Active Pickups Seem to be Frying Up Some Bacon

SWDPitviper

SWDPitviper

Dec 29, 2018
8
12
4,551
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Montara (San Francisco) California
#1
Hi Folks!

To make rehearsals easier, I provide a fairly nice bass rig in my studio for any bass player that is working with me. It's an SWR 350X Head with a 2 x 10" SWR Working Man's cabinet and a GK 1 x 15" cabinet. The 350X incorporates a tube Pre-amp and a solid-state Amp with separate Active Pickup and Active/Passive Pickup input jacks. It sounds great and has been virtually noiseless (except for normal single-coil hum) for years. In the last few months, however, as soon as my bass player plugs in and turns up, a bacon-frying sound begins whether he's playing or not.

If he turns the guitar's volume controls all the way down, the noise stops. He plays a 5-String Fender Jazz bass (2000's vintage I believe) with Active pickups and a switch to change them to passive (ostensibly). Changing them to passive improves things, but does not eliminate the noise entirely. Something that I believe is common to Fender Jazz basses, a hand on the strings or bridge mutes the 60 cycle hum, but does nothing to change the crackling noise. Plugging into the Active/Passive input (vs. the pure Active" input) improves things slightly but I think that is just because that input is lower gain across the board (the opposite of what I would have expected, actually)

Here's where things get interesting. I tried a few things (lifted the ground via the switch on the back of the amp and by using a ground lift adapter at the AC plug, placing a DI between the bass and the amp input, plugged the amp into a UPS / Filter, etc) but got no change. I finally assumed the amp had an issue and went out and bought a used Hartke Model 5000 that was noiseless in Guitar Center when I tested it (except for a fan that sounds like a Harrier jet taking off) ... I got it home, hooked it up and it had the exact same noise characteristics as the SWR.

That's when I got serious and tried multiple basses ... as it turned out, my Epiphone T-Bird with active pickups caused the exact same noise under all of the same circumstances (with both amps), but my old Aria Pro II ZZ-Bass (with passive Bartolini humbuckers) is quiet as a mouse in either input of either amp.

So I THINK I can safely assume 2 things:

1) It ain't the amp
2) The problem only exists with Active Pickup basses

I'm down to either:

1) Dirty AC power (which I THINK I eliminated by using the UPS because in a UPS, the AC is rectified into DC which charges the battery, and then DC off the battery is re-converted to AC and filtered)

2) Some kind of interference in my studio that only Active Pickups are sensitive enough to pick up.

Any suggestions of next steps (or even pointing out that I skipped a step somewhere) would be welcome. I'm [email protected] if you want to take it offline.
 
#2
Oh and if it helps, I have swapped input and output (speaker) cables, racked up a Furman power conditioner ahead of the amp's AC cord, and plugged a cable into both inputs of the amp without a bass attached which resulted in the hum you would expect but zero crackling even at full amp volume. Just trying to be thorough with everything I've tried.
 
#3
What’s new in the studio? Lighting perhaps? Fluorescent lighting, dimmers, neon lighting, etc. can all cause a bass to pick up noise. Is your studio the only presence in the building, or do you have neighbors who might have installed something new?

I seriously doubt the issue is caused by active pickups. First, what you really mean is “active circuitry”, as the two basses you list as culprits use passive pickups with an active preamp. Second, the Jazz in passive mode still exhibits the symptom. Third, a sample size of two is statistically not sufficient to assign correlation.

I’m betting that something new is present in the building’s electrical environment, and the basses which aren’t shielded well are picking it up. Either do a thorough shielding job on the Jazz, or find the culprit in the building, or put EMGs in everything. :cool:
 
#4
I would agree that everything points to interference and a new RF noise source ... different amps with different cables and different basses displaying the same noise is the logical giveaway ... however, one bass with no active circuitry at all displaying zero noise vs two very different manufacturers basses with active circuitry displaying the same noise feels like a pretty definitive correlation to me. Weird, however, that my Agile Ghost 6-string with Seymour Duncan Blackouts (Active Circuitry) does not display the same problem plugged into a Fender Hot Rod Deluxe (this just occurred to me ;-( )

The EMG option, while intriguing for my own basses, is a non starter for guests bringing their own axes ... and there is a fairly new potential noise source ... my studio is in the bottom floor of my home, and I added 28 solar panels with each panel having a microninverter on it ... the noise did not seem to start then but nearly a year later so maybe an inverter failed and is inducing noise on the ac line

Thanks for the thought provoking response.
 
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#6
Preamp sizzle is pretty common on active basses, especially the more modestly priced ones (that includes many Fenders). A high quality preamp that will fit inside the control cavity of a bass is really a challenge to make, and usually not cheap at all. To keep prices competitive some compromises are made. And noise is most often the compromise that is made - it can be costly to eliminate.
 
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#7
Thank you both for your responses

Diabolusinmusuc; no the sizzling noise does not stop when you touch the strings, bridge, orpickups.

Turnaround; are you suggesting that the noise actually comes from the electronics of the basses? I think I would have noticed that noise when I bought the Thunderbird and my bass player has been using the rig for several years ... I'm reasonably certain the sizzling noise is a recent thing.
 
#8
SWDPitviper said:
Thank you both for your responses

Diabolusinmusuc; no the sizzling noise does not stop when you touch the strings, bridge, orpickups.

Turnaround; are you suggesting that the noise actually comes from the electronics of the basses? I think I would have noticed that noise when I bought the Thunderbird and my bass player has been using the rig for several years ... I'm reasonably certain the sizzling noise is a recent thing.
Click to expand...
I am sure the noise is from the electronics. If it only started recently it's likely that the preamp is malfunctioning or has a weak battery.
 
#9
Stranger things have happened, but two different basses (a Gibson and a Fender) with active pickups display the same behavior in the studio ... a third bass with passive pickups is stone cold silent ... i changed batteries on both active pickup basses with no joy ... I agree that the noise correlates to active pickups but two basses having failing electronics at the same time in the same way just tugs at my brain ... really suspecting that there is a new source of rf in my studio but I have no idea how to verify it or eliminate it ... tinfoil hat maybe ? Lol
 
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#10
If you have a small battery-powered amp (like a Blackstar Fly), you could plug the bass in, make sure it buzzes, and then go turn off one breaker at a time until you find the one that kills the buzz. Then check everything plugged in to that circuit.
 
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