Delano preamp issue?

brstma

brstma

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#1
Please skip to post #5 for updated details

So it seems my amp is making this "whine" noise and somehow only this one bass is amplifying it when in active mode and only when the bass volume is up to 98-100%. I attached a file so you can hear as I turn the bass volume up and down and step on the cable which reduces the level of the noise.

Details:

I just got a bass that has a Delano active/ passive preamp system. When in active mode I hear a high pitched whine only when the bass volume is at 98-100% range. If I back it off a hair it goes away completely, almost like the volume pot switches the noise on and off. In passive mode it doesn't do it, with other basses it doesn't do it.

While experimenting I found that my amp is actually making this noise. With no cable plugged in the noise is only present when I turn the master volume on the amp to 0 or up to 100% range. On 0 it's very faint so I never noticed it. At 100% it's quite loud, and in between 0 - 100% it goes away. I have tried a Hum X and ground lift adapter but it's always the same.

With this bass connected it doesn't matter what the amp volume is, if I turn the bass volume to 98-100% I hear the same noise but much louder than from the amp alone. Below 98% the noise is gone completely; it just cuts off. If I step on the cable while the noise is audible it changes the level (gets quieter), and if I get closer to the amp it gets even quieter. I have tried different cables too. This sound does come through the DI of the amp to the PA only when the bass is connected. With the amp alone or with other basses connected the noise does not come through the DI

I assumed it could be a grounding issue so I checked all the grounds inside the bass and all is well, but there is no shielding of any kind.

When I connect this same bass to 3 other guitar amps I have it doesn't have any issue.

I have another bass with active system and it doesn't do this with the same amp, and my friends play their basses here twice a week and this has never happened. At least 5 different basses get played through this amp each week. ( I play drums too)


I'm wondering if the push pull volume pot could be bad, or the onboard preamp has an issue, except that this bass works fine through 3 other amps I have. I know the source of the noise is the bass amp, but why is it only this bass magnifies the noise greatly and only when the bass volume is all the way up?

What could it be?
 

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#3
Take the bass and amp into another room and plug into a different electrical circuit. Does it still whine?

If so, substitute "another building" for "another room" and repeat.
 
#4
Finally had some time to fool with this. I tested the rig elsewhere and the results are the same. The noise is definitely from the amp but it's weird that only this bass (out of 5 tested) has this happen. It only amplifies the noise when in active mode with bass volume at 98-100%. If I back it off a hair more it goes away so no big deal, and no issues when using it with any other amps or in passive mode. And it's actually a touch louder in passive mode than active mode.

I did find the pickup wire beneath the bridge pickup had a cut in the shielding and bare wire was visible so I taped that up.
I put copper shielding tape in the cavities since there was nothing at all but no change.
 
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#5
So I was playing through another amp with headphones on and I do hear a noticeable noise increase on this amp too when the bass volume hits the 98-100% range. On this amp it's more like a standard hiss noise you'd hear from a noisy preamp. But below 98% it goes away completely, almost as if the volume pot is an on / off switch for the noise, while the bass volume doesn't change much at all.

it's a Delano sonar 3 preamp and volume is push pull for active / passive, and in passive mode there's no noise, in active mode it's only present when at the 98-100% range

So now I am back to thinking it could be the volume pot or the preamp on the bass.

Is there a way to check either without replacing parts?
 
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#6
You could, if you're handy with a soldering iron, temporarily bypass the pot and run the pickup through the preamp straight to the jack. If the noise is gone, then suspect the pot. If the noise persists, run the pickup through the pot to the jack, bypassing the preamp. For completeness' sake, you could also bypass them both, and wire the pickup straight to the jack.
 
#8
Well, I'm pretty sure it's the preamp now.

First I bypassed the volume pot and connected the preamp out direct to the jack: the noise was present full volume 100% of the time.

Then I bypassed the preamp by routing the blend knob out (both pickups connect direct to it) direct to the jack: noise is gone
 
#10
Yes, but only the one amp has the funky high pitched whine noise. This noise is present in the amp with no bass connected, but it's very, very low in volume. I only hear it if my head is right next to the cab in a dead quiet room. When I noticed the noise a few years ago it was suggested by several TB'ers that it is probably digital components in the amp starting to fail. This noise comes through the speakers, but not through the DI in either pre or post EQ mode.

When I plug this bass into the amp (and only this bass does this, and only in active mode) the high pitched whine noise seems to somehow feedback through the bass and amplify in volume but only when the bass volume is at 98-100% - and the noise is then present through the DI. Once the bass volume knob hits 97% or lower the noise "switches "off and the sound is clean. In passive mode all is clear through the full range of the volume sweep.

Through other amps it's just a typical hum/ hiss noise that is only present when the bass volume hit's the 98-100% range. It just sounds like a typical noisy preamp, but I've read that this pre is super clean and clear.

I have 5 other basses to test with, and have had 6 others in the past since I first noticed the noise in the amp, and none have this happen. So there is definitely something going on with just this one bass
 
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#11
and I have checked all the slodering and wiring using the Delano wiring diagram. I re-soldered a loose ground wire and added copper shielding - and upgraded the active treble pot to a Delano active / passive combo treble / tone control. But no change in the noise situation
 
#12
So it's something having to do with the power section of that amp (since it doesn't come through the DI) and how it interacts with the Delano preamp. If the problem were solely in the Delano pre, I would expect it to manifest with any of your amps. Hmmm...
 
#13
Yes, it is a strange issue. I definitely hear an increase in noise through other amps when the bass volume hits 98-100% in active mode, but it's what I would usually consider acceptable preamp noise.

And when I have the bass volume up so the whine noise can be heard (through this amp) the noise gets quieter when I move closer to the amp, or if I coil the cable up on the floor and step on it. It's similar to a ground issue but opposite of anything I've experienced before. But backing the volume off a hair or putting it in passive mode at any volume makes the noise go away
 
#15
Well, you certainly could swap out the preamp for another and see if the problem disappears. Expensive perhaps, but sometimes parts substitution is an effective approach.
 
#18
I got the new preamp system and swapped them out and there's no change. So the preamp did not have a problem.

But it is very strange that this preamp system is the only one that has this effect with the noise originating from the amp.
 
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