Turntable Preamp Question.

Discussion in 'Audio Hardware' started by Jack Williams, Oct 9, 2018.

  1. Jack Williams

    Jack Williams New Member Thread Starter

    Location:
    Ohio
    I have a Audio Technica At-LP 120 turntable. There is a view out there that unhooking the internal preamp improves the sound but then you have to buy an external preamp. I have a Rotel stereo system with a preamp that the turntable plugs into, if I were to unhook the turntable preamp would I still have to buy an additional external preamp in order to run my turntable? Which leads me to my next question, if not then how do the two preamps work together?

    Thank you,
    Jack
     
  2. StuJM84

    StuJM84 Forum Resident

    Location:
    Kent, UK
    You only need 1 Phono Preamp. If you remove the one from your ATLP120 then plugging it through the Phono stage of your Amp is all that is needed. Many Amps havent had a Phono stage for a number of years now and so some people have to buy an external Phono Preamp. There is an case that people believe the you get a better sound from a good external over a good internal one, but thats for a different day.

    So no, if you have an Internal (which you do in your Rotel), you do not need to buy an External. Enjoy your music!
     
    Jack Williams likes this.
  3. chargrove

    chargrove Brilliant Genius

    Location:
    Fort Worth, TX
    Nope only one but go ahead and buy one anyway. :D
     
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  4. Gibsonian

    Gibsonian Forum Resident

    Location:
    Iowa, USA
    Your 120 and Rotel will be all that you will need to play records. Well some speakers. Am guessing the sound quality and S/N ratio will be better without the cheap pre in the TT.
     
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  5. 4011021

    4011021 Forum Resident

    Location:
    Brazil
    The signal from the cartridge/stylus need to be equalized/amplificated before it hits the amplifier stage. This is done by the phono stage. This phono stage can be internal inside the turntable, an external dedicated device, or internal in an amplifier (the phono inputs). You will use only one of these three alternatives, because the signal should not be equalized/amplified twice before the amplifier stage. If you use the TT phono stage, you don't need an external one and you won't use the phono inputs on your amplifier. If you bypass the TT phono stage, than you need an external phono stage or to use the phono inputs on your amplifier.

    This is what you need for the TT to work.

    About sound quality, a general rule is that a dedicated phono stage will provide the best sound quality. So if you want the best possible sound quality, you should bypass your TT phono stage, connect the TT to a good external phono stage and then connect it to your amplifier in an input different than the phono inputs.
     
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  6. Jack Williams

    Jack Williams New Member Thread Starter

    Location:
    Ohio
    That's the problem, GAS.
     
  7. Jack Williams

    Jack Williams New Member Thread Starter

    Location:
    Ohio
    I have a Rotel RC-980BX Stereo Control Amp. which plugs into a Rotel 981 Stereo/Mono Power Amp. The 120 plugs into the Rotel RC-980BX, it's the only place to plug it into. So if I am understanding you correctly I can unsolder the internal preamp in the 120 and use the RC-980BX as the amplifier?
     
  8. Jack Williams

    Jack Williams New Member Thread Starter

    Location:
    Ohio
    I'm not sure if I want to unsolder the internal preamp, don't really know how much difference it would make. I know there is a "discussion" concerning how much difference it really makes.
     
  9. 4011021

    4011021 Forum Resident

    Location:
    Brazil
    If the Rotel has a phono input in the back (I think it does), yes, you can plug your turntable directly in the phono input of your Rotel. I don't know of it will sound better though, I have no experience with the Rotel or with the AT-LP120.
     
    Jack Williams likes this.
  10. LeBon Bush

    LeBon Bush Hound of Love

    Location:
    Austria
    I just checked - your Rotel has a Phono input on the far left of the unit's backside:

    [​IMG]

    All you have to do now is to unsolder the internal preamp (it is said that it's not exactly the best one around, more for plug-n-play than actually enjoying your music ;) ) and connect the table to this phono input - you're done! :)
     
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  11. toddrhodes

    toddrhodes Forum Resident

    Location:
    South Bend, IN
    Looks like it has both MM and MC phono inputs:
    [​IMG]


    I'm just guessing but I'd bet that Rotel pre is better than the built-in AT phono pre. If it can be defeated in the table without soldering, it would at least be easy to try. You most likely have an MM cartridge so just set the Rotel accordingly and defeat the pre in the AT. If you have to desolder the pre in the AT? That's your call at that point. I'd do it, but not everyone is comfortable doing that. Any competent electronics repair shop could probably do it for you for minimal cost.
     
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  12. Jack Williams

    Jack Williams New Member Thread Starter

    Location:
    Ohio
    Thanks for your help, I appreciate the response.
     
  13. Jack Williams

    Jack Williams New Member Thread Starter

    Location:
    Ohio
    I pretty good a soldering so I think I'll give this a try. I appreciate your help and everyone else that has commented on my post.
     
  14. Jack Williams

    Jack Williams New Member Thread Starter

    Location:
    Ohio
    Thanks, I appreciate your input on this.
     
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  15. Guitarded

    Guitarded Forum Resident

    Location:
    Montana
    My guess is the Rotel will be a step up from the internal pre on your turntable.

    I know that a seperate will be an even bigger step up from that.
     
  16. JohnO

    JohnO Forum Resident

    Location:
    Washington, DC
    This video goes all through one way of doing the removal, but most importantly it includes before and after (removing the LP120 preamp) samples. You can hear the difference with computer speakers, and you will really hear the difference with headphones. The comparison starts at 21:53 in the video. The "after" will be the sound of the better preamp you start using. Your Rotel's preamp is better.

     
    Last edited: Oct 11, 2018
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  17. Jack Williams

    Jack Williams New Member Thread Starter

    Location:
    Ohio
    Thanks John appreciate this. I listened to this video the other night, was a little skeptical but when he played the two back to back I could hear the difference.
     
  18. Jack Williams

    Jack Williams New Member Thread Starter

    Location:
    Ohio
    So let me ask you this. Since my Rotel has a preamp and the 120 has a preamp and I have the 120 plugged into the Rotel is the signal going thru two preamps?
     
  19. JohnO

    JohnO Forum Resident

    Location:
    Washington, DC
    No, the problem with the LP120 is that even when you switch its preamp "off" the sound is still affected negatively by its lesser preamp. It is "off" but it is not completely out of the circuit.
    I don't want to knock the model completely, it is popular and acceptable. But cutting its preamp completely out of the circuit allows better results with a better preamp. Just turning the LP120 preamp "off" doesn't help much because it is still in the circuit from the cartridge to the better preamp. It is a puzzling design, they didn't even have to do that.

    If you have the LP120 preamp "on" and plugged into your Rotel CD or AUX or Tuner or Tape input, you are using only the LP120 preamp, and your (better than LP120) Rotel phono preamp goes unused. Your Rotel phono preamp, with the MM/MC switch (you will use MM) shows that it is even better than many amps that do have a phono preamp but no such switch (and are effectively MM only).
     
    Last edited: Oct 11, 2018
    Jack Williams likes this.
  20. guidedbyvoices

    guidedbyvoices Diver Dan

    Location:
    Alpine, TX
    I have an LP120. When I first got an external preamp, the schiit mani, I played it for a while without ripping out the internal, then I eventually removed the internal.

    I found using the Mani first was an EQ improvement for sure. Definite upgrade. Removing the internal added some clarity. Some feel removing it's a huge improvement, I felt removing it was a more modest improvement to my ears. However it's a cheap DIY tweak and IS an improvement so it's worth eventually doing. I am not mechanically inclined, but following a youtube video, I did it from start to finish and listening to records again in under 3 hours.
     
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  21. Just Walking

    Just Walking Forum Resident

    Location:
    Abingdon UK
    Just been looking at the Rotel RC-980BX schematic, and the RIAA stage is a very nice design. It uses two exceptionally low noise transistors (2SD786) as a differential pair with a constant current long tail load. The following stage is a NE5532, which is a superb op-amp. There is also a DC servo to set the input voltage equal to zero - that means that there are no capacitors in the signal path. The RIAA is a mixture of passive (to set the 75us time constant precisely) and active around the NE5532 to set the 3180us and 318us time constants.

    All the MM/MC switch does is change the load resistor and gain.

    It really would be hard to better both the circuit topology and RIAA accuracy (they quote +/-0.2dB, and I would wager that is conservative) in an external RIAA stage.
     
    Last edited: Oct 12, 2018
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  22. Just Walking

    Just Walking Forum Resident

    Location:
    Abingdon UK
    Thought so - the resistors are 1% tolerance, and the capacitors have an F tolerance code, which is again 1%. So the RIAA accuracy in that Rotel will be better than +/-0.1dB, and probably (since 1% is the maximum tolerance) +/-0.05dB . Which is exceptionally good.

    So bypassing the turntable RIAA stage and connecting the cartridge to the Rotel is precisely the right decision.
     
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  23. Jack Williams

    Jack Williams New Member Thread Starter

    Location:
    Ohio
    Wow thank you Just Walking I really appreciate you going to all that trouble. Very good to hear that the Rotel 980 has that good of a preamp in it. I bought the system in 1998, the only unit I've had to replace was the CD player. Oher then that I've been very pleased with it.
     
  24. Jack Williams

    Jack Williams New Member Thread Starter

    Location:
    Ohio
    Plan on doing it today. Thanks again for your help.
     
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  25. Jack Williams

    Jack Williams New Member Thread Starter

    Location:
    Ohio
    I have it plugged into the Phono jack. I appreciate your input on this JohnO.
     

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