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About make an audio power amplifier.

Discussion in 'General Electronics Chat' started by Nikolai Petrenko, Jan 30, 2016.

  1. spec

    spec Well-Known Member Most Helpful Member

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    Yes Warfdale speakers were very good value. I used their Bronze 8 RS/DD dual concentric speakers in quite a few home made-speakers. They did have a coherent sound because there were no electrical cross over. As you say they were quite efficient too.

    [​IMG]
     
  2. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The "wizzer cones" in those very cheap Warfdale speakers beams high frequencies straight forward so that they are not heard at the sides.
    I found an article http://troelsgravesen.dk/WharfedaleSuper8.htm about the old Warfdale speakers that show that its "straight sided cone" has severe breakup at 3kHz which produces a +12dB peak! The wizzer cone made a mess of higher frequencies so it was removed.
     
  3. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    100 W woofers with 30 W domes is essentially what I have in my speakers, these http://starchive.phxaudiotape.com/viewtopic.php?f=12&t=357 made by Avid 102's (I won them). The tweeters were fused separately at 1 to 1/1/4 Amp. I was frequently blowing tweeters. ~100 W amp.

    The grill design was neat. Grommets on the particle board and about 1/4" studs, so the "finishing" was pretty easy. The fuse was easily accessible from the front, but with a low-profile holder. I DID actually knock the tab off the holder once and had to replace the holder. The tweeters will die with high temperature.

    Here http://electronics.mcmelectronics.com/search?cataf=&view=list&w=dome+tweeter&x=0&y=0 are some dome tweeters. I replaced mine with tweeters from Radio Shack.

    I never used a ribbon tweeter before.

    I did hear some https://en.wikipedia.org/wiki/ESS_speakers ESS speakers that used the Air Motion Transformer.

    I''m inclined to suggest that Electrostatic, AMT, ribbon, dome are better in that order.
     
  4. dave

    Dave New Member

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  5. spec

    spec Well-Known Member Most Helpful Member

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    Thanks for that AG. :arghh:
     
  6. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Hifi tweeters are not designed to play the very high distortion from acid rock "music". The high power high frequency distortion from amplifier clipping wipes out a hifi tweeter in no time.
     
    • Agree Agree x 1
  7. spec

    spec Well-Known Member Most Helpful Member

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    That is one of the reasons for having an amp with a big voltage and current margin. It is quite true that tweeters are vulnerable although I have never had a problem in that respect with any type of music. To be safe though it would be wise to put a power monitoring circuit around the tweeter or in the power amp.

    I have seen plenty of tweeters blown by high frequency amplifier instability though, especially with MOSFET amplifiers.

    spec
     
  8. Nikolai Petrenko

    Nikolai Petrenko Member

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    Here is my crossover: (Now I have more than enough opamp to use because my bro have a lot.) All power supply wires are omitted in the shematic to reduce clumsy :D
    Crossover-sch.png
    And here are PCB layout for preamp and crossove sections, I decide to make seperated boards because they have different widths:
    (1) Preamp:
    Preamp.png
    (2) Crossover: Crossover.png

    NOTE: The ground connection to the power supply unit of the crossover board is omitted because if connect, it will create ground loop. It is the reason why power supply terminal in board #2 are only have Vcc and Vee connectors.
     
  9. spec

    spec Well-Known Member Most Helpful Member

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    Be best to put a 47R resistor between IC2A and C1 and IC3A and C3

    No Volume or balance controls?

    You have omitted one of the most important aspects about a preamp design, the power lines.

    Some of your component name and values cannot be read because they clash.

    The output impedance of the base pre amp to the base sub is way too high (5K).

    Please use the circuit in post #351 which we have already discussed.:meh:

    spec
     
    Last edited: Jul 23, 2016
  10. Nikolai Petrenko

    Nikolai Petrenko Member

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    What is it purpose?
    They will be connected by wire. Put them in the board cause me don't know how to arrange parts well. The wires will be as short as posible, of course.
    I have omitted them in the schematic because it is too hard (for me) to draw clearly.
    Because they are on the board, not on the schematic. I will post coloured version.
    But will it cause problem? Input impedance of the power is 24k.
    I can buy 12k5 resistor but 5k not available (why?).
     
  11. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Sallen-Key Butterworth highpass and lowpass filters are good for audio because their passband is flat and their cutoff is sharp. But yours are not Butterworth.
    If the gain of the opamp is "1" then the feedback capacitor value should be double and the feedback resistor value should be half. Your highpass opamp gain is "1" and your values are the same in your highpass filter so its output will be -6dB instead of -3dB at the crossover frequency.
    If the capacitor values and resistor values are the same then the gain of the opamp should be about "1.6" but your lowpass opamp gain is "2" so it will have a peak at the crossover frequency.

    Guess what? Your filters are second-order and since it is an even number then the phase shifts cause cancellation at the crossover frequency. A common fix is to reverse the phase of the tweeter or woofer but that causes a +3dB peak at the crossover frequency. Experts use Linkwitz-Riley instead of Butterworth alignment and reverse the phase of a driver for a flat response at the crossover frequency. A Linkwitz-Riley crossover has opamps with a gain of "1" and capacitor values and resistor values are the same.
    You can look at Linkwitz-Riley crossovers in Google.
     
  12. Nikolai Petrenko

    Nikolai Petrenko Member

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    What I am going for is Linkwitz-Riley crossover. They give advantage: flat sum response, and allow me to use single capacitor instead of double, since 0.2uF are not available.
    But I forgot that Linkwitz-Riley are use with gain=1, while my mistake schematic use with gain=2 :banghead:.
     
  13. Nikolai Petrenko

    Nikolai Petrenko Member

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    Update for previous foolish version:
    Preamp:
    Preamp.png
    Crossover: Did like Mr.spec advice :D
    Crossover.png
     
  14. audioguru

    audioguru Well-Known Member Most Helpful Member

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    I am glad that you know about it.
     
  15. Nikolai Petrenko

    Nikolai Petrenko Member

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    I was surprised by it performance against traditional Butterworth filter like flat sum response, require only one type (value) of capacitors (because I choose LR2 version).
    But the phase of low-pass output are inverse 180° with the high-pass one. So in the layout above, I used half of NE5532 as inverting unity-gain , but also have a selector (phase-ctrl connector) in the layout to select inverted or non-inverted.
     
  16. Nikolai Petrenko

    Nikolai Petrenko Member

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    My preamp power supply, came from Elliott 48V phantom power supply:
    PSU.png
     
  17. gary350

    gary350 Well-Known Member

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    This is a very good amp I had one once.

    [​IMG]
     
  18. Nikolai Petrenko

    Nikolai Petrenko Member

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    Oh no! My amp now is solid-state, I don't have money build any Western valve amp above 5W. I will build GU-50 50W amp. :D
     
  19. gary350

    gary350 Well-Known Member

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    If it is solid state then it is not the same amp. Dynaco made some wonderful tube amps, 30, 60, and 120. They were the master of that time in excellent quality kit amps. The 30 was plenty loud it made all the sound I wanted and then some.
     
    Last edited: Jul 28, 2016
  20. Nikolai Petrenko

    Nikolai Petrenko Member

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    Thank for info. I am interested in solid state amp more than valve amp. I only like using valve amp as guitar amp, where than valve distortion is more interesting.
    I will buy Russian valve like 6N1P-EV, 6N2P-EV and GU-50 to build 50W valve amp. GU-71 will be use if more power are considered. Western valve like ECC82 and EL34 are too expensive for my budget and pretty hard to buy.
     
  21. audioguru

    audioguru Well-Known Member Most Helpful Member

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    A long time ago before transistors, vacuum tube valves were used in amplifiers, TVs and radios and needed a huge and expensive output transformer. The valves did not last long so they were cheap and sold everywhere, even in corner convenience stores that had a "tube tester" to measure how much the old tubes wore out. I suspect that the tube testers measured low on purpose so that more replacement tubes were sold.
     
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