Static/distortion/crosstalk from effect send jacks

Discussion in '2488 and DP-24/32 Digital Portastudios' started by shaddart, Jan 21, 2019.

  1. shaddart

    shaddart New Member

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    Hi, I just bought a used DP-24 - needed midi or I would have bought a new one.

    I only have one problem with it (besides dodgy transport buttons)

    when I send a signal out of the effect send to another device there is intermittent static / distortion.

    I adjust the send levels but it doesn't help . It may be fine for a minute or two but then the weird static
    distortion starts happening ( and it's intensity seems to be dependent on the volume of the signal)

    Also, I get a ghost signal coming out of effect send 2 when I am only sending to effect send 1.

    Weirdly when I send out of effect send 2 I also get the distortion but no signal out of send 1.

    When I monitor the effect sends with the "Monitor select " button, there is no distortion or static=- it
    only happens when I plug a cable (yes i tried other cables :) ) into either of the send jacks.

    OK thanks, I love this machine - I am not looking forward to opening it up and not sure what I would look for.

    thanks.

    Paul
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  2. -mjk-

    -mjk- Well-Known Member

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    I bought a used DP-32 for the same reason. I recommend spraying each control (except the encoders) and every connector jack on the entire machine with a good contact cleaner. The crosstalk stumps me, but all the other issues are most likely oxidation related.

    Try a forum search on the team "Deoxit" for more information. Be sure and select the "site results" tab.
  3. shaddart

    shaddart New Member

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    thanks for the tip. Ironically, my current work around wouldn’t be possible without the midi jack - i synced up my old, almost discarded fostex vf80 ex via midi and sent the track i wanted to vocode to it and recorded it- now i can send it to my kong ms2000 for vocoding with (why not) some distortion effects from the fostex - hilarious work around and yes i have too much time on my hands. Thanks to my now ex- girlfriend ha ha.

    so can that contact cleaner evaporate ok spraying it in there - oh never mind i will read the thread
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  4. -mjk-

    -mjk- Well-Known Member

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    Deoxit is specifically designed for that purpose.
  5. shaddart

    shaddart New Member

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    Bump- I tried the deoxit, through the 1/4" jacks, using swabs and using coated 1/4 inch plugs.

    The noise continues so at some point I am going to have to open up the unit.

    Does anyone have any hints of what I should look for in there?

    I believe this is an early unit, judging by the serial number, it appears to be one of the
    first 400 that were produced.

    maybe something like a bad or bridged solder joint?

    ok thanks.

    Paul
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  6. -mjk-

    -mjk- Well-Known Member

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    1. Is the distortion present only when using external devices?
    2. Send 1 goes to the internal FX. If you use Send 1 on the internal FX, do you hear the distortion, say in a reverb return?
    3. When you hear the distortion on Send 1 on your external device, can you hear the distortion on the monitor bus for Send 1?
    If your answers are Y, N, N, then there could be either a problem with the cable from the output jack of Send 1, or a problem with the jack itself.
  7. shaddart

    shaddart New Member

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    No, it only appears from the physical jack- not in the monitor bus (if I select the send) nor on an internal effect.

    I have used several cables that are good, with exact same result- and really it's not a consistent distortion, it varies in intensity. Also, like I said before, even with effect send 2 turned off, I can hear the distorted effect send one signal from another cable plugged into the effect send 2 jack.

    thanks!

    i'm wondering if there is something inside between the 2 jacks or their signal paths on the board. I will find out when I get the guts to open her up.

    Paul
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  8. Mark Richards

    Mark Richards Well-Known Member

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    Edited:
    This post had wrong info re the Send knobs. Thanks -mjk- for pointing that out. Leaving this post so the following 3 posts make sense.
    Last edited: Feb 2, 2019
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  9. -mjk-

    -mjk- Well-Known Member

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    Wait! Aren't those encoders, and not potentiometers?
  10. -mjk-

    -mjk- Well-Known Member

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    I think the only two things in common with Sends 1 and 2, is the ground path.
  11. Mark Richards

    Mark Richards Well-Known Member

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    You're right mj. Thanks.
    I wasn't fully awake on that one. Apologies to the OP. I edited that post to remove my suggestion.
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  12. -mjk-

    -mjk- Well-Known Member

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    Paul, I wonder if the D/A converter chip is going bad. Send 1 is routed to the internal FX in the digital domain. Just before the Send jacks are D/A converters. The block diagram shows separate blocks, but they could be on the same chip. It seems your issues exist on the analog side of the converters.
  13. Arjan P

    Arjan P Well-Known Member

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    It's a long shot, but maybe this issue is related to a possible ground loop? Are the effects units you send to on the same (grounded) power supply? Doubtful since you said the distortion is also related to FX send volume, but who knows..
  14. shaddart

    shaddart New Member

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    that will definitely be one to check/ i’ve heard rumors about bootleg chips..... thanks.

  15. shaddart

    shaddart New Member

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    OK, I still haven't opened up the unit- I ordered some better solder tips and a replacement DAC.

    I found the schematic online and identified the DAC that is at the effect send outputs. It's a 2 channel DAC (AK4384) that handles both sends. I looked up the data sheet for the DAC and
    discovered that the chip can be used in parallel (2 channel) or serial mode-

    Since I am hearing both sends coming from a single jack I am suspecting that the chip is
    in serial mode when it should be in parallel mode. I guess this could be a problem with

    1. the chip itself - internal defect
    2. shorts/ bad solder joints/ etc on the board interfering with the signal to the pin that sets
    it to parallel

    3. a software bug in my firmware which doesn't seem possible ( I have the latest)

    Anyway I repost again when I learn more. I'll try cleaning and examining the board(s), then
    installing a new chip.

    Paul
  16. -mjk-

    -mjk- Well-Known Member

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    Thanks for the update Paul. Looking forward to the next one.