My project "JLH-69"

Discussion in 'DIY' started by Zampotech, Feb 8, 2019.

  1. Zampotech

    Zampotech Facebook Friend

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    The purr1n theme AliExpress / eBay JL Hood 1969 Class A Amp excited me.

    I decided to make my own "JLH-69"

    Ordered coolers.

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    They arrived today. Had to order at 8 amps. Fewer they did not sell.

    Each cooler dissipates 70 watts of heat.


    I changed the amplifier circuit a little. The speakers are not connected to a common wire.

    [​IMG]

    Such inclusion of speakers will allow to reduce a background and to improve symmetry. But this of course need to inspect.

    I made an approximate design and made drawings for laser cutting and manufacturing of body parts.

    Two design options.
    The design is classic. Nothing extra.

    First "DOCENT"

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    The second "PROFESSOR"

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    Front mounted VU meters



    the back of the amplifier is the same in two versions.

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    Now I start to make PCB.
    After the holidays in China will order a few boards factory quality.
     
  2. Cspirou

    Cspirou They call me Sparky

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    So the negative output is isolated from ground with a capacitor? I haven't seen that before.
     
  3. Zampotech

    Zampotech Facebook Friend

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    He's isolated. Negative and positive half-wave sound should have the same path. IMHO

    There is another positive point. The power supply voltage ripple is the same in magnitude on the two speaker wires. As a result of pulsations it is not audible. The background is greatly weakened.
     
  4. purr1n

    purr1n Finding his inner redneck

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    Virtual AC ground.
     
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  5. Zampotech

    Zampotech Facebook Friend

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    Continue, step in the manufacture of PCB

    I'll order the circuit boards at the factory. But to avoid errors, I will make the first printed circuit Board myself.

    To do this, I draw the topology of the Board. One picture will all four boards.

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    I print a picture of conductors on a transparent film.

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    Unfortunately, modern laser printers do not provide the required black density. Therefore, we need an operation to increase the density of black. This is done in acetone vapors.

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    After two or three hours, the desired black density is achieved.


    Cutting off the right amount of future PCB.

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    Gluing the photoresist. There is a small defect, but it is insignificant.

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    Exposed ultraviolet lamps.

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    During the exposure, the lamps glow similar to the glow of Vavilov-Cherenkov in water nuclear reactors:D

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    Board after exposure lamps.

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    Then process the Board in a solution of soda ash. Not illuminated areas are washed off

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    Treated with ferric chloride.

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    Processing result


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    Wash off with a strong alkali the remains of the photoresist.

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    Now it remains to drill holes and cut the Board.
     
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  6. purr1n

    purr1n Finding his inner redneck

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    ^ that's so awesome. This will be very interesting without the big cap at the end.
     
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  7. Zampotech

    Zampotech Facebook Friend

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    Symmetrical flow of current through the speaker will probably give an increase in quality.

    [​IMG]
     
  8. Zampotech

    Zampotech Facebook Friend

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    My friend gave me a good idea today. He suggested making a " JLH " for low-sensitivity headphones such as the HiFiMAN HE-6.
    The project begins to split. I will produce "Big JLH" and "small JLH" only for headphones.

    I am sure that the circuitry of John Leslie Hood will show its advantages.
     
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  9. Zampotech

    Zampotech Facebook Friend

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    Preparatory work.

    I was faced with the problem of measuring the parameters of power transistors.It is important to install transistors with the same parameters in the amplifier. The sound quality depends on it.
    I have an old professional device for measuring millions of transistor parameters. But it can only measure low-power transistors.
    I had to build a small device to measure the parameter "Beta". This is approximately equal to the gain of the transistors.

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    The device is simple, but it allows you to very accurately pick up a pair of transistors at currents close to operating currents.

    During the measurement, I immerse the transistors in a glass of distilled water. Very hot.
     
  10. Zampotech

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    The next sequel

    While I have no TCT5200 transistors for large JLH. They are ordered but not yet delivered.

    My friend and friends of his friends are insistently asking me to make an amplifier for planar headphones.
    I probably talked too much about the merits of JLH. "My tongue is my enemy"
    Decided to make them ready for headphone amps or kits.

    For a little JLH made PCB
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    Prepared radiators
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    Made a small mock-up for testing.

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    Until soldered only one channel. This is enough to clarify the denominations and modes.

    Today amplifier made the first breath :D

    [​IMG]


    What's on the screen means half a watt at 16 ohms. It's small. But while the supply voltage is only 12 volts.
    The next step is to increase the supply voltage
     
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  11. Zampotech

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    Continuation

    Testing has shown that the amplifier works very well with conventional transistors of old types. And modern transistors with high gain (Darlington transistors) do not work very well.
    Darlington transistors begin to work only with large "currents of rest. At a current from 2 amps and above. For a headphone amp, that's a lot. Amplifier on conventional transistors starts to work well at 0.3 A. And very good at 0.5 А.

    Or I got the wrong type.

    I bought a large number of vintage germanium transistors (photos provided by the seller)


    These are high-frequency transistors of medium power P605

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    This is also an average power transistors GT402 and GT404

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    Have germanium transistors 346 drawback and one advantage. They're very musical.
    Owners of amps with germanium transistors emphasize musicality.

    Amplifier on germanium transistors will of course not a small.

    I'm thinking of getting a wonderful sound from an old circuit and old transistors.
     
    Last edited: Feb 18, 2019 at 11:54 AM
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  12. purr1n

    purr1n Finding his inner redneck

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    Germanium. Go big or go home.
     
  13. Cspirou

    Cspirou They call me Sparky

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    Oh dang, etching your own PCBs is pretty baller
     
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  14. dBel84

    dBel84 Friend

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    I don't think I have ever seen such a spread of germanium transistors.. dB
     
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  15. Zampotech

    Zampotech Facebook Friend

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    That's because I have a precision laminator. Here it is.

    [​IMG]

    Unfortunately, the secret of making such devices humanity has lost, as the secret of building the Egyptian pyramids.
     
  16. Taverius

    Taverius Smells like sausages

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    An elegant weapon for a more civilised age. |\/|
     
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  17. purr1n

    purr1n Finding his inner redneck

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    @Zampotech: can SBAF commission this JL Hood variant and have this amp sent to various members? Your tweaks are simple and brilliant. Those are always the best.
     
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  18. Zampotech

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    Yes, certainly. I am always open to communication with respected members of the SBAF.

    Initially I need to make an amplifier in a civilized form. Then to not be ashamed of their work

    I am a freelancer, I have time for development and manufacturing.
     
    Last edited: Feb 20, 2019 at 8:19 AM
  19. Cspirou

    Cspirou They call me Sparky

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    At a makerspace they had a class to etch your own PCB. It was to make our own Arduino trinket using a laser printer transfer with an iron. You are right about the black not being dark enough.

    If I were to do it again I would prefer to use a CNC mill. Although forget about it for 4-layer boards.
     
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  20. LetMeBeFrank

    LetMeBeFrank Won't tell anyone my name is actually Francis

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    @Zampotech Seeing the pictures of you making your own circuit boards brought back some good memories. In my highschool electronics class (back in 2004) for our final project we made our own linear power supplies. We designed, printed and etched circuit boards and hand soldered everything. We even cut and drilled the acrylic enclosures. It was a great learning experience.
     
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