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RF issue with McIntosh RF

A

AlamoMCN

New Member
I recently purchased an MR 74 tuner and MA 6100 preamp/amp. Single owner, a meticulous PhD in electrical engineering. No mods in any way, all original. Sounded wonderful in his home, with none of the issues below.

Since setting up in my home and pairing with my AR ES-1 tt I have encountered two issues:

1) RF feedback present when amp is turned on in Phono setting and connected to tuner. When tuner interconnects are unplugged from preamp/amp, there is no feedback. Put away original interconnects and bought new ones that are shielded. No change in RF. Still present.

2) There is now a loud pop through speakers when turning off tt, if the MA 6100 remains powered during cut off of tt. If I turn off preamp/amp and wait a moment for it to power down, pop disappears.

Suggestions on how to address/troubleshoot are much appreciated. Thanks for your time.
 
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If that is true about no mods, then both units are well past their 'sell by' date and need to be recapped, which would include an alignment with the tuner. All problems sound like bads caps. Is your TT of a similar vintage and plugged into the back of the MA6100?

You might also try reversing the AC power plug on each unit. You never know about what they want in the way of hot/neutral. Try one at time and run your noise test after doing each one in turn. You never know and a whole lot easier than a recap/alignment. While I would send my gear to Terry for the work, about 10 years ago I bought an MR75 from a fellow in San Antonio who told me it had recently been gone through by the authorized McIntosh folks some place north of San Antonio (New Braunfels seems right, but it could have been San Marcos). Either it needed nothing or they did an excellent job as it was a very nice tuner.
 
Thanks

According to McIntosh, the only authorized repair location in SA is Bjorn's and I'd have to go all the way to Austin for the next closest location. Bummer.

Thanks for the tip, I'll try reversing the power plugs next. As for the tt, yes it is of the same vintage but it is not plugged into the amp. Plugging it in to amp has no effect on the "pop" at power down.
 
Is your system grounded? Drive a 6' copper stake into the ground and run a #12 or 10 awg from the ground post on MA 6100 to the ground rod. Or if more convenient to the nearest copper water pipe. Reversing the plugs one at a time is a great suggestion. Make sure all input connectors that are not used are terminated with shorted RCA plugs. IF you are near some big transmitter antennae you are going to have to be meticulous in your wiring practices.
 
Thanks for your assistance, everyone. Tried reversing the plugs but it did not solve the issue. Will work on grounding next...

Again, your time and attention is appreciated.
 
Do you mean crosstalk or RF? Is tuner ON when listening to phono?
 
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Hello !

Yes I think that you are in front of diaphony ! very easy to check .
If you listen a source take note witch input you are using .
If the audio signal "walking" in the MA6100 is far away from phono tracks you will not hear anything but if the audio signal (CD or tuner) is very closer to phono tracks , if your high level source is on (CD or Tuner) you will hear it if PHONO input is selected
The only way to " cancel " this is to find tracks far away from each other ! no other issue except if you switch off the unlistened source !
 
Hello Clinic-audio,

Are you saying the proximity between inputs on the input selector switch and/or the input RCA jacks on the rear will make a difference to signal leakage? I would never have thought of that.
 
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