 ohm 102 dB/mW sensitivity) so it seems the Crimson amp doesn’t like lower impedance phones.

Could the 33 ohm output impedance be responsible for the distortion? I’m interested in any opinions on this before splashing out on a new amp. I’ll try to test them with other equipment but options are a bit limited tbh.

Thanks
Stephen

 

[ProtegeManiac]

I’m experiencing some distortion with my Shure 1840 cans when driven from a SPL Crimson DAC/amp interface.

The SPL headphone output impedance is 33 ohms which is apparently pretty high. The Shure 1840s are 65 ohm 96 dB/mW sensitivity. When driving a pair of old K240M 600 ohm headphones I get plenty of loud clean signal so it isn’t the amp outright.

Output impedance is a spec of the headphone amp circuit, so technically, it is the amp outright that is the likely problem.

With a 50-100Hz sine wave test tone the problem is pretty severe IMO. Raise the volume to an average listening level and the output starts to sound saturated, soft clipped, distorted or whatever you might call it. Something similar happens with my Shure SRH 840 closed back cans too (44 ohm 102 dB/mW sensitivity) so it seems the Crimson amp doesn’t like lower impedance phones.

Could the 33 ohm output impedance be responsible for the distortion? I’m interested in any opinions on this before splashing out on a new amp. I’ll try to test them with other equipment but options are a bit limited tbh.

Very likely considering the sensitivity of the Shures is even higher than the AKGs, so it's not like it's just clipping. You can always just try a relatively cheap but powerful enough (to make sure it isn't clipping) low output impedance amp like the Schiit Magni3.

 

[StephenGareth]

Very likely considering the sensitivity of the Shures is even higher than the AKGs, so it's not like it's just clipping. You can always just try a relatively cheap but powerful enough (to make sure it isn't clipping) low output impedance amp like the Schiit Magni3.

Thanks for your reply. Only one way to find out if it is the amp or not..

 

[SilverEars]

Check out the distortion measurement of the SRH1840. That's signficant. It could be due to combination of things. Such low damping factor increases distortion, and according to this graph already quite high. I agree with ProtegeManiac. Try something with low output impedance.

https://www.innerfidelity.com/images/ShureSRH1840.pdf

 

[StephenGareth]

Thanks for the info SilverEars. Doesn't look good. I've plugged them into everything I can get my hands on at the moment which isn't much... a MacBook Pro, an iPad Pro (< 2 ohm output impedence allegedly), a Topping TP21 class D amp and an analog synthesizer. None of these are great tests but I always get this warm saturation effect in the low end way before any clipping from the amp running out of juice. Which for what I use them for is a deal breaker really.

It could be new headphones time. Again. That's how this hobby goes....?

 

[ProtegeManiac]

Thanks for the info SilverEars. Doesn't look good. I've plugged them into everything I can get my hands on at the moment which isn't much... a MacBook Pro, an iPad Pro (< 2 ohm output impedence allegedly), a Topping TP21 class D amp and an analog synthesizer. None of these are great tests but I always get this warm saturation effect in the low end way before any clipping from the amp running out of juice. Which for what I use them for is a deal breaker really.

It could be new headphones time. Again. That's how this hobby goes....?

If it's happening on the iPad Pro and you're not running any bass boost or EQ then it's definitely the headphone.