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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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    You will be more than happy with the Self Simple Amp :cool::cool:
     
  2. spec

    spec Well-Known Member Most Helpful Member

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    Just a word about the effect of transistor parameters on the performance of an audio power amp, in this case the output power transistors:
    Take two ends of the spectrum: the MJL3281A/MJL1302A and the 2N3055/MJ2955. The graphs below show a major difference in the consistency of the hFE for the two transistors, and when you look at the other parameters on the data sheets and do a worst case analysis the MJL3281A has radically better characteristics. Notice that at 10A IC the 2N3055 has practically had it, but the MJL3281A still has an hFE around 70. This would be reflected in the amplifiers current drive capability and distortion figures. Other amplifier characteristics would also be affected.

    ETO_MJL3281A_current_gain_2015_11_25.png ETO_2N3055_current_gain_2015_11_25.png
     
    Last edited: Feb 1, 2016
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  3. Nikolai Petrenko

    Nikolai Petrenko Member

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    Oh, I see. TIP35 has better characteristics than 2N3055. It may not good enough for your genius hearing, but at least may enough for me :D.
    I will consider to build Leach amp later, when I can make money, not take from my parents.
    I am still an audiophool but at least I know what is music :).
     
  4. dave

    Dave New Member

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  5. spec

    spec Well-Known Member Most Helpful Member

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    Hi Nicolai,
    It is not a question of what is good enough for me or otherwise. I am just presenting information for you or anyone else to consider. It makes no difference to me either way. :wideyed:
    You can use pretty much any transistors you like, but you will not get the very best performance if you do not use the very best components.
    The TIP35/TIP36 will give a perfectly good performance, I never said different. :mad:
     
  6. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Here there are different types and races of people. Some types play real music and sing very well but another type make odd sounds called RAP which is where a person from that race talks loudly in a nasal monotone while there is a loud beat in the background. It is not music but they think it is. A steel band is also odd but interesting. I hate to hear RAP playing on the radio. I forgot to say that I also hate to hear the noise from bagpipes.
    Do you have odd "music" playing in your country?
    Are you or have you been a musician? When I was little I took piano lessons. I played a trombone in my high school band and we toured all over the place and won prizes. I almost developed "perfect pitch" also called "accurate pitch" where a person's brain becomes an accurate frequency detector and that person can identify the frequency (the musical note) of a sound and re-create it without a reference frequency. Many singers sing poorly and they use electronics to correct their pitch when it is wrong. During a recording a poor singer sings the same song over and over many times and they pick out only the correct parts. When they sing live they sound awful or they play the recording and lip sync to it.
     
  7. spec

    spec Well-Known Member Most Helpful Member

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    Hmm, interesting. I can tell when something is out of tune but that is about it. Do you think anyone can develop perfect pitch, or do you think it it a natural born talent.
     
  8. audioguru

    audioguru Well-Known Member Most Helpful Member

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    I do not think anyone can develop perfect pitch because there are some people who are tone deaf and do not like nor understand music. They cannot sing, whistle a tune nor hum a melody. I have music playing in my mind all the time when I am not playing it on my sound systems.
    Right now I am thinking about the pitch of a tone. I guess it is 220Hz. Audacity software says it is 218Hz so I was close.
     
  9. Nikolai Petrenko

    Nikolai Petrenko Member

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    Sorry :(.
    I mean simple amp may not make you happy fully. I don't think negative.
     
  10. spec

    spec Well-Known Member Most Helpful Member

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    Perhaps I misunderstood you Nikolai.

    Don't be fooled by the name Simple Amp, it is far from simple. It is only simple in Douglas Self's terms and is much more complicated and refined than many of the amp circuits you see in mags and on the net.

    I would be very happy to have a Self Simple Amp (SSA), with the right components, in my main hifi, and that would be with some very revealing and unforgiving speakers.

    Where the Leach amp scores is in it's huge current capability. Also the parallel transistors mean that individual transistors are not being stretched even when the amp is sourcing massive current peaks. But the SSA will also have a good current capability, probably around 6A peak worst case with ordinary transistors, much better than the average amp. Average tolerance current would probably be around 10A peak, but I haven't worked it out in detail for specific drivers and output transistors.

    By the way, the current capability of the SSA is calculated by: 6mA * hfe driver * hfe output, but is limited by the hfe drop-off at high current of the output power transistors. Since the Leach days there has been significant advances in semiconductor design and fabrication so much more capable power transistors are available now. If you want to see some beauties take a look at the MAG series.

    With power transistors chosen for low distortion and high current capability, around 40A peak would probably be achievable with the SSA. Alternatively the VAS quiescent current could be increased and parallel pair output transistors could be used. Parallel transistors do have their own problems though so it is not a win win situation.

    Most high end amps either have custom made power transistors or transistors specially selected from a standard run by the manufacturer.
     
    Last edited: Feb 1, 2016
  11. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    The Leach was a bear to put together. I accidentally made a "mirror-image" of the PCB and I was able to use it. It was difficult to discover that I did. I switched the NPN's and PNP's and swapped the polarity of the bias regulator. I'll tell you what though, I learned to fix power amps from the experience. Without a scope and Variac, it would have been hopeless.

    The Leach is a fast amplifier. I did "impact restoration" on music, a processor that can make say the hammer hits on a piano stand out. With one amp I repaired, I tried to use the signal processor. It could not handle it, at all. The sound was extremely distorted.

    My pre-amp is rated for 0-100 kHz. Much higher than the "audio bandwidth". The Leach was rolled off at 40 kHz.

    Here's http://www.facstaff.bucknell.edu/mastascu/elessonshtml/freq/freq4.html an "interesting" site, where Fourier analysis is used to show the terms of the odd harmonics of a sine wave that can be summed to make a square wave (the wave they used wasn't exactly square). This, is my basis, where a higher bandwidth amp in generally necessary to reproduce a transient. Three harmonics is two terms. So, 3 Khz at 5 terms would be 30 kHz bandwidth. At 5 terms, the signal looks pretty good.

    The "high current" capability basically allows the amp to overcome speaker resonances.

    Being about your age and with the lack of available funds, I'd go with something simpler. I actually went with an NE540 based design.
     
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  12. Nikolai Petrenko

    Nikolai Petrenko Member

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    Agree.
    I started to learn guitar in June 2015. I think it is pretty late. I should begin more early, such as 2012, when I have a lot of free times after school, unlike now.
    I have seen many bad singers mod their pitch. Their direct sing are far different from their records.
    I sing very bad, like bull roar :facepalm:.
    Odd traditional "music" in my country not much, so I can't say.
    I like RAP. What kinds of music you like?
    I like classical, non-lyrical, rock, pop, EDM, ......... My favourite artists are:
    - Classical: Beethoven (author :D)
    - Non-lyrical: Bandari, Richard Claderman, Kenny G.....
    - Adell, Maroon 5, Linkin Park..........
     
  13. audioguru

    audioguru Well-Known Member Most Helpful Member

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    When I was pre-teen up to my mid 20ies I loved to hear classical music live and recorded until I heard it all too many times. I never liked acid rock but I liked some normal rock music. For the past 20 years I like some pop music. When I hear a singer or song for the first time I know immediately if the singer/song will become a hit and my skin gets "goose bumps" each time I hear it.

    I was confused when I first heard Adele's "Hello" song. Now I love to hear it.
     
  14. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    This is an aside about Ampzilla:

    http://www.10audio.com/ampzilla_2000.htm
    http://www.davidsaudio.com/html/gas_line.html
    http://www.updatemydynaco.com/HistoricDocuments/ampzilla_web.pdf
    Idea of repair costs: http://www.ebay.com/itm/190595990979?rmvSB=true

    Taming Ampzilla (comprehensive testing)
    http://waltjung.org/PDFs/Taming_Ampzilla.pdf

    There are a number of reasons why I wanted to post this.
    1) I have heard the Amplifier. It was impressive.
    2) I almost built it.
    .. a) ) The GAS100 IC was the reason why I did not.
    .. b) We now know what that IC is
    3) getting the BEST performance requires expensive tools (e.g. distortion analyzers)
    4) Construction of an amp required attention to detail
    5) Transistor and component matching contributes to the performance.

    There were 3 amps that were of legendary performance: The Leach Amp, Ampzilla and the Dynaco 400. These were also in the era of the Crown DC150. A neighbor had one.

    A very early amp was the Crown DC300 http://www.prosoundweb.com/article/...0_amplifier_leads_the_solid_state_revolution/ . Also an am I heard. I wasn't too crazy about the sound. It was used as a transducer amplifier in University settings. A neighbor had one.

    It's unfortunate that I've grown out of my love of music. The music itself is not appealing. FM radio is not appealing. Everything sounds way to compressed so it can be played with an earbud. CD's probably really did it for me. So has DRMS. Maybe a 5.1 or 7.1 surround sound system would get me motivated again.
    I had a cassette deck that would really outperform a lot of stuff.

    I own this model (RSB-100) Cassette deck. Tapes made and played on it would probably surpass vinyl (metal tape, dbx noise reduction). http://hificassette.com/TechnicsRSB100/Technics_RS_B100.pdf Specs: http://www.classic-audio.com/technics-rsb100-p-80.html http://www.tapeheads.net/showthread.php?t=37410
     
  15. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Why do audiophools use adjectives that have nothing to do with sound when talking about expensive audio gear?
    Do they cheat and look at the price of the amplifier first before saying how good it sounds?

    An audio amplifier that costs as much as most new cars? Why? I bought a 2.1 sound system for $25.00 on sale and I am pleased with its sound. It does not produce audible distortion, it goes low and high enough and it plays loud enough.
     
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  16. Mikebits

    Mikebits Well-Known Member

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    Yeah, I want to do some distortion measurements but not sure my equipment is adequate. I have FFT on my scope, and a pretty descent audio generator, but that's about it. Just so happens I was in the process of characterizing a few op-amps to compare to data sheet specs. I want to see how close my numbers get to the data sheet. I will post my results in a new thread when I get done. I too have lost interest in music, I just do not like the tunes these days. Classical all sounds the same to me, and boring:(
     
  17. spec

    spec Well-Known Member Most Helpful Member

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    Hi Mike,
    Because of the vanishingly low distortion of good opamps- there is a raft of superb audiophile types available now- and good audio power amps, it is almost impossible to get any meaningful distortion measurements, even with the very best equipment. The only meaningful assessment is to listen.

    About music and loss of interest- I find quite the opposite. There is so much music available- I have 348G Bytes worth, and counting- that I would be amazed if you did not find a load of music that you liked.

    One problem is that the quality of run-of-the-mill sound systems- TV, Radio, mini systems, etc- seem to have taken a dive, although car (auto) sound systems are still pretty good. In the UK we have Digital Audio Broadcast (DAB) radio and the quality, by design, is not a patch on the original FM. At John Lewis (large UK department store) I heard about 20 ordinary systems that someone else was reviewing, and it surprised me that all but two were just awful. That would not have been the case 20 years ago. Sony, for example, were famous for having a good sound- not anymore. I bought one of their radios four years ago and had to take it back because the sound was so bad. The set wasn't cheap either.

    I listen mainly to lossless digita music files (.flac, .wav, and .alac) stored on a computer and played back through an external DAC and headphone amp. The quality is pretty good and even decent .mp3 audio files don't sound that bad. The kit is not that expensive either. The beauty of phones is the quality of the sound, and also you do not disturb the missus and neighbors, too much. :p A good DIY project would be a high end phone amp, but I wouldn't contemplate doing a DAC.

    I don't know what system you have at the moment, but perhaps if you heard some music on a decent system it might rekindle your interest in music.
     
    Last edited: Feb 6, 2016
  18. Nikolai Petrenko

    Nikolai Petrenko Member

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    sorry because I disappear for several day, I had a bad fever and flu, lied on the bed for over 1 day, headache so terrible :confused::confused::confused::confused:.
    Circuits for my transistors amp seem by mostly well now. For speakers protection I will use crowbar protection circuits, fuse in power supply circuit are above 6A. Also add delay circuit to remove thumps sound.
    My next concentrated is a small tube amp for my guitar. Just low power, about 1-3W.
    I can buy Russian tube 6N1P easily and cheap (about 1$). They are origin Soviet-era, so don't worry about quality. One man from Romania posted circuits (like I need):
    [​IMG]
    Preamp for output stage:
    [​IMG]
    Need only 3 tube=> 3$ :p:p:p.
     
  19. spec

    spec Well-Known Member Most Helpful Member

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    Hi Nicolai,

    I had exactly the same bug for about a month- it is going around the UK at the moment- very nasty.

    What guitar do you have? I have a dreadnought six steel string Yamaha, now 36 years old, and a Crafter ST120 Fender Stratocaster copy in black.

    You will have some fun building guitar valve amps. I suppose you know that, unlike hifi, low distortion is not the objective- quite the opposite. You will not be a proper valve man until you have your first belt from 400V DC :D

    It is generally thought that EL84 pentode valves (tubes) produce the sweetest and most cutting sound in guitar amp output stages. But triodes are nice too- very sweet.
     
    Last edited: Feb 6, 2016
  20. Nikolai Petrenko

    Nikolai Petrenko Member

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    EL84 no more in Vietnam since 2005. Most EL84 come from things left after war ended, many people hunted them, no more for me.
    Only 6N1P are good and cheap. I don't need to loud, just enough for me to practical with my sister, brothers... and for a room in the future :D.
    I have many small EI transformers which will draw heater and HV for tubes.
     
  21. spec

    spec Well-Known Member Most Helpful Member

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    Nikolai

    I wasn't suggesting that you should go for EL84s- just background information. No, I think that the 6N1P is an excellent choice and will be ideal for a guitar practice amp. You will be surprised how loud they sound with paper cone, high mag, speakers too.

    spec

    PS, 6N1P data sheet: http://www.radiotechnika.hu/images/6N1P.pdf
     
    Last edited: Feb 6, 2016

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