C28 phono output question

G

geddy402

Active Member
Recently hooked up my turntable to my C28, which has been sitting idle for a few months. I plugged into phono 1 input and noticed the left channel was quite a bit weaker than the right. Switched to mono and things evened out. Figured it had to be the preamp.

Plugged the turntable into phono 2 and the signal seemed even weaker. Then I looked over and noticed that it was still set to phono 1 but a weak signal was coming through. Turned the input selector to phono 2 and both channels were coming through loud and clear. Switched to the other inputs and there was phono signal coming through all except Aux and Tape.

So the question I have is what can be causing this? I know, the answer is a lot of things can be causing this and you won't know unless you open it up and test it, but was wondering if anyone had a hunch on what it could be.

After some quick research it could be the selector pot being dirty since its been sitting for a while, but didn't aggressively turn it to see if that fixed it.

Thanks for the help!
 
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Could be the PH1 upper control pot(s) need cleaning since L/R level controls are provided for each PH1 & PH2 inputs. Selector may also need to be cleaned.

Frankly, if I owned a C28, I'd seriously consider having the upper controls bypassed altogether since they are known to become noisy/intermittent over time as they are so seldom used.
 
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What @62caddy said (can I still say ditto in 2021?).

The controls can be cleaned, they’ll get dirty again, so original vs less problems.

Another problem that the C28 has is the drain/ground wires’ crimps on the shielded interconnect cable inside the unit. Do a search for C28 (or C-28 or C 28 depending on how it was posted) and look at the sticky for McIntosh tips & tricks and you should find reference to as well as the repair required. It’s pretty much 100% and when not if it will need this service. It can introduce hum as well as channel cross-talk problems, noise, and your phono inputs are the most sensitive.

It might not be THE culprit here but it might be A culprit.

The C28 is a very nice preamp when in good working condition, getting and keeping it there is its downfall (it is now old enough to get a senior discount at restaurants so give it some love).
 
geddy402 said:
Thanks! Just to make sure, the pots are the ones on top and switches are on the face, right?
Click to expand...

The volume and balance controls are also potentiometers. Are the bass and treble controls on the C28 step switched? Maybe someone can answer the best product to use. If in doubt use F5.
 
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Bass, Treble, Volume, Balance, and I believe Loudness (Comp). Anything on there that doesn't "click" and select a function is a potentiometer (variable resistor).
 
That and volume control issues is why when Davie Obrien told me about the new C-29 coming down the pipe line at A MAC amp clinic I ordered one immediately and kept it for thirty years with no issues of any kind other than exercising the controls occasionally if they had set still to long. We would travel a lot after I retired. I updated to a C-34 for next. So now I only have to worry about the loudness and balance control needing exercising. Having gold rear connectors helps, too. No intermittent RCA connections any more. I will say a functioning C-28 has a sweet sound that modern pre-amps don't have. Especially the phono section. It went well with my two 275's and later calmed down the 2100's a bit.
 
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Swap the cables from the TT to preamp and see if the left channel is still the weaker or does it move to the right channel?
 
Again caddy you are correct. I just checked mine and the (4) front panel Bass and Treble controls are stepped/multi-position switches so regular DeOxIt D5 is fine.

I haven't used mine in years, and never was a bass & treble turner so I didn't remember.
 
Thanks for the suggestions. I’ll pick up some of the fader lube, sounds like that’s a safe solution for both the upper pots and input selector.

So, do you just squirt a little bit right on the front of the shaft after you take off the knob?
 
I believe there is a tutorial here on AK somewhere, but no, you need to get to the back of the potentiometer.
 
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