# 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.

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1. ### NoiseNinjaExperimental-psychedelic-ambient-noise-droneBanned

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.

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?

Last edited: Dec 15, 2017
2. ### Killed_by_DeathSnaggletooth

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.

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

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4. ### NoiseNinjaExperimental-psychedelic-ambient-noise-droneBanned

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?

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5. ### Killed_by_DeathSnaggletooth

That's correct.

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6. ### NoiseNinjaExperimental-psychedelic-ambient-noise-droneBanned

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.

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7. ### Killed_by_DeathSnaggletooth

Play around with the values, here's something else to consider:

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.

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

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9. ### PassinwindI know nothing.Supporting MemberCommercial 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. ### NoiseNinjaExperimental-psychedelic-ambient-noise-droneBanned

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

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

11. ### PassinwindI know nothing.Supporting MemberCommercial 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.

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