[tz1963]

Sorry if this is the wrong place to post this, but I can't find the old EE threads anymore.
I have MiniMax Dac, using the fuse and tube provided my Wayne (I'm in the UK).
A few months ago the dac developed a small but irritating hum.
I have taken out the tube, but that does not seem to help. I have tried it in different sockets, but to no avail.
Every now and then the hum disappears for a short while, but then returns.
Is there anything I can do about this?
Any advise more than welcome.
Thanks,
Tom

[Levi]

I would put the original fuse, tube and OPamps back and see if that helps.

[tz1963]

Thanks Levi,
It seems to have worked!
I can't tell you how chuffed I am. As I'm in the UK, the idea of having to send the dac half-way across the world for repairs didn't have much appeal.
Let's hope it stays like this.
Cheers,
Tom

[wilsynet]

Are you going to change one thing at a time now and see what brings back the hum?  I bet taking out the tube doesn't re-introduce the hum.  My money's on the fuse.

[tz1963]

Actually, I've noticed the hum returns after some time  .
I did try taking out the tube and leaving in the original fuse, but that did seem to make the hum worse.
What happens is that the hum builds up slowly and goes away when I put my hand on the dac.
Does this mean it's a grounding issue?

[Wayne1]

A fuse cannot cause a hum.

Usually a hum means you are getting a 60 or 120 hz noise along with the signal. There may be something going on with your output cables.

It is also worth checking your AC ground. Slowly work through your installation of the DAC. Disconnect and replace you output cables, AC cable and input cables.

Make sure your entire system is plugged into the same circuit. If one piece is on a different circuit, the ground potential may be different.

If you have cable or satellite TV plugged into the system, remove the connection and see if the hum goes away. Some TV signal suppliers use a different ground than the AC does.

You can also tie all your gear together. Run a wire from the cases of all the components to each other.

[wilsynet]

Does the hum emanate from the speakers or the DAC itself?

[tz1963]

Thanks for the suggestions.
The hum comes from the dac itself, not the speakers.
I'll try doing what Wayne suggests.

[Wayne1]

Thanks for helping narrow down what the hum is, wilsynet.

tz1963,

This "hum" is a mechanical noise that comes from the DAC?

If that is the case, then it may be the transformer vibrating. You may want to take off the top cover, when the unit is disconnected from the mains. The transformers may have come loose from their bolts. You might want to try tighten then and any loose screws.

[Rocket]

Hi,

I lived with hum from a cornet phono stage and put up with it for about a year.  I eventually found out that when the cdp was left in standyby mode (which is normally how I left it) it cause the hum in the unit.  I turned the cdp off at the power socket and problem solved.

Hum is very irritating.

Regards

Rod

[wilsynet]

What happens is that the hum builds up slowly and goes away when I put my hand on the dac.
Does this mean it's a grounding issue?

Sounds like it's mechanical to me.  I'm with Wayne, may be a very small amount of transformer hum which is resonating through the chassis and building up over time.

What I'd do is take off the top plate and see if you can identify where the hum is coming from.  If and when you go tighten the bolts on the transformer, I'd leave the unit off and disconnected from the mains for a day before operating on it.  Not sure about you, but I'm not much for being electrically inclined -- but I've heard stories where caps haven't fully discharged after a week in shipping, so I'd leave it off for a day.

I once had a mechanical hum problem with a TRL Dude, and I ended up loosening a couple of the screws on the top plate and the hum went away.

[tz1963]

Well, I finally got round to opening the MiniMax. The transformer seemed to be very firmly in place.
But then I noticed that it was connected to 230 volts (I bought the dac in France) but where I live (the UK) we have 240 volts 
So I connected the power to the 240 volts thingee, which was easy enough. When I switched it on, the hum was still there  .
Could I have buggered up the transformer, by having it run on too high a voltage?
I've now taken the lid off while having it on; there's still a slight hum. I'll see if it gets worse over time.
 

[wilsynet]

So where is the hum coming from -- with the unit open, can you hold your ear over the chassis to figure it out?

I believe running at 240V when the transformer is configured for 220V or 230V will cause the transformer to run under more strain and may cause hum.  Whether permanent damage could manifest itself as permanent hum, I'm not sure but I suppose I wouldn't be surprised.

I'm not electrically smart, but there was a conversation on Audiogon about this a little while ago.

http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1146465464&openfrom&1&4#1