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Help! New problems with C22, MC225 setup

A

Acheron

New Member

Hi all,

I’m in the process of building a new system with an original C22 (rebuilt) and MC225 (also rebuilt). I have yet to get new speakers and turntable—currently running the amp and preamp with my old bowers and wilkins speakers and fluance turntable.

Prior to today everything was working beautifully—absolutely amazing sound for about a month after getting it all together. But today something has gone very wrong.

Audio is SEVERELY distorted and muddy. The volume will also not go past 30-40%

Any ideas how to troubleshoot this? Is it a bad tube? Something else? Any advice is appreciated!

I’ve attached a video of the severely distorted audio I’m getting.
 
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Do you have other sources, preamps, power amps or speakers around for substitute testing? If so, replace each of them one at a time to narrow down the issue to one of the components.

But first check to make sure you don't have a shorted speaker wire.

Is this problem in both channels? If so, start by switch the speakers to see if the problem states with the speaker or not. And so on.
 
If you can narrow it down to either the C22 or MC225, the next thing to check would be the tubes. Most obvious thing is to see if the tubes are all still glowing.
 

It’s both channels. And my tubes are all glowing.

I attempted to narrow it down... all I have is an old Onkyo Receiver TX-8255 to test with so I was able to take the C22 out of the equation and test everything else. Plugged in the MC225 but honestly tough to tell—the audio was definitely improved but still not great and zero volume control. Volume at maybe 20%.

I don’t know if this is because the MC225 is what has the issue or because the MC225 and the Onkyo receiver aren’t totally compatible.

I also tested my speakers and turntable with the Onkyo only (225 removed from equation). Everything worked as it should.

So I’m still not totally sure if the C22 or the MC225 but has to be one of them... so far sounds like the C22 is the culprit but curious to hear your thoughts.

I’ve posted the audio of the MC225+Onkyo 8255+B&W speakers+Fluance table. As you can hear, it’s improved significantly but still not great.
 
If it is on both channels, and for sure it's the MC225, then it is common component to both channel within the amp.
2 things come to mind: the power supply or the first 12AX7 tube on the left.
- First try to swap the 12AX7 with a spare to see if the problem remains.
 
Thanks for the feedback everyone.

So just to be clear—there’s no chance that the C22 could be the culprit? It’s definitely the MC225?
 
Yes it could.
If you have another amplifier, swap it and you'll rule the amp out or not.
 
Brice said:
Yes it could.
If you have another amplifier, swap it and you'll rule the amp out or not.
Click to expand...

And to do that, hook up the speakers to the Onkyo receiver, take the output of the C22 and send that into the Aux (or any line level) input of the receiver, and see if the sound is okay.

I’d leave the Onkyo volume at low-med at first, and use the C22 volume knob as normal.
 
cnolanh said:
And to do that, hook up the speakers to the Onkyo receiver, take the output of the C22 and send that into the Aux (or any line level) input of the receiver, and see if the sound is okay.

I’d leave the Onkyo volume at low-med at first, and use the C22 volume knob as normal.
Click to expand...


Thanks for this idea—did not know I could do that.

I checked it as you suggested with turntable to C22 to Onkyo to speakers. The audio matched exactly to my first post—extremely distorted and muddy.

So it appears the C22 is actually the culprit. Any ideas on what my next steps should be? Is there a reputable place to have it authentically rebuilt? It seems as though the go to guys for this kind of work aren’t doing it anymore.
 
Acheron said:
Thanks for this idea—did not know I could do that.

I checked it as you suggested with turntable to C22 to Onkyo to speakers. The audio matched exactly to my first post—extremely distorted and muddy.

So it appears the C22 is actually the culprit. Any ideas on what my next steps should be? Is there a reputable place to have it authentically rebuilt? It seems as though the go to guys for this kind of work aren’t doing it anymore.
Click to expand...

Probably the best these days is Audio Classics ,although certainly there are other local folks around the country that might be able to help. But AC specializes in McIntosh restoration and so they most likely are your best bet.

https://www.audioclassics.com/
 
It does sound like you've narrowed it down to the preamp. To make certain, I might still want to test the amp by itself with a variable-volume source like a phone or tablet or a CD player with a variable output. If you use something like a phone, turn its volume all the way down, use a 3.5mm-to-stereo-RCA cable to connect the phone to the amplifier, then play some audio on the phone and CAREFULLY turn up the volume until you hear something from the speakers. If that sound is clean, you've ruled out the MC225 as the problem.
 
Also, is the distorted/muddy sound from your C22 the same on all its inputs or just on the Phono input? You might check the others also, in case something has gone wrong with the phono circuits only.
 
Agree with above suggestions, first try another line level source through your C22 to eliminate the phono section.
Then, take a line level source such as a CD player, tuner, tape deck, etc, and plug directly into your power amp.
This should conclusively point at the culprit.
 
Don't you just love owning older stuff with tubes. Yes I admit I have a 50 year old MC 2505 thats never been touched and a 50 year old MPI-4 that needed repair 10 years ago when the tube failed. My 40+ year old MR-80 needed a tune up 12 years ago as did my C-34 5 years ago. The MVP models need a little maintenance now and then. Every thing else including the 50 year old turntable and linear arm just keep plugging along. Of course you need a new cartridge every now and then. The only issue I have is the HT processors become obsolete every time you turn around. Then, too Mac keeps changing the colors of their meters from a nice warm medium green of the 2505 to the stark blu color of the latest MC 207. With the 0lder 206 and 207 being some where in the middle So 4 different amps have 4 different colored meters.
 
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