[Soundbuff]

Lately I notice I'm hearing a very faint buzzing (not transform hum) sound coming through the HD 650's when listening to my MPX3. Is this a sign my 6cg7 RCA Cleartops (of unknown age) could be going bad and may need to be replaced?

Where can you buy RCA cleartops (6cg7 type)? I'd like to get another set as a backup and to see if it will eliminate this faint buzzing.

What normally happens when tubes start to fail? Thanks

 

[Len]

I thought MPX3 were all 6SN7, or is yours custom built? In any case, it's likely the tube(s). Singlepower amps are OTL if I recall, so it's not the transformer. It could be bad caps or resistors, but chances are it is the tube.

Tube can start to become noisy as they fail. Some fail catastrophically but most die a slow death. Sonically, you'll hear a compression of sound over time, but since it is so slow, you may not notice it for a while (if ever).

I'm sure some members here have 6CG7 available for you. I'll let them chime in.

 

[Soundbuff]

P.S. the buzzing increases in volume as the gain control is turned up.

 

[jamato8]

If it increases with the volume control increased then it most likely is the signal coming in. It sounds like you are picking up EMI. you might want to check the position of the ic's and the grounding scheme.

John

 

[braillediver]

Is the buzzing equal on both sides?

Can you swap the tubes right to left and see if it’s in both channels?

Have you swapped inputs right and left to see if the buzz stays on one side?

If it has a right and left channel output tube would both go bad at the same time.

You should contact Mikhail and ask some questions to help identify the problem.


Good Luck

Mitch

 

[Soundbuff]

I now believe 90% of the buzzing is caused by EMI interference from my Bel Canto DAC 2.

I usually listen at the second level of volume on the MPX3 ("8 oclock"). The buzzing is barely audible at that level but you can hear it, especially if no music is playing.

At the third level ("9 o'clock") the buzzing is very audible. When I unplug my Bel Canto DAC 2, the buzzing drops dramatically and can again only be barely heard (perhaps there is some EMI from the MPX3 itself?).

I don't know what to do about this. The IC I am using (an Audiogeek Nitrogen) is about as far away from the power cords for the MPX3 and Bel Canto DAC 2 as it can be. Maybe I should get some heavily shielded power cords for the MPX3 and Bel Canto DAC 2?

I am thinking about buying a better power strip too. Wireworld has one called the Tundra and The Cable Co. is having a sale on them for about $70 I believe. All my stuff is plugged into an old computer power strip, which is plugged into a PS Audio Ultimate Outlet. My MPX3 is also plugged directly into the Ultimate Outlet, and the wall outlet is correctly grounded.

Any recommendations for power cords or any other suggestions? Maybe the tubes aren't going bad after all.

 

[sacd lover]

That sounds like a ground loop. Try lifting the ground on the dac with a cheater plug.


Quote:

Originally Posted by Soundbuff I now believe 90% of the buzzing is caused by EMI interference from my Bel Canto DAC 2. I usually listen at the second level of volume on the MPX3 ("8 oclock"). The buzzing is barely audible at that level but you can hear it, especially if no music is playing. At the third level ("9 o'clock") the buzzing is very audible. When I unplug my Bel Canto DAC 2, the buzzing drops dramatically and can again only be barely heard (perhaps there is some EMI from the MPX3 itself?). I don't know what to do about this. The IC I am using (an Audiogeek Nitrogen) is about as far away from the power cords for the MPX3 and Bel Canto DAC 2 as it can be. Maybe I should get some heavily shielded power cords for the MPX3 and Bel Canto DAC 2? I am thinking about buying a better power strip too. Wireworld has one called the Tundra and The Cable Co. is having a sale on them for about $70 I believe. All my stuff is plugged into an old computer power strip, which is plugged into a PS Audio Ultimate Outlet. My MPX3 is also plugged directly into the Ultimate Outlet, and the wall outlet is correctly grounded. Any recommendations for power cords or any other suggestions? Maybe the tubes aren't going bad after all.

 

[Soundbuff]

Quote:

Originally Posted by sacd lover That sounds like a ground loop. Try lifting the ground on the dac with a cheater plug.

Need some education. I've heard of the term ground loop but don't know what it means or what causes it. Also, what does it mean to lift the ground, and what is a cheater plug ?

 

[jamato8]

You are often better off to have just one component going to earth ground. Grounding can be a real bear if you starting getting into problems with it and it can cause a lot of hum and sometimes distortion. If you have both components grounded then buy a plug that allows you to plug the 3-pronged plug into a two socket AC outlet. It is called a cheater plug because you are supposed to ground the item. But since you have the amp hooked to your source it will ground as long as one of the items is left with the 3 prong plug. I would float the source (CD player or whatever) and keep the amp grounded. You can buy an adapter plug for about a dollar. Current flows on the ground in small amounts, depending on the component and when you have both items, or three as in a source, preamp and amp the flow can be from the ground of one to the other and you no longer have a good path for all of the grounds of the individual components and hence hum or buzzing can occur.

John

 

[Soundbuff]

Thanks for the very good explanation of ground loops. Very interesting.

I tried plugging the power strip into the PS Ultimate Outlet using a cheater plug (what I usually call a 3-prong adapter) to de-ground everything except the MPX3 which is directly plugged into the Ultimate Outlet. It did not fix the problem, the hum was still there.

I then tried an experiment and disconnected my Stereovox HD XV digital cable from the Bel Canto DAC 2 (I run both a toslink from my Denon mini system, and a coaxial HD XV from my Sony DVD/VHS player to the DAC 2).

The hum disappeared completely, no matter how high I turn the gain control. Go figure?

Maybe I'll just return the HD XV since I don't really need two transports and don't really hear much of a sound difference between them anyway.