Static In My Tubed Preamp?

Discussion in 'Audio Hardware' started by Barnabas Collins, Jan 22, 2016.

  1. Barnabas Collins

    Barnabas Collins Forum Resident Thread Starter

    Location:
    NH
    I've had a really annoying problem with my McIntosh C2300 preamp recently, but only in the phono stage of the preamp. Very often, when I finish playing an LP and lift the record off the turntable, I'll hear a really loud, insistent thumping sound coming through my speakers and visibly shaking the speaker cones. It's really, really loud and I've gotten in the habit of lowering my volume before taking the stylus off the record for fear of damaging my speakers. The only way the noise stops is if I turn the preamp off. It only happens in the phono stage. For what it's worth, I'm running vintage Mullard tubes. Any idea what this might be? Is it static? And is there a way to prevent this from happening?

    Thanks for any suggestions.
     
  2. Coricama

    Coricama Forum Resident

    Location:
    Marietta, GA
    Ever get an answer to this problem?
     
  3. levimax

    levimax Member

    Location:
    California
    Sounds like low frequency oscillation in either the pre-amp or amp. This will not happen in a properly function system. You need to get the pre-amp and amp checked out and fixed (should not be hard for a qualified tech).
     
  4. KT88

    KT88 Forum Resident

    Static induced DC generation perhaps? It could be a LF oscillation also caused by the static discharge. A subsonic filter might help, but the likely culprit is failing coupling caps in the phono stage or line stage of the preamp. If your amplifier is DC coupled, it could destroy your woofers.
    -Bill
     
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  5. Barnabas Collins

    Barnabas Collins Forum Resident Thread Starter

    Location:
    NH
    Wow, this is a blast from the past!

    Yes, I had the issue taken care of by McIntosh. Apparently, there was a known issue with certain serial numbers of the C2300 where some kind of static discharge was emanating from the MC stage. I got it taken care of over a year ago and it's been fine ever since. Basically, exactly what KT88 notes above. Did you bump this thread because you're having a similar issue?
     
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  6. Coricama

    Coricama Forum Resident

    Location:
    Marietta, GA
    Well I just got it yesterday and I'm having problems with the MC phono stage. McIntosh put out a service bulletin about it in 2008. Involves replacing 2 capacitors. Im going to check my serial numbers when i get home. The guy i bought it from never used the MC input, only had CD player and HT hooked up. I got a feeling I'll need to have the thing shipped off for repairs. The noise stops completely when I place my hand over the glass above the MC tubes. Where did you send yours, McIntosh?
     
  7. Barnabas Collins

    Barnabas Collins Forum Resident Thread Starter

    Location:
    NH
    I brought my unit to the dealer and he sent it to McIntosh. They should be able to fix it for free if you have it under warranty. I was only charged the $20 to ship via FedEx. I never tried placing my hand over the glass of the MC tubes. I just shut off the unit and turned it back on again. But during the static filled winter months, I was doing it a lot. I can forward you a thread from another forum detailing this same issue when I get home if you're interested.
     
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  8. Coricama

    Coricama Forum Resident

    Location:
    Marietta, GA
    This service bulletin describes my problem perfectly. I've disconnected everything, including the outs to the amp and the meters, especially the right meter, are still pumping up and down. It's used and over 3 years old so no warranty. I have a reputable audio guy here in town, I guess I'll drop it off tomorrow. I wish I could post the service bulletin so you could see it. Although my unit is acting differently than what yours was, it sounds like it was the two capacitors they probably replaced in your unit.
     
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  9. Barnabas Collins

    Barnabas Collins Forum Resident Thread Starter

    Location:
    NH
    Good luck with your repairs. I just checked the McIntosh website to see if they have a service center near you, but it looks like the closest one is 150 miles away. I had the same problem so I just went through my dealer. It's a pretty easy fix if they just have to replace a couple of capacitors.
     
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  10. Coricama

    Coricama Forum Resident

    Location:
    Marietta, GA
    Does it matter if it's an official McIntosh service center if it's out of warranty? I have a trustworthy guy I've used before, he refurbishes Mc stuff for resale and manufactures his own tube gear. I'll just copy the meat of the service bulletin and paste it.

    Model……...C2300
    Date….Apr. 9, 2008
    CN…………. 20514
    File…. C2300.SB01

    Observed Performance When listening to an MC Phono, a static discharge may trigger a repetitive
    popping noise, occurring about once a second.
    Serial Numbers Affected YA1001 through YA9999
    Modify Units X In for Service
    X w/reported symptoms
    What To Do Replace capacitors in the MC Phono preamplifier section.
    Note: The C2300 is RoHS compliant. Lead-free soldering is required.
    Parts Required Part No. Description Qty.
    06445500 Cap MPF 0.0033uF 5% 63V 2
    Procedure 1. Disconnect all cables from the C2300.
    2. Remove top and bottom covers.
    3. Remove tube tray assembly.
    4. Locate C54 and C55, Monolythic Ceramic Capacitor, 0.001uF on the Main
    PCB, near the MC Phono input jacks.
    5. Remove C54 and C55 and replace with 06445500, 0.0033uF capacitors.
    6. Replace tube tray assembly and top and bottom covers.
    7. Test the C2300 for proper performance.
     
  11. Barnabas Collins

    Barnabas Collins Forum Resident Thread Starter

    Location:
    NH
    I'm sure you'll be fine with your local guy if he's familiar with McIntosh and tube electronics. The service bulletin you posted describes my problem precisely. My unit number is YA1081. The good news for you is that you shouldn't have to wait too long get your C2300 serviced, unless he's really backlogged. I had to wait a month from the time I dropped my unit off to the time I picked it up after it had been shipped to and fro Binghamton, NY.
     
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  12. Coricama

    Coricama Forum Resident

    Location:
    Marietta, GA
    I'm listening to SACDs on it right now, man it sounds good. I hate to part with it now that I know what I've been missing. I played one album yesterday and the phono stage sounds great while music is playing! I was going to play around with swapping the tubes around tonight, but that description nails the problem I'm hearing and my serial numbers fall in that range. I can't fault the seller either, he had bypassed that input completely in the setup.
     
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  13. Barnabas Collins

    Barnabas Collins Forum Resident Thread Starter

    Location:
    NH
    I hear you. But you'll be glad you got it serviced. Even if you have to pay some out of pocket, you'll have piece of mind. And a working C2300. :) Let us know when you get it back home!
     
  14. Coricama

    Coricama Forum Resident

    Location:
    Marietta, GA
    Will do!
     

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