Need help identifying strange sound

All,

I need your help in identifying a sound - the file is here:

http://twin-x.com/groupdiy/displayimage.php?pos=-1853

I've heard it from a few different sources, the one in the file is from an Electrodyne 1604 with all of the channels bussed (max gain at the summing amps).

I've also heard it on the output of a transformer coupled mic preamp, but only when it was powered off. It did not change what I was hearing if the power mains were plugged in or not. (secondary acting as a pickup coil?)

The problem seems to reside at the location, that is when I bring offending pieces of gear to my shop they no longer pick up this sound, powered up or not. It has varied slightly with time of day, but not to the degree of ever disappearing completely.

I really hope someone here has heard this sound before and can point me in the right direction - I have my suspicions about the source (pole pig perhaps?) but without knowing exactly what I'm up against it's difficult to have a plan of attack.

Thanks in advance.

Frank

Sounds digital to me. There is residual hum way down too. Check for ground loops maybe? Also it may be coming in on the AC source. You might try a line conditioner. Wireless network harmonics? Goodness, I hope you can find it. Just to be safe however, I'd make myself an aluminum foil helmet, cause they could be nearby and might be trying to read your thoughts! :twisted:

Sounds like some motor related noises I've heard. Very large current draw motors in adjacent buildings.

sounds like a combo of noises both which seem to have a pulsating to it. Motors come to mind But what throws me is the ground hum which is also pulsating with the cricket like sounds. My question would be to describe in as much detail as possible the location, time of day every detail you can think of. It's possible your picking up interference from another electrical source be it a motor, a generator, who knows

:?

Interesting, I hadn't heard the ground noise pulsating with the chirpy noise.

The sound of interest here is the chirpy bit - the Electrodyne desk has its own issues with noise and such, the hum seems to be related to lack of termination of unused inputs at the combining networks, but it seems especially adept at picking up that cricket-like sound. While we are looking pretty far down on the signal to noise here, it's at the sort of level that would go mostly unnoticed for rock but spoil folk. This desk and other pieces that pick it up don't do this at my shop.

Sounds digital to me

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I've had one person remark that the chirpy bit sounded like an RS232 port looking for a handshake.... hmm.

Sounds like some motor related noises I've heard. Very large current draw motors in adjacent buildings.

Click to expand...

Also interesting - I have a plan (see end of post)

On to the specifics:
There is a pole pig about 50' from where the gear in question picks this up, there is also a house on the same pole pig as this studio (the engineer's home). The house is paralleled off the pole pig via a master breaker which resides in the service panel in the studio.

So it goes like:

Pole pig->
studio service panel -> master breaker -> house panel ->house
studio service panel-> master breaker -> studio panel ->studio

This is a mastering studio, and this noise has never presented a problem to his mastering gear.

The Electrodyne desk was a restoration job done by yours truly. Most of a working (wood!) frame, except the bastards cut out the edge connectors to sell with the parts. My work was refitting the board with the proper edge connectors, and other odds and ends to get her passing signal again. Once complete it did not exhibit this behavior in my shop. The owner has spent a bit of money both fixing and outfitting this relic, only to have it be unusable in his studio. All audio and chassis grounds follow a star-style arrangement, and I have followed convention with what remained wired in the board as far as grounding and floating shields. Every module has a grounded external chassis.

So far we've unsuccessfully tried:

running it from a charged but unplugged UPS
shutting off the rest of the studio (not at the breaker panel though)
toying with floated shields
all manner of grounding / ungrounding

It should be noted that this desk is not the only piece of gear that is picking this up - and I say "picking up" because of the behavior exhibited by the LA-602b amplifiers, both in the console and in a "lunchbox" as mic preamps. These things run at 40-45db of gain all the time. When ON they are CLEAN. They pick up the "cricket like" noise, but only when powered OFF. They do this regardless of any connection to ground, to AC mains, whatever. When the electrodyne desk or lunchbox is ON, they do not output this sound. They aren't any sort of virtual ground amp.

Within the desk I have isolated the main cause of pickup to be the combining networks by jumpering them out. In situ the more channels you assign, the louder the "crickets" get. These networks are a very early virtual ground summing design. They do have shields over them that are grounded - but here's something else: Two of them I unpotted and updated - without their shields they exhibit the same amount of pickup as the shielded ones. At the time I did that my own DIY summing mixer was using identical networks - I even tested them out for a few days - no "crickets" ever.

I feel like the problem is in "the air" - but if so exactly what is putting it there ? Motors? How would I go about assessing the quality of the grounding in the structure?

My current plan of attack is to basically shut the whole place down save 1 outlet, and if the "crickets" go away start building breaker by breaker until they come back. Of course I'll try a few other outlets if they don't go away.

Thanks to everyone for their input!

Frank

Sounds like maybe demodulated RF, based on the non-effect of the UPS source and the OFF vs ON behavior (biased junctions being less likely to detect than unbiased).

How susceptible is the setup to other radiating sources, like cellphones, carbon-brush universal motor appliances like heatguns, hairdryers?

How susceptible is the setup to other radiating sources, like cellphones, carbon-brush universal motor appliances like heatguns, hairdryers?

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I haven't yet given it the cell phone test, although my phone seems to be less likely to couple into things like guitar amps, etc. than others.

On next visit (Sunday or Monday) I will experiment with a heat gun and a cell phone.

Sounds like maybe demodulated RF

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Location wise the building is close to the top of a hill - maybe this means it's getting hit by more spurious signals in general?

Perhaps this is too broad a question, but can you give me some more examples of where demodulated RF might come from?

Frank

It sounds like some artifact of a signaling system, with airborne RF being demodulated ("detected") by some nonlinear junction in your electronics.

If it were AM radio for example, you could actually hear the audio (and figure out what station it was eventually). Perhaps someone in here that works with transmitters for various purposes will recognize the distinctive signature from your audio clip.

This mystery has just been solved. An electronic dog fence was the culprit. Many many thanks to everyone who contributed their thoughts.

I will look into posting a schematic for the dog fence! :grin:

Actually, if at all possible I will draw and post a schematic since examination of the dog fence electronics might compare well with some of the theories presented in this thread.

Thanks again all!


Frank

:guinness:

Dog-Gone-It!

:grin:

Keep the dogs in the studio, no noices like that! ;-)

Matti