Amplifier Sensitivity, Decibels, and You!

Discussion in 'Solid State' started by 240 Volts, Jan 30, 2006.

  1. michaelhigh

    michaelhigh mind's eye music

    Messages:
    6,141
    Location:
    Lenzburg, IL
    I appreciate the math in the OP, but I really suck at math, failed algebra, and have a system that works for me. I set the volume at a comfortable level, with the tone controls flat, and then I add tone, usually quite a bit, because I like strong, authoritative bass and the clear quality of the bright part of the signal in the treble range as well. Then I ease up the volume to distortion (This is if I'm doing more than casual listening, which is rarely; I like low-level seshes.) and then back off the amount it takes to eliminate the distortion, which occurs on the impact of the bass, bass guitar, or bass drum. This seems to work for me. I'm an EQ guy, I like loudness and usually extreme EQ because of my usually low volume settings. I find a lot of vintage products can be light in this regard. My speakers also can't handle mass doses of EQ, so it only works well at low levels. I never go over 10 or 11 o'clock on the volume knob, regardless of the receiver or preamp. Power amps usually get turned up to at least 7. When I use outboard gear in a pro audio rig I try to achieve unity gain (7 out of 10, no higher) across the effects and the trim (gain) on the mixing board, set the channels no higher than 7 as a reference point, then control the system volume from the masters, and never go above 7 there... That's how I do it, and nothing gets blown up, especially not my eardums.
     
  2. Pauln

    Pauln Active Member

    Messages:
    481
    Location:
    Houston
    I know this is a confusing topic for we who don't work with these kinds of calculations. I've looked at this thread and have tried to walk through some figures for myself...

    My example is my Sansui AU-6500

    I start by looking at the phono/EQ stage which has a sensitivity of 2.5mv
    I think this figure is meant to indicate the input level at which the phono/EQ stage should output 100mv which is the input sensitivity of the preamp stage.

    20*log(100mv/2.5mv)=32db

    The preamp stage has a sensitivity of 100mv
    800mv input sensitivity of the main power amp.

    20*log(800/100)=18db

    The main power amp has a sensitivity of 800mv at which it provides rated power of 28W, so I need to figure how much volts are being output from those watts.

    SQRT(28W*8ohm)=15V at rated power

    So, back to volts...

    20*log(15/.800)=25db

    So this is not so hard!

    +32dB Phono/EQ
    +18dB Pre Amp
    +25db Power Amp
    -----------------
    +75dB Overall

    Did I make any mistakes?
    Pauln
     
    Last edited: Dec 22, 2010
  3. tdat7192

    tdat7192 Well-Known Member

    Messages:
    993
    Location:
    Westchester Co. NY, USA
    Wow! I love math and just wish I had all my manuals on hand to play!

    Thank you!!!
     
  4. Brent87st

    Brent87st New Member

    Messages:
    10
    Well that confirms my suspicion that FM used to sound better than it does now, unless my hearing is just going to hell... [​IMG]
    [​IMG]
    [​IMG]
     
  5. moejr

    moejr Super Member

    Messages:
    2,150
    Location:
    Londonderry NH
    I cannot for the life of me make this work. I got the aux input of my receiver which is 200mv. The output from cd is 2.0V or 2000 mv. If you divide 2000 by 20 you get 10. But if I multiply that by 20 like I am assuming what the formula is telling me to do then I get 200 again. I am confused
     
  6. Pieface

    Pieface New Member

    Messages:
    24
    If you are getting ~+20dB with a CD player into a vintage amp...

    Is there any rule of thumb for knowing where on the dial you will run out of gas? My Sa7500 only has 1-10 volume marking not dB as on some amplifiers.

    Thanks.
     
  7. verde57

    verde57 Check the 'Reset' box if

    Messages:
    83
    Location:
    Romania
    On a new receiver like Yamaha RS-500 the input sensitivity is 200mV for CD
    an the volume adjustment is reasonable enough, it goes from -90 to 16dB and at about -30 its starts to go loud.
    Is the volume adjustment smooth because of the large scale of the volume Knob or what?
    Where does gain intervenes in this situation?
     
  8. oblomov

    oblomov Well-Known Member

    Messages:
    545
    Location:
    Alexandria, Virginia
    I beleive you are skipping the logarithm step:

    log(10)= 1

    then multiply by 20= simple enough, -20db
     
  9. SynergyGuy

    SynergyGuy New Member

    Messages:
    1
    Hey guys, can someone help me, I was given an RX V 471 that was damaged in a lightning storm. The standby light comes on, and thats it. I've tried the 10 second reset, checked the fuse, and visually inspected it. If I push the hdmi, or av input buttons on remote, the red light will blink. And thats all it will do. How can I chase down the problem, I wont sleep till I fix this thing.
     
  10. mdross1

    mdross1 Active Member

    Messages:
    221
    Always enjoy listening to or reading articles from people who know what they are talking about. When I first got seriously hooked on electronics found Heathkit my first was the AA-1640 power amp then built near 20 more kits.
    After that got into speaker building seriously big speakers. Wanting to protect everything hooked an oscilloscope and monitored clipping. Once realizing no way could I ever stand listening to any music near the clipping point of our amplifiers was much more at ease with the volume knob.
     
  11. Shoreweeper

    Shoreweeper New Member

    Messages:
    5
    Location:
    Nova Scotia Canada
    Correct me if I'm wrong but I am buying a restored Marantz 1090 soon and I believe it's input is rated for 1.5 volts. My source sends out 2 volts so I should be looking at max volume at around 3/4? Not that I want to achieve max volume I'm just curious.
     
  12. fred soop

    fred soop Super Member

    Messages:
    1,778
    Then we have the loudness wars making it difficult to even purchase good quality music these days. Here is a link to a video where this is discussed, complete with waveform displays. This web address will also link you to additional material covering the same.

    http://www.youtube.com/watch?v=WPTe2CSknvY

    Back in the day, some top 40 radio stations would run their continuously variable turntables at a slightly higher speed so their station would sound "brighter" even playing the same music. In Detroit, we had WXYZ at 1270 and WKNR at 1310, very close together and quick to tune between them. They both played the same music and competition was hot but WKNR sounded "brighter" with the faster turntables.
     
  13. donpipo

    donpipo New Member

    Messages:
    10
    Last edited: Feb 18, 2014
  14. aneufeld

    aneufeld New Member

    Messages:
    12
    Thank you, this gives me an understanding of my problem. My preamp has way too much gain for my apm. The preamp volume control, the entire volume range, from inaudible to ear busting/clipping, occurrs within just a few degrees of rotation. I am wondering, the current volume pot is rated at 100k ohms, I think. What about a MUCH lower resistance pot? And how low can I go? For argument sake, us something lost at, say, 100 ohms?
     
  15. aneufeld

    aneufeld New Member

    Messages:
    12
    OK, it seems that the problem I am having relates to an amplifier/source sensitivity "mis-match". Specifically, all of the volume control possible on my preamp is accomplished within just perhaps 10 degrees of rotation. My question: Can I fix this by decreasing the resistance of the volume pot? Replacing the existing 100K with something with much less resistance? Is something lost by doing that? And what would be the limit? For argument sake, what would happen with a 100 ohm resistant pot? Thanks for discussion.
     
  16. bare

    bare Super Member

    Messages:
    1,992
    Pad it down.
    Fit a Pot (temporarily) on it's output(s) Twiddle it until it pleases, gain wise.
    Measure the Pot's resistance at the position that pleased.
    THEN fit/splice in a similar value resistor 'inline' with your interconnect (s). Job done.
    This means that you don't to fool with the Pre OR the Amp ...Just the interconnects.
     
  17. aneufeld

    aneufeld New Member

    Messages:
    12
    Thank you for taking the time to answer this. I appreciate it.
     
  18. greg s

    greg s Active Member

    Messages:
    230
    Location:
    gillette wyoming
    and so one of my great mysteries is solved. i couldnt figure out how a set of speakers with a cumulitive value of 275 rms was being driven to distortion by a 20 watt nakamichi. now i understand
     
  19. greg s

    greg s Active Member

    Messages:
    230
    Location:
    gillette wyoming
    i decided to try this out as my yamaha cd player has an adjustable volume for just that reason apparently. not only does my stereo sound better but i think it may just be a little louder than before. :banana:
     
  20. Noddou

    Noddou New Member

    Messages:
    18
    Good Evening All
    I can understand the maths of it all ,however I would find it very handy to know where's about in the system these calcs can be confirmed and what tooling would be required ?
    Cheers
    Merry Xmas from Aus ...
     

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