2408 mk2 - Can I purchase a new power transformer?

[digdoug]

The power transformer in my 2408 mk2 is buzzing (mechanically) very badly. This buzz is now present in the audio path and can be heard in the monitors and on recorded tracks.

Can I buy a new transformer from MOTU? This unit cannot possibly be under warranty, but I am proficient with a soldering iron and would like to do the replacement.

Here's a long shot (and probably terrible) idea - is there any way to re-lacquer/dip the transformer to silence it or convert the unit to use an external power supply?

Thanks folks,
DW

[HCMarkus]

Call MOTU!

I'm sure you could convert to external PS, but it would take some work.

[Phil O]

The power transformer in my 2408 mk2 is buzzing (mechanically) very badly. This buzz is now present in the audio path and can be heard in the monitors and on recorded tracks.

If that's the case, it might not be the transformer (or not JUST the transformer). There's a possibility that there's a problem with the power supply that's causing the transformer to buzz. You could replace the transformer only to find that the problem doesn't go a way. If it's affecting the audio, chances are there's a power supply issue beyond just mechanical hum. But I'm speculating - just a heads up that there may be more problems.

Phil

[digdoug]

If it's affecting the audio, chances are there's a power supply issue beyond just mechanical hum.

Phil, if you have a minute or two, could you elaborate a little bit? I really need some help. Here are my observations: The buzzing can be heard clearly in the room and actually felt if you put your hand on the MOTU unit. It seemed to start all of the sudden and under the same conditions as always (although it did start after some on-site recording gigs). No other piece of equipment in my studio makes noise and I have never had any ground loop issues or other noise-related problems.

I'm just not sure what this all means. Thanks
DW

[Phil O]

A heavy load on a transformer can cause it to make noise. Too heavy, of course, and you'll be popping the power fuse. But maybe it's just at that point of making noise, but not blowing anything. Yet! This could be caused by failure of something in the power supply or by something else in the system overloading the supply. It could be any number of things that are causing it. I'm guessing that if it's simply loose windings in the transformer that would not cause enough electrical noise to get onto the audio. (Not impossible just improbable.)

It also could be exactly what you think it is - a bad transformer. All I'm saying is there are other possibilities, and to jump in and replace the transformer without some troubleshooting may be premature.

Phil

[billruys]

It seems strange that physical buzz is making it into your recordings. Are you sure that the noise is not just leaking into a microphone somewhere?

If there is a further problem in the power supply, it's quite likely to be the failure of an electrolytic capacitor just after the rectifier. This would cause electrical ripple that would make it into your recordings.

The other possibility is that a diode has gone bad in the rectifier. This could possibly cause the transformer to buzz physically and create electrical buzz, as you would only have half-wave rectification.

This is all just speculation, but as Phil points out, if you don't know for sure, replacing the transformer may not fix your problem.

[digdoug]

You were right, there was more to it.

I came down this morning and the 2408 was no longer buzzing. My configuration changes from time to time, so I may have lost it along the way and not noticed. There was still, however, a ton of audible noise in certain channels.

Through trial and error, I noticed that when I disconnected all 4 balanced line ins from one of my preamps (Vintech 473), I could nearly eliminate the noise.

The 2408 and the 473 are side-by-side in the same rack, so I removed the 473 from the rack, reconnected everything, and voila, barely any noise. It appears that the unit was not only grounded to the rack and the screws on the bottom of the 473 had scraped through the paint of the 2408 chassis, and were making direct contact with it. I'm not sure that this matters in all situations, but it seemed to be causing bad things to happen in mine.

If I arm a track to record and load up the Voxengo SPAN plugin, I see that what little noise I am still hearing (240Hz, 360Hz, and a bunch of stuff around 6k, primarily) is now peaking at about -67dBfs. I'm not entirely sure if I'm measuring this right, but based on a few test recordings, I think I can work with this.

I am 100% positive that I was previously hearing and feeling noise coming from the top right side of the MOTU 2408. What happened I wonder? Anyway thanks everyone for the advice!
DW

[mikehalloran]

It sounds like the ground loop from hell.

Back to the op. MOTU has an exchange program for these. You get a remanufactured unit. They do not offer parts nor a schematic for DIY. I'm not certain of the current price but it was $99 plus shipping and your old unit.

The common problem with these is the FW port. Elsewhere in the Mac threads there is a suggested fix with not enough information for me but it may be useful to some - or not. I can't find it at the moment. Mine is now 7 years old so I wonder how long...