Amplifier Sensitivity, Decibels, and You!

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

  1. Hyperion

    Hyperion Roobarb & Custard Subscriber

    Messages:
    39,131
    Location:
    Hertfordshire, UK
    Check the specifications of your units for the input and output levels required for proper operation.

    Merry Xmas from the UK :)
     
  2. Sean Custer

    Sean Custer New Member

    Messages:
    38
    Location:
    Tampa Florida
    My Sansui 9090 would shake the walls!!!!!

    Back in the 70's when Mid Fi receivers ruled department stores it was super competitive and companies like Sansui, Pioneer, ext needed to sell their product and one of those ways was they used designers to come up with great looking face plates and control layouts after all you judge by looks first. Another way was the volume control when i was 14 my Sansui 9090 & later Pioneer sx 1080 paired with my Altec 605a duplex speakers would shake the walls in my 12x10 bedroom with volume control turned up 2/3 by half way my speakers distorted and my ears ringing!!!! Real Hi Fi gear looks are second to sound and the volume knob is calibrated and not going to give up all the amps power before half volume. As far as input sensitivity i pay absolutely no attention to it at all other than when buying phono cartridges and i have never had a problem turning down my volume to compensate for a louder than normal recording i have also never been able to tell a difference between the 2 cd players i use one Luxman 1.9v and one Adcom 2.5v. Try it yourself with 2 sources mine both run through Aux inputs play identical cd's and switch back and forth between the two and see for yourself. And let your ears be the Judge not math or some silly numbers. Why do some products with specs not as good as others sound so much better????
     
  3. EvanF

    EvanF AK Member

    Messages:
    160
    Sony TA NR10, Pioneer M25

    TOTL of Japan, the likes of which will never be seen again.
     
  4. OldRedneck

    OldRedneck Ate up in the head

    Messages:
    326
    EchoWars, thanks for another 'splainin'!

    Now where's the TI-30 forum :D
     
  5. Northwinds

    Northwinds Huh? Turn what down? Subscriber

    Messages:
    10,047
    Location:
    Connecticut
    Too bad you can't hear it as I do since the SPL's are causing the camera mic to overdrive but no distortion even when the meters are flat to the right and I can still put gas to it. Several members have been here and can attest it's quite a fun experience when your right there hearing and seeing the amp in action. Of course, VU meters are different from dB meters but it is sort of interesting that with a well built amp with tons of headroom can cruise at these levels without doing anything except maybe popping a speaker fuse. I run 10A 250v out the amp to the speakers the speakers themselves only have 4A 250v just to ensure I do not blow them up and I have went through a few packages LMAO

    I note that the dbx, EQ and DSS unit in the bottom is no longer used. It's there for recording only which I don't do anymore

    http://vidmg.photobucket.com/albums/v514/maxwedge426/DSCF6987_zpsvy8mjrp5.mp4
     
    Last edited: Oct 6, 2015
  6. PPstereo

    PPstereo AK Subscriber Subscriber

    Messages:
    171
    As I often am, late to the party on this fine "vintage" thread.

    Didnt read all the responses, so I imagine im not the first to say, another reason I like my power amps with clip lights.

    Leaned allot on this subject and related topics. Much from others and from elliot esp site.

    And wow does an eq change the scope of things for many good and bad reasons with sound. All in how u use it.

    I remeber the moment it really hit home for me how much power a speaker system can really gobble up. I was driving my ads l810 speakers with a 300+ wpc at 8ohm amplifier. Granted it was good and loud but when I saw the clip lights flickering I was shocked. Maybe I shouldnt have been but it was a real eye opener for my naive self. And this amp can easily do 2ohm stereo all day long, pro amp.

    Changed my view of how much power an amplifier can be asked to deliver cleanly. Certainly made seeing the clip lights flash when driving my 4430s far less of a surprise lol...

    Never mind what passive speaker xovers add to all this....

    All these complications are why I love also reading post here and on esp and the various other pro sound sites. Brings us newbs slowly up to speed to the pros out there.

    As others said, thanks for taking the time to write and share this here.
     
  7. Quadman2

    Quadman2 Super Member

    Messages:
    2,590
    Finally I can understand/appreciate the gain feature of my Yammy receiver. Thanks Richard.

    Q2
     
  8. DalDames

    DalDames New Member

    Messages:
    1
    Hi...as per my knowledge the general tendency of the output voltage of sources creeping up over time is interesting. I think its partially related to the greater stability of a higher voltage signal (in regards to noise pickup), but also the fact that since louder sounds better, at least in a momentary comparison, newer devices sound 'better' right after being plugged in, because of the slight boost in volume.

    pcb assembly
     
    Last edited: Jun 9, 2016
  9. Bassblaster

    Bassblaster Super Member

    Messages:
    1,697
    Location:
    Cambridge, Ohio
    can approve, my Fisher amp is rated 50W at 150mV but my PC has 300mV on the 3.5mm output. with PC at full tilt and the Fisher amp up half way +/- 5% it's putting out about 55-60W. it begins to clip at 65W so i keep it below that...obviously
     
  10. gvl

    gvl Active Member

    Messages:
    461
    Anyone has an explanation why many manufacturers continue to insist on 500mV or so input sensitivity? Seems modern digital sources tend do send 2Vrms out which significantly compresses the useful range of volume controls, attenuators can be used in between but may lead to degraded SQ.
     
  11. Vaalman

    Vaalman New Member

    Messages:
    16
    Location:
    Brussels, Belgium
    Thanks Richard, for the great post. Helps a lot in undertanding those specs and why they are usefull.
     
  12. toddalin

    toddalin Super Member

    Messages:
    1,567

    In your usage it is relative. But, in the case of sound level measurement it is an absolute where 0 dB = 20 micropascals of pressure.
     
  13. toddalin

    toddalin Super Member

    Messages:
    1,567

    This would infer that your power amp makes 320 watts. I'm kind of doubting that. :idea:
     
  14. Hufsredo

    Hufsredo New Member

    Messages:
    47
    Location:
    Hanford CAli
    It seems to me that a sensitivity reduction box would be quite simple to make using a 10k dual gang pot (or less, I just happen to have several) and some RCA jacks high in, low out, set to match the tunner loudness. -20 db on my reciever with the cd is damn loud.
     
  15. Pauln

    Pauln Active Member

    Messages:
    481
    Location:
    Houston
    How are you getting the 320W figure?
    Here is what I have tried for the power amp stage:

    If I use voltages I have the input voltage of 0.8V to get rated output of 28W, so I'm looking to comprare the output voltage at rated power.
    28W=V^2/8ohm so V=15 at rated power, then 20*log(15V/.8V)=+25.5dB
    I'm still comparing volts, but is that still considered "potential or pressure" at this stage?
    Mistreating volts as power or intensity, 10*log(15V/.8V)=+12.7dB
    Looks better?

    If I convert volts to power, I have 0.8V^2/8ohm=0.8W as if the pre-amp output was treated as "power" and applied to the speaker load, so then 10*log(28W/0.8W)=+15.5dB
    This also looks better, but I'm not sure I can use the pre-amp output like that since it really sees the power amp's input impedance... hmm...

    If I use the input impedance of the power stage I have 0.8V^2/40Kohms=0.000016W so 10*log(28W/0.000016W)=+62.4dB
    That's not right, but maybe it is unfair to use two different loads... 15V^2/40Kohms=0.005625W so 10*log(0.005625W/0.000016W)=+25.5dB

    I'm bouncing around and running out of things to compare... :)
     
    patate91 likes this.
  16. toddalin

    toddalin Super Member

    Messages:
    1,567
    For amplifier ratings 20 dB = 100 dB watts.
     
  17. whoaru99

    whoaru99 Epic Member

    Messages:
    38,173
    Location:
    LoTL
    I believe that would be 20dBW = 100W.
     
  18. toddalin

    toddalin Super Member

    Messages:
    1,567


    Most power amps require ~2 volts to reach their rated power. By sensitivity, I think they mean that at 800mv you get 1 watt output.
     
  19. whoaru99

    whoaru99 Epic Member

    Messages:
    38,173
    Location:
    LoTL
    The specification is often misunderstood.

    Input sensitivity does not mean maximum permissible, it means minimum required for the unit to put out rated voltage or rated power.
     
  20. whoaru99

    whoaru99 Epic Member

    Messages:
    38,173
    Location:
    LoTL

    What are you trying to calculate, the gain of this amplifier?

    If so, and 0.8V input gives 28W output (presuming 8 ohms), then the gain of the amp at 8 ohms is 25.5dB as you first calculated.

    As a side note, 28W would be 14.5dBW.
     
    Last edited: Jun 11, 2017

Share This Page