It is said that all guitar amps hum. Yesterday, in the living room and also at the retirement home gig the amp did not hum. This was the first time I tried the California Blonde amp by SWR. Today at home in the office the amp hummed, and the hum was proportional to the gain. Two guitar cords we're tried with same result. With the Washburn acoustic guitar plugged in, with its piezoelectric bridge pickup without any inherent gain, I tried powering the amp from all outlets in the same room. Still hum. I unplugged a nearby desktop fluorescent lamp. Still hum. I turned off the computer and monitor. Still hum. I pulled out a Garmin watch power supply from the outlet and the amp made a single pop like you get when you pull the instrument cord out. What? How can pulling a power transformer from an outlet make an amp pop? And, if I don't have the instrument cord in the jack, the amp makes no hum regardless of gain. I checked all outlets in the man cave and they all show good neutral and ground.

I then tried an amplified acoustic-electric Ovation mandolin. It has a 9 vDC battery and a small preamp onboard. Very little hum.

I then tried an amplified acoustic-electric Epoque violin. It has a 9 vDC battery and a small preamp onboard. Very little hum.

I then tried a simple piezoelectric pickup that can be inserted into a violin bridge. Lots of hum.

So, it seems that piezoelectric pickups are hummers, and amplified pickups are much less so.


School me, please.

This message has been edited. Last edited by: 4MUL8R,

Sounds to me you lost the chassis ground somehow, interally.

I understand the words of your diagnosis, but don't understand how the hum goes away without an instrument cord plugged in if the chassis ground is not there. Could you please clarify?

I'm sorry. I skimmed your post too fast and made a hurried reply.

After reading your post in full, your guitar pickups are picking up interference in the air. Did you try your guitars after you unplugged the Garmin? You were on the right path by unplugging everything, espescially the fluorescent light.

Also, are your jacks clean and the wires still soldered?

Monster brand instrument cables. A few months old. Rarely used. Coiled carefully and stored in a box. Haven't checked those connections, though.

One little trick I've used on my bass guitar jacks is to use a .25 caliber bronze brush to clean the contact surfaces. Also works well for 1/4 inch headphone jacks. Make sure your amp is turned off if you plan to use that brush to clean the instrument input jacks on the amplifier.

Great idea! I think I'll replace the 9 v DC batteries in the instruments that have them as well.

Just curious...what color was the outlet you plugged into at the nursing home?

Beige. 110 v and through a Belkin surge box.

quote:

Originally posted by 4MUL8R:
Beige. 110 v and through a Belkin surge box.

Oh. Darn. Thanks.