SEX 4 Noise Floor

[ScottAstroNut]

I have a question regarding the noise floor of the new SEX 4.

I have been running the SEX 3 as a headphone amp for quite a few years, and really love that amp. When listening to high impedance headphones, such as my 300 ohm Sennheiser HD 650's, the SEX 3 is dead quiet. However, when I switch to low impedance headphones, such as my 38 ohm Grado 325x's, I can easily hear noise even at lower volume settings. It's not such a problem when actually playing music, but it is something I become aware of in between tracks with the Grado cans.

Is the noise floor of the SEX 4 much lower than that of the SEX 3? Would it be worth upgrading to the SEX 4?

Thank you!

 

[Paul Birkeland]

Hello Scott,

For either amp, I would generally suggest wiring the output transformers for 4 ohm output if you want to use Grado headphones.

-PB

 

[ScottAstroNut]

Hi Paul,

Thanks for the quick reply and for the recommendation.

I'm pretty sure that my SEX 3 is currently configured for 8 ohms, as I have also been using 8 ohm speakers. I'll have to check. What effect would I see when using 8 ohm speakers with the SEX 3 configured for 4 ohms?

Thanks again!

 

[Paul Birkeland]

You'll deliver a little less power to the speakers, distortion will go down, and damping (bass control) will increase.

 

[ScottAstroNut]

All in all, it sounds like switching the SEX 3 to 4 ohms is a no-brainer.

Just out of curiosity, though, how does the noise floor of the SEX 4 compare to that of the SEX 3?

Thanks!

 

[Paul Joppa]

In a severe case, you can try an attenuator between the amp and headphones, at the price of losing the same amount of gain and power. For example, a 6dB attenuator will reduce the noise floor by 6dB, you'd need to turn the volume knob up, and a 2-watt amp becomes a half-watt amp.

The original [stereo] SEX amp had an attenuator of sorts in the form of a 120-ohm resistor in series with the output; which attenuates low-impedance phones more than high impedance ones. Unfortunately, the special headphone jack needed to switch those resistors out when using speakers became unavailable and no replacement could be found. Since the series resistor had other problems with phones like the Grados, we elected to just remove the resistor.