SOLVED: loud bass frequencies cause clicking sound

input level should be max 150mV going into the pre-amp line in (not phono, that should be 2.5mV max). Lower the CD player output, they are notorious for outputing 2V or more at 100 %.

You will need to find the numbers on the transistors, the service manual only lists McIntosh part numbers, not the ID. If your tester numbers are accurate you have at least three bad ones.
 
HP - Where did you see those 3 are bad and where do I find correct subs? The numbers I listed are from the C24 service manual.
 

Attachments

  • 13.08.2025_21.49.35_REC.png
    13.08.2025_21.49.35_REC.png
    21.4 KB · Views: 4
Those are McIntosh service department part numbers, not the actual transistor ID number (would be 2SA.... most likely since they are all NPN). McIntosh bin numbers don't tell me the transistor manufacturer's number.

A transistor that tests as a diode or resistor is shorted or open (or otherwise dead), and you have two with VERY low base current and/or Hfe (gain). Two transistors of the same type should have very similar numbers on your tester, usually the only thing that varies much is the actual gain for each one and the current, and those should be close.

The transistors will have numbers on them, starting with an "A" most likely, but could be anything. Given that these are late 60's transistors, they may be metal cans with silk screened numbers.
 
HPM - The 132-501's, 132-503's and 132-504's are black with red dots and covered with paint such that I cannot see the full numbers. I'll get the numbers from the silver pan-shaped transistors in a sec...

EDIT:
132-026 and 132-502 numbers: F017-747
All the others are the black, paint-covered ones and from what I can piece together from the few numbers exposed on some of them, their numbers are F01-740 and F01-739 and one has numbers that end in 011.
 
Last edited:
Someone knows, somewhere! Very hard to suggest a replacement when we don't know what was in there to start with.
 
HP - See my EDIT in the above post. I added numbers I can make out. I guess I'll call McIntosh and see what help they can be.
 
grind and HPM - Tested with C24... You guys were right !! I turned down the output volume on the CD player and no more distortion !! You guys are the best ! THANK YOU SO MUCH !! I was really vexed with this issue. No wonder I couldn't find any bad components. THANK YOU EVERYONE for replying.
 
Last edited:
I’d look further if this was my setup. It’s either your CDP output is uneven between channels or preamp has uneven gain. Swap CDP cables and see if problem moves to opposite speaker
 
grind - I believe I've said in earlier posts that I swapped L&R amp input cables and the distortion did indeed move channels. But I also noticed when I cranked the preamp volume to louder than I would ever listen normally, that I heard the distortion in both channels, one channel more significantly than the other. At this point I'm relieved that I can keep the C24 in my system because its high end reproduction is significantly better than with my Little Dot preamp.

EDIT: I will look into the "bad transistors" list (if I can find it for my C24).
 
Last edited:
thornev said:
grind - I believe I've said in earlier posts that I swapped L&R amp input cables and the distortion did indeed move channels.
Click to expand...
I understand that both channels give you this click when overdriven, but swapping CDP output cables will tell you if this unevenness (one channel does it at lower gain than another) is coming from the CDP, if it follows the cable swap
 
I suspect replacing the transistors would be a good idea -- after all, they are 55 or more years old and most of those old transistors are noisier that modern ones. From what I've found, they are very similar to the usual suspects --- KSA992, KSA2690, etc.

However, if it works for you as is you could leave it alone unless it starts making more noise. Replacing all the carbon composition resistors won't hurt either, metal film or metal oxide resistors are much quieter. If you have a lot of background hiss, it's probably the resistors.
 
Oh damn, the substitutions are right on the schematic !

Q101 > 2N720 (T018 case)
Q102 > 2N657 (TO-39 case)
Q103 > 2N3390 (TO-92 case)
 
Hmm, long, long obsolete, would have to find modern equivalents. I haven't seen a metal case transistor for a long time!
 
You must log in or register to reply here.
Back
Top Bottom