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About make an audio power amplifier.

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

  1. Nikolai Petrenko

    Nikolai Petrenko Member

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    Yes, although low power, but tube amp always very loud. My friends sometimes make his neighbors awake by 50% volume of 2W 6N6P tube amp.
    6N1P draw more heating current than 6922 but better bass response .
     
  2. spec

    spec Well-Known Member Most Helpful Member

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    Nicolai,

    Bass response is generally dictated by the output transformer rather than the tube.

    spec
     
  3. audioguru

    audioguru Well-Known Member Most Helpful Member

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    I think the speakers that were powered many years ago from vacuum tube amplifiers had not much resonance so that the poor damping from the amplifier did not create a boomy sound. I think those old speakers are not made anymore.
    Modern speakers have strong resonances that are damped by the extremely low output impedance of a modern solid state amplifier.
    Then a modern speaker driven from a vacuum tube amplifier will have poor damping of its resonances which will sound boomy and the higher frequency "cone breakup resonance" will sound shrill.
     
  4. dave

    Dave New Member

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  5. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Mikebits: Here's an audio OP-amp comparison. http://tangentsoft.net/audio/opamps.html The primary use was a headphone amp.

    Nickoli: With a non-Op amp pre-amp generally you end up with capacitors in the signal path as coupling caps. Eliminating those does wonders. Thus you can have a totally direct coupled design (capable of amplifying DC) all the way out 100 kHz. You can as my pre-amp did, have both a DC coupled output and a non-DC coupled output. OP amp sound quality is evaluated in the link above. A separate headphone amp is a good idea. The Op amps are evaluated subjectively and electrically. I've seen some other evaluations as well. His list isn't exhaustive. However, the cream of the crop OP-amp seems to be about
    $20 USD,
     
  6. Mikebits

    Mikebits Well-Known Member

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    I want to do this for my own edification and to see how my test setups work. For THD I think I need to make a center F notch, to measure noise and harmonics. But thanks for the link.
     
  7. Nikolai Petrenko

    Nikolai Petrenko Member

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    Not a problem. Transformer, why not?
    6N1P has better bass response than 6922. One guy show me his homemade tube amp, L channel use ECC88, R channel use 6N1P, then he turn on "Mystic dream", both of us can hear less bass in L channel anyway.
     
  8. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    Go for the tube type, Nik!

    To my ear, NO solid state amp can hold a candle to even the simplest tube amp.

    I restored an old Seeburg jukebox with a 1947 amp with a couple of 6L6 finals in a push pull arrangement with a honking output transformer feeding one 4Ω 14" speaker with an electromagnet that was the inductive filter portion of the power supply.

    Incredible sound reproduction from 78rpm records.

    Then again, I know I have rather plebeian audio tastes...
     
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  9. spec

    spec Well-Known Member Most Helpful Member

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    Nikolai,
    What you are seeing there is one tube performing differently to another tube in a particular circuit. No tube, or transistor for that matter, has a better base performance than another. Bass is just low frequencies and if you examine the characteristics of tubes and transistors on their data sheets you will see that there is no drop off at low frequencies. There is a drop off at high frequencies though. The low frequency performance of a transformer output amp is solely dictated by the transformer not the tube or transistor per se.

    The primary impedance of the transformer should match the V/I characteristics of the tube anode for maximum power transfer. As the anode V/I characteristics are different for different types of tube so one tube will produce more base than another for a given transformer design. But if the transformer is designed to suit each tube in each case, the bass performance will be identical.
     
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  10. spec

    spec Well-Known Member Most Helpful Member

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    78s and Seeburg jukeboxes, that brings back memories. The first record I ever heard on a jukebox in 1957 was Ricky Nelson's 'Be Bop Baby' That was a 78 too.

    Valves, and especially old valve equipment, do have an appealing sound that is hard to reproduce with solid state, and valves still reign supreme for guitar amps.

    Plebeian tastes... no. We all have different tastes and the only criteria is that you get a system that you like. Audiophile systems, which much of this thread is about, are not appreciated or liked by many people who describe a system with detailed high frequencies as sounding tinny. In the radiogram days of the 1950s it was thought that all base and no top was the best sound. That was true for some jukeboxes too.

     
    Last edited: Feb 7, 2016
  11. Nikolai Petrenko

    Nikolai Petrenko Member

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    Heater use AC instead of DC current make sound more sweet. (?)
    I have no 16ohm speakers, but transformer allow me to use 4ohm ones.
    I also concentrate to protect my amp from kids and pets.
     
  12. spec

    spec Well-Known Member Most Helpful Member

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    There is no difference in the sound of a tube whether you use AC or DC for the heaters. But DC is much better for practical reasons: you will not get induced mains hum in your amp.

    I am not too sure what you are saying about speakers and the transformer. What transformer do you have specifically? And what speakers? Are you saying that you have 4 Ohm speakers?. If so, a 4 Ohm speaker on a 4 Ohm transformer will be fine, but for maximum power output and low frequency response the output transformer should be designed to match the V/I characteristics of the anode of the output valves.

    As a general rule, an audio transformer will operate better with a lower turns ratio; the leakage inductance will be lower. This means that a 16 Ohm transformer will be better than a 4 Ohm transformer. This is the main reason why 16 Ohm speakers were popular in the valve days. Speaker manufacturers like 4 Ohms, because that is better for the speaker voice coil design and construction. 8 Ohms is now popular because it suits the V/I output characteristics of directly coupled (transformerless) solid state amplifiers.

    By the way, you should never operate a transformer output amp open circuit or you may get high voltages that could destroy the transformer. On guitar heads (amp with no speakers) you have a switched jack socket so that when a speaker is not plugged in, an equivalent value resistor is switched across the output transformer for protection.

    Safety is paramount with valve amps, because of the high voltages so, as you say, you must design and build adequate safety measures, including protection for reasonable misuse. You must be particularly careful to ensure that dangerous voltages cannot get on the input jack and thus on to the guitar. You must also provide good ventilation to allow the tubes to lose heat by convection.
     
    Last edited: Feb 6, 2016
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  13. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    There certainly is, the 'valve sound' is all about 'poor' quality (which some people seem to like), high distortion, high noise levels, poor frequency response etc.

    A little added mains hum is all part of that 'sound', so it's important to use AC rather than DC heaters, as it makes it more authentic and gives the sound people remember form the distant past.
     
  14. spec

    spec Well-Known Member Most Helpful Member

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    :p:p:p Don't beat about the bush Nigel- just come straight out with it!
     
  15. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    Without which Jimi Hendrix could not have created the sounds that he did :cool::cool::cool:. Woodstock, Star Spangled Banner - freaking awesome.

    Fender's most popular guitar amps are tube types for a reason. My humble belief is that tube types, aside from their inherent failures at purity, also contribute a concurrent sympathetic response to the sounds around them. A mechanical (grid vibrations), effect, ever so slightly behind the timing of the initial pick/strum/slide that adds a sounds dimension a solid state amp is mechanically incapable of producing.

    Not everyone's cup of tea, but I'm one of the "some people" crowd and it's music to my ears. I am a proud purist of the impure (musically speaking).
     
  16. spec

    spec Well-Known Member Most Helpful Member

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    All I have to say is thank goodness we are all different. By the way, there are some superb valve amps on the market. Mind you they have prices to match.

    When you boil it down to the basics a valve and transistor are both the same: they are just devices for controlling current. When it comes to guitar amps there is a difference because valves can be made to produce distortion which adds to the guitar sound. Actually, it is the combination of the valve, the output transformer and the speaker that contribute to the coloration. To illustrate the point, if you play an electric guitar through a hifi amp it sounds bland and uninteresting.
     
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  17. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Brilliant guitarists sound that way because they are brilliant - the equipment is a relatively small part of the final result - Hendrix would sound great on anything.

    Likewise, a crap guitarist sounds crap whatever they try and play - and I don't count myself as even that high :p

    I'm also a big believer in valve guitar amps - WHERE IT'S CALLED FOR - particularly in heavy metal, where you really want that fat over-distorted sound.

    But for many 'gentler' :D types of music transistor amps are to be preferred, and many studio recordings are done on transistor amps, even when the guitarist uses valve amps live on stage.

    As for playing guitar through a HiFi amp, it's been done to great success over many decades - if you're not wanting distortion, but just pure guitar, it can be good as anything else.
     
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  18. audioguru

    audioguru Well-Known Member Most Helpful Member

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    When I was young my hearing was excellent so I could not stand hearing the fuzz and garbage sounds produced by deaf electric geetar players. All they wanted was to have THE LOUDEST noises they could produce. Their impaired hearing heard the fuzz poorly so they turned it up too high.
    My city is on the edge of a huge lake and there is an island about 3km out. The rock concert on the island could be heard clearly in the city!
     
  19. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    I've been involved in a LOT of music - you need female guitarists, they don't seem to have the testosterone fed desire for making ears bleed :p

    It makes sound engineering much easier with girls playing the instruments.

    To be fair, sound travels VERY clearly over water such as a lake, so that would be pretty normal.
     
  20. Nikolai Petrenko

    Nikolai Petrenko Member

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    Power supply for transistors preamps must be much cleaner (free hum and noise) than for opamp, so I need to use voltage regulators. IC regulator make the circuit bigger and more expensive, and each preamp will not consume over 10mA current so I decide to use zenner diode. Will the circuit below work well??? (for 3 preamps)
    simple power supply.png
     
  21. spec

    spec Well-Known Member Most Helpful Member

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    Hi Nikolai,

    Nice decoupling, but not sure what the 6 x 15V Zeners will do (have I misunderstood your schematic). Go for voltage regulators, which would be much much better. You can get 100mA regulators which are small and cheap- sorry. :facepalm:

    spec
     
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