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'biiiiiiiiiiiiiiiip' interference noise coming from AC splitter unit

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'biiiiiiiiiiiiiiiip' interference noise coming from AC splitter unit

Postby ore_terra » Wed Oct 07, 2020 10:47 am

hi all

we had a brand new AC machine installed in the studio and it generated an audible and annoying 'biiiiiiiiiiiiiiip' in tube amplifiers. it's insignificant in solid state amps, and you dont hear it in headphones, monitors, etc.

I'll list the - unsuccessful - actions we've taken so far to tame it:

1. Earthing (despite that's not a "classical" earth noise): 1st thing we did when we moved in was to hammer a 2m copper rod into the ground. all ground noises disappeared.

2. double check the connections of the AC machine and electrical board by a skilled guy. OK.

3. we took a different phase from the main board (out of the studio) and fed AC splitter from it. however it's still sharing the neutral with the rest of the installation, what I guess is why this was also unsuccessful.

4. I wanted to cry and started googling like crazy... I bought one of these furman "power conditioners". plugged a '76 deluxe reverb to it and the biiiiiiiiiip was still there. And accordingly I returned the Furman to Mr. Thomann :)

we have another AC machine in the small room connected to the same electrical board, that doesn't generate any noise. but we cannot just record with the door between rooms open as that's the room we use to crank amps.

next steps?

- I know 1st thing you guys will tell me that if it's a faulty unit I should complain and get it replaced, but relationship with the landlord is not easy and I'd rather not get to that point. It was really a pain in the ass to get the AC installed and we're the only users in the complex with these "special needs" when it comes to electrical noises.

- what about EMI/RFI filters? would these be useful with the 'biiiiiiiiiiiip'? are they to be installed in the AC mains or in any other device mains?

- someone suggested to connect A/C neutral to our ground rod... is this likely to do more good than harm?

well... I just remembered we havent checked the compressor (outdoor) unit connections :lol: :lol: I'll get it done and report back.
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Re: 'biiiiiiiiiiiiiiiip' interference noise coming from AC splitter unit

Postby ef37a » Wed Oct 07, 2020 10:54 am

Um? Am I being thick or just old and confused? "AC Machine"?

And you should not have two phases in the same room. The chances of a problem are very low but it is said not to be good practice.

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Re: 'biiiiiiiiiiiiiiiip' interference noise coming from AC splitter unit

Postby Hugh Robjohns » Wed Oct 07, 2020 11:04 am

I'm presuming AC is referring to air conditioning units -- the OP is in Spain.

And it's not unusual to run AC on a different phase of the supply.

But I'd be surprised if the mains supply is the problem here. It sounds more like a radiated noise problem to me.
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Re: 'biiiiiiiiiiiiiiiip' interference noise coming from AC splitter unit

Postby ore_terra » Wed Oct 07, 2020 11:05 am

yep.

Air Conditioned. only remembered to add the slash "A/C" at the end of the post. sorry.
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Re: 'biiiiiiiiiiiiiiiip' interference noise coming from AC splitter unit

Postby ore_terra » Wed Oct 07, 2020 11:10 am

Hugh Robjohns wrote:But I'd be surprised if the mains supply is the problem here. It sounds more like a radiated noise problem to me.

so do you think the filters wont do anything?
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Re: 'biiiiiiiiiiiiiiiip' interference noise coming from AC splitter unit

Postby Hugh Robjohns » Wed Oct 07, 2020 11:44 am

ore_terra wrote:so do you think the filters wont do anything?

I'd be surprised. Everything is connected to the mains supply, but you only have "an audible and annoying 'biiiiiiiiiiiiiiip' in tube amplifiers. it's insignificant in solid state amps, and you dont hear it in headphones, monitors, etc."

Tube amplifiers are often particularly prone to picking up radiated interference because of the high-impedance nature of the circuitry.

And if you're talking about guitar amps, then it's also quite likely that it's the guitars picking up radiated interference, and the tube amps are allowing that interference to be demodulated more easily than the solid state amps.

So some experiments moving the amps /guitars around will probably help to identify whether this really is a radiated interference problem.

How do the two units in the A/C system communicate? Is there an RF link of some kind between them? Or perhaps there's some sensing circuitry in the studio unit that's causing a problem...
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Re: 'biiiiiiiiiiiiiiiip' interference noise coming from AC splitter unit

Postby ef37a » Wed Oct 07, 2020 1:25 pm

Air CON! DOH!

Valve amps are usually better than solid state for RFI but yes, if you have a badly screened input that will cause trouble.

If the valve gear is some high faluting "tweaky" kit then they may not have fitted the customary input grid stopper resistor in the mistaken belief that it reduces the treble response of the unit. They also may want to advertise an "extended HF response for superb transient response". All a sausage beginning with B.

Re phase. Yes if the A/C unit is hard wired, probably in armour, it can be on another phase but should not be if a free standing plug in jobby.

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Re: 'biiiiiiiiiiiiiiiip' interference noise coming from AC splitter unit

Postby ef37a » Wed Oct 07, 2020 3:54 pm

I should also say, not ALL tooob amplifiers just have toobs in their signal path!

No by a very long way and that includes some very 'classic' guitar amplifiers from way back.

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