Recent hum in stereo system

[MechEngVic]

Wait. Is the Maverick a tube DAC? Have you tried replacing the tube in there???

[babadono]

41 minutes ago, glens said:

I thought he reported recently that a different DAC solved the problem?

Yes Sir. But I just assumed he woud want to get his higher priced (better quality?) unit back functioning properly.

[Frank1938]

13 hours ago, MechEngVic said:

Wait. Is the Maverick a tube DAC? Have you tried replacing the tube in there???

The Maverick has two RCA outputs, one tube and one SS. Both produce a hum. What is curious is that I can run short RCA cables from the DAC SS output to my Parasound preamp to listen with headphones and there is no hum. I know, I know. 40 years of dealing with many stereo components but this one is very strange. Thanks again for your interest.

[Frank1938]

13 hours ago, babadono said:

Yes Sir. But I just assumed he woud want to get his higher priced (better quality?) unit back functioning properly.

That's indeed correct. It's now a matter of not admitting defeat 😁 See my previous post.

[babadono]

Does the Parasound Pre have a 3 prong power cord?

[Frank1938]

15 minutes ago, babadono said:

Does the Parasound Pre have a 3 prong power cord?

Yes, it does. It's the Zphono USB preamp and digital interface. 

[babadono]

OK let´s focus on what doesn´t work but did previously and should now.

Have you been able to try a cheater plug on the Maverick DAC?

[MechEngVic]

13 hours ago, Frank1938 said:

The Maverick has two RCA outputs, one tube and one SS. Both produce a hum. What is curious is that I can run short RCA cables from the DAC SS output to my Parasound preamp to listen with headphones and there is no hum. I know, I know. 40 years of dealing with many stereo components but this one is very strange. Thanks again for your interest.

depending how the unit is wired, a failing tube might still affect the SS side. The fact that the hum started suddenly... That tube is the first thing I would check.

[Frank1938]

12 hours ago, babadono said:

OK let´s focus on what doesn´t work but did previously and should now.

Have you been able to try a cheater plug on the Maverick DAC?

A cheater plug is the first thing I tried: on the McIntosh, Maverick DAC and iMac. Hum remained. 1) McIntosh amp: CD player is directly connected to the integrated amp on the same 20 amp circuit with no hum; 2) iMac is now connected to the new inexpensive DAC i bought at Best Buy, optical connection with no hum, seemingly eliminating the iMac; 3) Maverick DAC, hum with RCA connections and with optical connection. It appears that the DAC isn't working, worked before and should be working now. It is important to note that I made no changes to the system before the hum started. See my following post and thanks again. Hope your vacation was enjoyable and Happy New Year.

[Frank1938]

11 hours ago, MechEngVic said:

depending how the unit is wired, a failing tube might still affect the SS side. The fact that the hum started suddenly... That tube is the first thing I would check.

Thanks for your continued interest. I understand that the DAC is a beast to open but it appears that I am going to have to make the attempt. It uses a GE Jan 5670W tube, which I don't have, so I'll have to look for one. My only question is why I can connect the Maverick to the Parasound preamp to listen with headphones and have no hum. I just now connected the iMac to the Maverick via USB and ran RCA cables, left and right, from both outputs (one at a time, just to be sure) of the Maverick to the Parasound preamp and listened with the headphones. Totally silent. 

[babadono]

My next suggestion if you really want to fix this is to invest in some dummy plugs from Jensen Transformers. About $10. Once you have them follow the instructions included or from the document I linked to in a previous post. There is a cause for this problem and scientific methods will determine the cause and how to fix it. Not guesswork.

It my turn out that you have Common Impedance Coupling when using the Maverick DAC to MacIntosh Integrated.

[Frank1938]

44 minutes ago, babadono said:

My next suggestion if you really want to fix this is to invest in some dummy plugs from Jensen Transformers. About $10. Once you have them follow the instructions included or from the document I linked to in a previous post. There is a cause for this problem and scientific methods will determine the cause and how to fix it. Not guesswork.

It my turn out that you have Common Impedance Coupling when using the Maverick DAC to MacIntosh Integrated.

O.K. I'll look into that. Thanks so much for all of your help. I truly appreciate it. So nice to have people like you on the forum.

[Islander]

Some time ago, I decided to try a designated subwoofer RCA interconnect, as opposed to the generic interconnect I had been using.  First off, as far as I know, there's noting special about such a cable, since a music signal is a music signal, so it was a frivolous purchase, buying something inexpensive on a whim.  It was a brand name interconnect, but priced under $15.

 

It didn't work.  As soon as the sub turned on,  a low hum immediately came from the sub.  Later, when I shut down the system for the night, the sub didn't turn off.  Its Auto On/Off feature normally worked properly, but on that occasion, the sub stayed on all night, humming softly to itself.

 

Re-installing the original interconnect solved the problem, so I returned the cable.  The salesman at the shop expressed surprise that the cable was defective, saying he'd never heard of such a thing.  "Whatever, just give me back my money."

 

So there you go.  A defective interconnect can cause a hum.  Hope this is helpful.

[babadono]

11 minutes ago, Islander said:

So there you go.  A defective interconnect can cause a hum.  Hope this is helpful.

Do ya think?

[Islander]

2 minutes ago, babadono said:

Do ya think?

 

Happened to me.  That's two reasons for hum that I've seen and heard in my system.  I hope there aren't any more.

[babadono]

Just now, Islander said:

 

Happened to me.  That's two reasons for hum that I've seen and heard in my system.  I hope there aren't any more.

I was agreeing with you for sure! As in for sure a bad cable can cause hum problems.

[Frank1938]

Thanks guys for your continuing interest. An update for the interested parties. I borrowed a DAC with a ground lift and that eliminated the hum when I switched to the ground lift . My electrician friend is coming to check the electrical tomorrow; I'll let you know the results.

 

Frank

[MJ Ucar]

I have the same problem i.e. same integrated amp connected to K-horns. It turned out that it is the MA352 transformers not being properly isolated. Unfortunately MA252 and MA352 are both very poor quality when compared to most McIntosh separates...