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Power control hum

T

Thoan

New Member
Gear is a C712 and a pair of MC7100s feeding biamped speakers. Only balanced connectors are used for audio

It would be really nice for the 12v power control feature to turn on the amps with the preamp, but hooking them up introduces a low-level but annoying hum. Any thoughts? Looking at the schematics, it's hard to see how this is possible, but there we are.
 
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Thoan said:
Gear is a C712 and a pair of MC7100s feeding biamped speakers. Only balanced connectors are used for audio

It would be really nice for the 12v power control feature to turn on the amps with the preamp, but hooking them up introduces a low-level but annoying hum. Any thoughts? Looking at the schematics, it's hard to see how this is possible, but there we are.
Click to expand...

Sounds like a ground loop. What are your sources?
 
Ground loop is a good suggestion, and I'll play with it a bit tomorrow. Sources are mostly an Oppo player, a media computer I built and a Mac MCD7005. The hum seems to be source independent. One of these months I'll get the vinyl going again.
 
Thoan said:
Ground loop is a good suggestion, and I'll play with it a bit tomorrow. Sources are mostly an Oppo player, a media computer I built and a Mac MCD7005. The hum seems to be source independent. One of these months I'll get the vinyl going again.
Click to expand...

The first step is to disconnect all of your sources and see if the hum is still there. If it goes away then the problem is with one of your sources. Plug one of them back in at a time until the hum comes back. When it does you found the cause of the problem. Once you know which source is causing the issue you can then go from there.
 
It doesn't appear that his hum is based on sources or those connections. His hum appeared when he hooked up the power control cable.

Are you using a mono cable?

Larry
 
I have 2 model OPPO universal players, and though I can`t say that the BDP-103 has 12v trigger in and out 1/8" jacks, I can confirm the my UDP-203 does, but my setup doesn`t use them..

So I suspect that you`re using your C 712 as your 12v triggering source for your MC 7100`s are possibly power cord plugged into different outlets(maybe even different branch circuits ?) and possibly picking up a ground loop, or the C 712 preamp`s power supply`s 12v trigger source has circuit has issues ?
I`m not fam. with your C 712 preamp..
You could try for grins, to lift your preamps grounded power cord with a ground lift "cheater" to see if that removes, or changes your low level hum.

And also see if your OPPO has a 12v trigger jack, and try hooking that to your MC 7100`s to see if the low level hum remains ?

I run a tri-amplified balanced cable connected living room system using 12v triggering to my 240volt wired Mc. MC 1201`s that reside in another adjacent room from a Furman surge/spike/power sequencer located in my living room`s A/V rack with no hum measured or heard.
Also make sure your 12v trigger cables/plug ends are in good order, I custom made mine using 1990`s RS twisted pair stranded wire that was sold as security house alarm wire, as I didn`t think I needed to use shielded cable for that application, even though the length was over 40ft.

Good luck, Thoan
 
VintageMac said:
It doesn't appear that his hum is based on sources or those connections. His hum appeared when he hooked up the power control cable.

Are you using a mono cable?

Larry
Click to expand...

It's still possible that it has something to do with one of the sources. The 12v trigger between two McIntosh components shouldn't be the cause of the problem since that is how you are supposed to connect them. I've had similar issues before and sometimes the 12v trigger makes the problem appear.
 
Another fairly easy solution, could be the use of a inexpensive smart/green power strip..
Plug the preamp into the control power socket, and a very low amperage 9v unregulated DC, or 12v regulated wall wart observing proper polarity (tip positive IIRC) from the wall warts output and connect that to the power amps..
When the preamp is turned on it after a few seconds engages the switched outlets which will power the wall wart, which the triggers the amps..
I had to do something similar yrs. ago to use a older Mc. preamp to turn on my 2 bedroom Mc. MC 1201`s/& 2 powered sub woofers via a 20amp Panamax surge/spike protector that had 1/8`s 12v trigger control input..
Worked perfectly for over a decade, until I replaced the bed rooms Mc. preamp with a later model with trigger outputs..

There should be excellent trigger ground loop isolation by this method.

Just a thought folks.
 
Bill Ferris said:
Another fairly easy solution, could be the use of a inexpensive smart/green power strip..
Plug the preamp into the control power socket, and a very low amperage 9v unregulated DC, or 12v regulated wall wart observing proper polarity (tip positive IIRC) from the wall warts output and connect that to the power amps..
When the preamp is turned on it after a few seconds engages the switched outlets which will power the wall wart, which the triggers the amps..
I had to do something similar yrs. ago to use a older Mc. preamp to turn on my 2 bedroom Mc. MC 1201`s/& 2 powered sub woofers via a 20amp Panamax surge/spike protector that had 1/8`s 12v trigger control input..
Worked perfectly for over a decade, until I replaced the bed rooms Mc. preamp with a later model with trigger outputs..

There should be excellent trigger ground loop isolation by this method.

Just a thought folks.
Click to expand...

You can also try one of these: https://www.xantech.com/product/dc-controlled-ac-outlet-AC1 I use one to turn on my old Marantz 2265B using my McIntosh preamp it works great.
 
Logan_Nolag said:
You can also try one of these: https://www.xantech.com/product/dc-controlled-ac-outlet-AC1 I use one to turn on my old Marantz 2265B using my McIntosh preamp it works great.
Click to expand...

That looks like it`ll work,
the OP has choices, just a matter of him selecting a power switching device within his desired purchase level/system configuration ..
Though where Iive, some level of spike/surge protection in the power switching is desirable/important at all my house`s room`s systems, & none seemed to be upfront conveyed offered within the link to your device..
Though I didn`t explore the details of your product, outside the direct link`s opening page !
 
Bill Ferris said:
That looks like it`ll work,
the OP has choices, just a matter of him selecting a power switching device within his desired purchase level/system configuration ..
Though where Iive, some level of spike/surge protection in the power switching is desirable/important at all my house`s room`s systems, & none seemed to be upfront conveyed offered within the link to your device..
Though I didn`t explore the details of your product, outside the direct link`s opening page !
Click to expand...

I don't think the AC1 has any built in surge protection. I have mine plugged into a Cyberpower rack mount surge protector and it works fine.
 
Thoan here, the original poster. I've overwhelmed by how many comments have been made! You guys have too much spare time!

The hum/ground loop is source-independent. You can also disconnect the C712's outputs and still get the hum -- it's passing through the Power Control cable, and yes, I am using mono 3.5mm cables for this.

In the course of messing about with cables and DeOxit, I was down to one Power Control cable, going from the "out" jack of one MC7100 to the "in" jack of the other MC7100. The C712 was not involved at all. Both power amps were turn on manually at the time (obviously, as there was no 12v control signal), and both hummed. (The old joke: Why do they hum? They don't know the words . . . )

I also grounded the gear together with wires attached to the chassis, something that worked pretty well in the C28/MC2105 days, but not any more.

So the hum is being introduced by the Power Control wires -- even though this circuit is independent of the signal path. Wow.

If I had some mono 3.5mm jacks on hand, I'd try making my own connectors, and maybe include a diode or two just for kicks -- next Mouser or All Electronics order, this happens. And long term, I could see making an Arduino-controlled set of relays to turn the amps on x seconds apart (there is more gear than the pair of 7100s). But I'm with Occam here, I'd like the simple solution to work.
 
Thoan said:
Thoan here, the original poster. I've overwhelmed by how many comments have been made! You guys have too much spare time!

The hum/ground loop is source-independent. You can also disconnect the C712's outputs and still get the hum -- it's passing through the Power Control cable, and yes, I am using mono 3.5mm cables for this.

In the course of messing about with cables and DeOxit, I was down to one Power Control cable, going from the "out" jack of one MC7100 to the "in" jack of the other MC7100. The C712 was not involved at all. Both power amps were turn on manually at the time (obviously, as there was no 12v control signal), and both hummed. (The old joke: Why do they hum? They don't know the words . . . )

I also grounded the gear together with wires attached to the chassis, something that worked pretty well in the C28/MC2105 days, but not any more.

So the hum is being introduced by the Power Control wires -- even though this circuit is independent of the signal path. Wow.

If I had some mono 3.5mm jacks on hand, I'd try making my own connectors, and maybe include a diode or two just for kicks -- next Mouser or All Electronics order, this happens. And long term, I could see making an Arduino-controlled set of relays to turn the amps on x seconds apart (there is more gear than the pair of 7100s). But I'm with Occam here, I'd like the simple solution to work.
Click to expand...

Maybe try using stereo 1/8" cables. Modern Mac power control cables are stereo so you can turn off the meter lights from the preamp. Not sure if it will do anything but I don't think it will hurt to try.
 
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