Q. What’s the noise coming from my Slate Pro Dragon?

I value SOS's opinion very highly and, when I wanted to add a versatile, quality compressor to my arsenal, I thought about the review in SOS July 2010 of the Slate Pro Dragon [see /sos/jul10/articles/slateprodragon.htm for the full review]. On the first unit I got I identified something that I thought was weird, so I got it replaced — but the second unit displays the same behaviour, which apparently hasn't been noted by anyone, so I'm kind of puzzled.

 
The noise that reader Eric heard coming from his Slate Pro Dragon is most likely from the transformer. It's very common in modern devices with these kinds of transformers, and is nothing to worry about.

The behaviour is this: if I send a track to the unit (it's more obvious with something like a guitar or vocals) with a normal level, have the input at around six, the output at around three to four, and the saturate knob on three, you can hear the track feeding the unit acoustically from within the Dragon itself. What I mean is, if you don't even connect the output of the Dragon to anything, and there's not a single monitor turned on, you clearly hear the sound feeding the unit, produced by something acting as a transducer inside the Dragon. When the saturate knob is on a lower setting, you really have to put your ear on the unit to hear something, but it's actually there.

It's so strange that, after having seen this on the first unit, I contacted Slate Audio, but, apparently, they were not aware of this either. That's why I thought that this first unit had a problem. So I was hoping you might have noticed something during your review.

Eric Robert via email

SOS Technical Editor Hugh Robjohns replies: I would suspect that the output transformer is rattling; the laminations move slightly in response to the audio signal passing through it, which create a varying magnetic field and cause the laminations to vibrate in sympathy, hence generating an acoustic output. Depending on the way the transformer is mounted, those vibrations can be amplified acoustically by the circuit board or case metalwork and become surprisingly audible. It's the same thing that makes small mains power transformers buzz annoyingly in so much modern equipment.

It's not unusual, and it's nothing to be concerned about. I hadn't noticed it in the review model, but I'm not surprised at that: there was always other noise going on when it was on test, I expect, to mask this effect. I have come across it in many other products, though. It's really not that unusual in devices with output transformers.

Published June 2011