Bottlehead Forum

Bottlehead Kits => Mainline => Topic started by: Loquah on December 02, 2013, 01:00:59 PM

Title: Output Impedance Switching Benefits
Post by: Loquah on December 02, 2013, 01:00:59 PM

I hadn't previously realised that the Mainline has an output impedance switch and it has me wondering now, why this is necessary? My previous understanding was that lower is always better. When is that not the case?

Title: Re: Output Impedance Switching Benefits
Post by: Paul Birkeland on December 02, 2013, 01:12:41 PM

Lower impedance taps deliver better damping and noise performance into high impedance loads, but at reduced power. If you have power hungry headphones, the higher impedance setting will give better performance.

Title: Re: Output Impedance Switching Benefits
Post by: Loquah on December 02, 2013, 01:24:21 PM

OK. Thanks Paul.

I guess it depends on how the output impedance is implemented then. The iRiver AK100 portable DAP has a 22ohm resistor on the output circuit which is completely redundant from a performance perspective (by all accounts and my personal experience). Does the Mainline OI switch just add impedance with a resistor or is it a output transformer winding? (I haven't gotten to that stage of the build yet)

Title: Re: Output Impedance Switching Benefits
Post by: Paul Birkeland on December 02, 2013, 01:36:15 PM

A 22 Ohm resistor at the output would be to shed some VT age and improve the noise floor. This would come at the expense of power and damping.

The Mainline switches the actual transformer impedance, no resistors are used.

Title: Re: Output Impedance Switching Benefits
Post by: Loquah on December 02, 2013, 01:51:29 PM

Great. Thanks for the explanation!  :)