Epiphany Acoustics Evolution Audio  Audio Emotion 
Results 1 to 7 of 7
  1. #1
    Super Wammer
    Join Date
     Apr 2009
    Posts
     1,286
    Location
     London
    Digital Source 1
     Sony xa5400es SACD
    DAC
     Auralic Vega
    Speakers
     SF Cremona/REL Storm
    Pre Amp
     EC4.8
    Power Amp
     EC AW180
    Headphones
     HD600
    In the Hi-Fi industry?
     No

    Power amp input sensitivity - please explain!

    Can someone please explain what the figures quoted for power amp input sensitivity mean and in particular how they relate to other components in a system. For example, I've been considering buying a new power amp for some time, but don't know how to match input sensitivity to my system. My current power amp (Quad 909) has an rca input sens. of 775mV and the balanced quadlink input is rated at 2Vrms. I use two sources, a SACD player and a DAC, which have analogue output levels of 2Vrms and 4.2Vrms respectively. My preamp is the Music First Magnetic transformer passive.

    Now, to my non-technical mind (and I am not an engineer) this means that if I play the DAC and set the preamp volume knob about half way, the pre amp should send a signal of about 2Vrms to the power amp, assuming that the position of the volume knob corresponds roughly to the amount of signal attenuation (I can hear you say 'what an idiot!'). The Music First is connected to the Quad via its rca inputs, so I assume that with this volume setting the 909 receives a signal of 2Vrms from the DAC and 1Vrms from the SACD, both of which are higher than the Quad's rca input sensitivity.

    Is this a problem? I ask because most of the power amps I've considered have input sensitivites of between 1 and 2Vrms. Any advice on how this works will be appreciated as I don't want to buy a power amp that doesn't match my system.

    Many thanks

    The Wiz

  2. #2
    Too much time on my hands SergeAuckland's Avatar
    Join Date
     May 2008
    Posts
     10,465
    Location
     Bury St Edmunds, UK
    Real Name
     Serge
    Turn Table
     EMT948, TRS9000, 401
    T/Arm & Cart
     AT33ML, TSD15, MC-15
    Digital Source 1
     SBT
    Digital Source 2
     Meridian 206
    DAC
     DEQ & CDQ
    Speakers
     Active B&W 801F
    Pre Amp
     Meridian 501
    Power Amp
     3 x Behringer A500
    Headphones
     AKG K270 KOSS Pro4AA
    In the Hi-Fi industry?
     No
    Quote Originally Posted by wizons View Post
    Can someone please explain what the figures quoted for power amp input sensitivity mean and in particular how they relate to other components in a system. For example, I've been considering buying a new power amp for some time, but don't know how to match input sensitivity to my system. My current power amp (Quad 909) has an rca input sens. of 775mV and the balanced quadlink input is rated at 2Vrms. I use two sources, a SACD player and a DAC, which have analogue output levels of 2Vrms and 4.2Vrms respectively. My preamp is the Music First Magnetic transformer passive.

    Now, to my non-technical mind (and I am not an engineer) this means that if I play the DAC and set the preamp volume knob about half way, the pre amp should send a signal of about 2Vrms to the power amp, assuming that the position of the volume knob corresponds roughly to the amount of signal attenuation (I can hear you say 'what an idiot!'). The Music First is connected to the Quad via its rca inputs, so I assume that with this volume setting the 909 receives a signal of 2Vrms from the DAC and 1Vrms from the SACD, both of which are higher than the Quad's rca input sensitivity.

    Is this a problem? I ask because most of the power amps I've considered have input sensitivites of between 1 and 2Vrms. Any advice on how this works will be appreciated as I don't want to buy a power amp that doesn't match my system.

    Many thanks

    The Wiz
    Volume controls are normally logarithmic, not linear. That means that at half rotation, you're sending out 1/10th of the signal level not 1/2. This is done because our hearing works logarithmically; "half volume" perceptually is somewhere around 1/10th or 20dB down.

    In your case, with a power amp of 775mV sensitivity, and an output of 2 or 4 volts, your volume control will be working towards the bottom of their range. Your Quad won't be getting more than 775mV as if it did, it would be horribly loud and distorted.

    If you're buying a new power amp, with a passive pre-amp then an input sensitivity of 1 to 2 volts is rather low for your sources. Your volume control will be around two-thirds up at normal listening levels and near the top for loud listening. There's nothing wrong with that, just that if you then get some sources that put out a lower level, like a tuner, you will find it difficult to get a loud enough listening level even at full volume rotation. Passives work at their best with higher sensitivity amplifiers, like the Quad and/or with high output sources like CD players and DACs.

    S.

  3. #3
    Super Wammer musicbox's Avatar
    Join Date
     Jul 2005
    Posts
     3,873
    Location
     Edinburgh
    Real Name
     Alan
    Turn Table
     Scheu Premier II
    T/Arm & Cart
     12" Unify + Glider
    SUT/Phono
     CEC PH53
    Digital Source 1
     Sony SCD-XA5400ES
    Integrated Amp
     Meier Corda Classic
    In the Hi-Fi industry?
     No
    You need to consider input impedence too.... I think the Sony SACD has fairly high output impedence and so might not like going straight into only 20Kohms input impedence on the Quad. this could result in very sleepy dull sound.

  4. #4
    Super Wammer
    Join Date
     Apr 2009
    Posts
     1,286
    Location
     London
    Digital Source 1
     Sony xa5400es SACD
    DAC
     Auralic Vega
    Speakers
     SF Cremona/REL Storm
    Pre Amp
     EC4.8
    Power Amp
     EC AW180
    Headphones
     HD600
    In the Hi-Fi industry?
     No
    Quote Originally Posted by SergeAuckland View Post
    Volume controls are normally logarithmic, not linear. That means that at half rotation, you're sending out 1/10th of the signal level not 1/2. This is done because our hearing works logarithmically; "half volume" perceptually is somewhere around 1/10th or 20dB down.

    In your case, with a power amp of 775mV sensitivity, and an output of 2 or 4 volts, your volume control will be working towards the bottom of their range. Your Quad won't be getting more than 775mV as if it did, it would be horribly loud and distorted.

    If you're buying a new power amp, with a passive pre-amp then an input sensitivity of 1 to 2 volts is rather low for your sources. Your volume control will be around two-thirds up at normal listening levels and near the top for loud listening. There's nothing wrong with that, just that if you then get some sources that put out a lower level, like a tuner, you will find it difficult to get a loud enough listening level even at full volume rotation. Passives work at their best with higher sensitivity amplifiers, like the Quad and/or with high output sources like CD players and DACs.

    S.
    Thanks for both replies - very helpful. The Music First's volume control is usually set to just over half way with the SACD and '3 notches' less with the DAC, given the latter's output signal of 4.2Vrms. This might seem high, but my listening tends to be classical and classical recordings seem to be transferred to disc at much lower volume settings than rock (or perhaps a relative lack of compression creates this impression!). I take your point, Serge, about caution should a low level device such as a tuner be used, but this is unlikely as I use a stand alone Freeview tuner connected to a DAC for radio. I suppose the question is are there good power amps with high sensitivity balanced inputs?

    The Wiz

  5. #5
    Superb Wammer pluto's Avatar
    Join Date
     Oct 2008
    Posts
     708
    Location
     Harrow, UK
    Real Name
     Pluto
    In the Hi-Fi industry?
     No
    Quote Originally Posted by wizons View Post
    ...are there good power amps with high sensitivity balanced inputs?
    Because the balanced interface is a legacy of professional practice, the sensitivity tends to be standard-ish. I'm not saying that you won't find exceptions, but the fundamental reason for the balanced interface is avoidance of electromagnetic interference and one way of achieving this is to feed high signal levels into relatively deaf inputs.

    The more sensitive an input, the more likely it is to bring interference up to the level at which it is audible.
    Audiophiles don't always have their heads buried in the sand...
    Sometimes they emerge to shoot themselves in the foot.

  6. #6
    Superb Wammer pluto's Avatar
    Join Date
     Oct 2008
    Posts
     708
    Location
     Harrow, UK
    Real Name
     Pluto
    In the Hi-Fi industry?
     No
    Quote Originally Posted by musicbox View Post
    You need to consider input impedence too.... I think the Sony SACD has fairly high output impedence and so might not like going straight into only 20Kohms input impedence on the Quad. this could result in very sleepy dull sound.
    There's slightly more to it than that. Loss of high frequencies ("sleepy dull sound") can be caused by excessively high source impedance but the input impedance of the receiving device has relatively little to do with it.

    Consider CD player A feeding into pre-amp B: HF (high frequency) loss is caused by the capacitance of the cable connecting A to B, The significance [of that amount of capacitance] increases with rising source impedance. This, in all likelihood, explains why cables "matter" to some and not others. A decent, modern low impedance output (say, <500Ω) will be more or less impervious to cable capacitance issues whereas anything >1kΩ will, to some extent, be prone to HF loss due to cable capacitance (which itself is a function of the cable structure and, above all, length).

    The input impedance of the receiving end doesn't really come into the HF loss equations (at least not to any significant extent) so anything above a few kΩ (10kΩ being fairly standard) should be absolutely fine.
    Audiophiles don't always have their heads buried in the sand...
    Sometimes they emerge to shoot themselves in the foot.

  7. #7
    Super Wammer
    Join Date
     Apr 2009
    Posts
     1,286
    Location
     London
    Digital Source 1
     Sony xa5400es SACD
    DAC
     Auralic Vega
    Speakers
     SF Cremona/REL Storm
    Pre Amp
     EC4.8
    Power Amp
     EC AW180
    Headphones
     HD600
    In the Hi-Fi industry?
     No
    Quote Originally Posted by pluto View Post
    Because the balanced interface is a legacy of professional practice, the sensitivity tends to be standard-ish. I'm not saying that you won't find exceptions, but the fundamental reason for the balanced interface is avoidance of electromagnetic interference and one way of achieving this is to feed high signal levels into relatively deaf inputs.

    The more sensitive an input, the more likely it is to bring interference up to the level at which it is audible.
    Thanks for your replies - very helpful. I thought one strength of the Music First magnetic transformer design is that it overcomes problems of impedance matching, so your comments are good news. It's interesting that interference increases with greater power amp input sensitivity: is this because the preamp signal output has to be set to lower levels, which increases the proportion of interference against signal? If so, isn't this one of the advantages of properly balanced signals, i.e., they increase signal strength (compared to unbalanced signals) and so reduce interference proportional to signal strength?

    I've just read a review of the Leema Hydra II power amp - it looks interesting and is about the maximum price I'm prepared to pay (I'd love to try the Gamut D200, but the mark up Gamut have introduced since the credit crunch is insulting). The Leema has a balanced input sensitivity for stereo 0dbW of 113mV for 1W output per channel and 1410mV for 149W output per channel, both at 1000Hz into 8 ohms. If I understand correctly, this means that at its maximum output (rated at about 149w/8ohms by Leema but measured at 175W by Hi-Fi News) its input sensitivity is 1.4V. In other words, the Quad 909 (rated at 2V for maximum output of about 140W) is 0.6V less sensitive than the Leema at about 140W output, but the Leema should match my system. Have I understood this correctly?

    Thanks for your help.

    The Wiz
    Last edited by wizons; 27-10-2010 at 12:00 AM.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •