Transformer Whine: Can it be rebuilt? Mirage S8 Subwoofer

[nobbnobb1]

Hi guys,

I'm trying to repair my Mirage S8 subwoofer (equivalent to the Energy S8.3) which is an excellent unit. It developed a light hum recently, which I thought was the capacitors. I replaced all the capacitors, and upon reassembly the buzz got louder. I thought I had messed something up electronically, but even when I swapped out the old capacitors it was still buzzing. So I inspected closer and discovered the noise is coming from the transformer. It's REALLY loud, which was surprising.

There are no specs on the transformer and no relevant part numbers. I Googled the generic markings on it and can't find anything. See attached picture. When plugged into 120VAC, it puts out 42VAC on both taps. Can anyone suggest any tips on finding a replacement? Or is it possible to rebuild this somehow? eg. if the windings are coming loose maybe I can dip it in some glue or whatnot to re-bond the windings?

This is an awesome subwoofer and I'd love to get it working again! Thanks!

[stj]

Re: Transformer Whine: Can it be rebuilt? Mirage S8 Subwoofer

check the screws are tight and then you can paint the windings with laquer - dont use superglue

[redwire]

Re: Transformer Whine: Can it be rebuilt? Mirage S8 Subwoofer

I would first check if it's a power quality problem - high mains voltage causes transformers to vibrate more, and high THD causes the higher harmonics to get heard as the louder buzzing. At night-time power quality is usually better from industrial customers not using power, compared to day time. So the buzz might get quiet at night and noisy during the day. You also might have a local dirty customer such as EV battery chargers causing a power quality problem. See if BC Hydro is cranking up the line voltage, what do you measure.

If it's the transformer, there's not much I find can help. The lamination bracket bolts can act as a somewhat shorted turn but things should then heat up. You can try tighten the bolts.

[nobbnobb1]

Re: Transformer Whine: Can it be rebuilt? Mirage S8 Subwoofer

Thanks for the replies. This one was weird. Initially, the whine was noticeable, but not that loud. So I went in, replaced the capacitors, then when I put it all together again it was LOUD. So I immediately thought maybe I did something wrong or the new caps were bad. I spent so much time adjusting the solder joints, swapping the old caps back in, to the point that the circuit board tracing fell apart (it was also really weak) in some areas and I have to improvise with some wire. Really disappointed in that.

I was a noob thinking that bad caps was causing the whine, and that the board was buggered. Pretty much ready to give up, but I gave it one more shot, plugged it in, and on closer inspection it seemed that it was the transformer making the noise. I unscrewed the 4 screws to the transformer, and to my disappointment, it did not come apart further than that. However, I put them back on again tightly and decided to plug in the transformer directly to 120VAC without the amplifier board. No hum! So it looks like that fixed it. I rebuilt everything again with thread-lock on the transformer bolts and also added hot glue to various areas on the amp board.

Buttoned everything up and now she's quiet. I don't think it was the caps at all. But oh well, they were 18 years old anyways and lower tier 85C rated brands (Jamicon, CapXon). I put in brand new 105C rated tier 1 caps into the amp and hopefully won't ever have to tear this thing apart again. Just a bit disappointed that I damaged some of the PCB traces. Should've maybe been more gentle and/or use less heat.