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vainajala

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Posts posted by vainajala

  2. Passive audio filters

    in Electronic Projects Design/Ideas

    Posted

    <bump>
    I understand this is not really a forum about loudspeakers, but here's some updates...

    This might be the final crossover's circuit... I just need to wait until the drivers arrive to me (about 2-3 weeks maybe).

    And when I get my "testing gear" (a speaker measurement jig+microphone+computer) ready, I can actually measure how well or bad these drivers perform in this application. And tweak the crossover if needed.
    Before that, I must trust my ears ;D

    The Jig: http://www.gti.net/wallin/audio/audua/audua.html

    post-2509-14279141694342_thumb.png

  3. Passive audio filters

    in Electronic Projects Design/Ideas

    Posted

    Hello Audioguru, and thanks for your reply :)

    1) If the woofer and tweeter are wired with the same polarity, then the system acts like a notch filter at the crossover frequency. If one driver has its wires reversed, then the system will have a 3dB peak at the crossover frequency. See my discussion of this matter and a link to a manufacturer's expert's comments, here:
    http://www.electronics-lab.com/forum/index.php?board=2;action=display;threadid=636


    Actually, I was going to connect the drivers with opposite polarity.

    2) The 12dB/octave filter for the woofer may not have enough attenuation at its 4dB response peak of 5800Hz. This peak gives a "nasal" sound and it is best to attenuate it with a steeper filter.
    The same problem may occur with the 1700Hz resonance of your tweeter, since it may reach the limit of its excursion and distort badly.


    This really got me thinking of using 18dB filters, for their better performance.

    3) Although zobel networks are good to flatten the impedance of inductive speakers, your low-impedance speakers in parallel with your low-value zobels results in very low impedances. Can your amplifier drive a 2 ohm load?


    My amp is a Sony's model STR-DE585, not a welding machine ;D But seriously, I think it's rated for nominal impedances between 6-16 ohms...
    If I use the filter component values determined by the basic calculations (with no Zobels), and simulate that with 7spice, the freq. responese has very large variations, caused by the inductance at the driver... I see no other way than using the Zobels :P

    4) A passive crossover ruins the damping of each driver by the amplifier.


    Of course this is a bad thing, especially when one wants only the highest quality and performance. But you see, my goal with this design is to create small 2-way loudspeaker pair with decent soundquality and complexity... So I think a natural choice for me is a passive crossover.

    I, and the expert linked in my discussion that is linked above, agree that a passive 18dB/octave Butterworth crossover network will solve most problems, and if you use the woofer's inductance as a component, then you simply must add only 1 cheap capacitor to the tweeter's filter, to obtain 18dB/octave Butterworth filters for both the woofer and tweeter.


    That's a great suggestion, but when using woofer's coil inductance as a 0,60mH inductor, I get crossover frequencies about 930 Hz for 18dB crossover... with formula taken from speaker design book.

    L=(80*Z)/f --> L=(80*~7ohm)/930Hz = 0,6mH

    IMHO, this could work well with 3-way's, but bit too low for 2-way :(

    Perhaps you can increase the resistances (and correspondingly reduce the values of the capacitors) of the zobel networks, to increase the impedance of the completed speaker as seen by the amplifier.


    I'll see what I can do! :)

    I have not checked that your filters' crossover frequencies match each other, nor that they match the parallel combination of each driver and zobel, nor that they match your drivers.


    These both filters have -6dB points at 3,05 kHz according to 5spice... should there be some "gap" between them, for example, -8dB at 3,05 kHz?

    Another expert also agrees to avoid a passive 12dB/octave crossover, and strongly recommends bi-amped speakers with active electronic crossover networks. I have heard many professional systems of this type and the sound is truely amazing!
    If you are capable and ambitious, then this is the way to go!
    This expert's articles are here:
    http://sound.westhost.com/lr-passive.htm
    What do you think about that?


    I think it's an interesting article...
    But for the bi-amping, I understand it is a great technique because there is no need for passive crossovers, but unfortunately I don't have resources and equipment for that kind of system...

  4. Passive audio filters

    in Electronic Projects Design/Ideas

    Posted

    Hi,

    I have in mind building small 2-way loudspeakers to my stereo system, because the old speakers are in so bad condition. The bass-element's foam surround has come really "weak" and it has many holes even though the surround hasn't been touched by hand practically at all! The loudspeakers are at least 15 years old, so it's really not a wonder :)

    I'm considering Vifa TC14WG49-08 as bass/midrange:
    http://www.d-s-t.com/vifa/data/tc14wg49-08a.htm
    and (maybe) Vifa D20TD-05-06 as tweeter:
    http://www.d-s-t.com/vifa/data/d20td-05-06a.htm

    They are most propably to be installed in 14 liter bass-reflex box tuned at 43 Hz.

    I knew something about different loudspeaker enclosure types (and how they work) before I was even thinking of starting this project.
    But I must admit that i'm quite a new-bie when it comes to crossovers. I haven't designed these before and I thought it might be wise ask you will they work before I start buying the crossover parts. They are quite expensive, you see...

    The pictures from analysis program 5-Spice follows. They are (at least they should be ;D) -12dB/octave filters, with Zobel circuits. Any comments are appreciated...

    post-2509-14279141684103_thumb.png

  10. Switching power supply

    in Electronic Projects Design/Ideas

    Posted

    Audioguru, thanks for information! I must try this when I have more time for this project...

    Ante, maybe the MAX626/627 driver could be used to drive the dual P-channel FETs then? And, should I get inverting (MAX626) or non-inverting (MAX627) driver?
    Also the max. 18VDC supply must be arranged for the MAX62*, that's one concern too.

    I'll maybe use 2-3 of IRF9540N FETs...

    post-2509-14279141651443_thumb.png

  11. Switching power supply

    in Electronic Projects Design/Ideas

    Posted

    I decided to test N-channel MOSFET as a switch transistor, and it worked well! Typical efffiency was 77% with 21W and ~74% with 55W.
    The heatsink was so small that the FET heated pretty quick with 55W and higher loads, so effiency in these loads is more "approximate".

    I had to make modification to circuit to drive the FET: I tied the emitters to the FET's gate (instead of collectors) and collectors to Vcc.

    This is very promising result, and at least using FETs, the base resistors can be eliminated. So I'm considering to use two or three N-ch FETs in parallel instead of BJTs...

    NTP45N06L N-ch FET
    http://www.onsemi.com/site/products/summary/0,4450,NTP45N06L,00.html

  12. Switching power supply

    in Electronic Projects Design/Ideas

    Posted

    About darlingtons...

    I tried a darlington transistor configuration with dual MJ15004 transistors. 55W halogen served as a load, again. Unfortunately I didn't measure the performance of that circuit (Iwas in bit of a hurry...), but the output-transistor got very hot (i almost burn my finger when touched it ::))
    I experimented some different base resistors from 330R to 10K with little or no impact on "heating-effect".

    I see you're discussing about darlingtons, well how about Sziklai configuration (also known as the complementary Darlington)? I suppose that the Sziklai-type has lower saturation voltage when compared with ordinary Darlington... I found this information from some finnish electronics website. Text was in finnish, so I put a translation in a form of a picture :)

    Some more Sziklai info here:
    http://www.ampslab.com/c200cfp.htm

    post-2509-14279141650086_thumb.png

  14. Switching power supply

    in Electronic Projects Design/Ideas

    Posted

    First of all, thanks for your help, it's surely needed ;)

    Audioguru,
    What do you think about using three MJE2955's in parallel, with 0,1R emitter resistor in each? By the way, are the "equalizing resistors" needed in switching applications?

    As far as I can understand in this transistor's datasheet, the HFE=~40 at IC of 3A. So with three transistors, max. 9A could be drawn with HFE ~40.

    So base resistors: 45V / (3A / 40 * 1,3) =460 ohms, and wattage: P = 0,075A2 * 460 ohms = 2,58W.
    Am I correct?

    9A would be actually more than enough, the circuit's current limit start at ~7,5A...

    MOSFET(s) might be good idea. Could P-channel fets be easily used in this circuit? IRF9540 or IRF5305 maybe? ???


    MJE2955: http://www.onsemi.com/site/products/summary/0,4450,MJE2955T,00.html

    post-2509-14279141649203_thumb.png

  17. Switching power supply

    in Electronic Projects Design/Ideas

    Posted

    I have now built the powersupply and tested it a little bit. I unfortunately can't test it thoroughly, because I don't have a variable DC-supply. I'll try it tomorrow with two car batteries in series, resulting 24V.

    I did some tests with a car battery charger as a mains supply, trying some 12V bulbs and small fans as a load. It did work quite nicely, and it lowered the output voltage to about 8-9V (charger's voltage is about 18V when not loaded).

    I also measured volts and amperes & calculated effiency "n":

    • With 21W car bulb: n=74%
    • small 12V/100mA fan: n=68%
    • 55W car halogen: n=46%

    (charger's max. current sets the limit here, it's only 4A)

    It definitely needs more testing, fine-tuning and of course heatsinking, but if it works after that, I think it will be worth of it :)

    post-2509-14279141648502_thumb.jpg

  21. Switching power supply

    in Electronic Projects Design/Ideas

    Posted


    Perhaps you could leave it as it is and later make a new REV?

    MP


    That's OK, if you say so!
    You know, I'm just trying to make it "even better" and easier to use... ;)

    I posted a picture about a thing which confuses me. I hope you can answer.

    What do you think about the R12's value? Is it correct? The TL494 needs supply current of 15mA MAX. My transformer gives about 45VDC, so can I calculate resistor value like this?:
    (45V-39V)/0,015A=400 ohms?

    Would be glad for help! :)

    post-2509-14279141642929_thumb.png

  22. Switching power supply

    in Electronic Projects Design/Ideas

    Posted


    vainajala,

    If you can fit a heatsink on the TO3 your home free.

    Ante ::)

    Heatsinking of the MJ15004 (in TO-3) is a problem, should I do a mofidied version with, for example, parallel-connected two or three BD912's (in TO-220)? Because TO-220 is way more easier to heatsink than the TO-3 in my opinion...

    If I end up using the BD912's, I don't think that the TL494 has current capability to drive paralleled transistors. So driver transistors might be a mandatory addition in that case...

    [glow=red,2,300]OR[/glow]

    Should I just stick with the original design?

  23. Switching power supply

    in Electronic Projects Design/Ideas

    Posted

    OK, time to flood the forum again with my pictures ;D

    Well, actually it's the same circuit, with a soft-start feature that should limit inrush current when starting. The board measures about 10,5 x 7,5 cm, and I designed it with the soft-start components in place.

    If I ever get this thing to work, could this be added to the "projects" -section....? ::)
    If you will take just one more Powersupply circuit! ;)

    post-2509-14279141642029_thumb.png

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