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The Black Dog: A stealth woofer. (part 1)

Discussion in 'Amps and Cabs [BG]' started by Ace Marconi, Jan 2, 2012.

  1. As an avid junque collector, recovering amateur radio operator, cheap Scottish bass (re)tard, and good ol'e farm boy, one of my frequent cures for G.A.S. entails hauling out the soldering iron, and digging into the collection for bits and pieces.

    Of late I have been feeling a certain depression, due to envy towards those acoustic guitar players, banjo pluckers and fiddle friends, with whom I jam, more or less weekly (sometimes weakly). They just whip it out, check the tuning, and they're off to the races. I have to set up an amp, find power, etc. Minus one to spontaneity.

    I admire the double bass players, however I haven’t enough time, or money (see cheap note above) to buy and learn a Bull Fiddle (would if I could). I have looked at the bass acoustic guitars, however they mostly seem to vanish into an acoustic void once the banjo winds up and the martins set to strumming, unless you use an amp. Meet the new boss.... The problem is not the usual indoor shows and practices. Plug-ins are plenty, and I can usually arrive early.

    When summer comes, and the music moves outdoors, busking on main street, or in the park, the system breaks down for me. I have tried running my practice amp on an inverter and battery, but things buzz, and there are even more wires to deal with. And some places even have a no amplifiers rule, if you can believe that !!!!? Hmmmph. :rollno:

    There are battery powered amps available on the market, but those with any output or stamina are way out of my fiscal ballpark (see cheap note above). I was digging through the Junque, looking for a part for my buddy, when I saw IT! In one gestalten flash, I saw the future, an answer! I forgot my quest, told buddy I didn't have one after all, and pulled out the graph paper instead.

    Over the next day or two, I assembled a small pile of components. A piece of drain pipe, some scrap 3/4 inch wood, a pair of heavy duty 10 inch woofers (8 ohm, ~100 wrms, 1 inch voice coil) from ported hi-fi speakers, a 12 volt gel cell worthy of robot wars, and IT! :hyper:

    “IT” was an older car stereo amp, about 50 wrms/ch. It sounded very nice in my old K-car, twice removed. I first tried ESP's simple bridging solution (phase splitter), to make it mono, but it started sounding a bit raspy above 20 watts or so. I tested it in stereo, and it was all good. So far so good. Next I modified the phase splitter into a flat preamp, and tested with the Fender beast. All good, although the dummy loads are smoking a bit on the low B.

    So far the only flaw in my plan is that this thing will be as heavy as a 100 watt combo amp, plus the weight of the battery. At least it will be cordless, wireless, and easily hidden. Gotta find some wheels....

    Next stop, the woodshed. Stay tuned. Should be some pictures coming soon too!
  2. ian_s


    Jul 10, 2009
    The battery weight is an insurmountable problem. Battery watts are heavy. But if breaking free of a wall socket is what you need, it's worth it...?
  3. The starting point. These are the items ripped out of the Olde Junque Shede


    My woodworking shop is at the other end of my yard, and can be heated . Normally projects in the dead of winter require justification, due to the extra electricity required for warmth. However this winter has been truly kind. A couple evenings with the tree torture devices have rendered a neat 14 inch cube for all of the elements to live in. Wheels have also been found, and hopefully a collapsible luggage handle can be added as well.

    The unit has been assembled once now, and then disassembled for painting, and installation of wheels & such. Even without any midrange driver there is enough mid to lend a clear tone, and although there is little fundamental in a cabinet this size, the growl is well defined. The amplifier unit itself seems to be fet based, as the distortion at maximum has a nice woody character. I have also provided a dc supply point to run the wireless receiver, and an input for stereo mp3 players, and things. The amp itself is running in stereo, with the bass input split across the two channels.

    There should be room on the control plate to add a headphone output, and perhaps DI output as well, if I find the right transformer in the shed. The grill panel is constructed as well, and will be covered with cloth. I seem to have figured out picture imbedding again, so hopefully another picture or two will make it into the forum shortly.
  4. will33


    May 22, 2006
    This is cool, I'll be following along here. Be interested to know how you "modify the phase splitter into a flat pre?". And of course, battery life. Good stuff there.
  5. christw

    christw Get low!

    May 11, 2008
    Dayton OH
    I'm interested too. This is exactly like something I would do when I have too much time on my hands in the winter so I'm watching intently. I'm also curious about the phase splitting.

    Anyways, this is my little winter project.
  6. Hi Paul,

    Yup that's the one. The little old Alpine amp didn't like it though. I am now using most of that circuit to pre the left & right channels of the amp. One for each speaker, in phase. It amounts to the same thing, really. I used NE5532 for low noise. I'm feeding that with the ipod inputs in stereo, and the level from the volume pot summed into both. I added another 5532 as a rail splitter, and more preamp before the volume control. Only a single rail power supply. Feeding that with the Tillman front end, more or less. A schematic will get posted eventually.

    I have an extra stage, just in case I want to twist the response for a change in voicing. That will be much later.

    More pics to come.
  7. will33


    May 22, 2006
    Now that is a cool little unit.

  8. I have returned from the woodshed, Thanks to the springlike weather, the primer coats are dry, and it's time for the next test assembly :hyper:


    Note the port tube in the lower right. Also note that you are seeing the grill baffle in place, waiting for it's cloth covering.

    The working control unit from several angles:




    Bluegrass practice time. Must go to train station now.

    See y'all later!
  9. JASON221


    Oct 6, 2011
    Very cool[​IMG]
  10. If you're only using a single rail y' ain't gonna get too far!!! :D

    Ho ho ho!
  11. One track mind, Paul. Strictly monorail. Just hangin' out under the tracks y'know?

  12. christw

    christw Get low!

    May 11, 2008
    Dayton OH
    I'm not ashamed to say I cracked a smile from that ^ little exchange. ;)
  13. As did I!! A smile a day help you work, rest and play! :)
  14. Most welcome Will. If you back out to the root of his site he has many useful little projects. A good one is his high pass filter project.
  15. will33


    May 22, 2006
    Yes indeed. Was reading through his passive crossover section last night but fell asleep before I reached the end. He's not a big fan of those things but seemingly for valid reasons.
  16. will33


    May 22, 2006
    I was about o ask what all those extra holes in the cabinet were for before realizing it was the grillcloth frame.:p
  17. Yes Will,

    Last time I cut out a grille cloth frame, I ended cutting the middle out of a larger board. Seemed a bit wasteful considering I was about to cover the grille with wire to keep boots out.

    It looks impressive (Mrs Marconi & Ace Junior think its a pity it gets covered with cloth, but we gotta keep the ciggy-butts & bugs out too! Let me find another picture here,


    Is everyone in ? Then Lets Begin.


    Starting to get finished. Beginning localized hunt for Rat Fur.


    Battery is fully charged. Gonna try to play all day at house volume, and see how this battery is. Surplus batteries come in packs of 4, out of which one is always High resistance failed, and one is usually poor. Not sure which one is the runt yet.

    BTW Big vote of :D for ESP website. There is more actually to be learned than just his schematics. He invariably instructs in his projects.
  18. will33


    May 22, 2006
    Absolutely neat work. What do you use that can last that long, a marine battery or something? Does the amp stay cool enough inside the cabinet? Any ideas of just changing the battery at long sessions? I imagine you have all this figured out, just curious.
  19. majortoby


    Jul 2, 2009
    Tampa, Fl USA
    I wonder if one of the smaller bfm designs wouldn't lend themselves to a project like this. After all, his horns are wicked efficient, which would certainly help battery life. And iirc, the jack 10 has a bit of a response bump in the upper mids, which would also help perceived volume. Your guys' thoughts?

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