Good god, what have I done.

Discussion in 'Amps and Cabs [BG]' started by Microbass, Feb 18, 2005.

  1. OK, my Trace arrived today.
    Now, I do not have cabs that are powerful enough for the amp, but obviously I'm thinking I can play at low volumes.

    Well, i plug in, and to my unknownst, the mute switch is on. The mute switch is different from the other Trace i've used previously. I'm thinking it's off, when it's on. I am still getting some sound, so I think, for some reason, that it's just 'cuz the speakers won't pull any power, hence low vol.

    however, when i go test the mute switch, I've got the gain knobs set at 9. FEEDBACK. INSANE FEEDBACK. Enough so that, one of my speakers has a small tear in it. I unplug, and give both the amp and cabs a while to settle down. I mean, it was so intense I almost crapped myself. Took away a few years of my life at that I'd think.

    After letting it settle, I turned back on, and played for a good 30mins, and all was well, all knobs and sliders work great. SO i go for a shower, lunch and misc things, so about an hour at least later I go to try 'er out again. Same bass, same set up, and for 2 minutes the volume was coming and going - like a wave; as if someone was very slowly turning up the volume to it's current setting, then turning it back down to almost nothing.

    ...What have I done to my power amp!? Ahhh!

    What I'm running:
    Trace AH250 GP12SMX
    two Laney 1x12 cabs, 100 watt RMS, 8 ohm
    each cab is in a different channel on the amp.

    Thoughts? :meh:
  2. hmm, on further inspection, this happens when I have the preshape on , which is absoulutly essential for my sound!

    arrgh. :meh:
  3. protoz


    Nov 30, 2000
    Sounds like your tubes have gone to crap. That happened to a friends Peavey 5150 at a show. Sounded kind of cool but he freaked out about it.

    Was the head new or used?
  4. head is used, and only the pre has tubes, as I've understood pre-amp tubes tend to be very reliable, and when they do go, you don't get any sound...?

    If i play for a while without the preshape button on, then turn it on (say 5mins with it off) this doesnt happen?! Sounds like a blown component to me... :meh:
  5. Kelly Lee

    Kelly Lee Yeah, I'm a guy! Supporting Member

    Feb 17, 2004
    Marana, AZ, USA
    I wish I could help but I have no clue.

    Get in touch with the guys at British Audio Service. Maybe they can help.
  6. Thanks for the link, Kelly, but if I have to buy any components, will be thru gmaudio, as they are UK based. :)

    Right, I have found that I'm having this volume thing happen when the preshape is on, and when I'm using preshape 1.
    So i believe that I've very likely blow an capacitor or something. I can't find the schematics online (i did a while back, still searching!).

    When the volume goes down, it's a crackly/clipping sound. now just low volume, which worries me, however, i do not get this when preshape 2 is used. Eek!

    Any thoughts? If anyone knows where to get schematics please post! ;)
  7. Kelly Lee

    Kelly Lee Yeah, I'm a guy! Supporting Member

    Feb 17, 2004
    Marana, AZ, USA
    Sorry man, I didn't see that you were across the pond!

    Here is a link to the schematic for your head: AH250SMX
    Its a .pdf file so you need Acrobat reader for it. British Audio service has the schematics and manuals for alot of Trace equipment.
  8. Yeh i had forgotten I'd found it on that site!
    Cheers tho, KL.

    Looking at the schematics, I think I've blown a capacitor or a resister.. possibly the op-amp itself?

    The circuit for the preshape (IC4 i think it was) is made up of 3 capacitors, 2 risisters, and is an op-amp...

    Guess I'll have to try n find a good tech around here.. Cheers guys. :crying: