MC501 Thermal Shutdown (part 2)

[Masterlu]

Originally Posted by JJinID

+1 - excitedly awaiting delivery of mine

Hang in there, pretty soon!

[JJinID]

[Yamaki]

Dan...I am contemplating the purchase of a pair of MC501's and I read this thread with high interest. The intrigue, investigation and culmination was riveting!

I very much appreciate the insight you provided regarding the MC501 operation and I was very happy to see that thermal shutdown is NOT a condition I need to worry about. I will be adding some air circulation to my rack if needed once the MC501's are in place.

Thank you again for your wonderful contributions here. They are very much appreciated.

[jdandy]

Michael.......You will love the MC501 amplifiers. They sound fabulous, have a boatload of power, and operate cool. Unless you cabinet is closed on the back and sides, I doubt you will need additional ventilation. Most of the time the MC501's cooling fins are barely warm to the touch. I am glad you found my information useful and I appreciate the kind comments.

[Charles]

Dan, I simply can't read this whole thread. it's too long. I'm sure you have switched the channels to verify that the overheating problem goes from the right channel to the left channel. If it does than the problem may not be the amps.

[jdandy]

Charles.......The issue was never the amplifiers. What I discovered and McIntosh verified was the balanced output connectors of the original MEN220 motherboard (a Lyndorf motherboard) were not actually balanced outputs. In fact they were unbalanced. In other words the balanced output connectors only had a positive (+) on pin 2 and both pin 1 and pin 3 were wired to ground. There was no inverted negative signal (-) on any pins. This caused the MC501 to see an unbalanced input and worked one half of the quad balanced amplifier much harder than the other half of the amplifier's balanced circuits.

The issue was not a defect in my particular MEN220. It was a design defect in the Lyngdorf motherboard that McIntosh licensed to use and did not identify before or during production. Once McIntosh had my MEN220 in for engineering to examine this issue was verified. McIntosh did the right thing by redesigning the balanced output stage to be a true balanced output (pin 1 = ground, pin 2 = positive, pin 3 = negative), upgraded my MEN220 and all other MEN220 units prior to serial number ZN1187. The initial upgrades were done with a daughter board added to the original motherboard. Then a new motherboard was designed to incorporate the upgrade and once it became available was retrofitted into MEN220's for those not already upgraded with the daughterboard upgrade.

So to make it perfectly clear, the MC501 amplifiers never had an issue. Once the MEN220 balance output issue was corrected my MEN220 and MC501's coexisted perfectly without any of the overheating issues present before the MEN220 balanced output issue was correctly identified.

[tdelahanty]

I seem to remember this issue coming up in the past. I vaguely remember there is an issue with the MEN220 not being able to run in true balanced mode ( a design issue with the MEN220). If one side of the 501 is hotter than the other I would suspect the signal drive to each Half (pos & neg) is not equal. Try RCA cables (single ended) and measure temps.

Dan take into account my memory resembles swiss cheese.

[Charles]

Originally Posted by jdandy

Charles.......The issue was never the amplifiers. What I discovered and McIntosh verified was the balanced output connectors of the original MEN220 motherboard (a Lyndorf motherboard) were not actually balanced outputs. In fact they were unbalanced. In other words the balanced output connectors only had a positive (+) on pin 2 and both pin 1 and pin 3 were wired to ground. There was no inverted negative signal (-) on any pins. This caused the MC501 to see an unbalanced input and worked one half of the quad balanced amplifier much harder than the other half of the amplifier's balanced circuits.

The issue was not a defect in my particular MEN220. It was a design defect in the Lyngdorf motherboard that McIntosh licensed to use and did not identify before or during production. Once McIntosh had my MEN220 in for engineering to examine this issue was verified. McIntosh did the right thing by redesigning the balanced output stage to be a true balanced output (pin 1 = ground, pin 2 = positive, pin 3 = negative), upgraded my MEN220 and all other MEN220 units prior to serial number ZN1187. The initial upgrades were done with a daughter board added to the original motherboard. Then a new motherboard was designed to incorporate the upgrade and once it became available was retrofitted into MEN220's for those not already upgraded with the daughterboard upgrade.

So to make it perfectly clear, the MC501 amplifiers never had an issue. Once the MEN220 balance output issue was corrected my MEN220 and MC501's coexisted perfectly without any of the overheating issues present before the MEN220 balanced output issue was correctly identified.

Excellent explanation. I suspected it had something to do with the MEN220. Folks owe you a debt of thanks for unearthing this complicated problem. I have always admired the 501's. I read their review in Stereophile.

[Vintage Pete]

Originally Posted by jdandy

Michael.......You will love the MC501 amplifiers. They sound fabulous, have a boatload of power, and operate cool. Unless you cabinet is closed on the back and sides, I doubt you will need additional ventilation. Most of the time the MC501's cooling fins are barely warm to the touch. I am glad you found my information useful and I appreciate the kind comments.

Michael....I'll just chime in here and reiterate what Dan has said with regard to the MC501 amplifiers. I own three of them, all on duty in my main system. I've owned them 6 years now and I can tell you they are fabulous amplifiers, nary a hiccup out of them in 6 years. They sound fabulous, with loads of power, very robust yet refined sound with a very sweet and liquid midrange quality. I am certain you will love them and I would recommend them without hesitation. And oh yes, they are eye candy as well. They are special.