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McIntosh MC60 with a noise, I need a little help

72.75.156.3
Posted on October 31, 2009 at 21:22:03
moonrize
Audiophile

Posts: 91
Location: At the Jersey Shore Exit 63
Joined: January 9, 2003
Contributor
  Since: November 5, 2007
 Both completely rebuilt top to bottom and play very well. Except that at idle with speakers connected and the amp turned up at least half way at the gain, (47k ohm termination at input) I get a wooshing sound from the speakers and a very faint hint of a buzz that goes up an down with the gain pot on the amp. Two amps and both do it. Again they play great yet I can hear that they are on because of the sound emitted at the speakers with my ears close to them. If I go to full power it gets a louder and the buzz gets louder. I can increase the noise level by touching the bakelite part of the input socket. Another words I can make it hum a little louder by touching the input octal. They seem to have super sesitive input circuits. If I run them with the gain at the 9 to 10 oclock position they are real quiet and when I turn up the preamp volume they seem to get to full output power and sound great. Should the MC60's be 100 percent quiet at full power?? Iv'e checked and rechecked all solder joints and grounds. It seems they are OK with the gains set low to the just below audible idle sounds at the speakers. I am using Aristocrat III's with all EV componets. Thank you!

RE: McIntosh MC60 with a noise, I need a little help, posted on November 1, 2009 at 05:17:39
Michael Samra
Dealer

Posts: 13134
Location: saginaw michigan
Joined: January 30, 2005
Contributor
  Since: June 24, 2005
 Moonrize
We have a couple things at work here.One is,you will notice that the first 12ax7 stage has a different socket and you want to make sure it is grounded as thats a 100 mu first stage.
Next,did you change the volume pots and associated resistors to that first tube because it sounds like your volume pots may not be properly grounded or had gone way up in value and its floating causing this type of problem.
See how those things go and let us know. Also,if you havent changed the 12au7 over to a 6cg7,do so. Its the best thing you can do to any mac amp and its just the filament wires you have to change..The improvement is exponential and I'm not exaggerating.
If the power supply waveform isn't pretty,neither is the sound in most cases.
RE: McIntosh MC60 with a noise, I need a little help, posted on November 1, 2009 at 19:02:16
moonrize
Audiophile

Posts: 91
Location: At the Jersey Shore Exit 63
Joined: January 9, 2003
Contributor
  Since: November 5, 2007
 Hi Mike and thank you for responding. I did check all my grounds, the pots are original and they are tight and read zero ohms to ground. I did not change the resistors associated with the inputs on either amp because they were all reading within tolerance. There seems to be very high microphonics in the input area. If I touch the c7 (now an orange drop, the buzz gets louder). C7 is only for the input octal, should I condider getting rid of it? The amps are for a customer and the request was no mods to the original design. A C20 will be used for the preamp. Also I really cannot see a difference between the first 9 pin 12AX7 socket and the other 9 pin sockets. When the amps play, they sound great, it is the in between tracks that the slight buzz becomes apparent if I have the gain at 11 o'clock or higher. I have a MC75 and it does have a different first 12AX7 socket. I have a MC30 and it is the same as the MC60's.

RE: McIntosh MC60 with a noise, I need a little help, posted on November 1, 2009 at 20:56:29
Michael Samra
Dealer

Posts: 13134
Location: saginaw michigan
Joined: January 30, 2005
Contributor
  Since: June 24, 2005
 Shoot me an email with a phone number at merccougar89@yahoo.com Its free for me to call you but I can also give you my number if you want to call but call only if it doesn't cost you because its free for me anytime..I teach tomorrow so I will up til midnight EST but I can't email you thru the asylum because you don't accept mail it says..I will gladly help you out and I love doing mac amps and I will give you killer ways to make mc30s and mc60s and mc240s sing like a dream.I love talking about old vintage gear.
If the power supply waveform isn't pretty,neither is the sound in most cases.

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