Amp/Pre-Amp question.

[cbevil]

Hi all, this is my first post here at Audioholics. I hope it's in the right forum.

Today I reprogrammed my universal remote to turn off my pre-amp when not in use. Prior to this I had just left it on, but my wife said she'd prefer it was off. No big deal. But the amp only turns off with a rocker switch in the back (not input from a remote), so it'll still stay on all the time.

A while after shutting down the pre-amp, I thought I heard a faint noise coming from the general direction of my stereo. I got closer, and sure enough, there was a slight hum coming from the speakers. When I turn on the pre-amp, the hum goes away.

Anyone have any idea why this is? The only thing I could think of was that the speaker cables run across some power cables (just the way my setup has to be right now) and they were picking up some noise from them. But I'd think if that were the case, the noise would not go away after turning the pre-amp on. But I'm no expert, so could be wrong.

For the time being I'm going to leave the pre-amp on, but any explanations/advice on this are much appreciated!

If it makes a difference, the amp is a McIntosh MC7100, the Pre-Amp a McIntosh C712.

 

[zumbo]

No 12v trigger?

 

[cbevil]

No 12v trigger?

I'm not sure what that is, so I Googled it. Looks like something for home automation or projectors, maybe to turn things on and off automatically. If I have one, I am not using it.

I'm also not sure if you are asking me if I am using this, and it could be the problem, or if I should be using it to turn the amp on and off. I checked the manual for the C712, and didn't see a 12v Trigger, but did see this:

"15. POWER CONTROL
This connector supplies a 5 volt, DC Logic 1 control signal to feed to a similar Power Control input on a compatible power amplifier or accessory. The POWER CONTROL signal is used to turn the AC power of the accessory component on and off. The POWER CONTROL connector uses single conductor shielded wire with 1/8 inch mini Phono plugs. Connections are to the top and sleeve of the plug."

(the manual is at http://www.berners.ch/McIntosh/Downloads/C712_own.pdf )

Checking the manual for my amp (which is at the same site, but wants me to log on in order to view it for some reason -- so I went and found my printed copy...) it looks like it has a power control input! So maybe this is a solution, get one of those cables and have it switch the amp on and off as well. Is this what you were driving at?

 

[zumbo]

Yep. That's it. Get the mini-plug, and you should be all set.

 

[highfihoney]

Hi,your c-712 has a 12 volt trigger on the rear panel,mcintosh labels their triggers as "power control",the model of your mc 7100 will dictate weather or not it has a 12 volt trigger,there were 2 versions of the mc 7100,what seperates the 2 versions are these features.

Early version has pan loc's,rca outputs only no balanced output's,no 12 volt trigger & a captive power cord.

Late model version does not have pan loc's,has both rca & balanced output's & it does have the 12 volt trigger which is labled the same as on the c-71"power control,this version also has a removeable power cord.

Radio shack carries the cable you need for $5 & they mostly have them in stock.

Berners mcintosh is a good site for information but the reason he wants you to log in is because he offers manual downloads for most of the mcintosh line & people turn around & sell copied manuals from his site on ebay so he started asking for donations in order to get manual down loads from his site.

The best site on the www for vintage mcintosh gear like yours is roger russell's site,if you have questions you can email him & it might take a few days for him to respond but he is a big help,he was the director of accoustic research at mcintosh labs for many years.

Here is his site.

http://www.roger-russell.com/aboutmc.htm

Most questions about your mac gear can be answered by emailing mcintosh lab's direct & talking to tech support,contact Chuck Hinton.

http://www.mcintoshlabs.com/contact.aspx

 

[cbevil]

OK, I think I got it. I never knew about that feature until just now...

My MC7100 has balanced inputs, so I think I am good in that respect.

The cable I am looking for, is it a cable with male 1/8" plugs on both ends? My wife has one of those she used to hook her iPod up to our Boston Acoustics HD Receptor Radio. But she never uses it due to the output from the iPod being so weak. She said she'd be happy to let me use it for turning the amp on and off, as she'd love for both the amp and pre-amp to be off when not in use.

Here is what it looks like:

http://images.channeladvisor.com/Sell/SSProfiles/20059948/Images/255-258.jpg

 

[zumbo]

That will get it.

 

[cbevil]

Awesome, thanks much to Zumbo and Highfihoney!

 

[cbevil]

Well, I tried this (took me a few weeks to get to it.. my setup is a pain to change/add cables). Unfortunately, it does not work for me. Either one of the components is broken, or the cable is not the right one (I know the cable is good, though, as we used it to pipe sound from an iPod into a tabletop radio). I'm betting it is one of the components, but I'm not sure how I would confirm this, or determine which one.

The other option I have is a power plug on the back of the amp -- apparently you can plug it directly in to the pre-amp and it will turn on and off power to the amp. I'm not sure this is a good way to do it -- will the amp get as much power as if it were plugged in directly? Is there any problem with cutting the power to the amp like that? I'd guess not, since it's designed for that, but it still makes me nervous...

 

[Don_T]

I could be wrong but...I think the problem is with the cable itself. The cable you are using is most likely stereo and the one you need is mono. I am not sure why a stereo plug will not work because one would think that the left channel would function the same as a mono cable but I had a similar problem using a stereo cable for a control link and the mono plug worked where the stereo cable did not.

Also, it is possible that the 12v trigger is not enabled in the setup of your pre-pro. With my AVR the 12v triggers must be activated in the setup of the system. Look into this first, then try the mono cable.

As for the power output on the pre-pro, I would avoid using that as the power source for the amp. I don't know the specifics of your equipment as to whether it can handle the power needs but in general it is best for power amplifiers to have their own power source.

Hope this helps.

 

[cbevil]

Ah ha! I totally missed the stereo vs. mono thing. Yes, the cable is stereo. I didn't know this would make a difference., but it makes sense when you think about it I'll drop by a local Radio Shack this week and pick up a mono cable (and find time to pull my components out of the cabinet again... arg). Thanks!

 

[Nick250]

One stereo cable = two mono cables. No need to go to Radio Shack and get a mono cable to test your system.

Nick

 

[moverton]

The other option I have is a power plug on the back of the amp -- apparently you can plug it directly in to the pre-amp and it will turn on and off power to the amp. I'm not sure this is a good way to do it -- will the amp get as much power as if it were plugged in directly? Is there any problem with cutting the power to the amp like that? I'd guess not, since it's designed for that, but it still makes me nervous...

That is a normal way to control the amp. They usually have a relay that protects them during power up. I have my power amp hooked up that way and it's worked for 10 years just fine.

 

[Relly Carreon]

Please help! I bought a Mcintosh mc7100 for my Monitor Audio Silver RX8 for 2 tower speakers which is rated 4ohms at 175watts rms but this power amp is only rated 150watts for 4ohms. Do you think this amp can drive my speakers without any problems? Thanks!

 

[lsiberian]

Please help! I bought a Mcintosh mc7100 for my Monitor Audio Silver RX8 for 2 tower speakers which is rated 4ohms at 175watts rms but this power amp is only rated 150watts for 4ohms. Do you think this amp can drive my speakers without any problems? Thanks!

Yes your amp will driver the speakers without any issues. In the future I suggest starting your own thread so your question doesn't get lost in an 8 year old thread.

 

[Seth=L]

Please help! I bought a Mcintosh mc7100 for my Monitor Audio Silver RX8 for 2 tower speakers which is rated 4ohms at 175watts rms but this power amp is only rated 150watts for 4ohms. Do you think this amp can drive my speakers without any problems? Thanks!

Please refer to the thread you started, that discussion belongs there, not in a thread that's 8 years old.

Edit: Damn Isiberian, you beat me. I was taking my sweet time making a reply to his other thread.

 

[Relly Carreon]

Yes your amp will driver the speakers without any issues. In the future I suggest starting your own thread so your question doesn't get lost in an 8 year old thread.

Thank you very much Sir. I only search the unit here so I ask a question without knowing that this is an 8 year old thread. Sorry Sir and thanks for your help.