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Monday, 12 January 2015

HPF Technology HPF-Pre 2

I've had a few folks asking for active bass cutter circuit for couple of different uses. First, a lot of stoner rock enthusiast want to split their signal for two amps and some blues folks want to do that too. And since in cases like these, the second amp is usually a guitar amp, which will perform in a happier manner if we don't feed them the lowest frequencies. I got tipped off with HPF Technology's HPF-Pre 2. Even though the main aim for the design is to address issues with double basses, the circuit will work great on other applications as well. This design is open and for mainly that reason, i strongly recommend getting an original unit if you find use for this circuit. The price is more than just right, so your savings won't be much by building one. So. If you can, please support the orginal design.

I built one already to see if the board works with J201s and 2N3906. It does. The frequency pot should definitely be dual gang logarithmic taper.

A quick overview from the author:
HPF-Pre is a preamp with adjustable high pass filter and phase switch for use with piezoelectric pickups on the double bass. It is intended to address the primary issues faced by bassists when playing through mainstream amps and PA systems. Foremost, HPF-Pre is a preamp. Its high input impedance ensures proper buffering of the signal from piezo pickups. It is battery powered and housed in a tough plastic enclosure with internal shielding. An adjustable high pass filter tunes out the subharmonic “thump” generated by the plucked bass, which otherwise can drive ported bass speakers to over-excursion. It is also a useful tool for coping with adverse acoustical environments and PA systems with excessive subwoofer support. A phase (polarity reversal) switch is provided to help control feedback problems. It could also help when setting up systems with multiple pickups, or a pickup and a microphone. Series 2 of the preamp adds an output volume control and an LED battery status indicator. The volume control is handy when your stage setup requires your amp to be out of arm's reach. HPF-Pre is an "open" design. I sell the HPF-Pre at a modest price from my part-time home business. Otherwise, you are welcome to build your own.

Check the site and get the original from https://sites.google.com/site/hpftechllc/home

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44 comments:

  1. HGE Contraptions12 January 2015 at 10:16

    Hehe!! Welcome baaaaaack! :)

    ReplyDelete
    Replies
    1. mirosol12 January 2015 at 14:33

      Slowly but not so surely. Main reason being the simpler schematics that are worthwhile to draw are getting really scarce...
      +m

      Delete
    2. Frederick19 January 2015 at 04:41

      Been looking everywhere for a Fuzz God II layout...

      Delete
  2. mikejoyce17 January 2015 at 17:19

    Is there a way to make this control-less? Like fix it at 30-35hz? I could deal with just a volume pot. I would like to implement this in the same manner as an sfx thumpinator.

    ReplyDelete
  3. cylens24 January 2015 at 11:15

    omit the dual pot and solder 2 resistors (100k will give you 35 Hz) where the pot should be: ie between Freq A1 and A2&3 rows and between Freq B1 and B2&3

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    Replies
    1. Sensei Tim10 October 2017 at 19:14

      nevermind... not enough coffee (and i also found the schematic.)

      Delete
  4. cylens25 January 2015 at 10:25

    i've built this circuit quite a few times using another layout and 2N3819s and BC327 with success. I've just tested J201s and I wouldn't recommend usuing them, using test tones, there's a fair amount of distortion...

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    Replies
    1. mirosol25 January 2015 at 12:45

      Strange. I didn't have any distortion on mine with J201s.
      +m

      Delete
  5. cylens25 January 2015 at 15:37

    I'm talking about sine test tones, i didn't notice audible distortion with a bass guitars (then, "why bother?", you could say :D ), but when testing the frequency response, a 100 Hz sine tone came out audibly distorted, which was not the case with 2N3819s. maybe my J201s (Tayda's) are to blame, though... I'll post a comparison soundclip when I have the time

    ReplyDelete
  6. cylens30 January 2015 at 14:22

    OK, so here's a soundclip:
    http://clients.cylens.net/diy/hpf.wav

    first pass is a pure 100 Hz sine tone
    second pass is through the HPF with 2n3819s
    third pass is the same circuit with J201s... notice the distorsion and 10 dB loss

    ReplyDelete
  7. Unknown9 February 2015 at 20:21

    do you know if a 2n5485 would work in place of the 2n4416s?

    Thanks,

    ReplyDelete
    Replies
    1. IvIark9 February 2015 at 21:50

      They're both N channel JFETs but it really is going to be a case of try it and see. Unfortunately the results from different JFETs is unpredictable and so we just don't know how they will react in the circuit. You are more likely to have success with JFETs used as gain stages like in this though, as opposed to when used as variable resistors in phasers and similar. So hopefully you'll have good luck.

      You can get the 2N4416 from Farnell though

      Delete
  8. Unknown9 February 2015 at 21:53

    If I got the 2n4416 from farnell, what would the 4 lead be connected to?

    Thanks

    ReplyDelete
  9. Unknown11 February 2015 at 17:44

    Going to try the j201's, but would also like to compare the 2N4416 as that was what was originally used. However, the 2N4416 has 4 leads (one for the case)....what would that get connected to?

    ReplyDelete
  10. Travis11 February 2015 at 18:26

    All you need are drain, source, and gate pins. Clip the fourth pin

    ReplyDelete
  11. Unknown4 March 2015 at 17:31

    hello,
    what is D1 ? a Zener 12v is ok ?
    thanks !

    ReplyDelete
    Replies
    1. Unknown4 March 2015 at 23:02

      Probably, I believe it's just for polarity protection.

      Delete
  12. Unknown4 March 2015 at 23:22

    Thank you Charles
    signed : Charles

    ReplyDelete
  13. Sonicguitars16 April 2015 at 11:33

    No way to let it work
    here my voltage
    Q1 D 4.81
    G 4.04
    S 4.04
    Q2 D 3.69
    S 2.89
    G 2.90
    Q3 C 3.12
    B 3.68
    E 8.85
    Someone can help me?

    ReplyDelete
  14. ZanBon6 May 2015 at 14:27

    This comment has been removed by the author.

    ReplyDelete
    Replies
    1. Unknown6 May 2015 at 14:33

      Hey, I think the diode in use here is just for polarity protection of the circuit - I believe a 1N4001 will do fine here. They are pretty stock standard.

      Delete
  15. ZanBon4 June 2015 at 10:47

    Hey, can anyone please point out what to do to eliminate the volume pot? Trying to fit in a small box and already can handle volume from other pedals.

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    Replies
    1. ξεναγός νεκρόπολης4 June 2015 at 12:42

      just ignore vol 1 wire, and take your output from vol 3.

      otherwise you could squeeze a trimmer in there to fix your output to the level you like.

      Delete
    2. ZanBon4 June 2015 at 13:43

      Ok, thanx! Petyxhmeno nick btw :)

      Delete
    3. ξεναγός νεκρόπολης4 June 2015 at 19:10

      thanks!i think this hobby grows really fast here in greece!!

      Delete
  16. ZanBon22 June 2015 at 09:43

    So, another backfire there, project done, works like a charm, pots and switch response right, but...
    When I set it aside, with no in and out jacks, battery dies in 1-2 days, with no apparent (to me) reason. Can you take a look and leave any opinions?
    Note I added a little battery check led, activated when only the Out jack is inserted. I hope you can understand by the wiring drawing I provide. Also a few photos of the guts.
    http://postimg.org/gallery/16nw218hw/

    ReplyDelete
    Replies
    1. ZanBon22 June 2015 at 09:46

      Hm, now it hit me... Maybe I should run the ground first by the output jack, and then into the vero and not parallel. So the circuit closes only when the jack is in. Silly me. :)

      Delete
    2. Unknown22 June 2015 at 14:02

      Heh there ya go!

      Delete
  17. Unknown10 March 2016 at 09:16

    This comment has been removed by the author.

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  18. Unknown10 March 2016 at 09:16

    This comment has been removed by the author.

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  19. Bassface 17 February 2017 at 10:43

    This comment has been removed by the author.

    ReplyDelete
  20. Unknown8 November 2017 at 00:21

    Hi everyone, I am looking for something like this but with out the preamp, just a simple sweepable high pass filter for sending a passive bass guitar signal to a guitar amp. Would you be able to help me out in seeing how to build only the high-pass part of the circuit?

    ReplyDelete
    Replies
    1. mirosol8 November 2017 at 06:19

      You can get unity level out of this. So it's not a preamp per sé. For active filter (that has sharp enough slope), you'll want this complete.
      +m

      Delete
  21. Marcos13 April 2018 at 19:27

    Hello, everyone! I've built the project, but with a lot of hum, and a high noise that increases when phase is changed. I'm using the 2n4416a. Something like that already happens to you?
    Thanks!

    ReplyDelete
  22. masonsjax27 November 2018 at 15:30

    This comment has been removed by the author.

    ReplyDelete
  23. masonsjax27 November 2018 at 15:32

    I'm planning to build one of these soon. I was wondering if anyone has done a vero layout for the series 3?

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  24. masonsjax10 December 2018 at 22:19

    Series 3 veroboard layout and discussion here:
    http://guitar-fx-layouts.42897.x6.nabble.com/F-deck-HPF-Series-3-td44880.html

    ReplyDelete
    Replies
    1. j-pee27 August 2023 at 11:44

      nabble gfx URLS should be corrected from:
      .... 42897.x6. ...
      to
      238.s1

      the whole URL after the "mod":
      http://guitar-fx-layouts.238.s1.nabble.com/F-deck-HPF-Series-3-td44880.html

      Delete
  25. Uriele8 October 2022 at 12:28

    Hello!
    When I invert the phase (signal from sw1 to sw2) i can't ear any sound. Can someone help me to figure out what and how to check please?

    ReplyDelete
  26. vin977 December 2022 at 23:14

    How would the circuit look without the phase switches?

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    Replies
    1. mirosol8 December 2022 at 05:33

      You could just use a jumper between switch wires 2+1 or 2+3. However, the switch is rather useful in this circuit...
      +m

      Delete
    2. vin9712 December 2022 at 15:33

      This comment has been removed by the author.

      Delete
    3. vin9713 December 2022 at 13:25

      Ok thanks, I will keep the phase reversal switch.
      How do I lower the cut-off frequency? Ideally down to the low B for 5 string electric bass.

      Delete