• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

C28 Preamp

jclusk@mnsi.

jclusk@mnsi.

New Member
Can anyone shed some light on my C28 preamp. Phono 1 and 2 are heavily distorted and unlistenable. I will take the preamp to a McIntosh registered tech this spring but before that I would like to give him a heads up. Thanks in advance. . . . . Chris
 
Register to hide this ad
If only the PHONO inputs the Tech should quickly look to the PHONO preamp stages and the INPUT switch. Less likely are the PHONO 1 and PHONO 2 trim switches as all four would need to be dirty/failing for your symptom.

Have you checked your PHONO on another preamp to be sure it isn’t the cartridge or wiring? Has it worked on this preamp before?
 
The C-28 had grounding issues, when I worked at the dealer, our tech didn't service them. If they didn't meet spec, and had never had the grounding issues looked at- we sent them to Mcintosh. It's very likely that your local tech is well aware of these issues as that pretty much every C-28 had them.
 
CruzBay. The stereo cabinet is in the lowest level in a two story home. The C28 and the rest of the equipment is attached to a two foot #6 grounding wire that is connected to a ground round that has been drilled through a concrete floor. Is an external ground source what you refer to? . . . . Chris
 
You are using the phono inputs with a turntable correct? Also, the turntable does not have an internal phono preamp. Some newer turntables have a phono preamp built in and some of those have a button on the back that lets you choose to bypass that preamp - you would need to bypass the pre on the TT. Phono inputs cannot be used with line level devices like cd or streamer - they are low level inputs with an added eq and will sound terrible with any line level device.
 
There is a McIntosh service bulletin about grounding issues in the low level input circuit (phono). See "service bulletin #2".
 

Attachments

I have read Refugee's reply and may I add that perhaps a turntable with a ceramic phono cartridge is being employed.
 
SaturationPt said:
If only the PHONO inputs the Tech should quickly look to the PHONO preamp stages and the INPUT switch. Less likely are the PHONO 1 and PHONO 2 trim switches as all four would need to be dirty/failing for your symptom.

Have you checked your PHONO on another preamp to be sure it isn’t the cartridge or wiring? Has it worked on this preamp before?
Click to expand...

Refugee said:
Yes. I should have mentioned that too. Ceramic cartridges are line level devices also.
Click to expand...
 
Cartridge is a top of the line Audio Technica. It works just fine if the turntable leads are plugged into the Tape Out inputs on the C28. . . . . Chris
 
jclusk@mnsi. said:
It works just fine if the turntable leads are plugged into the Tape Out inputs on the C28. . . . . Chris
Click to expand...
Tape OUT or Tape IN? It shouldn't play at all if connected to the tape OUTput jacks.

Secondly, what's the turntable you're using? Does it have phono preamp circuitry built in?
 
jclusk@mnsi. said:
Cartridge is a top of the line Audio Technica. It works just fine if the turntable leads are plugged into the Tape Out inputs on the C28. . . . . Chris
Click to expand...
As others have postulated, sounds like your turntable has a built in preamp, especially if it works just fine plugged into the Tape In inputs. The turntable may have a button which allows you to bypass that preamp for use with the Phono inputs. If it does not, then just continue using the Tape In inputs if that doesn't bother you.
 
Last edited:
My mistake, I should have typed Tape In. Table is a Sota Sapphire that was rebuilt by Donna Bodinet's group ten years ago. It has no built in preamp. With all the replies I have received I am getting closer to the problem. Guess I will have to get the C28 rebuild kit. . . . Chris
 
If it works fine on the Tape In on the C-28 then it does indeed have a Phono Pre built in. If not it would not work well in the tape in (line level) input. Look for a switch on the back of the turntable. What TT are you using?
You do not need the C-28 rebuild kit for this issue.
 
jclusk@mnsi. said:
My mistake, I should have typed Tape In. Table is a Sota Sapphire that was rebuilt by Donna Bodinet's group ten years ago. It has no built in preamp. With all the replies I have received I am getting closer to the problem. Guess I will have to get the C28 rebuild kit. . . . Chris
Click to expand...
I think @Refugee has posted your answer above.

Also, "C28 rebuild kit", that's a good way to mess up a good C28, especially if it's a HiFiAudio/HiFiAudioRocks/CaptainFantastic kit.
 
jclusk@mnsi. said:
Table is a Sota Sapphire that was rebuilt by Donna Bodinet's group ten years ago. It has no built in preamp.
Click to expand...
Hmmm... Is the level low, when input to the Tape In? It should be very low volume and very thin on bass if there is no phono pre. I just saw that it is a Sota Sapphire (Nice Table!!) I could not find any factory iterations of this table with a phono pre installed. Could one have been added during the rebuild? Do you have another table to test the C28 Phono input with?
Anyway - let us know what happens - this one has me curious.
 
I'm puzzled as well. It should sound dreadful at the TAPE inputs if there's no built in preamp and the volume would need to be set abnormally high.

It's not a MC (moving coil) cartridge is it? If so, that type of cartridge will not work with the C28 without a special MC preamp.
 
You must log in or register to reply here.
Back
Top Bottom