At-pl120 Preamp removal

Discussion in 'Audio Hardware' started by n240sxle91, Feb 9, 2016.

  1. n240sxle91

    n240sxle91 New Member Thread Starter

    Location:
    Minnesota
    So I've read a lot of threads that mention removing the preamp from the at-lp120 helps improve the audio quality of the table. My question is does this mod apply to the at-pl120 as well, or did its preamp bypass switch fully bypass the preamp making this mod unnecessary on the at-pl120 model?

    Thanks!
     
    picassoson likes this.
  2. RPhelps

    RPhelps Active Member

    Location:
    Athens, GA
    be nice to think so.....
     
  3. Dr. Metal MD

    Dr. Metal MD Forum Resident

    Location:
    Coruscant, Ohio
    I would assume so, but what are the differences between those two models? They look identical.
     
  4. thommo

    thommo Forum Resident

    Location:
    London, England
    I first heard about the preamp thing with regard to the older (non-USB) AT-PL120, so I think it's more that the newer version also has the issue, rather than it being introduced with the update.

    I notcied a big improvement (more than I was expecting to be honest) when I ripped it out of mine. I just directly soldered the tonearm cables to the phono outs (via the little circuit board) and bypassed the preamp entirely.
     
  5. n240sxle91

    n240sxle91 New Member Thread Starter

    Location:
    Minnesota
    Thommo, do you have the at-pl120 or the at-lp120?

    I searched the forum for "at-pl120 preamp", but nothing came up about removing it. Only for the at-lp120.

    Dr. Metal MD, the real difference is the LP120 has a circuit board with a USB connection.
     
  6. Dr. Metal MD

    Dr. Metal MD Forum Resident

    Location:
    Coruscant, Ohio
    Ahh, okay. If that is the only difference, than I suspect the preamp is still in issue in both models. Take the bottom part off and take a look. If it looks nearly identical to what is in the tutorial videos, then you can safely bet you should use the guide and remove your preamp.
     
  7. n240sxle91

    n240sxle91 New Member Thread Starter

    Location:
    Minnesota
    Ok, I took my AT-PL120 apart and I don't think this mod is needed for that model. I believe it's the USB/Audio board on the AT-LP120 that causes the problem. From what I can see if you use the preamp bypass switch on the AT-PL120 it completely bypasses everything else. I took a picture for you guys to look at. If you follow where it comes in from the arm, it goes to the board directly beneath it. It then goes directly to the bypass switch board. From there it either goes back to the main board, or it goes directly to the RCA cord. So, I believe that means the bypass switch actually works on the older AT-PL120. Thoughts?

    [​IMG]
     
  8. n240sxle91

    n240sxle91 New Member Thread Starter

    Location:
    Minnesota
    Here is a close up of the switch board. The output is on the left hand side of the picture. I followed RED and it does in fact bypass everything when the preamp is switched to bypass! There will be no audio quality gain by removing the preamp out of the AT-PL120 model. I'm surprised they didn't use the same design for the newer AT-LP120. Time to put the table back together again!

    [​IMG]
     
    Last edited: Feb 9, 2016
  9. n240sxle91

    n240sxle91 New Member Thread Starter

    Location:
    Minnesota
    This might be easier to follow. I show the path of the red wire here.

    [​IMG]
     
    picassoson likes this.
  10. n240sxle91

    n240sxle91 New Member Thread Starter

    Location:
    Minnesota
    The above picture makes sense to me, but I see that I didn't mark it as clear as I could have.

    Following the red wire; the INPUT is on the lower right side, the wire out to the preamp is the upper right side, the wire coming back from the preamp is the middle wire on the right side, and the OUTPUT is on the left side.

    Hope that makes sense to everyone!
     
    thommo likes this.
  11. thommo

    thommo Forum Resident

    Location:
    London, England
    Definitely the "PL", non-USB version.

    In your first picture, in the circuit board on the left, you can see the tonearm wires exiting the arm and joining the left "arm" of an extended "U" shape of 4 tracks - I soldered the phono outs to the other end of those tracks and didn't snip any other wires.
     
    Last edited: Feb 12, 2016
  12. n240sxle91

    n240sxle91 New Member Thread Starter

    Location:
    Minnesota
    Well I can't say what you did didn't make any difference, but after using a multimeter to test continuity I can say that in the bypass mode the preamp is indeed bypassed 100%. By going directly from the tonearm your improvement might be from something in the wiring other than the preamp causing the problem, or it could be placebo. I'm definitely not saying it was a placebo! Just that it is a possibility.
     
  13. thommo

    thommo Forum Resident

    Location:
    London, England
    I'm more than willing to admit it's a possibility (probability) of some placebo action, although I didn't just rely on audio memory, I did a before/after needledrop for the comparison. Either way, I was out of warranty, and it was my standby table by then, so no real problem if I botched it. :thumbsup:
     
    picassoson likes this.
  14. n240sxle91

    n240sxle91 New Member Thread Starter

    Location:
    Minnesota
    Thommo, even though the preamp is completely removed from the path when the switch is bypassing it, perhaps the wiring going from the arm to the switch and then to the RCA cables is enough to degrade the audio quality a bit. That would explain an increase if fidelity. Now I'm considering doing the mod again. Not that I don't trust that you gained some fidelity, but I wish others who had this model would chime in on if they did the mod and if they heard any difference. That would help us figure out if maybe your unit just had some poor wiring and this fixed it, or if we're all in the same boat. I guess I could mod mine and find out!
     
  15. glenlp151

    glenlp151 New Member

    Location:
    Minneapolis, MN
    THANK YOU THANK YOU THANK YOU! I have the same turntable and was having the same confusion about the pre-amp (whether it should be removed like the USB one). This really clears it up.

    On a side note, I suggest if you do have the AT-PL120 (non-USB) you get yourself a external pre-amp (I use those ART DJ ones). I did tests last night, and you can clearly tell an improvement over the internal pre-amp, especially in the clarity of brass sections, for example.
     
  16. AppleCorp3

    AppleCorp3 Forum Resident

    I've got the PL version and got very confused by seeing the LP (and thought I had gotten it wrong) so I guess that's what the difference is.

    I've found that with an external preamp and just upgraded to an Ortofon Blue and what a difference over the Shure m97xe! It's like there was a blanket over my speakers until now.

    Maybe the OP is right, and the issue is only with the USB version?
     
  17. picassoson

    picassoson Well-Known Member

    Location:
    New York City
    Hi n240sxle91, I was wondering if you happened to know where the preamp might be in this model. I have the PL version as well, and tried out the LP version mod, but couldn't get it to work. Part of the mystery is what this extra board is that I snipped inbetween the switch and the tone arm. I thought it was the pre-amp, but now I'm not so sure. I don't see this board in any of your pictures, so now I'm really confused, and worried that I snipped something important. Do you have any idea what that board may be for? Thanks!

    [​IMG]
     
  18. P2CH

    P2CH Well-Known Member

    If you're going through the process of bypassing the internal USB and preamp, why not also eliminate the splicing of the RCA cables to the wiring that routes to the main board? Maybe it's an issue of cable length but I'd prefer to solder right to the board versus piecing two shielded cable assy's. together.

    This might involve removing and reinstalling the black cable relief from the bracket in order to release some extra length of RCA cable to reach the board, or maybe even going one step further and installing a better quality and longer set of RCA cables all together?
     
    picassoson likes this.
  19. n240sxle91

    n240sxle91 New Member Thread Starter

    Location:
    Minnesota
    picassoson, I believe you cut the wrong wires. Your table is probably a different revision of my table, but the bypass is the same. If you follow the wires' path from the tone arm you'll see they go directly to green board, and then to the bypass switch. Even though they go to that green board they aren't going through any circuitry. Follow the wires' path and you'll see the bypass fully cuts out your preamp. Just solder your wires back together, flip the table into bypass mode, get a external preamp, and you'll be all set to go! Hope this helps!
     
    picassoson likes this.
  20. P2CH

    P2CH Well-Known Member

    I think he did it right.
     
  21. n240sxle91

    n240sxle91 New Member Thread Starter

    Location:
    Minnesota
    I could be wrong, but I believe he cut the wires off from the tone arm. If I'm right, as it sits right now his table won't work.
     
  22. picassoson

    picassoson Well-Known Member

    Location:
    New York City
    Thanks for the quick responses! :)

    I'm pretty sure I wired out the tone arm correctly - I may try P2CH's suggestion to just replace the wire and go directly into the board if there was something wrong with my soldering job... may try temporary caps this time to just test the connection.

    What worries me is that cut I foolishly made to the board I circled which I thought was the preamp. The switch routes through it, but it's also connected to the main board.. which is where I cut it in a way thats difficult for me to repair without figuring out how to reinstall that plastic connector piece it plugs into. Trying to do some more reading about circuit board repair to figure out if that's fixable...
     
  23. n240sxle91

    n240sxle91 New Member Thread Starter

    Location:
    Minnesota
    I believe you have two options right now. You can either solder a new rca cable to what you've cut and go straight to a preamp, or you can repair the cut you made and just use the bypass. The bypass cuts out the preamp completely on our model. Either way will remove the preamp from the equation. I didn't cut mine in case I sold it. That way someone could choose to use the preamp if they wanted to.
     
  24. picassoson

    picassoson Well-Known Member

    Location:
    New York City
    Thanks, yeah - still not sure what option to go with. I really want to remove the preamp... I've always been bothered by it and the bypass hasn't worked that well for me. I still get an annoying inner hum either way.

    The big issue for me now is that cable I cut from the main board to the middle board with the plastic molex like connector. I'm pretty sure that was the power to the middle board, and unless I can figure out how to reconnect it I'm worried that even if I re-hook the switch back up the way it was it still won't work.
     
  25. n240sxle91

    n240sxle91 New Member Thread Starter

    Location:
    Minnesota
    Because of the photobucket ordeal, and the fact I can't edit my photo links in the above posts, I am reposting my findings with new photos.

    As noted before, I do not believe the AT-PL120 benefits from removing the preamp. If you follow the diagram below you will notice the switch completely cuts out the preamp. If you have the USB model (AT-LP120) then removing the preamp should in fact improve audio quality.

    AT-PL120 pre-amp wiring diagram
    [​IMG]

    AT-PL120
    [​IMG]
     

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