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Comments for boozehound labs jfets

Current Discussion: Main discussion

  1.   #1
    AndrewT's Avatar
    R.I.P.
    did you check and measure your Ebay jFETS?

    Post your results.
    __________________
    regards Andrew T.
     
  2.   #2
    jan.didden's Avatar
    diyAudio Member
    Also, you may have fried something else in addition to the JFETs.
    Any BJT, diodes, zeners on that unit?
    Electrolytics often also go with reversed polarity.

    Jan
    __________________
    Cable: a potential source of trouble interconnecting two other potential sources of trouble - Erik Margan
    Linear Audio pubs and articles . The SilentSwitcher now at diyaudio store SilentSwitcher. Keeping in touch with SY.
     
  3.   #3
    Hikari1's Avatar
    diyAudio Member
    Replace the 4 electrolytic caps. I bet your problem will be solved.
     
  4.   #4
    oltern8's Avatar
    diyAudio Member
    Hi

    No I didn't check the jfets. They were purchased as match quads i have a multimeter with an adapter but am unsure how to use it to check them. There are no diodes or bjt and I removed the 4 electrolytic caps as I prefered the sound using my bozure psu1 power supply which uses panasonic fc caps.

    is it possible to check the transistors with my multimeter and adapter? the adapter appears to be for pnp & npn type transistors.
    The transistors were posted to me from the usa is it possible that they were damaged by an electrostatic charge in transit or when i installed them.

    thanks for everyones help

    oli
     
  5.   #5
    Hikari1's Avatar
    diyAudio Member
    The phono stage should work without the electrolytic caps but the caps do provide some benefit as they provide a little decoupling for each gain stage, basically better isolating each stage, power-wise. Leave them out for now.

    Now, assuming everything is hooked up correctly, it has to be the jets. They are the only active device in this simple preamp. And they are the only devices (other than the electrolytic caps) that could be damaged by reverse voltage.

    Are you sure you have the power hooked up correctly? The board is labelled poorly, the pad closest to the "Power" text is actually ground. Looking at the attached pic the power pad closest to the top of the pic is positive. I bet this is what got you in trouble in the first place.

    Test with your meter. Measure between the "+" pad on one of the caps and a power solder pad. When you find the power pad that reads "0" or close to it on your meter this is positive. The negative solder pad on your power in should also have "0" continuity or close to it with the "ground" pad on the other side of the board.

    If power is hooked up backwards and you still had the electrolytic caps on the board they would be damaged and possibly save the jfets. If you dont have caps on the board and you hook up the power backwards the jfets may be damaged.
    [image]JFET-Phono-Preamp-Kit-Contents.jpg|thumb[/image][image]Boozhound-Labs-JFET-Phono-Preamp-Kit-Schematic.png|thumb[/image]
     
  6.   #6
    oltern8's Avatar
    diyAudio Member
    Yeah i connected the negative instead of the earth...what a plonker. mystery solved.

    thanks

    oli
     
  7.   #7
    Hikari1's Avatar
    diyAudio Member
    [QUOTE=oltern8;4047837]Yeah i connected the negative instead of the earth...what a plonker. mystery solved.

    thanks

    oli[/QUOTE]

    You shouldnt have any negative power...just pos and ground. Is this because of the psu you are using? Try 16 aa batteries. This phono likes batteries and 24v. Or just use the positive and ground outputs of the psu.

    Your jfets may be ok.
     
  8.   #8
    oltern8's Avatar
    diyAudio Member
    thanks hikari.

    looks like i've blown them a bit annoying but you live and learn. I will install some panasonic fc on the board for possible protection purposes when i get some more jfets.

    thanks

    oli
     
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