After looking for a nice Mark Levinson number 30.6, I have finally found one. It completes my Levinson reference front end. It replaced my 360S. It was an awesome upgrade. I never knew that bass could be so detailed!

My system consist of:
No 32
No31.5
No 30.6
No 336
B&W 800 Diamonds

My question is, the power supply of the number 30.6 has a low frequency hum to it. I have tried changing outlets. I moved my cables around some. There is no sound from my speakers with the system on, dead quiet. Any other ideas to try to get rid of this hum? I can't hear it when the music is playing. But when my listening room is quiet I can hear it......

I love the mark Levinson 300 series!

Old School, direct your question to Ivan aka Masterlu. He may be able to help you.

That sounds like a transformer. This is a mechanical hum induced by some sort of resonance between wires or the core.
A very common problem especially if gets older and the resin (if used)!dries up.
Often the hum varies over time as a DC component present on your mains line can influence it.
This could be a tricky one to solve, as this kind of hum is stubborn.

A wooden cabinet can amplify this as well

I checked the pls-330 supply on the web.
Indeed two fairly large toroidal transformers are used for the left and right analog power supplies.
If you know what you are doing and use great caution (I don't want fellow forum members to die because of my instructions) you could lift the cover and very carefully run the unit while the power supply is open.
If that made it louder you could investigate isolating the cover with some dampening sheets.
Also if you put some controlled pressure on the transformer it can become less or more.
By all means if you are not comfortable ask a service guy to invest the root cause.

Good luck
Peter

Indeed, may be as simple as a slight tightening of the bolts that hold the xformers in place. Ask ML. The one time I contacted ML thru their website in the past several months they did respond to the question (asking about their support for vintage ML like yours - the answer was yes), albeit, took about 10 days.

BTW - great system with a great R2R ladder DAC. :thumbsup: Many folks are starting to 'look back' at this older technology for their 'preferred' sound. Please post a pic or two of your system for our edification.

That was it! I tightened the transformer down on the power supply, no more hum. It was actually quite loose....

I would love to add a photo of the system but I don't know how.......

Great!! Glad it worked for you.
Think you have to become a 'subscriber' in order to post pic's.

Glad you managed to solve your problem, I had a complete ML Ref set, including the ML33Ref, I sold the ML32 / ML33? MML31.5 and I kept the DAC ML30.6 and a transport ML37, for my taste I still give a lot pleasure, this set is much better than my Yamaha CD-S3000!