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Help with Presonus Blue Tube DP

Discussion in 'Electronic Repair Modifications DIY' started by GrandfatherFlump, Apr 7, 2005.

  1. I read the manual but it really isnt that good lol Its for people who are familiar with preamps, I am not.

    Someone plz break this down for me and how to use this thing. I have a rode NT1 Condensor MIc.
  2. therecordingart

    therecordingart Well-Known Member

    Enable the phantom power!
  3. lol yes i know that, the 48v button


    i said a breakdown! lol not 4 words!

    hook ups and all that $*^t.
  4. therecordingart

    therecordingart Well-Known Member

    I'm not clear on what you want to know....how to hook it up to your computer? How a preamp works?

    Here is what I can come up with for you off of the top of my head since I'm not sure what you are asking..........

    -You need an XLR Female to Male cable to plug the mic into the preamp
    -48v phantom power must be on to power the mic
    -If you are planning on plugging the preamp into your "standard" computer soundcard you'll need a either a female XLR to 1/8 inch or a 1/4 inch to 1/8 inch cable...your choice. Plug that into the line in on your soundcard

    If it's already hooked up....disregard what I just typed. Here are easy to understand terms on what all of the knobs and buttons do/mean from left to right on the unit:

    -48v phantom power provides the power to mics like condensers which need it to operate.
    -the zero with a line through it is a phase reverse. Since you wont be using two mics on the same source for now...I won't go into it...just make sure this light is off.
    -PAD is like a volume adjustment, but in button form. This button activated will drop the signal -20db. This is useful when recording loud sources like snare drums and stuff, but won't be needed on vocals
    -the 80hz button is a high pass filter. What it does is cuts out any frequency below 80hz. 80hz is like the hit or kick in a bass drum. It gets the subwoofers pumping and on some things like electric guitar...you don't want 80hz or below!!!!
    -think of the Gain knob as a volume knob for the mic which will increase it's sensitivity to your volume.
    -the tube drive knob can be bypassed...in which case you'll have a clean solid state sound....the more you crank it...the more the tube will saturate the sound and make it "warmer" but potentially noiser depending on the unit.

    I hope I've answered some questions! Let me know if you'd like me to elaborate on anything.
  5. Ok well now there's a new problem lol I know everythings working and my voice is being picked up and all but in Cool Edit Pro...its not picking up and recording my voice! I installed a new soundcard and maybe I have to make sure CE is using that one and I think it is but im just lost lol

    damn it.
  6. therecordingart

    therecordingart Well-Known Member

    I've used Cool Edit, but can't remember all of the menus off of the top of my head. What I would do is go into the HELP section and read up on how to record a track. You have to select your soundcards input on the track that you want to record to. Also, in the audio preferences you have to make sure that your soundcards ins and outs are set to the default.
  7. MisterJoe49

    MisterJoe49 Active Member

    It looks like you are very familiar with Phantom Power. I hope you can help me. I too have a Presonus Blue Tube preamp with a Phantom Power issue. I learned a little about Phantom Power and mine doesn't work. The +48v button lights up but my AKG 220 condenser mic doesn't respond. It responds when I disconnect the Presonus preamp and use my Mbox by itself. I measured the Phantom voltage on the Presonus and it is only +10 volts. I contacted Presonus Tech Support and they want me to ship the unit to them and also pay a $75 bench fee. I would like to fix it myself but I can use some help.
  8. Boswell

    Boswell Moderator Distinguished Member

    Is this the DP version of the Blue Tube pre-amp? What type of meter did you use to measure the PP voltage on the Presonus? Did you have the microphone attached at the time of making the measurement? Were both pins 2 and 3 at the same voltage? Do both pre-amp channels measure the same? Does plugging the microphone into one channel affect the PP voltage on the other channel?
  9. MisterJoe49

    MisterJoe49 Active Member

    Presonus Phantom Power

    Thank you for asking some good questions. I'll try to be clear. My preamp is the BlueTube Dual Path. I used a Simpson meter to measure the voltages on pin 2 and 3 of the female end of an XLR cable. It makes no difference if I connect the XLR to chan1 or chan2. The readings are the same. I read about +10 volts without the mic connected. I thought about the fact that a load might change the voltage reading but I did the same test with my Mbox and I get +48 volts on the XLR without the mic. The mic responds to the Mbox but not the Presonus. I was hoping to get better quality with a preamp instead of the Mbox by itself with it's own built-in preamp. I have not tried connecting the mic to chan1 while measuring chan2. That's a thought.
    I contacted Presonus again and they told me that the questions I asked were way out of reach for their Tech Support. But how do you explain that if I ship the unit to them and pay a $75 bench fee, they'll know what to do.
    Well, if you're ready I'll give the extra details that I gave them.
    I opened the preamp and found 3 voltage regulators mounted on a heat sink in the Power supply section. It appears that there is one common power supply that feeds both channels.
    Two of the regulators looked ok to me and one was suspect. The suspicious one is an LM317HVT. I believe it is the one that supplies Phantom Power. The input voltage was about +70 and the output was about 13 volts. When the unit is all closed up, I get +10 volts. That is the best I can do with Google and without a schematic.
    If I get brave enough I'll shop for a regulator LM317HVT and replace the old one.
    I was an Electronics Tech once but it is easier at work than at home. I had a lot more resources at work. I usually had schematics, test equipment, parts, soldering tools and a well lit bench. And, I had working units to compare with.
  10. Boswell

    Boswell Moderator Distinguished Member

    This smacks of poor design. The maximum input-output voltage rating of an LM317HV is 60V, which is OK if the 48V output is functioning, but with 70V source, a short to ground on the regulator output (not the XLR pins) would over-volt the regulator, probably destroying it.

    Before changing the regulator, I would check that the resistor to ground from the regulator ADJ terminal (pin 1 on the T package) is a respectable value. For a 48V output, it should be around 38 times the resistor from the output to the ADJ terminal. If that resistor is 240 Ohm, the resistor to ground should read around 9.2K. You would have to lift one end of it to check it using a multimeter.

    The 2011 section of this thread should really be split off into a separate topic and moved to the DIY Pro Forum. Jeemy?
  11. MisterJoe49

    MisterJoe49 Active Member

    Presonus Phantom Power

    You know your suff and I really appreciate you sharing all this with me. I will open the preamp up again and try to follow your advice but it will take at least two weeks. I am away from home at this time. But you touched on another question.

    My AKG 220 mic has a -20db switch on the front and when I didn't get a response the first day I took it out of the box I switched the attenuation off. Is it possible that the Presonus preamp got jolted in my effort to get the mic to work? The mic is ok now that I'm using my Mbox by itself with its own Phantom Power. Also, I had never used Phantom Power before and I may have had both turned on at the same time. I know better now but could that have caused the regulator to blow?
    You mentioned poor design and I agree. I had mentioned it to Presonus Tech Support. Even if I screwed up, I would expect a fuse or a reset button or some other protective circuit in there somewhere. If you don't mind following up on this, please let me know what you think. This forum is impressive compared to others where you post a question and don't get an answer for a year, if you get one at all. Thank you.
  12. Boswell

    Boswell Moderator Distinguished Member

    I'm not sure I understand your comment about having "both turned on at the same time", but nothing you did with the mic attenuation switch would affect the phantom powering arrangement. Between the 48V PP source and the XLR inputs are 6K8 resistors, so even the Presonus PP circuit shoud be proof against short circuits on the XLR inputs.
  13. MisterJoe49

    MisterJoe49 Active Member

    Presonus Phantom Power

    Thank you so much for your quick responses. What I meant when I said I may have had both turned on at the same time is this: I have my Mic connected to the XLR input of the Presonus Blue Tube preamp and the output of the Presonus connected to the source input of my Mbox. Both of these boxes have a Phantom Power switch. It's possible that I turned on the Phantom Power on both boxes at the same time for a few seconds. If I did, then the Phantom Power of my Mbox was fed not only to the XLR input of the Mbox but also to the output of the Presonus at the same time. I wonder if it hurt the Presonus output circuit. The Mbox and the mic are still ok.
    I started to shop for an LM317HVT and they appear to be inexpensive with the exception of shipping charges. I still hope I can avoid messing with the circuit board.
  14. Boswell

    Boswell Moderator Distinguished Member

    What type of input connector on the Mbox did you plug the Blue Tube into? Did the cable you used from the Blue Tube have XLR connectors or TRS jack plugs on the Mbox end?

    It would be the natural connection to use the TRS jack inputs of the Mbox to take the Blue Tube output and digitize it for interfacing to the computer. Phantom Power is only applied to the XLR terminals of the combo input connector.

    Even if the Blue Tube output got a dose of 48V PP from the Mbox, it should not have affected the Blue Tube's own PP regulator.
  15. MisterJoe49

    MisterJoe49 Active Member

    Presonus BlueTube Phantom Power

    I used an XLR cable to connect the mic to the BlueTube and a short XLR cable to connect the output of the BlueTube to the Mbox Source in. So you're telling me that the regulator should not have popped even though I did not handle the situation as carefully as I would have liked.
    I've been trying to tell Presonus the same thing but they are not offering any more help without a $75 bench fee plus shipping. It's just not worth it for me.

    No, I didn't connect to the TRS jack as you suggested. When I checked the Mbox manual I understood it differently. So I used the Source in. The XLR cables are XLR on both ends.
    I understood it to be an external input level and I tried the button which selects MIc, Line, Instr. I tried all three positions. I thought the TRS was for a different purpose. But when I get this Phantom Power issue resolved I'll try the TRS input.

    Is there a way to use the Phantom Power of the Mbox to power the mic and also use the BlueTube preamp with PP turned off? Is there an adapter or something? I was looking at a +48 power supply on Ebay as another option. But I would still need an XLR adapter. I also browsed for a regulator LM317HVT. Thank you for all your input. I welcome all your questions. Just fire away. I can use the education. This is a great forum.
  16. Boswell

    Boswell Moderator Distinguished Member

    I would advise strongly against using an XLR-XLR cable to connect the output of your Blue Tube to the Mbox input - it just invites trouble. Use an XLR(F) to TRS jack cable.

    There is no easy way of using PP from the Mbox and at the same time taking the mic signal through the Blue Tube, although how you might do it would make a challenging Audio Tech exam question. There is nothing against using an external PP supply for the mic, but really, I would fix the PP regulator in the BT first.

    If it was the application of 48V to the outputs of the BT pre-amp that caused the PP regulator to fry, it's not going to be the only thing that needs fixing. However, I think it is more likely that you simply have a dead PP regulator, and its demise did not corellate with any PP applied to the pre-amp output.

    Can you get hold of a dynamic mic (e.g. SM57 or SM58) that you can try with the BT pre-amp? That would show you whether the signal path through the BT and Mbox was working OK and that you just have a PP issue in the BT.
  17. MisterJoe49

    MisterJoe49 Active Member

    Thank you for being so patient with this issue.
    Yes, I do have an SM58 which I was using before I bought the AKG 220 condenser mic. The SM58 was working with the BluTube preamp before and after the Phantom Power blew.
    I tested both BlueTube channels with my SM58 and Phantom Power turned off.
  18. Boswell

    Boswell Moderator Distinguished Member

    Thanks for the info about the correct operation with the SM58. It could have saved several lines of posting if you had mentioned that at the outset.

    Where we are:

    (1) Change the Phantom Power regulator in the Blue Tube.

    (2) Get either an XLR(F)-TRS mic cable or (second best) an XLR(F)-TRS plug adaptor that you can use with your existing XLR cable. You will need two if you are going to be using both channels.

    (3) Don't ignore the second point. It's looking as though you were lucky this time, but the Phantom Power mistake will happen again.
  19. MisterJoe49

    MisterJoe49 Active Member

    Presonus BlueTube Phantom Power

    Since my last post, I've replaced the LM317 Regulator. After a lot of begging and pleading Presonus was nice enough to send me one. After I replaced the regulator I took some voltage readings and they looked very hopeful. I had +46 volts on the Regulator output. But when I closed the BlueTube preamp I still had the same PP problem. I reopened the BlueTube hoping to find something obvious and stupid that I did. But I ran into a bigger snag and I believe you may be able to help me.
    Hindsight tells me that I should have paid closer attention to your advise about the ratio of the resistors but it was tough working without a Schematic and I was anxious for results.

    When I reopened the preamp I took some continuity readings in the power supply section. Suddenly there was a spark and the circuit breaker popped on my Simpson. The preamp was unplugged at the time. i reconnected the power adapter to the preamp and found that the voltage readings that I had before were gone. A capacitor must have kept its charge a little too long. I need your thoughts on this one. Could my soldering have opened a discharge path for a capacitor? I didn't get sparks before with the preamp unplugged.

    If anyone has a Schematic to a Presonus BlueTube DP, I would love to see it. I asked Presonus already and they gave me a policy speech.

    With your help I may be able to fix this thing even without a Schematic. First I need to know how the Phantom Power from the regulator gets to the XLR input. I tried tracing with continuity checks but it was too much guesswork.

    This is getting lengthy. If I was unclear about anything please let me know.
    Bottom line. Phantom Power is gone and I could use a Schematic.
  20. Boswell

    Boswell Moderator Distinguished Member

    There's something odd here in what you describe. If the BlueTube was not plugged into the circuit breaker, how could anything you did while poking around inside it cause the breaker to trip?

    As I mentioned previously, shorting the PP regulator output or its feedback sense pin directly to ground with the power on would destroy the regulator device. This would be the case even with no power supply attached if the reservoir capacitors were still charged from a previous use.

    You have to ask yourself why the PP output voltage disappeared between your seeing it there with the lid off the case and it not being there when you put the lid on. Was the replacement of the lid the actual cause of the PP volts disappearing? Is this what happened in the first place, maybe to the previous owner? Does any of the mechanics of the lid and its fixings come near the PP circuitry?

    I don't have a circuit diagram (schematic) for the Blue Tube. The phantom power circuitry on this type of pre-amp usually consists of the 48V regulator which then goes via the PP switch to pairs of 6K8 resistors attached to pins 2 and 3 of each XLR input. Apart from decoupling and r.f. suppression capacitors, there's generally not a lot else.

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