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interesting article about "transistors vs tubes" in audio

Discussion in 'General Electronics Chat' started by unclejed613, Nov 28, 2011.

  1. unclejed613

    unclejed613 Well-Known Member

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    btw if anybody doesn't know this yet, NEVER run a tube amp unloaded, it's bad for the output transformer.

    there have been ways developed to get a lower output impedance from a tube amp, such as cathode driving the output transformer. E-V made one with cathode drive, and a nested feedback loop with an impedance control. you could dial the output impedance from -1 ohm to +8 ohm.
     
    Last edited: Dec 5, 2011
  2. Sceadwian

    Sceadwian Banned

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    -1 ohm output impedance? That's a trick!
     
  3. unclejed613

    unclejed613 Well-Known Member

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    you can do a lot with feedback you wouldn't think possible. look up NIC Negative Impedance Converter
     
  4. dave

    Dave New Member

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  5. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Yamaha had some speakers that were driven with an amplifier that had negative impedance or zero impedance.
     
  6. bountyhunter

    bountyhunter Well-Known Member

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    I remember some amps that had adjustable output impedance on the control panel via a slider pot that adjusted the impedance from about -1 Ohm to 1 Ohm, with zero as the center (nominal) value.
     
  7. unclejed613

    unclejed613 Well-Known Member

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    that was a Yamaha.... don't remember the model number off the top of my head, but it had voltage and current feedback to accomplish the variable impedance. i have the service manual somewhere on my computer... there's info on how to do this here http://sound.westhost.com/project56.htm
     
  8. tvtech

    tvtech Well-Known Member Most Helpful Member

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    Anybody remember NAD from the eighties?. New Acoustic Dimension. I have the little 3020A integrated amp and it is still working 100% after all these years.

    Can basically drive any speaker still with control. Tiny little 20W @ 8 Ohm rated amp. Balls of note. And an outstanding design still. Rotel at the time tried their best to whip the 3020 by using IC output devices. NAD used discrete transistors.

    And NAD won hands down. Very few old Rotel's out there now of the same vintage that have worked as hard as the little 3020A. See here:http://nadelectronics.com/about-nad

    Back on topic....it is one thing to hear the best and then purchase the goods....I was a salesman and was fortunate enough to hear the best of both glowing bottles and silicon in the same room. Demonstrated the equipment for potential customers in the same room. Same acoustics. Same time....

    And I have to say, I have huge respect for Audio Research tube amps. Clean and dare I say...classically orientated...

    Then came the Krell beasts. Uhm.

    Rock solid control of bass and the speakers. Clean tops. The amp is telling the speaker what to do. Period. Absolute control.

    Memorable day for me way back in 1987 with a customer with a permanent grin on his face whilst listening to Pink Floyd Dark Side of the Moon flat out on Krells and Wharfedale 601's at full throttle.

    We almost broke the building down with the demo. I will never forget it. After drilling the 601's for around half an hour flat out, speakers were good for a lot longer.

    We used them the the next day again...

    Sigh. I left the shop and went back to my place and revved my 3020A.

    Cheers,
    TV TECH
     
  9. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Years back there used to be a record shop in Matlock Bath (on the corner opposite the railway station entrance for anyone who's been!) - now most record shops had either little booths to go and listen in, or fairly poxy little stereo systems.

    This one had huge Goodmans speakers, either a Leak or Quad amp (I can't remember which now), a Garrard 401 turntable, SME arm, and Shure V15 pickup.

    Basically it was 'state of the art' for it's day.

    So you'd find a record you fancied, and ask him to demo it for you - it would sound amazing, so you'd buy it!.

    Then when you got it home it didn't sound half as good :(
     
  10. audioguru

    audioguru Well-Known Member Most Helpful Member

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    I laughed every time when I entered an appliance and furniture store that sold sound systems. The salesmen always connected the speakers OUT OF PHASE then cranked up the bass as high as it could go to try to produce some bass.

    I would sneak around the back of a speaker and correctly connect it IN PHASE then turn down the bass control to normal and have very good bass.
     
  11. unclejed613

    unclejed613 Well-Known Member

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    i worked there in 1985 and 1086 when they were in Norwood MA.
     
  12. Mr RB

    Mr RB Well-Known Member

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    But even then, when most surround system say "Stereo" on the display it's just another surround processor setup to try to make the surround sound good with stereo input. It will still be applying frequency cuts/boosts, delays and phasing etc to the different channels, just they will be the changes the manufacturer thinks will work well when playing a stereo source.

    I'm even against a mono sub when playing stereo. The sound was mastered in the studio into two independent channels and should be played back as two independent channels.

    Having said that with very new CD releases there is a growing tendency to butcher the mastering so the CD sounds better when played back on surround systems... Yech. :(
     
  13. unclejed613

    unclejed613 Well-Known Member

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    i can do 5.1 surround sound (from a 2 channel stereo source) with op amps, and some algebra, as a matter of fact this weekend i'll put down what i've got in my head for a design down in the form of a schematic. i'll also see if i can find any more of those articles (these two were labeled "round three and round four")
     
  14. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    And you've still got two independent channels - there's no positional information in the bass, below a certain frequency you can't tell at all where it's coming from - hence the need for only one sub (PA usually uses two or more subs, simply to get the power though), which you can hide out of the way (a friend used to have a sub disguised as a glass topped coffee table) :D
     
  15. unclejed613

    unclejed613 Well-Known Member

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    actually, there is phase information in bass that the brain does process, and it is directional information. this effect disappears above 400hz or so. try this experiment with headphones. feed 100hz into one channel, and 100.25hz into the other channel. it sounds like the source of the sound is rotating around you once every 4 seconds. do the same at any frequency below 400hz, and you can see how the brain processes phase informatio. as soon as you get above about 400 to 405hz, the effect disappears entirely. i've done this experiment, and it is a very strange experience, especially when you get to 400hz or so and the effect literally evaporates. starting at 20hz (keeping 0.25hz spacing between both channels at all times) the effect is difficult to discern, but it is there, and becomes more pronounced as you approach 400hz, then evaporates as you pass 400 hz.
     
    Last edited: Dec 7, 2011
  16. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    I don't see how that has anthing to do with sub-woofers?.

    Headphones are completely different to speakers, and you're feeding each channel directly (and only) to each ear.
     
  17. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Many years ago I built an "SQ Surround Sound Full-Logic Decoder" using Motorola ICs. It produced surround sound with 20dB channel separation when playing SQ-encoded vinyl records and sounded realistic.
    When playing an ordinary stereo record it produced some weird effects in the rear channels, usually when there was reverberation in the recording studio or theater.

    I think Dolby Full-Logic decodes stereo the same.
     
  18. nsaspook

    nsaspook Well-Known Member

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    Bass management into a separate sub-woofer channel is needed in most rooms because the room-modes at low frequencies make the best position for a sub-woofer different than what's needed for best stereo separation and sound-stage for the LR speakers. To get the best low frequency response over the largest area it's critical to place the sub(s) correctly to minimize the effect of room-modes.

    I use the multi-sub(4) method in my main media room.
    http://www.electro-tech-online.com/custompdfs/2011/12/multsubs.pdf
     
    Last edited: Dec 7, 2011
  19. Sceadwian

    Sceadwian Banned

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    As the frequency goes lower so does the ability of the human ear to determine direction in the first place, so if you're going to lose positional information bass (a few hundred hertz and lower) is fine which is typically what bass speakers produce.

    UncleJed, Nigel is right, just because you can hear it with headphones doesn't mean there's usable positional information, you've only demonstrated that a sine wave very slightly out of phase can be detected at all at that frequency, this has nothing whatsoever to do with the positional sense of complex waveforms in the real world. Take a look at how large an elephants ears have to be to detect infra sound direction.

    I understand this is only my personal experience and it's based on a very specific set of speakers/audio setup and software that was driving it, but good stereo reproduction from a 5.1 surround system is VERY possible, it's better than any two speaker setup than I have ever heard for both filling the room and still maintaining enough positional information for good stereo effects. Of course the best of the best stereo reproduction can only be had with headphones I would say a good 5.1 can have a bigger room filling sweet spot than a two speaker setup, again, if the room and the speaker and the software all cooperate.
     
  20. Sceadwian

    Sceadwian Banned

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    nsaspook, the room modes you're talking about though have nothing to do with recovering positional information from the sound, only avoiding room resonance.
     
  21. nsaspook

    nsaspook Well-Known Member

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    I agree with you and Nigel about the lack of positional clues in bass done right. The main reason that some people see the effect is because of poor placement, port noise noise and overloaded speakers from using too much EQ and power to obtain a flat response. This is discussed in the paper.

    My comments were mainly directed to Mr RB. I forgot to include his quote.

    This seems to be the good and correct way to create the ideal playback condition but the reality is usually very different.

    My old HT page. http://www.nsaspook.com/
    Four 12 inch woofers inside gutted 1970's era RS Nova-9/optimus-5 speaker cabinets (nice old wood) with rebuilt Nova 8 full range custom three ways for fronts.
    Low frequency room response after good speaker placement, room treatments and a Little EQ.
    http://mysite.verizon.net/res02dad/sitebuildercontent/sitebuilderpictures/freq.jpg
    LFE equipment: http://mysite.verizon.net/res02dad/...ilderpictures/.pond/PC170091.jpg.w560h747.jpg
     
    Last edited: Dec 7, 2011

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