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Fender Preamp 0054137000 Response Curves

Discussion in 'Pickups & Electronics [BG]' started by khutch, Nov 19, 2012.

  1. khutch

    khutch Praise Harp Supporting Member

    Joined:
    Aug 20, 2011
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    There isn't any question here, just some information I am sharing in case someone looks for it later on. I have two active basses with the preamp in the title and I recently bought another one (another preamp that is) from the TB classifieds to put in another bass. The previous owner had parted out a Reggie Hamilton Standard Jazz. I know that he had had trouble getting the preamp to work right but I do not know if that is the reason he decided to part out the bass. I got the complete control plate with the active/passive switch and all the pots and knobs along with the preamp. As it turns out there is nothing wrong with any of it except for two things: the detent on the mid pot does not work, and the preamp does not have the dual section volume pot that a Reggie Hamilton preamp should have. As I received it the active/passive switch was only partially wired in and that along with the volume pot issue undoubtedly was the reason it was not working as expected. Evidently the TBer I bought it from had purchased the bass used from someone else and one of the previous owners must have made some modifications or repairs that were beyond his grasp. I hope that was not the reason for the part-out but the bottom line is that the measurements on the preamp that I just took should be representative of the breed. At one time the preamp was used in MIA as well as MIM basses but I've heard without verification that lately MIA basses use a different preamp.

    The chart below shows the frequency response of the preamp in the flat as well as all the cut/boost settings. This is the information I was curious about and since I had a preamp cut out from a bass it was easy to measure the response without disassembling anything. I measured it using a PicoScope 3206 digital oscilloscope that plugs into a USB port and uses your computer screen for the display. It has a signal generator output that can drive the preamp and even sweep the frequency if you like. Anyway the first chart below shows the conventional way preamp responses are presented. At each frequency point the response of the flat setting on the preamp was used as the 0 dB reference. It gives you a nice, neat plot that is useful even if it does not give you the whole picture.

    [​IMG]

    This second chart shows the true frequency response. I never see plots like this on manufacturer's websites so I assume that they all use the type of plot above to convey the relative effect of the pot settings without complicating the results by including the corner frequencies on the preamp itself. As you can see below the preamp has both high and low frequency rolloff even when set to the flat position. In this case the corners are about 10 Hz and 10 kHz. For this plot the response at a single frequency chosen at random, 400 Hz, was used as the 0 dB reference.

    [​IMG]

    The midband gain of the preamp in the flat position is 0 dB (ie, unity gain). I tried to measure the noise output but the noise on my DSO is higher than the preamp, it did not matter if I had the probe connected to the preamp or not, the noise was the same either way. The opamp in the preamp has a Texas Instruments logo and the model number 2062C so it is certainly a TI TLE2062C JFET input dual opamp. The input noise level is typically 40 nV/root-Hz which is middle of the road. You can get opamps that are at least 20 dB better - or worse. The current drain is 530 uA and significantly quieter opamps will generally draw more current than that. The pinout is standard for an 8 pin DIP dual opamp so you could swap in a quieter opamp if you wanted to trade some current for less noise. I've never found the noise level to be objectionable.

    Well if you have always wanted to know more than what Fender tells you, there it is. Enjoy.

    Ken
  2. Handyman

    Handyman Supporting Member

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    Sep 4, 2007
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    Good work! I just ran across this thread since I just picked up a late 90s Precision Deluxe, and have been Googling for info about the preamp. I'm glad to see that when set flat, it pretty much is in the frequency range I'd care about for a bass guitar.

    Your plot does confirm one thing: The mid control's Q is massively wide. No wonder dialing it back sounds more like a volume control than a mid scoop.

    The thing seems decent enough that I think I'm going to order the replacement mid pot. The one on my new bass is near death, and makes a horrible racket if its touched.
  3. Stealth

    Stealth Supporting Member

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    Feb 5, 2008
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    Thanks for the explanation and A/Fq graphs. The mid control definitely looks like it should be narrower for it to be a versatile pre.

    I wonder if the Jaguar preamp is like that, but minus the midrange control?

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