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Transistor equivalent

Discussion in 'General Electronics Chat' started by Nikolai Petrenko, Oct 24, 2015.

  1. Nikolai Petrenko

    Nikolai Petrenko Member

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    Any circuits?
    Speaker protecting IC, I know uPC1237.
     
  2. spec

    spec Well-Known Member Most Helpful Member

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    Only circuits in my head. I have never built a protection circuit. All my amps have run naked. I will need to investigate. Thanks for reference to uPC1237: will evaluate.

    Apart from turn on/off thump suppression, at the moment the only other function needed is amp out put signal mean level = 0V, from DC upwards. That encompasses all significant problems with PSU and amps. Disconnecting the speakers from the amps under fault conditions will also protect the amps to a degree.

    The next function would be a frequency dependent average power output detector: 10W (10Hz to 200Hz) 5W (200Hz to 3KHz) 2.5W (3KHz to 40Kz) 0W (40KHz upwards). These are just notional figures at the moment, but do illustrate the principle.
     
  3. Nikolai Petrenko

    Nikolai Petrenko Member

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    Yeah. Now I pause concentrate on speakers protecting circuits.
    Ah, preamp! Any suggest? 60W amp 2.1 require any preamp? If yes, how gain will be well? I want my amp don't have any ICs! Only transistors, diode => preamp and sub filter use discrete transistors.
    I became tired with modern storage device like USB or SD.... I love antique ones like cassette, CD, even floopy disks and gramophone records. But cassette very hard to find now (very pouplar before 2007), floopy disks too low capacity and gramophone records particlularly expensive so I don't have any disks and player, may I found broken ones at "high-end" junk yard? ( at least I know how to repair cracked gramo. records with a candle or super glue :D:D:D). I prefer CD to other audio sources like mobile phone, computer,.... I will conbvert an old CD-rom into CD player :p.
     
  4. dave

    Dave New Member

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  5. spec

    spec Well-Known Member Most Helpful Member

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    Hmm, quite a lot of ground there. I don't think you need to worry to much about speaker protection. It is a separate sub system that can pretty much be bolted on anytime. Besides which, unless you get very fancy, speaker protection circuits are fairly straight forward.

    Developing a good transistor preamp would be impossible for me to do just on paper. It would also require an inordinate amount of time.

    My advice is to get a good DAC and use lossless digital audio files like .FLAC stored on a computer as your main source of music. In addition to that, you can input any other source you like, including CD, vinyl, cassette and reel-to-reel.

    As an aside, I had a hifi shoot-out yesterday at a friends house. I bought a pair of bookshelf speakers for £30 from a secondhand store and he had bought a pair of Mission bookshelf speakers for £28 from Ebay. Both speaker pairs are as good as new. He has speakers in every room: huge transmission lines in the front room, BBC monitor speakers in the dining room, and the Missions in the study. Then he has more speakers amps and decks in his surrounding buildings. The source we used for the day was a reasonably good CD player and an upmarket AV system.

    The sound was great, with the transmission lines being the best. The BBC monitors were the most natural. The small Mission speakers sounded quite good too. My £30 speakers sounded quite acceptable and produced a surprising amount of bass for the size of the cabinets. They were very inefficient though and needed a lot of drive (100W amp used). I bought the speakers to replace the sound system of our plasma TV so they will be more than adequate for that job.

    My point here is that a decent digital source sounds pretty good. Also the surprisingly different character of the sound from the different speakers, all being driven by the same source. I suspect, though, that the Missions and my speakers were not run in.

    Another point is that we were driving all the speakers with the same 100W RMS amp. The small speakers were quite happy even played loud (re our previous discussions about driving small speakers with high power amps).
     
    Last edited: Jan 28, 2016
  6. Nikolai Petrenko

    Nikolai Petrenko Member

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    I have found some transistors preamp using BC549-559 in sound.westhost.com:
    Single supply:
    [​IMG]
    Dual supply:
    [​IMG]
     
  7. Nikolai Petrenko

    Nikolai Petrenko Member

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    I have known about Lossless format, I am trying to download .flac as much as I can, then burn into CD.
     
  8. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    spec: (me: pest, your sub-conscious or 'shadow') ;)

    Your thoughts on collapsing, somehow, the other rail when 'the other rail' fuse blows? I don't like when it happens which is why most amps that I've worked on don't fuse the rails, just the mains. Personally, I like fusing each rail.
     
  9. spec

    spec Well-Known Member Most Helpful Member

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    Go for it Nikolai,

    The dual supply version would be better.

    The standing current flowing through Q2L and Q3L is defined by VBE Q4L/R9L= 0.6V/100 Ohms = 6 mA.

    The standing current through Q1L = Q3L VBE/ R8L= 0.6V/2K2 = 273 uA.

    The closed loop voltage gain is 1+ R6L/R5L = 4

    Perhaps remove VR1L and R4L (not sure what they are for).

    R6L and R5L look very high, but perhaps that is part of the sound of this pre amp.

    You could experiment by making R6L 2k2 and R5L 1K

    Stabilised power supply lines of around +- 12V would be a good move. But you could adjust the supply line voltage to hear the effect on the sound.

    The capacitors will probably contribute a lot to the character of the sound so best use polycarbs.

    Pollycarb capacitors across the supply lines would be a good move.

    A pollycarb capacitor from the base of Q2L to the positive supply line would be a good move.

    You may like to put a 50p or so capacitor from the collector of Q3L to the base of Q3L to shape the open loop frequency response.

    You could also experiment by putting another BC549 in the base of Q3L with the new transistor collector going to 0V. Put a 5K6 resistor between the base of Q3L and the negative supply line. Increase R8L from 2K2 to 3K9 to keep Q1L standing current more or less the same.

    You can experiment by changing the value of R8L to hear the effect on the sound.

    Also experiment by replacing C2L with a link.

    I will be interested to learn what this pre amp sounds like.
     
    Last edited: Jan 28, 2016
  10. spec

    spec Well-Known Member Most Helpful Member

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    Why do you not like collapsing both supply line if one goes? Makes a lot of sense to me. Fusing both rails independently is very dangerous for your speakers- I know :banghead:

    How have you got on with the weather in Delaware? I understand the storm has passed now.
     
    Last edited: Jan 28, 2016
  11. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    A) I am IN FAVOR of collapsing both supply rails if there is a failure of one.
    B) I am IN FAVOR of fusing each supply rail.

    Question is: How to do (A)?

    No comment on regulated supply rails. No experience. No comment on tracking regulated power supplies for power amps either. No experience.

    12-15" and dug out with no Internet for a day and a half.
     
  12. spec

    spec Well-Known Member Most Helpful Member

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    Right.

    About doing (A). The circuit I posted will blow both power line fuses if there is an imbalance in the supply lines. I also posted a stabilized PSU circuit where both supply lines collapse if one collapses. There is a whole load of ways to achieve the same result. I don't think it is a difficult task.

    Glad to hear that you survived the storm :wideyed:
     
  13. Nikolai Petrenko

    Nikolai Petrenko Member

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    Thanks. I will try, but find good transistors first, then capacitors. Resistor easy
     
  14. spec

    spec Well-Known Member Most Helpful Member

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    There are a whole load of transistors that will be suitable for the pre amp: BC184/BC214, 2N3707/2N4058, BC109/2N4058 for example. Just look for low noise high hFE at currents between 200uA and 12mA, and VCEo of at least 30V. The transistors do not even need to be complimentary. Q4L can be pretty much any small signal PNP BJT. Q2L is also not too critical.
     
    Last edited: Jan 29, 2016
  15. Nikolai Petrenko

    Nikolai Petrenko Member

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    No, I didn't ask for what transistors I should use. I just want to find genuine BC549-559.
     
  16. spec

    spec Well-Known Member Most Helpful Member

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    right
     
  17. gophert

    gophert Active Member

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    Isn't it about time to start a new thread? This question doesn't seem to align with your thread title at all,
    Transistor equivalent

    And your initial question has been answered long ago.
     
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  18. Inquisitive

    Inquisitive Super Moderator

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    • Like Like x 1
  19. Nikolai Petrenko

    Nikolai Petrenko Member

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    Sorry because I make you annoy. It is my mistake, I should make new thread since page 20
     
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  20. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Why not just call the thread "building a stereo from scratch"?. Then it all fits. The "transistor equivalent" title hasn't worked for a "long time".
     
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  21. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    This thread "switching LED" That I've been involved with has also morfed. The whole point is it's a project and it's in chat.
    I don't even know what to call it. It is the design of an "air flow" testing system to evaluate engines, I think. However, instead of being in question/answer form, it's been in a advisory/mentor form. The last portion of the thread after a LONG lapse was involved in testing a PID phase angle controller for a universal motor.

    The actual "switching LED" has evolved from indicating pressure with an LED, to some discussion of selecting setpoints via a rotary encoder (never taken to completion), BCD switches to a comprehensive Arduino control using a PC software package that has graphing for the HMI.

    Incidentally, I never knew where this project was going to end up.
     

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