Trace Elliot standby "pop" modification?

Discussion in 'Amps and Cabs [BG]' started by Bass-only, Apr 10, 2003.

  1. Bass-only

    Bass-only Supporting Member

    Oct 9, 2001
    I have an AH300SMX head that has the nasty "pop" when you throw it into or out of standby.

    I understand that the newer Trace heads had eliminated that problem and that there is a modification that can be done to the older units to fix the problem.

    Does anyone know what is needed? Is there a description or schematic available?

    Any assistance is greatly appreciated!
  2. Hmmm thats odd...

    I also have a AH300SMX and mine doesn't pop when you put it on standby?

    I appreciate that this ain't much help, but perhaps it just needs some minor repair rather than a modification?
  3. Bass-only

    Bass-only Supporting Member

    Oct 9, 2001
    Okay - I just got the scoop straight from the Trace Elliot service folks (okay, Gibson!).

    Prior to before 1996 many of the SMX preamps had the same problem. When you engage the standby switch after the amp has been on (and sat) for a while, a "pop" is heard!

    It was common with the AH250SMX line, and made it into the first few AH300SMX heads also (before being caught and corrected).

    There is a 1M resistor that needs to be connected between two points on the circut board. It can be done without removing the circut board and can be done in minutes.

    If anyone wants the PDF with the details, e-mail me!
  4. silex65


    Aug 23, 2008
    Hallo Bass-only,
    nice to meet you in the Talk Bass Forum. I have got the same Probleme with my Trace Elliot AH 250SMX Year `93.
    Would you please so kind to send me the detail information as a PDF to me. My e-mail :

    Thank you for these helpful information.
    With kind regards
  5. jcrbassman


    Nov 10, 2006
    I know this is an old post, but I also have had this trouble since day one with my AH250SMX. It is not a good thing to have the "pop" go into a house board, and then through the venue PA. (Through DI) The first, and only time it happened, I had the sound man say "What the **** was that!" I now always have to give a heads up that my bass channel needs to be muted between sets. I know it's a long shot, but hey Bass Only, do you still have this modification/information handy? Peavey, the new owner of Trace has no clues. I email Gibson recently about this mod. Don't know if they can still assist with the information. HELP!!!
  6. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    Basically the pop is caused by the caps charging after the amp is switched to operate. Putting a 1MΩ 1W resistor across the switch terminals will allow the caps to partially charge but there will not be enough to power run the pre-amp.
  7. jcrbassman


    Nov 10, 2006
    Thank you Bass-only for the pdf file. The modification is completed now. Simple, yes. I'll check the house PA at the next show that I do. Thank you also BassmanPaul for the added input. Seems as though you have knowledge on amplifiers, as I read in your profile. You guys helped me tremendously...
  8. Bass-only, Hello I joined this site for information about bass equipment just recently. I got the bug real bad. I saw your post about poping and said, OMG!!!. Thats exactly what my AH250SMX does & it drives me nuts and its embarrassing when I am out practicing. I thought it came damaged. It all makes sense now older trace made in the uk. Can you help me as well with a pdf. My email address is Did you fix the issue yourself? thanks for your time and effort. Mark.
  9. strat65


    Jan 4, 2007
    Does anyone know the watt value of the required resistor? Bass-only was kind enough to send me the Trace memo for the fix. The memo states "solder a 1M resistor (72-RM1M)".

    I'll guess the "1M" means 1 megaohm, but no watt rating is given.

    Any help would be appreciated.