1. Please take 30 seconds to register your free account to remove most ads, post topics, make friends, earn reward points at our store, and more!  
     
    TalkBass.com has been uniting the low end since 1998.  Join us! :)

How do I connect a simple DIY passive HPF to an input and an output jack plug?

Discussion in 'Pickups & Electronics [BG]' started by NoiseNinja, Dec 14, 2017.


  1. NoiseNinja

    NoiseNinja Experimental-psychedelic-ambient-noise-drone Banned

    Feb 23, 2011
    Denmark
    So I made a post in this thread Dropping the bass - love at 50Hz yesterday, and haven't got any answer yet, and probably won't since the thread and post will most likely, and in fact already have, be buried by other threads and posts, so turning to this this sub forum instead for my answer, which is where it really would belong anyway.

    My post was pretty much like this, and concerning the instructions and calculator found on this page: High Pass Filter Calculator :

    So I decided to make my own HPF box.

    Basically just a box holding the quite simple circuit for a passive HPF, consisting of only one capacitor and one resistance component connected to an input and an output jack plug.

    I've gone for a cut off frequency about 37Hz using a +/-1% tolerance 47nF capacitor and a +/-1% tolerance 90.9 KOhm resistance (90.9 KOhm is the actual value of the resistance displayed on the dealers page. Guess they measured them or something).

    Since, despite the fact that most people seem to agree on leaving the roll off at 50Hz, as far as I am informed the fundamental of the E string is about 41Hz, so I'd rather leave that untouched.

    Anyway, apparently I am dufus at reading even the simplest schematics, so while I understand how the two components are connected to each other, I am not quite sure how they are supposed to be connected to the input and output jack I am going to attach to the box to keep the myriad of components in this highly advanced circuit in. :p

    In other words which component of the circuit is supposed to be connected to the input and which to the output, and do I use the shield (ground) of the wire to connect them or the tip (hot lead) of the wire?

    Could someone please help me out with this perhaps?
     
    Last edited: Dec 15, 2017
  2. upload_2017-12-14_19-38-50.

    Input from bass goes in at top left, output from top right.
    Ground is the bottom of the resistor. (sleeve side of instrument cable)

    I would suggest using a lower value of cap & a higher value of resistance, otherwise you will lose a lot of signal to ground.

    upload_2017-12-14_19-42-32.
     
    NoiseNinja likes this.
  3. BadExample

    BadExample

    Jan 21, 2016
    Injiana
    Maybe tie the ground to case as well, if it's not grounded by the jack.
     
    NoiseNinja likes this.
  4. NoiseNinja

    NoiseNinja Experimental-psychedelic-ambient-noise-drone Banned

    Feb 23, 2011
    Denmark
    Ok, thanks a bunch.

    So if I understand this right:

    Input hot > top left
    Input ground > bottom left

    Output hot > top right
    Output ground > bottom right


    Am I correct?
     
    Killed_by_Death likes this.
  5. That's correct.
     
    NoiseNinja likes this.
  6. NoiseNinja

    NoiseNinja Experimental-psychedelic-ambient-noise-drone Banned

    Feb 23, 2011
    Denmark
    Thank you. :)

    Can't find any components with those exact values you suggest, but I take if I connect a 3nF and 1.2nf capacitor in series, that would give the same result as one 4.2nF capacitor?

    4.2nF together with a 1MOhm resistance gives a cut off frequency about 37.9Hz which is also fine by me.
     
    Killed_by_Death likes this.
  7. Play around with the values, here's something else to consider:

    upload_2017-12-14_20-23-49.

    With a 1 MegOhm pot you could easily vary the resistance down to 860K Ohm.
    You want some leeway on either side of 37 Hz to adjust.

    add: 5 nF = 5,000 pF
     
    Last edited: Dec 14, 2017
    NoiseNinja likes this.
  8. BadExample

    BadExample

    Jan 21, 2016
    Injiana
    Caps work opposite of resistors (as far as series/parallel calculation). Parallel those two to get your desired result.
     
    NoiseNinja likes this.
  9. Passinwind

    Passinwind I know nothing. Supporting Member Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    Your title says LPF, but you actually mean HPF, right?
     
  10. NoiseNinja

    NoiseNinja Experimental-psychedelic-ambient-noise-drone Banned

    Feb 23, 2011
    Denmark
    Of course, my bad, should totally have been HPF.

    I'll correct it to avoid misunderstandings, right away.
     
  11. Passinwind

    Passinwind I know nothing. Supporting Member Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    Cool. One potential problem with that passive HPF calculator is that there's no field for the source impedance, so the results will vary depending on what pickup(s) you are using. Hence KBD's recommendation to use a high value R1 to minimize loading. Another thing is that the slope of the filter isn't very steep, so you can't just leave 41Hz alone unless you tune very low. If you tune to 37Hz you will be cutting quite a bit at 41 as well. But if it sounds good it is good, pretty much.
     
    Killed_by_Death likes this.

Share This Page