1. callum
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  3. Sunday, 27 December 2009
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I experienced a weird high frequency oscillation at church this morning (sounded like very high feedback). It occurred when I switched the BluEQube on. The level in the FoH was way too low for it to be regular feedback and it was clearly related to the treble in the patch I was using since I could reduce it by cutting the treble off. I could have my main rig turned off and it still happened so I am left pondering what it was.

I realise this will have something to do with my rig (Behringer Bass V-amp pro), the PA system, not just the Dingwall, but I wondered if anyone else had come across this? Is there something peculiar to that circuit that could cause that?

Callum
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dfries Accepted Answer Pending Moderation
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Assuming that your bass feed to FOH is thru a direct box, did you try the ground lift on the DI?
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[quote="dfries":2lupcb5x]Assuming that your bass feed to FOH is thru a direct box, did you try the ground lift on the DI?[/quote:2lupcb5x]

I didn't as I normally associate earth problems with hum, but I'll check it out. The v-amp has has direct balanced out, but there might be a ground lift switch on the back somewhere which I bumped when fiddling in the rack.
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Hi Callum, the Behringer Bass V-amp pro is full of digital processing, and that may also be creating that sound and leaking it in. I had a behringer rack gtr tuner that I had to punt as it was introducing hi frequency artifacts similar to what you mentioned. And my iPhone intermittently makes a heck of a noise thru every piece of gear I have if I don't turn it off, if that helps! Good Luck!
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Ah - just checked down the bowels of the rack and there was a ground lift switch on the back of the v-amp which was "lifted". It could quite easily have been bumped by the powerboard I have in the back of the rack so I'll report back on what happens next week.
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Nope, still there regardless of the setting of the ground lift. When I have more time I'll try swapping mixer inputs and leads to eliminate any dodginess there.
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Hampton Accepted Answer Pending Moderation
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I have an ABII which has HF oscillation when the BluEQube is on. Sheldon suggested I alter the wiring layout in the area behind the controls. Unfortunately it didn't help. I've given up on it because I haven't found a use for the BluEQube, but I'd be interested to hear if you can nail it down.
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Sheldon Dingwall Accepted Answer Pending Moderation
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We haven't experienced the noise issues you're describing. However the bluEQube coil will pickup some EMI due to it having a small coil. So a little hum is normal.

The electrostatic noise (the high frequency stuff) should be filtered out by the shielding.
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[quote="Hampton":3trsutxh]I have an ABII which has HF oscillation when the BluEQube is on. Sheldon suggested I alter the wiring layout in the area behind the controls. Unfortunately it didn't help. I've given up on it because I haven't found a use for the BluEQube, but I'd be interested to hear if you can nail it down.[/quote:3trsutxh]

What amp output were you using at the time? Mine only occurs when the FoH is plugged in (one of the balanced outs), but even at an extremely low volume (way below what you would consider normal feedback would occur). It doesn't happen through my main rig even at high volumes, although once the FoH starts the oscillation, the main rig amplifies it too.

Anyway, I'm confident it's not a fault with the BluEQube, but it's obviously something about the design of that circuit interacting with high-pass patches, probably digital effects, and maybe balanced outputs. Lots more experimenting to do (when there aren't too many people around to annoy/deafen).
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Hampton Accepted Answer Pending Moderation
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I'm aware of it (as aliased noise) through an older Eden combo amp, current EA gear, and it's plain to see on an oscilloscope straight from the output jack on the bass - a 600mV peak to peak oscillation around 25kHz. It's most noticeable with the volume around 3/4 and some active treble boost.

Again, since I don't use the BluEQube and cut treble more often than boosting, it's not much of an issue for me.

It's also quite possible you and I are seeing different phenomena. Mine is clearly within the bass' active circuitry whereas yours may result from downstream amplification ground or loop concerns. If you have a friend with a scope you could easily determine whether or not your bass is the source of oscillation.
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Sheldon Dingwall Accepted Answer Pending Moderation
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Aguilar's can have some high frequency oscillation issues. We had one that was causing trouble at 100kHz.

Does it do this in passive?
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No - it's quiet in passive mode.
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callum Accepted Answer Pending Moderation
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An update on this - I changed the balanced output for FoH on the V-AMP to the other channel and no noise with BluEQube. I wonder if there is some L+R/L-R effect happening here (although it wasn't on a stereo effect preset). I'll need to verify my findings next week when I have more time - could be someone just turned down the FoH on me...
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It's a bit odd to resurrect this thread after so long, but I noticed I never reported what the cause was. It turned out it is the hearing aid loop in the church. If this is disabled the BluEQube doesn't squeal. This might help someone track down the same issue.
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Thanks for reporting the answer. That is a crazy combination I wouldn't have expected.
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