McIntosh MC452 - Power Guard Lights- Help Please

[Dynophile]

Guys,

I need some help please.

A couple days ago I turned on my MC452 in the morning and heard a strange short crackling click sound. I then played vinyl with volume set at 50 and saw the power guards flash intermittently on both sides. I've been playing a lot the previous days due to the stay at home corona virus lockdown.

I immediately turned it off and ordered new tubes for my C2300 preamp since it's been 4.5 years and they are due to be replaced. I installed the new tubes, but a couple of them did not fit tight as the others. I turned it on again and heard the same short crackling sound.

There is a constant hissing sound from my left speaker on MM phono, MC phono, and CD. Also, when I push mono button, it does not sum the speakers.

I tried playing vinyl, but there is no sound from both speakers. Just, faint music whisper sound from the McIntosh unit.

I tried playing CD, but there is sound from right speaker only. I played at low volume 30 so power guards were not triggered.

I'm not sure if the problem is coming from my amp, preamp, or speakers. Or from the tubes.

I would be grateful for any kind of help and advice. Thanks.

[Dynophile]

I just realized I installed RCA cables on MC phono, and not MM phono. I switched cables to MM phono.

Now there is music coming from right speaker only for both Vinyl and CD playback.

Hissing on left speaker still present.

[-E-]

Swap the cables (L to R and R to L). Isolate if it is the amp or the pre causing the noise.


Once you isolate which unit is the cause, disconnect everything while inspecting for possible shorts. Reconnect one at a time to further isolate if it was a simple contact short or if something is really wrong.


If something is borked, pray it's the pre - shipping or hauling the 452 to a dealer requires some muscle.

[Dynophile]

Thanks. I'm not sure what you mean by swap the cables (L to R and R to L).
I swapped the speaker cables (L to R and R to L). At volume 46 the right power guard lights up. After swapping, the same right power guard lights up. I'm assuming the problem is not in my speaker as the power guard light would have moved to the other side to follow a defective speaker. Also, when I play CD, the power guard lights up on the left side when at volume 41.

I removed, reinstalled and matched the tubes again. Now there is no hissing sound on both MM phono and CD. There is a slight hissing sound on MC phono, but I don't use that one. I also unplugged and replugged everything including stereo mini cables and made sure balanced XLR cables are snapped securely in place.

But as soon as I turn on the system I hear a horrible click sound and can tell right away the problem is not fixed. I heard a similar horrible click sound and gas leak sound around 4.5 years ago. I replaced those tubes on my preamp and fixed the problem the last time.
I think the problem may be in my preamp, and maybe some of the new tubes don't work properly.

But I don't know how to isolate if it's the amp or preamp that has the problem.

[damacman]

Plug a pair of headphones into the C2300 with the MC452 off. Are the problems present via the 'phones? Report back.

[miner]

Switch the cables from preamp out to amp in. If the noise changes to the other channel you will know the preamp is the culprit. If noise remains in same channel amp is the issue.

[jayvis1]

An easy way to check would be to connect your OPPO's FR and FL outputs directly to the inputs of your MC452 and play a CD using the OPPO as a preamp. If you still get any of the issues you mentioned, the problem is your amp. If not, it's most likely your C2300 preamp.

[Masterlu]

jayvis1... Welcome to AA!

[Dynophile]

Thanks everyone. What a great McIntosh community we have here. I called Audio Classics and that is exactly what we did. We connected the MC452 directly to the MCD500 variable outs and played a CD. The power guards went on around volume 54 and the vu meters were bouncing around the middle, nowhere near the 450 watt output power.

The problem is in the amp. But I'll go ahead and send both in for servicing. Now I just need to find a service that will pack and palletize this beast of an amp for freight shipping.

[Masterlu]

Originally Posted by Dynophile

Thanks everyone. What a great McIntosh community we have here. I called Audio Classics and that is exactly what we did. We connected the MC452 directly to the MCD500 variable outs and played a CD. The power guards went on around volume 54 and the vu meters were bouncing around the middle, nowhere near the 450 watt output power.

The problem is in the amp. But I'll go ahead and send both in for servicing. Now I just need to find a service that will pack and palletize this beast of an amp for freight shipping.

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