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retubed the IOD.....

Discussion in 'Amps and Cabs [BG]' started by jasonbraatz, Mar 17, 2002.


  1. jasonbraatz

    jasonbraatz

    Oct 18, 2000
    Oakland, CA
    well i got my new JJ's, biased, and threw them in.

    and it's STILL distorting. like - there's two distortions going on - one even with the drive all the way off and the blend on direct, and then the actual tube distortion when i turn up the drive knob.


    F!@)$*&#)%(*@&#)(*&(!!!!!!!!!!!!!!!



    so i have to take it in AGAIN!!!



    is anyone else having IOD reliability problems?
     
  2. mthoople

    mthoople

    Nov 1, 2001
    Denver, CO
    Is the non-tube distortion "farty"? You probably still have a bad TL072 op-amp. I blew the input buffer TL072 on my Grand Prix twice. After the first time, I started keeping a full set of spares with me. There are seven TL072's in both the GP and the IOD. At $0.49 each, a full set is cheap insurance. In your case, its most likely the input buffer or one of the summing amps in the EQ circuit.
     
  3. jasonbraatz

    jasonbraatz

    Oct 18, 2000
    Oakland, CA
    man that's wierd....that's what was replaced when i took it in before. do they blow often?


    where can i buy a big handful of them?
    how do i test which one it is?

    also - my blend knob is crackly, whats up with that?



    (then again...i shouldn't have to. why do these break)
     
  4. mthoople

    mthoople

    Nov 1, 2001
    Denver, CO
    I thought you said they only replaced one. Its possible they missed another bad one.

    Most electronics parts stores will carry them. RadioShack.com has them for $0.59 each. You'll want the DIP version.

    Since they're cheap, I usually just replace them all. The easiest way to find the bad is:
    1) Replace them all
    2) Try each one of the old ones in the input buffer position (usually closest to the input jacks)

    I would guess that the crackly Blend is a dirty pot or a broken solder joint.

    I think mine have been blown when my cable hasn't been plugged into the bass completely, sending 9V DC back to the pre's input and the input buffer. I've done the same repair to other bass amps, so I wouldn't say its just an SWR issue.
     
  5. jasonbraatz

    jasonbraatz

    Oct 18, 2000
    Oakland, CA
    AH! so would that also happen if i didn't have the effects loop cable plugged in all the way? (cos that happened a few days ago)


    would radioshack the store have them in stock do you think?
     
  6. mthoople

    mthoople

    Nov 1, 2001
    Denver, CO
    I don't think that the effects cable could blow an op-amp, but its possible.

    Regular Radio Shacks may have them. But if they do, they'll cost more - probably about $1.20 each.

    BGavin has a schematic at his webpage:

    http://www.ofgb.org/reference/Music/Swr/Interstellar Overdrive Schematic.jpg

    If you use the Active input, half of U2 is the input buffer (the Passive input uses half of the preamp tube). The effects cable could have shorted the output on half of U4.
     
  7. jasonbraatz

    jasonbraatz

    Oct 18, 2000
    Oakland, CA
    hey i just ordered 15 of 'em. at under 12 bucks with shipping it shouldn't be too bad - and the online store said the storefronts won't have them anyways.


    and in that schematic i count 10! TL072's...so i'll probably replace one at a time until it fixes it.


    thanks for all your help man, and <cross your fingers> hope this works!!!
     
  8. mthoople

    mthoople

    Nov 1, 2001
    Denver, CO
    I've found that the "in store" data in the RadioShack.com listings is not always correct. But even if a store did have them, they would probably only have a few.

    There are 7 TL072's in the IOD. Each TL072 is a dual op-amp: two op-amps in one package (similar to a 12AX7). In the schematic, they are called out as U1A, U1B, U2A, etc. U1 is the IC, A and B refer to each op-amp in the IC.

    Let me know how it goes!