Oboe Pro Hum

suspect · « **on:** 31 Dec 2005, 03:37 am »

Hi,

I recently built an Oboe Pro, and I'm noticing hum on the phono channel (no inputs or cables connected).

The CD and AUX channels are super quiet all the way up to full volume, but the phono channel has what seems like a 60Hz hum, barely noticeable at half volume, but quite glaring at full vol.

I've checked and re-checked the board, and can't think of any reason
why only the phono channel would be picking up hum. I'm auditioning the system through the headphone out.

Any experiences from others who have built the Oboe Pro ?

Thanks.

hagtech · « **Reply #1 on:** 31 Dec 2005, 06:51 pm »

Let me get back to you on this one...

jh

hagtech · « **Reply #2 on:** 2 Jan 2006, 09:33 pm »

Hummm. Ok, I had to fire up one to see what was up. I think the problem is external magnetic fields. My OBOE is pretty quiet, but not when I place it next to a power amplifier or soldering iron.

Can you try pickup up the OBOE while listening and turning it / moving it around? See if the hum comes and goes. That would indicate interference from an external field. Phono circuits are always susceptible to both electric and magnetic field induction, gain at low frequencies is really high.

jh

suspect · « **Reply #3 on:** 11 Jan 2006, 04:59 pm »

Hi,

I tried one thing: I got a shielded power cable (I had skimped
on buying the recommended shielded cable from digikey and had
used an old power cord). That seemed to help a bit.

I think shielding will help further. I'll wrtite back when I've put
the pre in a nice shielded chassis.

After having used the system for a bit, I'm quite happy with it.