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Thread: Bypassing Peavey Tubefex DSP / turning it analogue

  1. #1
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    Bypassing Peavey Tubefex DSP / turning it analogue

    Hello all,
    this is a long shot but has anyone here tried to bypass the DSP on a Peavey Tubefex? Mine just got back from a 8 month trip to Peavey but they were not able to fix it. I didn't get a full report but judging by similar stories I have found on various websites, the issue was probably the DSP chip which is hard to find because production ended in 2002.
    Peavey was very nice and sent me the schematics so that I can maybe do something with it myself. At the moment I'm looking at just going straight from the tube pre to the outputs. That should be easy enough. But i would be really nice to have at least an EQ as well. So far I haven't been able to determine if the EQ is done by the DSP as well. I think so because the EQ is after the AD converter in the flow chart...
    Any thoughts and comments are welcome!

    Cheers,
    Andy

  2. #2
    Supporting Member Jazz P Bass's Avatar
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    Post the schematic?
    Sad state of affairs with this DSP stuff.
    Worse comes to worse, if you are successful in 'bypassing' the DSP, you can put an EQ pedal in front of the input.

  3. #3
    Old Timer Gtr_tech's Avatar
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    If you have the schemo, this should be gravy. What I would do is bypass the DSP section and insert a buffered loop with adjustable send/return levels in its place. That way you can use it for whatever analog or digital effect you want.
    The farmer takes a wife, the barber takes a pole....

  4. #4
    Old Timer Gtr_tech's Avatar
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    Post the schemo if you would. I'd like to see what they have goin' on inside the box....
    The farmer takes a wife, the barber takes a pole....

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    Quote Originally Posted by Gtr_tech View Post
    If you have the schemo, this should be gravy. What I would do is bypass the DSP section and insert a buffered loop with adjustable send/return levels in its place. That way you can use it for whatever analog or digital effect you want.
    Cool, thanks for the replies. I have the schematics. I'll upload them when I get home. The computer froze when I just tried to do it.

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  7. #7
    Supporting Member Jazz P Bass's Avatar
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    That's a guitar amp?
    Good luck with that.

  8. #8
    Senior Member Enzo's Avatar
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    It is a digital FX system with a bit of preamp tucked inside. I am going to look at it a while, but this really is not something for a novice to try.
    Education is what you're left with after you have forgotten what you have learned.

  9. #9
    Senior Member Enzo's Avatar
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    OK, here it is, my answer:

    NO.



    From the input, a couple op amp stages and right into the ADC. On the othe end, from the DACs, a couple op amps and out the jacks. There is no preamp there to bypass the DSP of, the whole thing is DSP. I am going crosseyed trying to even find just where the tube interface lives. But those tone controls, well all the knobs, are encoders, not pots. They are talking in digital bits. The volume controls for the input and output stages are done with digital pots.

    The signal lines on the tube board have names like TBIN, CRUNOUT, LEADOUT. If someone with better eyes can see where those lines come from or go to, I'd appreciate knowing.
    Education is what you're left with after you have forgotten what you have learned.

  10. #10
    don't forget the joker g-one's Avatar
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    Quote Originally Posted by Enzo View Post
    The signal lines on the tube board have names like TBIN, CRUNOUT, LEADOUT. If someone with better eyes can see where those lines come from or go to, I'd appreciate knowing.
    Probably not better eyes, but with PDF set to 400% ...
    The page before the tube schem. has the relays, on relay T1401 & T1403 (area B6, I sunk your battleship) I see CLENOUT, CRUNOUT, LEADOUT.
    Not sure if those are the points you are looking for or if those lines go to several places.
    "Thank you. Now on this next one , ladies and gentlemen, I'd like you to pay attention to my tone - not so much my singing or the band... " - JP Lepage

  11. #11
    Supporting Member Jazz P Bass's Avatar
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    Can you attempt to find out 'exactly' what the problem is.
    Peavey should be able to tell you.
    I find it strange that Peavey 'bailed' on the repair.
    They are usually on top of there own equipment.
    There is a company in Florida that shows stock on the DSP56002 ic.
    Link: Parts Matching DSP56002PV66 - America II Electronics
    IF that is the problem.
    g-one likes this.

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    dsp56002fc66_7505.jpgGood gravy Batman!! You`re going to need awesome solder skills!

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    I don't think that this is so difficult that you'd need Batman. Any company that assemble SMT boards can do it - you don't have to do it personally. As Jazz P Bass says, I would at least try to find out what is the problem. If you have schematic, this is not that difficult - I don't know why Peavey couldn't do it.

    Mark

  14. #14
    Senior Member Enzo's Avatar
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    All it takes is one proprietary chip in the thing becoming unavailable and the repair won't happen. If it were a TL604, they could dummy one up - like they have done already - but you can't knock out a new mask ROM from parts. PV is first rate supporting old models, better than anyone else I can think of, but this unit is 18 years old after all. Things that were state of the art then are passe now, and may not be available, especially if they are esoteric parts.

    If you have schematic, this is not that difficult - I don't know why Peavey couldn't do it.
    Markus, did you look at that schematic set closely? I sure as hell don't see it as simple.
    Education is what you're left with after you have forgotten what you have learned.

  15. #15
    Supporting Member Jazz P Bass's Avatar
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    Number 1, there is not a Truth Table or description of all of the pin assignments.
    A flow chart might help.

  16. #16
    Senior Member Enzo's Avatar
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    Ah, yep there they are on the relays.


    I can sorta read it, it is after all really just a computer. Your input goes right into an ADC, which results in a serial data stream. The same ADC takes the FX return. That puts it in the digital domain. Now you have the CPU and its RAM and ROM, and those communicate with the DSP chip. A lot of this thing is tied up in interface, the rotary encoders and LEDs, the switches, MIDI, memory card, control, and housekeeping, and of course, the DACs, which turn it all back into analog for your ears.
    Education is what you're left with after you have forgotten what you have learned.

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    Quote Originally Posted by Enzo View Post
    Markus, did you look at that schematic set closely? I sure as hell don't see it as simple.
    Yes, I looked at the schematic. It looks very close to one of the latest TC Electronics bass amps - all digital (which I was fixing). When I said that "this is not so difficult", I was talking about desoldering the 132-pin chip (I was answering to Fragger post). I wasn't talking about fixing the amp in general. You, most probably, understood something else.
    Until in the amp there are no vaporized tracks/components, and you have the schematic, fixing it is still possible. Especially, that you can buy this obsolete chip. But it is not easy; it requires having a signal generator, an osciloscope and a lot of knowledge about digital circuits (including DSP). Still, having all this is not impossible.

    Mark

  18. #18
    Senior Member Enzo's Avatar
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    Assuming THAT chip is what it needs, but there are other LSIs in there as well. I have every confidence in the Peavey team, and I suspect the "cannot repair" diagnosis wasn't based on not being able to figure it out, I'd wager on inability to source a part. Just as they no longer have transformers for Classic 20 or pull-switch volume controls for CS800..


    Yes, unsoldering and replacing the IC is not dificult. I was thinking that diagnosing the problem would be anything but trivial even for an experienced tech, and certainly over the head of a novice.
    Education is what you're left with after you have forgotten what you have learned.

  19. #19
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    Taking into account that OP said:
    Quote Originally Posted by asg-pro View Post
    That should be easy enough.
    the whole task may be quite difficult for him. It does not look like he has required tools and knowledge. But who knows?

    Mark

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    Hi all,

    I have a TubeFex with the typical battery problem. Can someone please send the schematics to ckgreve@gmx.de? I need to be sure that I fixed all the damage that the battery did before I think about switching to no-bat mod. The link above does not work :-(

    Thank you very much,
    Kai

  21. #21
    Senior Member Enzo's Avatar
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    Peavey has them and will send them off if you request from customer service. You might try Peavey-Europe first, but if they can't help, contact the main factory.
    Education is what you're left with after you have forgotten what you have learned.

  22. #22
    Supporting Member Jazz P Bass's Avatar
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    Peavey Tube FX Schematic

    Here is a reposted, resized schematic.
    Attached Files Attached Files

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