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Amp problem

Discussion in 'Amplifiers & Receivers' started by trash, Sep 22, 2010.

  1. trash

    trash Member

    Hi guy's

    I have been a member at S&V for 8 yrs but only 6 posts in that time. I really hate to type.

    I have a problem with my 2 channel system and hope you can help.
    My system consists of a SS amp, tube pre-amp, and tube source. I always use the rule of thumb amp last on first off. When I power up the pre-amp is muted and zero volume. Sometimes when I press mute off there is a loud thump from one woofer. Like a needle droping on a record, mind you there in no volume at this point. All connections have been checked and are good. Each component has been checked seperatly and works fine, but together is when the problem occurs.

    Any thoughts?
     
  2. Zing

    Zing Retired Admin Famous

    Has this always happened or is this something that just recently started to happen?
     
  3. PaulyT

    PaulyT Behind the Curtain Staff Member Administrator Moderator Superstar

    Hey trash! Welcome! And try to post a little more often... ;)

    My guess is that there's a slight difference in "resting" voltage from the preamp outputs when the mute is on vs. off. May not be much, but when you un-mute, there's an instant step up/down in voltage that your amp and speakers see as something like the onset of a square wave, which is the thump you're hearing.

    The other possibility (just shooting in the dark here) is that your preamp has to adjust between no load (muted) and load (un-muted) but zero volume, and electronically this takes a brief moment and causes a transient voltage swing that translates as a thump after amplification.

    Whatever the cause, probably not much you can do about it without altering the electronics... Is it just in a single channel? You could also un-mute the preamp before turning on the main amp.
     
  4. Rope

    Rope Well-Known Member Famous

    I do too, but that doesn't stop me from blabber typing my ass off, and the great thing, etiquette, spelling, grammar, and coherency don't count, so, post your ass off. We'd all love to hear what our members have to say.

    Now, on the the THUMP problem (told ya I was a blabber ass). Is there a subwoofer involved, as in 2.1 or just the speaker woofers? Make the preamp the last thing you power up in the supply chain, and if there's a subwoofer involved, make certain it's set to the auto on/off. That way it will have to receive a signal before powering up.

    Rope
     
  5. trash

    trash Member

    Thanks for the replys.

    The problem started after the addition of the tube pre-amp.

    Its a 2.0 system. Subs are for HT
     
  6. soundhound

    soundhound Well-Known Member

    As PaulyT mentioned, it is probably a small DC voltage present on the output of your tube preamp which, when the muting relays open, discharges into the input of your power amplifier (there should be a loading resistor on the output of the tube preamp to do this discharging, but it might not be present, or of a value which does not pull down the voltage completely). Short of analyzing the circuit of both the power amp and tube preamp, there is really nothing you can do. What you can do however is to not use the muting function on your preamp. You would continue to turn your power amp on last and off first.
     
  7. trash

    trash Member

    Thanks Soundhound

    I had suspected it may be DC leakage to the amp from the pre-amp.

    Ihave been warming the pre-amp for 10 min minimum before turning on the amp and haven't had the problem since starting that way
     
  8. DIYer

    DIYer Well-Known Member Famous

    It takes that long? Tube gears do react slowly to turning on and off than transistor gears but I was thinking couple minutes would suffice. Does the problem persist if you let it warm up less than 10 minutes?
     
  9. trash

    trash Member

    I'm sure it wouldn't take 10 mins, however I let the system warm up for about an hour per the amp mfg recommendation.
     
  10. soundhound

    soundhound Well-Known Member

    Is the power amp running in class A? Unless the amp has really, really huge heatsinks which must be up to temperature, there is really no need to let an amplifier warm up that long. With traditional class A/B amps, the heatsinks are up to operating temperature, and the bias has settled to its normal value within maybe 15 minutes max. Beyond that, its just wasting electricity.
     
  11. trash

    trash Member

    The amp is a Pass 250 and only the first 15 watts are class A.
    The longer everything warms the better it sounds.
     
  12. Zing

    Zing Retired Admin Famous

    ONLY? I'd say that's pretty good. :handgestures-thumbup:
     
  13. Rope

    Rope Well-Known Member Famous

    With an efficient speaker such as a horn, 15 watts class A would make your sack shrivel and your ears bleed. :eek:

    Rope
     
  14. soundhound

    soundhound Well-Known Member

    The 7 watts I have in my SET amp which drives my high frequency horn above 500Hz will produce about 113 dB per side. That's just the SPL above 500Hz. I never listen anywhere near that level though.

    BTW, there are two varieties of class A; single ended and push-pull. Of these two, single ended will produce the best listening quality, whether tube or solid state. Push-pull (also known as differential) tends to cancel out the even order harmonic distortion, leaving only the more obnoxious odd order harmonics with nothing to cover them up.

    Class A in a solid state amplifier is costly to do because the amplifier is dissipating half its rated power continuously, even with no signal. This requires a lot of heat sinking.
     
  15. Rope

    Rope Well-Known Member Famous

    Interesting information regarding differential amplifiers, which ATI (Pure Balance) uses as a key selling point, and touts the following benefits,

    1) Lower Noise
    2) Double the slew rate
    3) Apparent gain in volume
    4) Immunity to stray fields
    5) Lower Distortion
    6) Reduction in all types of amplitude distortion
    7) Immunity to hum
    8) Better transparent performance

    however, it seems the marketing department left out the drawbacks you list.

    Rope
     
  16. DIYer

    DIYer Well-Known Member Famous

    The marketing department did? :eek: Why they must be sane!
     
  17. soundhound

    soundhound Well-Known Member

    Uh....My most recent job was as an engineer at ATI, working on the designs of their amplifiers.

    In my most humble opinion, most of the benefits listed above are pure marketing BULLSHIT...the remaining ones are "improvements" which do not improve anything of value. :angry-tappingfoot:

    I could write a book, but I've got to go to my birthday party in a few minutes. :eek:bscene-drinkingdrunk:
     
  18. Razz

    Razz Well-Known Member

    NO B-DAY PARTY SH!!!! We want info!!!!!

    .......make sure you have a beer for me! :eek:bscene-drinkingcheers:
     
  19. Rope

    Rope Well-Known Member Famous

    I'm confused. I thought Altec was employed by ATI? :laughing:

    I will say, my AT2003 has a much lower noise floor (virtually non-existant) than its Bryston predicessor.

    Rope

    BTW, if you going to be knocking a few down remember not to use the cammonde, bottles or cans, or don't flush and do a dip out. Think of the $$$$$$$$$$$$$$$$$$$$$$$!!! :happy-smileygiantred:
     

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