AliExpress / eBay JL Hood 1969 Class A Amp

Discussion in 'Power Amps' started by purr1n, Apr 25, 2017.

  1. Priidik

    Priidik MOT: Estelon

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    Nothing wrong with that. It is not ideal, and with a keen eye you noticed that in my schematic I have damping circuit (snubber) over the diodes, usually 100nF + 100 ohms will do.

    Here, apples-to-apples. The snubbers removed, series inductor removed (1nH is less than straight wire) and current increased to about 4.7 A. Diode dissipation is now about 2 W.
    Note, as Mr @murray hinted about storage capacitors, the snubber as well will practically not affect the diode dissipation, the point of it is to reduce the dU/dt for it to not produce radio frequency noise, thus it would spread out the peak over a wider area.
    upload_2020-10-16_9-24-50.png

    At some point it is best to start building the damn thing, the LTspice can trap you into infinite 'polishing-wank'.
    Besides it is fun to burn some components once in a while, diodes and most transistors are cheap. Use eye protection!
     
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  2. Mihnea

    Mihnea Rando

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    Thank man! Indeed, I need to start soldering the damn thing. Anyway, I want to place a fuse right on the transformer sec , because that is the most expensive part.
    So you think that the toroidal that I have should be enough to get those clean 18V DC? I need to be sure before I order the second one. I still have the option to return it and exchange for something with higher sec voltage.

    Mihnea
     
  3. Priidik

    Priidik MOT: Estelon

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    Can't really tell what transformer you have, the pic link doesn't work for me.
    From the sim I see about 27 V peak.
    I will assume two secondaries each 19V rms. And 200VA total power.
    To have 5 amps comfortably available at +/-18V in the psu output and you insist on linear regulators (which would drop at least 5V to counter grid and load fluctuations) then this hypothetical tranny would be a bit shy in both voltage and power headroom.
    22..24V per sec and 200VA per sec (400VA total) would be more like it. With more voltage headroom you can play with inductors after the rectifier. (bonus, 24V and 400VA is a common industrial piece, abundant)

    Also, beware when you measure transformer sec voltage to open loop (voltmeter) then you get somewhere around 5..10% higher reading. The stated sec voltage is for full load conditions.

    Regarding fusing, some trannies have bi-metal thermal switch built in to cut the power.

    Bonus tip: when screwing around put a 100W halogen lamp in series with the primary. When you short the secondaries the lamp would just turn on and protect the downstream.
     
  4. Mihnea

    Mihnea Rando

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    Thank you for the tips! And indeed, the transformer is 2x19V RMS 300 VA (2x7.9 A)! :)
    I will trade it back and get the 24 V version. I think is for the best.
    Thank you again,
    Mihnea

    *I'm absolutely positive that I'll throw some more questions your way at some point. I hope you won't mind.
     

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