Bottlehead Forum

Bottlehead Kits => Legacy Kit Products => Smash => Topic started by: jimiclow on February 06, 2015, 06:46:50 PM

Title: Hum
Post by: jimiclow on February 06, 2015, 06:46:50 PM

I just finished building my Smash this morning.
I'm hearing a hum with my ear few inches away from the speaker (95db sensitivity).
How much hum (in mvolts) is to be expected in this preamp?
Less microphonics than the Quickie.

Title: Re: Hum
Post by: Paul Birkeland on February 07, 2015, 05:40:50 AM

The missing piece of the equation is how much gain your amplifier has.  With your ear right up near the driver, I wouldn't be surprised to hear a little bit of noise, especially with speakers of your sensitivity, and would be more present with an amp having 20+dB of gain.

Title: Re: Hum
Post by: jimiclow on February 07, 2015, 10:07:49 AM

Thanks Paul!
It's actually the Sex amp. I'm just probably used to the Quickie being DC.
Would the Bee Pre have the same amount of hum as the Smash?

Title: Re: Hum
Post by: Paul Joppa on February 07, 2015, 10:26:52 AM

Turn the SEX amp down, and the Smash up to compensate - that may solve your problem. Or move the speakers so your ears are at least a foot away from them ...  :^)

Otherwise, you can start exploring the possible causes of the hum - power from the same outlets, disconnect all input interconnects, shorting plugs on the Smash input, effect of volume controls (both Smash and SEX) - these are the usual starting points. It can be a long journey.

Title: Re: Hum
Post by: jimiclow on February 07, 2015, 04:11:46 PM

Thank you PJ!
I'm trying to rule out whether the hum is related to the build. I omitted the balance control and use only one input to simplify things. The hum measured only 0.3mv which I think is very low. Power supply capacitors were changed to 330uf. This will be my main preamp for the Stereomour.