Help! Haunted new limiter spookily sings the program material sans speaker

[poppaflavor]

A brand new limiter I just received is reproducing the audio of the program material it is processing. Like audibly reproducing the program material even with no speaker in the signal path. And, like, freaking VERY audibly loud. It's quite disturbing. My brand new comp seems haunted :-/

Two questions-

1) What might be causing this?

2) A device voicing program material so loudly with no speaker can't possibly be acceptable industry standard can it?

I recall seeing a thread here on GDIY before about this type of issue, but have been searching for a couple days and just can't find it. I have found threads out in the wild interwebs that may describe similar hauntings but don't seem to match these symptoms.

I have seen some descriptions of microphonic tubes "singing" (this is not that from what I can tell, this is wide frequency program material reproduction at audible levels). I have seen descriptions of output transfos "singing" but these seem to be on power amps for guitars/bass, and do not apply to a simple limiting amp clone.

To be frank, I'd actually have rather encountered magic smoke coming from this band new comp, and shipped it back unheard, than to have the device hauntingly sing back the program material with no speaker in the signal chain.

Here is a shared google drive link to a couple of impromptu vids. They should be shared and accessible. You can hear the program material volume increase as I dip the phone which is recording the video/audio into the chassis near the device components.

 

[scott2000]

maybe a little wipe down with some holy water....

weird...

 

[thomasdf]

That an Audioscape unit, by the looks of it ? What do they have to say about this ?
One of my 1176's output transformer sings songs, too, from time to time when driven very hard.

 

[RuudNL]

I once had a transistor amplifier that produced sound!
It seemed that the power transistors actually produced the sound.
Not very loud, but audible...

 

[poppaflavor]

That an Audioscape unit, by the looks of it ? What do they have to say about this ?
One of my 1176's output transformer sings songs, too, from time to time when driven very hard.

You are correct, but through the videos I didn't mean to expose the device manufacturer. I was seeking context here before reaching out to the manufacturer. I was really hoping to get insight such as you've provided here. Thanks very much for describing the 1176 output transfo experience. That helps

I once had a transistor amplifier that produced sound!
It seemed that the power transistors actually produced the sound.
Not very loud, but audible...

Fascinating! I need to dive in more closely and put a tightly directional mic against the individual components inside this device. Now you mention it, I'm not sure where the heck this sound is coming from. Much of the device components are under the apron so not sure where the audio is coming from.

 

[Evertide]

Transformers with just air around the winding will do this...

 

[poppaflavor]

Transformers with just air around the winding will do this...

Could you please clarify? By 'air' do you mean the individual wires of the winding are not resin/epoxy coated or that there was not a dipping stage where the wound transfo was dipped in resin? Perhaps both?

 

[Evertide]

Not dipped to prevent singing...

 

[scott2000]

AudioEscape

 

[thomasdf]

Haha ! My thought ...

 

[poppaflavor]

Not dipped to prevent singing...

Thank you. Since the transfos are outside the case I'll try to peek at them and reply here as to whether they are dipped.

However, there are several transfos in the device and some are canned. Would you possibly be able to direct me to which type of transfo might be the crooning culprit? There seem to be input, interstage and output (along with power) transfos onboard.

 

[pucho812]

As it’s a unit in current production by a manufacture, talk to their tech support. Ideally they should support your product.

 

[Harvey Birdman]

I think I'd drive the unit with pink noise then get in there with hypercardioid mic, something like a Sennheiser e-608 or AKG C516, and locate which component the sound is emanating from. The reason for using a constant broadband noise as opposed to program is it will make it easier to monitor level changes. You don't even need to listen to it, just watch the VU as you move the head of the mic around the various components. Hope this helps.

 

[sodderboy]

If someone didn’t say it,
Record it!
Studio ghosts in the machine are magical.
If it works as spec’ed, you get two in one.
Mike

 

[Mr. Moscode]

I suggest you input an oscillator, sweep it across the band and see where the resonances are and where they come from. Start at low levels so as to not make everything sing at once. You can make a simple one ear stethoscope with a piece of plastic tubing, or get a cheap one.

Or send the "damned" unit back to the maker and make them fix/replace it. Depends on what your time is worth chasing this down.

 

[Gold]

I've had film caps be microphonic. There is one particular cap in the Neumann VG66 electronics that is microphonic and it appears to be baked into the design. Replacing the cap with a new one makes no difference. I don't know what the mechanism is that causes this though. It is in a place where there is high signal power. After the power(drive) amps.

 

[pucho812]

I've had film caps be microphonic. There is one particular cap in the Neumann VG66 electronics that is microphonic and it appears to be baked into the design. Replacing the cap with a new one makes no difference. I don't know what the mechanism is that causes this though. It is in a place where there is high signal power. After the power(drive) amps.

I have had other gear produce sound in the chassis if I need it a loud enough signal. For example, I recently fixed an original 1176 revD that if I turned up the In and Out controls and then fed like a +26dBu signal, I could hear the test tone coming out the chassis. I didn't bother to investigate further as who will never do something that daft in normal operation but it could be heard. I suspect it came from the output transformer.

 

[Mr. Moscode]

Caps are electrostatic transducers. Feed it a 1k square wave and it will sing.

 

[guze]

the 2n3055 inside a neve clone preamp i have in here emits whatever is playing when driven VERY hard. I had to open the lid and discover where it was coming from

 

[Khron]

the 2n3055 inside a neve clone preamp i have in here emits whatever is playing when driven VERY hard. I had to open the lid and discover where it was coming from

Is it the transistor itself, or the output transformer?