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Seeking active Hi Pass filter for fun and profit ...

Discussion in 'Amps and Cabs [BG]' started by 4Mal, Oct 13, 2009.


  1. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge
    Profit in the sense that I want to prevent blowing up woofers by inadvertantly driving them into over excursion under 40 cycles...

    Active - I would like to run this in the effects loop of my WT-800.

    I don't want to incur the in-efficiency of a passive filter if at all possible. The WT-800 is biamp ready and I intend to use that. Just gotta be able to set a protective lower limit ...

    Smaller is better. If I could cable this thing, power it and embed it in the rack, set and forget, never to be seen again - that would be sweet!

    So I'm thinking of a device along the lines a Francis Deck's hfp box but with some twists... Any suggestions ?
     
  2. Hoover

    Hoover Banned

    Nov 2, 2007
    New York City
    check RDL (Radio Design Labs) also
     
  3. Passinwind

    Passinwind I know nothing. Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    Eden should've already done that. Before you do anything I'd ask them where the internal high pass filter is set. If they can't or won't tell you that, maybe some techie type could measure it for you? :cool:
     
  4. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge
    ooo.. ya think ? I figured it would let you go all the way to DC ... Yep gotta check that out. Long as that BMS 12 isn't selling on EBay, I'm working up a 12+6.5 based on it and the B&C and over excursion just below 40 would be a definate possibility based on what I'm seeing in WIN Isd ...
     
  5. Hi.

    With a tube amp You wouldn't have to worry about that ;).

    +1 to that.

    A rough measurement can be done with a PC-based signal generator (WinISD). Just feed the amp input with a beefy enough signal and lower the frequency.

    Do have Your grounds on the same potential though.

    Regards
    Sam
     
  6. rpsands

    rpsands

    Jul 6, 2007
    Phoenix, AZ
    I have a passive one of these in mini-pedal form and it works just fine. I'm sure it's not amazingly efficient but it doesn't seem to impact my audible signal too much.
     
  7. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    FWIW TB'er "silent fly", owner of Silent Fly FX out of the UK, has custom-made me a small active high-pass for exactly this purpose. It scopes ruler-flat down to 35 Hz, and only about 3dB down at 30 Hz, and drops sharply from there, reaching 24dB down around 25 Hz (IIRC). It's the size of a small stomp box, it runs on 9VDC, it is designed to run at either line level or instrument level, and it can run either balanced or unbalanced, and in fact it also works great as a DI, converting unbalanced to balanced. It's called the "Thumpinator", as it terminates subharmonic string thump noise.

    [​IMG]
     
  8. Jim C

    Jim C Is that what you meant to play or is this jazz? Supporting Member

    Nov 29, 2008
    Bethesda, MD
    Fantastic idea.
    Are these in production or one off's?
     
  9. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge

    Ok so can you elaborate as to the brand ? The effficiency part of the equation was me thinking of a traditional passive crossover design. Those suckers can absorb a lot of power I'm told.
    Ahead of the amp, the efficiency thing isn't really an issue. Coloration could be though ...
     
  10. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge

    Hey Bongo - that's pretty dang cool! If the Eden isn't already doing it for me - so far that looks to be a nice sold approach.
     
  11. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    They'll absorb a lot of cash too. At the least you need a 3rd order filter, and the components to build a third order 40Hz passive high pass filter will run you well over $100.
     
  12. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Mine was the first, but he had a whole batch of circuitboards made up so he can make more of them to order. His email is "max (at) sfxsound.co.uk".

    I don't know what his "regular" asking price will be. It's a great item!
     
  13. rpsands

    rpsands

    Jul 6, 2007
    Phoenix, AZ
    Mine is before the amp, runs right before my compressor. Since it's instrument level it's a lot lighter components-wise and a lot cheaper than the coils that have to deal with speaker pushing wattage.

    I had it made by GutterMouth from HCBF - Ian League. It's a nice little box, doesn't take any power. It has two options, a gentle rolloff around 75hz and a steep rolloff around 55hz IIRC (I prefer the gentle rolloff around 75hz). He's mentioned he could do a more complex one with opamps and stuff but this one was quite cheap and he suggested I try it out first - it works fine for me and the low B sounds just great.
     
  14. Gearhead43

    Gearhead43

    Nov 25, 2007
    NorCal
    What about the $50 HPF-Pre? It's got a hi-pass filter and can be run in an effects loop.
     
  15. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge
    :scowl:
    I wasn't aware of that. Fdeck's site makes it sound like it is designed to interface piezo pickups to an amp among other things... have you done that - run it in the effects loop I mean ? A/B tone wise ?
     
  16. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Piezo buffering is indeed the original purpose of the HPF-Pre. It will handle lower impedance signals just fine, and will work in an effects loop.

    However, I am somewhat cautious about recommending this preamp for electric bass, because my design begins to distort when input signal levels reach roughly a Volt peak-to-peak. Electric basses, and FX loops, can produce higher signal amplitudes than that.

    But my design, using op amps instead of discrete transistors, could handle much hotter signals.
     
  17. Gearhead43

    Gearhead43

    Nov 25, 2007
    NorCal
    I have run mine in the effects loop and didn't hear any distortion, this was with upright though but I don't see how it would make any difference.
     
  18. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    I have one of those FMODs, and there are a couple threads about them that are worth checking out. They do work, but the slope is not extreme so you may lose a bit of the lows you don't want to lose, and there is definitely a net loss of overall signal level.
     

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