Isolation Transformer

[agedhorse]

Most XLR DI out interfaces are electronically balanced driven by a dual opamp. There are coupling capacitors on the hot and cold pins to block DC. Common mode noise could be your issue, to which agedhorse mentioned too.

The pin 1 ground lift switch in an electronically balanced DI won't disconnect from earth, rather "isolate" by connecting through a 10k resistor and 10nF bipolar cap in parallel. This is to bleed off any radio frequencies as the long XLR cable acts like an antenna if not tied to earth.

There are many different ways to achieve a ground lift circuit. Most do not use 10k resistors to earth/ground in the lift position.

 

[DB56]

Well we had the next gig at the same club and I tried the Rolls isolation transformer as well as a different outlet on stage. Can't be sure that the outlet wasn't on the same circuit. Either way, the noise was still there. Not sure what to do other than use my 30 year old Ashdown that made no noise at all.

 

[Jim C]

How about using an outboard DI box with the low impedance side going to the PA and the through jack going to your amp? Pretty sure this would solve your issues while still allowing a DI.
Ever have a soundman not want to use you built in amp DI? This is usually why as typically no good can come from it.

 

[B-string]

Just a thought. Run this by RAG in a private message. He rarely gets to scan though many different threads and you didn't mention your GK in the title. He may take a little time to get to your message (or not). It's worth a try. I'm confident in agedHorse experience with ICE modules and in general designs not to mention live sound quirks. It may be something singular to the DI interface design of your GK he can be of special help with. BTW he tends to be a man of few words, just the way he is.

 

[frankie5string]

Betting some piece of kitchen equipment like a fridge compressor or an electric pilot for the stove is somehow vomiting noise onto the power lines in the club via the lights. Sometimes it's just a really filthy/grimy air passage around the refrigerant compressor that's loading it down or causing it to run hot that puts that whine back onto the power lines. It could even be harmonics coming through from the equipment.
I've been to a few dodgy clubs over the years where that sort of thing seemed common.

Is there an old NOAA/Weatherradio station running nearby?

 

[B-string]

I could even imagine an older mistreated desk with HF noise. If the DI is especially wideband in the GK that noise can find a path to the class D power amp?

 

[DB56]

How about using an outboard DI box with the low impedance side going to the PA and the through jack going to your amp? Pretty sure this would solve your issues while still allowing a DI.
Ever have a soundman not want to use you built in amp DI? This is usually why as typically no good can come from it.

Thanks Jim, that's a really good thought. At this point it's definitely something to try as I kind of feel we've tried everything else. I really appreciate all of the ideas I'm getting here in the forum and hope that it's definitely not my amp. I really like the GK and it doesn't seem to have this problem anywhere else.

 

[DB56]

Just a thought. Run this by RAG in a private message. He rarely gets to scan though many different threads and you didn't mention your GK in the title. He may take a little time to get to your message (or not). It's worth a try. I'm confident in agedHorse experience with ICE modules and in general designs not to mention live sound quirks. It may be something singular to the DI interface design of your GK he can be of special help with. BTW he tends to be a man of few words, just the way he is.

Thanks B, I appreciate your advice. I'm pretty new to this forum so I'm not sure who RAG is or how to private message him. Sounds like he may have some insight into GK amps. I've used Ampeg most of my life and the GK is a new experience. I'll take all the help I can get.

 

[DB56]

Betting some piece of kitchen equipment like a fridge compressor or an electric pilot for the stove is somehow vomiting noise onto the power lines in the club via the lights. Sometimes it's just a really filthy/grimy air passage around the refrigerant compressor that's loading it down or causing it to run hot that puts that whine back onto the power lines. It could even be harmonics coming through from the equipment.
I've been to a few dodgy clubs over the years where that sort of thing seemed common.

Is there an old NOAA/Weatherradio station running nearby?

I know what you're talking about. I've been in HVAC tech almost as long as I've been playing bass. I've heard what those kind of equipment malfunctions can cause. Considering the condition of the club it wouldn't surprise me.

 

[B-string]

Thanks B, I appreciate your advice. I'm pretty new to this forum so I'm not sure who RAG is or how to private message him. Sounds like he may have some insight into GK amps. I've used Ampeg most of my life and the GK is a new experience. I'll take all the help I can get.

RAG is https://www.talkbass.com/members/rag.31102/ The owner, President and founding engineer of GK. I think there should be a hyperlink (it doesn't display for me until posted). Krueger sold off his interest quite a while ago and was the mechanical engineer IIRC.
I stopped collecting amp schematic quite a while ago while dealing not only my own health issues, but long slow losses of my drummer and my lead guitarist. I guess you can say I've been in a corner licking wounds. RAG (rag here) knows your amp well, he designed it.

 

[Kerem Koseoglu]

In a certain club, I had a similar problem. Upon changing the fancy active DI box with a passive Radial JDI, the noise was dramatically reduced. Not sure why, but might inspire you - you can try running from your bass to a good passive DI into the desk and see what happens.

Similarly; my former Fender Ultra Jazz was notoriously noisy in some venues (even in passive mode), while my P and Sadowsky M5 were not.

 

[B-string]

The strangest thing I have come across was when I adopted a pair of the early Peavey IPR class D power amps. Test them both individual and very happy with them. Took the cruse ship anchor Yamaha mains and the monitor amps out of the rack. Mounted the IPRs in the half rack and it "could" be handled by one person now. Awesome! Patched everything in and was ready r to run the Driverack setup again. Powered everything on and set up the reference mic. NO SOUND at all. Signal path checked and all good through up to the output of the Driverack? Powered one IPR, good clear sound, powered up the second, silence. Powered the second only and good clear sound, powered the first and good sound BUT the second fell silent again. Long made a little shorter, if I had the two IPRs on separate circuit breakers they would run, on the same circuit, no go. I think BobbyBld is still around and he help me like an absolute prince. Seems there was a small error found in the power protect IIRC and prepaid labels to send off, back in no time. I am no novice to electronics, but to class D I admit at that time to be clueless. How is that for an off the wall problem. I did do my best to work through the problem and provided clear step by step diagnostic which I bet helped. Never leave out details and don't skip a systematic process. Remember how you spell ass-u-me. Assume helps no one.

 

[anderbass]

Well we had the next gig at the same club and I tried the Rolls isolation transformer as well as a different outlet on stage. Can't be sure that the outlet wasn't on the same circuit. Either way, the noise was still there. Not sure what to do other than use my 30 year old Ashdown that made no noise at all.

I suggested powering your amp with a long extension cord from the exact same outlet as the soundman's mixer, not just a different outlet on stage.