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Ampeg SVT-3 Pro audible pop on power on

Discussion in 'Amps and Cabs [BG]' started by gastric, Aug 12, 2012.


  1. gastric

    gastric Professional product tester for hire

    Jun 8, 2009
    Raleigh, NC
    Source Audio BETA tester
    Testing an Ampeg SVT-3 Pro and have the following behavior observed:

    * Nothing connected other than AC and speaker
    * Master volume off
    * Power on unit
    * Wait for power up delay
    * Hear relay in amp switch on
    * Hear an brief but audible POP! through the speakers with a quick decaying hum similar to an old tube TV when you first turn it on
    * POP! noise does not increase with master volume control
    * Otherwise the unit seems to sound and function properly - no noise, crackles, power offs, odd sounds, etc.

    Some further troubleshooting:

    * Remove tube from V1
    * Repeat process
    * Still hear the POP!

    * Engage MUTE button
    * Repeat process
    * Still hear the POP!

    * Plug patch cable into power amp in jack
    * Repeat process
    * Still her the POP!

    I've seen some other threads where someone suggests DC offset issues in the power section, others where they say the relay popping noise if normal.
     
  2. RickenBoogie

    RickenBoogie

    Jul 22, 2007
    Dallas, TX
    Normal. many solidstate amps do this as the capacitors charge or discharge, forget which. Not to worry.
     
  3. lokikallas

    lokikallas

    Aug 15, 2010
    los angeles
    Sounds like a bad cap. I had one, and as long as the amp was muted the amp would click on, but the speakers were silent. If I powered it on without muting I would hear a little click through the speakers too after the warmup.
     
  4. gastric

    gastric Professional product tester for hire

    Jun 8, 2009
    Raleigh, NC
    Source Audio BETA tester
    Mine makes the audible relay noise through the speakers even when muted or with the preamp effectively bypassed (V1 tube removed, power amp in plugged in).

    Definitely some sort of power amp noise and related to the relay clicking on. It's not loud enough to blow a speaker, but in the bedroom it's audible. Honestly, the physical relay noise is probably louder than the speaker noise.
     
  5. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    An audible pop would be due to a small DC offset.

    Shouldn't have one at all, really, but the question of normal or excessive depends on how loud the pop really is.
     
  6. gastric

    gastric Professional product tester for hire

    Jun 8, 2009
    Raleigh, NC
    Source Audio BETA tester
    I guess my question is whether it's a sign of impending doom and gloom and a significant repair bill (needs a while new power section vs a few new IC or caps) or just an annoying pop I can ignore at startup.
     
  7. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    Measure the voltage across your speaker cable. It should be close to zero volts.
     
  8. gastric

    gastric Professional product tester for hire

    Jun 8, 2009
    Raleigh, NC
    Source Audio BETA tester
    Stuck my digital multimeter onto the speaker cable, powered on. It's solid at 0V prior to the relay clicking on, then starts at around 2.3V and quickly drops to 0.5V and over the course of another 60 seconds finally starts reading 0.02V or so. I captured a video but will need some time to get it uploaded.
     
  9. Did you do this with the cab not connected? The cab should not be connected for this test. Even so that is a little long to null out. May be in need of a bias adjustment.
     
  10. gastric

    gastric Professional product tester for hire

    Jun 8, 2009
    Raleigh, NC
    Source Audio BETA tester
    Speaker cable unplugged from cab, multimeter clipped onto the unplugged end. It does dip down below 1V fairly quickly let me get the vid up so you don't have to imagine what I'm seeing. I'm good at following directions and am all about DIY but I have no real electronics knowledge to figure it out myself. If I can get a general diagnosis I can ask my tech for a quote to see if buying the amp is with it.

    The plan is to use it as a bedroom amp and kept as a backup when my tube heads are in the shop or what not. Amp is priced well so a $60 repair is doable or I can talk the seller down further.
     
  11. gastric

    gastric Professional product tester for hire

    Jun 8, 2009
    Raleigh, NC
    Source Audio BETA tester
    CLICK HERE FOR THE HORRIBLE LOOKING VIDEO.

    First time I've tried to share a movie taken with my iPhone. Was wayyy too hard trying to figure out how to use iMovie to shrink the size down from 250MB to something small enough to share, and it mangled the aspect along the way.

    Anyway, that should let you see what I'm seeing. Note the beeping in the beginning is one of the battery backups I have computers and network gear running off of. Apparently the power on of the amp is causing a brownout on the 15A circuit running in the room.

    By the way SUPER DUPER thanks for all the awesome help thus far.
     
  12. gastric

    gastric Professional product tester for hire

    Jun 8, 2009
    Raleigh, NC
    Source Audio BETA tester
    Checked a different amp, it turned on, no +2V spike, and it immediately held steady at -0.035V or something like that as I forgot to write down the specific value.
     
  13. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    The 3PRO has a specific circuit to drive the offset to zero. It should be operating all the time, I don't see a reason why it should wait until the relay has closed.

    Bias adjustment might be in order, if the existing bias is very low.
     
  14. gastric

    gastric Professional product tester for hire

    Jun 8, 2009
    Raleigh, NC
    Source Audio BETA tester
    Thanks for everyone's assistance. I emailed all of this info, and the video, to my tech for a non-binding quote. Based purely on the info I've provided here his comment was that he was betting it was a tricky issue and > $100 repair as opposed to something simple. Too much of a gamble for me to take on.

    I did prefer the tone / sound of the 3 Pro over the newer 7 Pro. Much richer, more tube-amp sound and performance to my ears, with the 7 Pro being much cleaner and brighter even though it also has some amount of tube tone to it.
     

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