ARC PH7


Hello everyone. Just want to run this buy you guys to see what comes out of it. I recently purchased gently used Audio Research PH7 phono preamp. The Preamp had 3 hours on the tubes according to the display. I have had it for a week now and till now it has worked flawlessly. Typically I will mute the preamp to change records, etc. Today I muted changed a record and when I unmated the right channel did not play. turned the unit off and waited for about 10 mins and powered it back up, and the right channel came back. muted/unmuted right channel goes out. According to the seller the PH7 lay dormat for a few years prior to selling it. I am wondering if it could be one of the tubes could simply be failing, but it seems more like a curcuit problem than a tube problem. Any thoughts or experience with this particular issue with the ARC PH7?
barnettk
Sounds like a muting relay sticking.

Noromance, Thanks It also happens if I put it in Mono as well. Both these buttons are connected to the same circuit board. I let the unit cool, reseated the tubes and it worked as expected until it got to operating temp, then the problem returned. 
Take the battery's out your remote.


Sfall, happens when I press the button on the front panel as well. Thanks
However that was after I pressed the mute on the remote to mute it. I pressed the mute button on the front panel to see if that would reverse it. I will try to mute without the remote to see if it makes a difference. I am willing to try anything at this point. 
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If R/L channels are mirror image, swap the tubes to see if it's a tube problem (problem shows up in left channel?).
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@dweller I have deduced with further testing that the problem is temp related. If I remove the cover and allow more ventilation the problem does not occur. Once the cover is put back on 15 mins later its back so I am thinking a resistor that is sensitive to heat or maybe a cap. Should  be an easy fix as the problem is easily reproduced. I found a guy here in Atlanta that specializes in tube gear and I am going to drop it off today. I will report back on what the problem turns out to be.. thanks for all the replies. 
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@barnettk
Instead of using the mute when silencing the output,you should just switch to another source on your preamp. That’s what I do !
yogiboy
Instead of using the mute when silencing the output,you should just switch to another source on your preamp
The mute circuit in ARC preamplifiers is also part of the component's protection system. If you don't have a properly functioning mute circuit, you're losing a margin of safety.

@yogiboy 
Hi Yogiboy. Yea with my other Phono stage that does not have a mute button I just simply roll the volume down. The mute button is very nice to have especially since it has a remote as well. Its not a show stopper however if its a bad circuit I am concerned that it could also cause other things to fail as well. Especially if its a bad Cap, so just to do my diligence I would like to get it resolved, but I appreciate the idea. Thanks



@cleeds 

The mute button does work. it actually works a little to good lol.. This problem happens when I "unmute" but I get where  your coming from. If the mute feature has any time of problem its not a good thing as the unit stays in mute during warmup to not allow you to use it till the tubes have gone past a certain power up.

You could try some freeze spray on suspect components. Not the tubes!!


@noromance 

I dropped it off at my local guys shop yesterday and we discussed this. It is one of the approaches he is going to take. Hopefully by cooling down whatever component is causing the problem will make for a faster turnaround. Otherwise he will have to trace it down with a meter which will take a little longer. We will see. One of he problems is that if I have the lid off it does not get hot enough to cause it to fail. The good thing is that once it's in the failed state it stays that way until you recycle power. I have a feeling that he will have to trace the schematic and determine where the culprit is. 
Hi guys well we found the problem with the PH7. The mute relay was bad. The tech found the problem in about an hour including the time it took to fail. Right under $200 to fix the problem. Hopefully we have had our glitch for this mission. 
Thanks for all the help. Back to the music. 
Ahhhhhh, all better...