Amplifier Sensitivity, Decibels, and You!

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

  1. gvl

    gvl Well-Known Member

    Messages:
    510
    It's just I don't like the fact I can't turn the volume knob past 11 o'clock as it gets too loud which is annoying.
     
  2. whoaru99

    whoaru99 Epic Member

    Messages:
    39,386
    Location:
    LoTL
    So you wish to have more resolution/fineness of volume adjustment?
     
    Bill Ferris likes this.
  3. gvl

    gvl Well-Known Member

    Messages:
    510
    Precisely.
     
  4. Pauln

    Pauln Active Member

    Messages:
    481
    Location:
    Houston
    Thanks, that was what I decided must be right... since I'm not using dBw or dBm, etc., just dB.

    Yes, the gain of the power stage... I made a model with the AU-6500 in the system from stylus to speaker a while back.

    Hey gvl, I can't go up above 9 o'clock on this amp without things getting way too loud - 'cause my La Scalas are 105dB/1W/1m... so I use the -20dB Mute switch. That allows me to get the position of the volume knob up about 12 o'clock for normal listening.

    If you don't have a built in mute attenuation you can do the calculations to estimate how much dB reduction would get your volume knob somewhat higher for your preferred listening level. Then you can get some in-line attenuators - they come in different reductions... like these:

    [​IMG]

    So, for example, the typical volume control on the older amps provides about -16dB when turned about half way up, and 11 o'clock might be about -22dB.
    If you want that 11 o'clock listening level with the knob at 1 o'clock (typically -12dB), then you want to add a 10dB reduction so 1 o'clock is the new 11 o'clock (1 o'clock is now total -22dB= -12dB -10dB).
    If you want that listening level with the knob at 3 o'clock (typically -4dB), then you want to add a 18dB reduction so 3 o'clock is the new 11 o'clock (3 o'clock is now total -22dB= -4dB -18dB).

    [​IMG]

    The line level attenuators would be placed between the source and the pre-amp input, so:

    phono EQ -> line attenuator -> phono input to pre-amp

    CD, digital source, etc. -> line attenuator -> aux/CD input to pre-amp
     
    Last edited: Jun 12, 2017
  5. gvl

    gvl Well-Known Member

    Messages:
    510
    I'm aware of inline attenuators, they are a reasonable workaround given they don't introduce issues due to impedance mismatch and such. They also tend to be expensive for what they are, but of course there is a DIY route. Still my question holds why many amps still use 500mV nominal input rating when all digital sources went to 2V output.
     
  6. Skelter

    Skelter New Member

    Messages:
    21
    Lots of interesting stuff here,.. too bad it seems I'm aretard,,LoL,..well o get basic idea..but math is not my thing...anyways here is is, I use Asus essence stx 2 soundcard that feeds my control amp nakamichi ca5(with pioneer gr777 eq in tapeloop) and that in its turn is feeding my nakamichi pa 7... since it's volume on the pc, and then also on the control amp.. how do I do to make sure I match the correct output from my pc soundcard with the inputs on the CA and PA.. prolly better with some other than pc as soundmedium, but it's what I got,and i don't know what is better....cheers from retardus
     
  7. patate91

    patate91 Well-Known Member

    Messages:
    607
    Location:
    Chicoutimi, Qc, Canada
    I have à question about the math, why the input impedance is not used? Maybe I just missed it and I have to admit I'm still trying to understand.

    My amplifier has those specs

    Lines (150mV / 50kOhm)
    Balanced (150mV / 600 Ohm)

    Cd player : 2v balanced??/unbalanced600ohm (I can't find impedance, still looking for it, should be 600 ohms for balanced)

    On the end I have to get the volume knob higher with Balanced than with Lines. Both has the same voltage.
     
    Last edited: Aug 21, 2017
  8. Alan0354

    Alan0354 Super Member

    Messages:
    2,679
    Location:
    Bay Area
    Answer my question above.

    If the first part is input specification, that means unbalance line input impedance is 50Kohm. The input impedance across of the balanced inputs is 600ohm.

    For CD player output, for imbalance, it's usually is low output impedance, so they don't specify that. They must include 300ohm resistor in series with each of the output of the balanced output pair, so the output differential impedance is 600ohm


    If the CD player has 600ohm balanced output impedance, you amp has balanced input impedance of 600ohm. You connect them together, there will be a divided by 2 of the output signal, that's the reason the sound is softer when using balanced connection.

    For imbalanced connection, the source usually has low output impedance and the input of the amp is 50K, so there is no divider effect. So it's louder.
     
    patate91 likes this.
  9. whoaru99

    whoaru99 Epic Member

    Messages:
    39,386
    Location:
    LoTL
    The input sensitivity is not a rating, per se. It's simply the minimum signal level that facilitates full rated output of the amp.

    The reason it is not higher is because many sources do not output much higher voltage as may a CDP when playing a disk with material recorded at 0dBfs. In those cases you'd run out of volume control before reaching the full capability of the amp, if you wanted to go that far.
     
  10. Rubber Ducky

    Rubber Ducky AK Subscriber Subscriber

    Messages:
    53
    Location:
    Denver, CO
    I'm comparing two power amps to potentially be driven directly from the analog outputs of my disc player (the player has a volume control). I don't have the amps yet, but I have the specs, and I'm wondering which would play louder with the same given input and the same rated power output.

    Player: Peak output level 2.1V

    Amp #1: Input Sensitivity 1.5V, Input Impedance 33k Ohms, 60W RMS per ch.
    Amp #2: Input Sensitivity 0.97V, Input Impedance 100k Ohms, 60W RMS per ch.

    Looking just at input sensitivity, amp #2 should play louder than amp #1 at a given input voltage, but amp #2 has triple the input impedance of amp #1. Doesn't input impedance play a role as well?
     
  11. Alan0354

    Alan0354 Super Member

    Messages:
    2,679
    Location:
    Bay Area
    Yes, Amp 2 will be louder because sensitivity is higher ( 0.97V full scale).

    Both input impedance are within range and should not make a difference. Output impedance from the preamp should be low enough to drive 20Kohm or higher. So that is not even in the picture.
     
    Bill Ferris likes this.
  12. patra710

    patra710 Active Member

    Messages:
    188
    Location:
    Beecher, IL
    Great post, thanks. Right now I have a Pioneer SX-9000 on my bench. It has two volume controls, one source and the other a master volume. First time I have seen this. One can control the source input.
    The next time that I have speakers hook up to it I am going to see if it an affect on the tuner and phono. I am thinking that it might switch those pots out for them, just a guess.
    This stereo was made in 1970, I wonder why it didn't catch on.
     

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