Is there a normal hum?

[Jeff Leites]

Short version - I built a Fender type stand alone reverb. It had some hum. I fixed it by removing some ground loops, and a bad ground connection. It then sounded real quiet... through the modest amp that I had. I joined a surf band, and needed a higher power amp fast (vs. my orginal plan to build a higher power tube amp). I bought a Crate Powerblock, which together with my reverb sounds nice and "surfy" to me... and very loud. Well, now at the higher volume, I hear some hum again when I mix in the reverb. There is no hum when the mix is in the dry position. It's not so loud that you would hear it when playing. I measured it with my sound pressure meter. At 6 inches, wth the amp set to produce 115 db or more when I play, there is 51 db of hum with the mix at 5, and 54 db of hum with the mix fully wet when not playing. Is this a normal hum?

 

Also, I now hear these really low level reverbed snaps, 1 or 2 a second, but erratic. It will stop if I play, plug, or unplug something it the reverb, or do anything to make it "pop", but it will eventually return.

[where02190]

 

At 6 inches, wth the amp set to produce 115 db or more when I play, there is 51 db of hum with the mix at 5, and 54 db of hum with the mix fully wet when not playing. Is this a normal hum?

 

 

Depends on the environment. Your average bar is way louder than 54db at 6 inches.

[philbo]

It could be coming from a number of places...

 

But one thing you could try (while the reverb is amped up and you hear the hum) is to wrap the pickup end of the reverb in aluminum foil, and touch the foil to ground (like, maybe the 'ring' on your guitar cord while it's plugged into the amp). My thinking is that it's possible the reverb pickup coil is unshielded.

 

To tell which end is the pickup end, unhook one end of the reverb & shake it (gently!). If it makes 'thunder' in the speaker, the end still plugged in is the pickup. If not, the unplugged end is the pickup.

 

If that helps, go find some conductive copper tape to wrap that end of the reverb tank. (One easy way is to Google for Strat shielding kits.) Be careful with the tape; if you think a paper cut is bad, wait till you get sliced by paper-thin copper! It really frickin hurts!

[Gus Lozada]

hummm.... no

 

 

[Jeff Leites]

Originally posted by philbo But one thing you could try (while the reverb is amped up and you hear the hum) is to wrap the pickup end of the reverb in aluminum foil, and touch the foil to ground (like, maybe the 'ring' on your guitar cord while it's plugged into the amp). My thinking is that it's possible the reverb pickup coil is unshielded.

 

Actually, when I was fixing the original "post build" hum, I found I had to isolate the reverb pan from ground (I had to prevent the pan from touching the chassis). If the pan came in contract with the chassis, it added hum that could be heard when the amp was at low volume. The input/output jacks on the pan must be isolated from ground the way they (Accutronics) build it, or the pan would be grounded by the connecting cables. One thing I added was a piece of sheet metal to cover the open side of the pan.

 

This is definitely not a hum that would be heard in a more active environment, it just bugs me that it is there at all.