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Help getting the best out of Wolf's Microdot mini sub.

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  • Help getting the best out of Wolf's Microdot mini sub.

    Hi Guys,

    I finished building Wolf's " Microdot " subwoofer yesterday. I was fun to build and is a really neat little speaker, measuring 6.25 inches on all sides. I am powering it with a Lepai 168 HA 2.1 amp partnering it with Chris Roemer's Pico Neo speakers. The Microdot adds substantial depth and fullness to the Pico Neos and the system is excellent for near field listening and will do well in a small room. I plan on using it in our 200 square foot kitchen if I don't gift the system to my nephew who is a college freshman. I tested it today on music and with the Stereophile CD test tones and it provides strong response from 100HZ to 50HZ but shows an 8db drop off from 50 to 40. All in all it works quite well with the PNs.
    But there are issues. While the bass goes deep, the very deepest bass is somewhat distorted and the excursion of the Tang Band driver and passive radiators appears to be about 3/8 of an inch. Also, the blue LED on the Lepai 168 HA amp, which i think indicates clipping, gets very bright when driving the Microdot at 63 HZ or below. I have a 12V 5 amp power supply in my Amazon shopping cart in the hope of helping the Lepai, but have not been able to find a Wolf-recommended 8 amp PS. Does anyone have a link for that or alternatively, a suggestion for a better, but affordable, 2.1 mini amp?
    Overall, I am very pleased with the combination of this tiny sub with the PNs and think it would be even more valuable with desktop speakers that don't have the impressive bass of the PNs. I would like to fine tune it to get its very best though, and any input in that vein would be much appreciated.

    Best
    Jay
    Microdot atop a Cerberus, itself considered a very small sub. A closer look at the Microdot, which is fully functional, but has not had the cabinet sanded and shelaced A view of the one PR of the Cerberus and one of the two on the Microdot

  • #2
    Like I said- the rumble filter should be close to 30Hz to avoid the distortion issues. If you use a 25W plate amp, you can likely adjust the rumble filter on it.

    I have this PSU:
    http://www.parts-express.com/mean-we...pply--320-3148
    ...and you can turn the voltage adjust pot up to get about 13.8VDC.

    Later,
    Wolf
    "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
    "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
    "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
    "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

    *InDIYana event website*

    Photobucket pages:
    http://photobucket.com/Wolf-Speakers_and_more

    My blog/writeups/thoughts here at PE:
    http://techtalk.parts-express.com/blog.php?u=4102

    Comment


    • #3
      Pllxo ...

      Comment


      • #4
        Pllxo ???

        Comment


        • #5
          Sure- that might be easier:
          http://www.parts-express.com/harriso...s-rca--266-248

          Later,
          Wolf
          "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
          "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
          "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
          "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

          *InDIYana event website*

          Photobucket pages:
          http://photobucket.com/Wolf-Speakers_and_more

          My blog/writeups/thoughts here at PE:
          http://techtalk.parts-express.com/blog.php?u=4102

          Comment


          • #6
            Originally posted by Drjay View Post
            Pllxo ???

            passive line level crossover

            Comment


            • #7
              You can create a 1st order HP filter simply by putting a cap in series with the L-R channels' positive inputs.The cap, in conjunction with the amp's input impedance will create the HP filter. I've done that in a signal cable to an amp to solve the same issue the OP is having. You can calculate the F3 of the HP filter given the cap value and the amp's input resistance.

              I took a look at the Lepai's PCB some time ago. And while there are different revisions, the board I saw had the positive side of the inputs connected in series with a 1K resistor to the master volume pot. That volume pot will mostly determine the input resistance of the Lepai. Since I was looking at a pic, I didn't know pot's value. And that value will effect the HP freq for any external PLLXO .

              If it were me, I would order some 0.068uf, 0.1uf, .22uf film caps and experiment with different values either using a single cap or paralleling caps to obtain different values (e.g., 0.068uf and 0.1uf yields 0.168uf). There's some "sites" where you can order a have dozen or so caps of a specific value for a buck or two (maybe $5 total for this approach). You may need to wait a week or two to get them.

              Not as pretty as the pre-made Harrison labs units but it should enable you to dial in a decent fix. And if you have the skills, you could cut two traces on the Lepai's PCB near the inputs, jumper the cut with the cap(s) putting the final solution in the box.

              If you need more "details", PM me.

              Lepai LP168HA PCB Bottom Rev 5.0a.jpg

              Comment


              • #8
                When I built my QMD (QUASI-Microdot) subwoofer, I used a Dayton 25W plate amp, which had a built-in HP filter, but was too low and not adjustable. I went in and modified a couple resistors to adjust the HP filter to a more appropriate setting.
                Last edited by 1100xxben; 12-20-2016, 08:54 AM.

                Comment


                • #9
                  FWIW, I measured a SA25 amp I bought for a future project to see what its response is. I simply measured the voltage across a 20 watt 4 ohm resistor. It is down 1 db at 30hz and rolls off at 12 db/octave below that. On the high end, it is down 1 db at 90 hz and rolls off at 6 db per octave above that (down 6 at 180 hz) with the low pass filter set to max. Between 35 and 80hz, its very flat. This is about perfect for the micro-sub project I have planned.
                  -Bob

                  The PEDS 2.1 mini system
                  My A7 Project - another small desktop speaker
                  The B3 Hybrid Dipole - thread incomplete and outdated

                  Comment


                  • #10
                    I considered trying the SA25 but was very nervous about trying to cut it down to fit. Would the driver and passives of the Microdot give the same performance in a box that was enlarged just enough to take the amp? Also, building a new box would be easy but it seems that some advanced builders are having problems getting adequate sealing. Thoughts?

                    Comment


                    • #11
                      Is there a link to Wolf's Micro-dot sub design?

                      Comment


                      • #12
                        Originally posted by Drjay View Post
                        I considered trying the SA25 but was very nervous about trying to cut it down to fit. Would the driver and passives of the Microdot give the same performance in a box that was enlarged just enough to take the amp? Also, building a new box would be easy but it seems that some advanced builders are having problems getting adequate sealing. Thoughts?
                        I used the SA25 and did not have to cut down the amplifier. I'm not sure what your dimensions are, but as long as you keep the volume the same, you can enlarge the 2 dimensions and shrink the third to accommodate. Since you're building a sub, and the entire frequency range of use is well below the baffle-step, there's no need to worry about modifying the baffle from the original design and causing problems.

                        Comment


                        • #13
                          Thanks Ben,
                          I will do that build soon. Do you have any advice about how to avoid problems with the SA25 leaking air? I remember a post where a very experienced forum member tried to seal it, struggled unsuccessfully and wound up having to replace a volume pot. My electronics knowledge and soldering skills are even poorer than my speaker building ones so I don't want to get in too far over my head here.

                          Best,
                          Jay

                          Comment


                          • #14
                            Originally posted by Drjay View Post
                            Thanks Ben,
                            I will do that build soon. Do you have any advice about how to avoid problems with the SA25 leaking air? I remember a post where a very experienced forum member tried to seal it, struggled unsuccessfully and wound up having to replace a volume pot. My electronics knowledge and soldering skills are even poorer than my speaker building ones so I don't want to get in too far over my head here.

                            Best,
                            Jay
                            If I remember correctly, the only problem I had with leaking was around the power cord. I used some "putty" to seal it off and don't remember having any other issues. I don't know how many holes are drilled in the plate, but I may have drilled some extra holes to put more screws in. The plate is really thin and if the screws aren't close enough together, It will flex and leak between the screws.

                            Comment

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