Solution for L2500 Preamp Hum

kirkm24 · #1 02-01-2008, 06:35 PM

I've read a ton of threads on here about the infamous hum of the L2K series basses. My USA L2500 had this problem and it was suggested that I shield it. I did that plugged it in.. buzzzzz. Tried plugging my amp into another wall outlet, buzzzzzz. Anyway, I decided to try a different IEC power cord for my amplifier head (Markbass LMII) as the hum was non-existent on another bass amp. With a different IEC power cord, the hum went away completely!

I hadn't seen this come across as a potential solution so I thought I would share the joy. I'm not sure if it is worth it or not but Monster has power cables that are heavily shielded and are supposed to cancel out electrical noise. For $49.99, I'm not sure if it is worth it. If you're still having hum problems try a new power cord on your amp!

sunbeast · #2 02-03-2008, 09:40 AM

Yeah- what alot of people don't realize is that no matter how much you ground and shield a bass, the grounding eventually terminates through the cable, through the amplifier, through the power cord, and ultimately at the electrical wall socket. If there is any sort of weak ground in that whole path, then all the shielding and "star-grounding" in the world won't help anything.

Karl

DavePlaysBass · #3 02-03-2008, 11:30 AM

What are the details on the IEC power cord. Is it a true 360 degree shield on the power lines that gets terminated on the green wire?

Another thing that would be interesting to test if the the power cord that had the problems is wired correctly. Are hot and neutral swapped? Is the safety ground connected? I ran across a power strip a while back that was backwards. And I have found a number of outlets that are wired backwards per one of those outlet testers. I have experienced hum when playing an outlet that I later found out had no ground and was reverse wired (talk about a recipe for disaster). In the process I burned up a ground connection in my amp. Since I have fixed the amp and only play in properly wired outlets, I have had fewer issues.

Dave

kirkm24 · #4 02-11-2008, 05:51 PM

Quote:

Originally Posted by sunbeast

Yeah- what alot of people don't realize is that no matter how much you ground and shield a bass, the grounding eventually terminates through the cable, through the amplifier, through the power cord, and ultimately at the electrical wall socket. If there is any sort of weak ground in that whole path, then all the shielding and "star-grounding" in the world won't help anything.

Karl

I guess my only dilemma is that with the same amp using the old power cord, my MusicMan basses didn't produce the noise. The G&L in every other situation I have used it has performed flawlessly.

sunbeast · #5 02-11-2008, 10:55 PM

Thats the beauty of well designed active electronics (ie- the MusicMan preamp)- low noise and low impedance. EMGs are the same way- pretty much silent through any sort of screwy amp setup. I think it is the pairing of very high impedance/ low output pickups with preamps (preamps in EMGs are actually built into the pickup) that makes both of these setups so quiet. The downside of course is that neither a MusicMan or any active-EMG equipped bass can be played passive.
The G&L preamp, on the other hand, is more like a line-level booster than a typical bass preamp- so it amplifies everything (including noise). High output pickups like MFDs are going to pickup more noise than extremely low output pickups like those in a MusicMan (the output of a MusicMan is dependant on the active preamp- a MusicMan humbucker without a preamp will sound extremely weak next to an MFD), and a badly grounded amplifier will let you hear all of it!

Karl

DavePlaysBass · #6 02-12-2008, 04:43 PM

After looking around some, the IEC chord for 120VAC power is not shielded. Just the standard three wire connection with appropriate wire gauge, insulation, and clearances. The point being, if one power chord worked better than another, I would say the bad chord probably has something like reversed wiring (hot and neutral) or a compromised connection on the ground wire.

DavePlaysBass · #7 02-12-2008, 04:49 PM

The G&L preamp was designed by someone attempting to get their Boyscout Badge in electronics. It would not pass for consumer grade electronics. It does not employ many basic techniques that real world circuit designers have used for the last 20 or more years. You hear about buzzing G&L preamps all the time. But I seldom hear about a buzzing Bart, Aguilar, East, EMG, or Audre preamp.

Having dogged the G&L preamp, I do like how it sounds with G&L pickups. But it could stand a robustness make over that would start with the PCB layout and shielding of the bass.

Dave