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Balanced D.I. Out noise

Discussion in 'Amps and Cabs [BG]' started by DJJazzV, Aug 16, 2007.

  1. DJJazzV

    DJJazzV Gambling is illegal at Bushwood sir... Supporting Member

    May 17, 2007
    New Jersey
    A problem I discovered last night is there is a lot of noise coming from the D.I. Balanced outputs in my Ampeg SVP-BSP preamp. The BSP has 2 D.I. Outs, and they both make the same noise.
    It is in the same rack as an Ampeg SVP-CL, and the CL's D.I. out is perfectly quiet. I can make the CL have the same noise as the BSP by pressing the Ground Lift switch. That points me in the direction of some ground issue with the BSP. The BSP does not have a Ground Lift switch, but it sounds as if the ground is lifted. Normal power amp/speaker operation is fine, with no noise or hum at all.

    I'm using the same cables, power source, etc. The only thing that was different was the power cable. I'll swap that tonight, but if that was the problem, I would assume the normal operation of the preamp would have hum or hiss noise through the speakers, correct?

    What else can I check, or must it be brought in for service?

    Thanks for your help.
  2. DJJazzV

    DJJazzV Gambling is illegal at Bushwood sir... Supporting Member

    May 17, 2007
    New Jersey
    I have an update:

    It seems I may found the problem, but still have no solution.

    The previous owner of the SVP-BSP preamp had used the grounding screw to attach a plastic clip to hold the power cable. I removed that screw and clip, and put just a screw back in the grounding hole, but that did not help. I pulled the screw back out, and the same noise. If I touch the screw or empty hole while it's on, the DI can hear a change in pitch, or click, but there is still a lot of noise.
    The preamp itself still works perfectly through normal bass and speaker operation. No hum or grounding issue at all.

    Could something have shorted out in the ground for the 2 DI outputs?

    It looks like it has to go into the shop.
    Thanks for your time.
  3. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    99 times out of 100 noise from a DI out is caused by not lifting the ground, not the other way around, and the BSP is probably noisy due to the lack of ability to lift the ground. Read why here:
  4. DJJazzV

    DJJazzV Gambling is illegal at Bushwood sir... Supporting Member

    May 17, 2007
    New Jersey
    Thank you!!! That document pointed me in the right direction, and the problem is solved!

    I learned that just because an XLR out setup (XLR-1/4" cable into 1/4" splitter) for recording direct works perfectly on:

    Ampeg SVP-CL
    Mesa Boogie Titan V12
    Mesa Boogie Walkabout

    doesn't mean it will work on an Ampeg SVP-BSP. I changed the 1/4" splitter to an XLR splitter, and that fixed the loud HUM! It works perfectly, and the BSP is back in the rack!

    Thank you again!!! :hyper:

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