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mboxler

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About mboxler

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  1. PC computer question

    If your motherboard has SPDIF out pins, and you have an open slot, this works great. I have one on my ASUS motherboard. https://www.ebay.com/itm/SPDIF-Optical-and-RCA-Out-Plate-Cable-Bracket-for-ASUS-Gigabyte-MSI-Motherboard/273133351510?epid=1247152598&hash=item3f98043256:g:Lf0AAOSwUIFavPhf
  2. 12volt amplifier for la scala vintage

    The TDA7297 is a wonderful chip amp!
  3. SOLD Reckhorn DSP-6 Digital Crossover - SOLD

    Hey Warren Yes, it is still available! Mike
  4. I'm in the process of re-capping my H2's, even though the original caps measured very close to 2uf. However, I was surprised to find out that the ESR measured from .85 ohm to 1.1 ohm on the originals caps. I then measured the inductor...4.17mh, but DCR of 1.6 ohms. I agree that inductors don't wear out, but I'm replacing it with a .22 ohm DCR inductor to see if the amp can better control the woofer. I'm curious if anyone else has measured the DCR on the original woofer inductors. Mike
  5. Did Al make these universals specially for you or are these Bob's A-4500's?
  6. Active Bi-Amping/Tri-Amping FAQ

    I'm sure this distance is buried somewhere in this thread, but using 48LR, at 400hz, introduces a 2.5ms/86cm delay times two, or 5ms/172cm delay. How many cm or inches does one add for the physical distance between the K-33 and the K-55 on a Khorn? Thanks, Mike
  7. Class D

    Curious how you came up with those voltages. The maximum TPA3255 input voltage is 7 volts p-p; however, at a 21.5 db voltage gain (or 11.9 times), that would equate to 83.3 volts p-p. With a 53.5 volt power supply, you're clipping. 4.5 p-p, or 1.6 rms gets you to max, so I would think your max input voltage would be 1.6 rms unbalanced and 3.2 rms balanced. Am I missing something? Mike
  8. I had tested this before, thought I'd try again. I find this stuff fun, but I'm weird. I applied a 5.05 volt, 1160 hz signal to a dummy crossover (yes, I named it after myself). I picked this frequency because at 1160 hz, the impedance of the 6.66 uf capacitor I used = 20.6 ohms, and the impedance of the 10.3 ohm resistor I had across taps 0-4 should double. This would be the resonance frequency, the frequency at which the voltage across the load (taps 0-5) should be down 3 dB. 6.66 uf cap between input positive and tap 5 of autoformer. Wire between input negative and tap 0 of autoformer. Wire between tap 0 of autoformer and one end of 10.3 ohm resistor. Wire between tap 4 of autoformer and the other end of the 10.3 ohm resistor. Input voltage, 5.05 volts at 1160 hz Voltage across cap, 3.61 volts Voltage across taps 0 - 5, 3.66 volts Voltage across taps 0 - 4, 2.58 volts Now the fun part. The impedance of a 6.66 uf cap in series with a 20.6 ohm load is 29.135 ohms. The current of 5.05 volts thru a 29.135 ohm load is .17334 amps. .17334 amps thru a 20.6 ohm load (the capacitor) = 3.57 volts...pretty close to the 3.61 I measured. Voltage across taps 0-4 should be 3.61 * .707, or 2.55 volts...again, pretty close to the 2.58 I measured. This confirms to me that the autoformer (at least when using it to attenuate the K-55 by 3 dB), doesn't have much if any affect. Mike
  9. Measuring K-33 impedance in K-horn.

    A first order filter is doesn't do much within a couple hundred Hz either side of resonance. If everything was perfect (2.4 mH inductor, 6 ohm load, 400 hz), the voltage to the K-33 is down 3 dB. At 500 Hz, it's down 4 db. At 600, around 5 dB. If both the K-33 and K-55 were perfectly crossed (first order) at 400 hz, they would each be down 3 dB. The voltage across both drivers combine at 400 hz, resulting in a 0 dB summed voltage. It would be a 3 dB bump when summed, but the voltages across each driver is 90 degrees apart. As you can imagine, even if the K-33 were crossed at 400 hz and the K-55 at 500 hz, the combination would be down less than .5 dB around 450 hz (I didn't do the math). Too little to make any difference. Again, this is voltage only. Driver sensitivity, cabinet, room, and kids will change everything. That's my theory anyway! Mike
  10. Measuring K-33 impedance in K-horn.

    Thanks for doing that! Odd that the impedance is lower at 50 hz in the horn than in free air (which I assume is the black graph). Mike
  11. Measuring K-33 impedance in K-horn.

    I'm bummed. At 60 Hz, I get around 4 ohms. At 1000 hz I get around 7 ohms. Could my K-horn's not be sealed well enough against the wall, or did I just waste time with this technique.
  12. Measuring K-33 impedance in K-horn.

    You caught on to my motivation. I saw that plot. Perhaps I'll try this at 50 hz and see if I'm still in the ballpark.
  13. I would like to measure the impedance of the K-33 in my K-horns at 400 hz. I've assembled a "patch cable" to place between my amp and the bass bin. The cable contains a 101.5 ohm 10 watt resistor that will end up in series with the woofer. The resistor actually measures 101.5 ohms. I have a free product on my Windows PC (fg_lite from Marchand Electronics) that allows me to generate the 400 hz signal. The chain will be PC-->DAC-->amplifier-->speaker cable-->patch cable-->right K-horn bass bin binding posts. These binding posts are connected directly to the K-33. When the signal is generated, I will turn the amp up until the tone becomes somewhat loud. I will use my Fluke 115 Trus RMS meter to measure the voltage across the right amplifier binding posts. I'll call the Vin. I will then measure the voltage drop across the 101.5 ohm resistor. I'll call this Vr. I will then calculate the current through the resistor. This will be Ir. Ir = Vr / 101.5. I will then calculate the voltage drop across the K-33, which should be Vin - Vr. I'll call that Vk33. Since the current passing through the resistor must be equal to the current through the K-33, I can calculate the impedance (resistance) of the K-33, I'll call that Rk33. Rk33 = Vk33 / Ir. This is what I ended up with... Vin = 6.325 volts Vr = 5.995 volts vk33 = .33 volts (man that's loud!) ir = .059 amps Vk33 = 5.887 ohms Does this method correctly measure the impedance of the K-33 at 400 hz? If so, I think I'll plot a few other frequencies just for fun. Sorry if this has been tried before. Thanks, Mike
  14. Class D

    Great catch! Where did you find that document? Even TI's website shows revision A document.
  15. Class D

    I posted that document here a month ago, wondering the same thing. Once I got the EVM, it was hard to tell if it was incorporated or not.
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