Popping at turn-off

[dgallagher52]

Just finished my SEX amp and it sounds fantastic! I noticed that when I turn-off the amp, a hear a popping sound in my headphones. I turned off the source (Ipod) and turned the volume all the way down before powering off. Is this normal? Is there a way to get rid of the popping. BTW, I wired the amp only for headphones and omitted the speaker wiring and binding posts. I also omitted the 120 ohm resistors on the output ( I am running 32 ohm Grado headphones). I was thinking I could install some high value resistor from each channel on the output to ground, say 22K ohm? Any advice would be appreciated. Thanks.
-D

 

[Paul Joppa]

The 10 ohm speaker terminal lad resistor was dropped some years ago, as it was unnecessary. The 120 ohm resistor remains standard because it's the old IHF (now IEC) standard for headphone circuits. The reason it's standard is that it roughly equalizes the output from a wide variety of headphone impedances from 24 ohms to 600 ohms. Without it, some low impedance 'phones sound better due to better damping of the LF resonance, but they can be very loud. That of course makes the turn-off transient louder as well.

I imagine that a search of the forum would turn up several discussions, since this comes up fairly often. I have proposed an L-pad (fixed or variable) at the output as a suitable way to reduce the sensitivity of low-impedance phones without raising their source impedance.

 

[JC]

Along that line, I was wondering if putting that 10 Ohm load on the speaker terminals might just have a beneficial effect in reducing the turn-off transient for phones of any impedance?  It seems like a cheap experiment, anyway.