[RESOLVED ]question: is low impedance hphone source of distortion in crack?

[ryhaigh]

I am getting what sounds like guitar amp distortion as I turn the volume up on my crack w. speedball whenhttps://bottlehead.com/smf/Themes/BHG/images/bbc/orderlist.gif using HE-400i cans (35 Ohm impedance). Higher volume = more distortion. With my HD650 cans (300 Ohm impedance) everything seems fine.

Here's my setup. PC (Jriver)-->IFI micro IUSB3.0--> IFI IDSD BL --> Bottlehead Crack w. Speedball ---> Headphones.  Tubes in Crack are Tung Sol 3002399 and Telefunken ECC 82 if that could somehow matter.

Is the difference in headphone impedance the cause of this? Is there another factor between the headphones I am not considering? Is there a potential issue with my crack build?

Thanks,

Ryan

[Paul Birkeland]

Yes, the Crack is not designed to run low impedance headphones.

[Doc B.]

From the descriptive paragraph on the Crack product page -

Crack is an output transformerless amp designed for higher impedance headphones like the Sennheiser, AKG and Beyer designs.

[Paul Joppa]

Here's a technical response:

The HE400i is 10dB less sensitive than (for example) the Sennheiser HD-650. That means it needs 10 times as much power for the same loudness, and thus 3.15 times as much current. The low impedance means another 3 times as much current compared to the Sennheiser. Total is thus nearly 10 times more current - and OTLs are limited by current demand, not voltage.

[ryhaigh]

Thank you all for the quick response!!