voltage sensitivy and Gain?

Discussion in 'AV Pre-Amp/Processors & Power Amps' started by TB303, Jun 17, 2015.

  1. TB303

    TB303
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    Hello People,
    I'm thinking of replacing my amp (integrated Classe CAP-2100) with a dedicated poweramp and have some questions about how to choose one.

    My issue is that I'd rather not use a pre-amp as I have one source and that source (Schiit Yggy) puts out a fixed 2v signal. My current amp (when in power amp mode) has 0.5v sensitivity, meaning it reaches its full output power (100w) with a 0.5v signal.
    My speakers (B&W CM10s2) are relatively efficient (90dB spl (2.83V, 1m) and i usually listen at around 65dB.
    In the current setup that means I need to attenuate the signal (in Jriver) quite substantially (-50dB) which I'd rather avoid.

    Looking at power amps (possibly the ATI 6002) I look at input sensitivity (1.95v with the ATI) and think that I'll need to attenuate the signal by a lesser amount because it is less sensitive than my current amp. However, it is a 300W amp, so if I feed it 1v (50% attenuation, not sure how much that is in dB) than it'll still put 150W into the speakers, actually sounding louder than my current setup...

    Is this accurate? am I missing something? Please advise

    thank you!
     
  2. mattkhan

    mattkhan
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    Half voltage is a -6dB

    If you go balanced out of the yggy you get 4V so you will have to attenuate by 6dB in the source just to get down to the input sensitivity of the amp. The amp then adds 28dB to that to produce about 49V. Driven into a constant 8 ohm then this gives you 49^2 / 8 ~= 300W. The figures are the same for unbalanced as the input sensitivity of the amp is 0.975V in that case and the gain is increased by 6dB to 34dB.

    Your current amp does 100W at 8 ohm from 1V balanced. This is sqrt(100*8) = 28.3V and this is a gain of ~29dB.

    all this means that, under the same conditions and signal chain, the ATi will be about 5dB louder (28.3 to 49V is a 5dB difference). If your only volume control is in jriver then you will need to attenuate further to achieve that.

    Ultimately you need a volume control. I don't really know what problem you see in doing this in jriver. Listening at 65dB is pretty quiet anyway.
     
  3. stephenbarnes

    stephenbarnes
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    For those speakers I wouldn't go anything higher then ATI 2002. ATI 6002 deserves higher end speakers- Nautilus, 800 series etc.

    As mentioned 65dB is pretty quiet, I doubt you even need power amplifiers for that. You're listening to background level volumes.

    Are you sure you are listening at 65dB? Do you have a spl meter at hand?
     
  4. mattkhan

    mattkhan
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    If you want to avoid attenuating that much because if the dither issue then you could just buy a vst plugin that does it "properly". Alternatively get a less powerful, lower gain amp.
     
  5. TB303

    TB303
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    Thanks people,
    A few corrections.

    My current amp does 100w from 0.5v (unbalanced) which is a higher gain than 29dB no?

    I have a friend (on this forum - Lokyc) who's using this amp with those speakers and feels they sound much better, I may choose to go for bigger speakers in the future.

    I'm measuring 65dB - 70dB via an spell meter app on my phone - I think its accurate.

    The VST plugin sounds interesting, can you recommend me a specific one to look for? That would work with Jriver on RPI?

    The reason I'd rather use less digital attenuation is because Mike Moffet the Yggy designer has specifically told me he doesn't like it. It could be that are many poor implementation (try attenuating a lot in Volumino, see how that sounds) - maybe I'm a perfectionist...

    Thanks for the advice
     
  6. mattkhan

    mattkhan
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    Yes 6dB higher, it makes no difference to the output though so everything I said holds true. It is the same for the ATi BTW.

    RPI? I think izotope do one as part of their ozone package, voxengo elephant is another, acourate convolver is another possibility that gives you a tpdf dither.

    He is not the one listening to your system :smashin: I think mwillems, on interact, covered the comparison of digital vs analogue volume controls and how jriver deals with it didn't he?
     
  7. TB303

    TB303
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    Thanks Mate,
    RPI stands for Raspberry Pi - my current digital transport of choice.

    I'll give the VST filters a go.

    I'd love to find a less sensitive amp, but wasn't able to find one with less gain (than 29dB or higher input sensitivity (than 2v)...
     
  8. mattkhan

    mattkhan
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    You could use an inline attenuator, it is just a voltage divider basically.

    RPI runs Linux so you would probably need to use something else. I imagine there are dither implementations around but I haven't looked.
     
  9. TB303

    TB303
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    Thanks Guys,
    I'd like to clarify that my calculations are correct:

    In the Classe 0.5v = 100W
    in the ATI 0.5v=75W (300W/1.95v)

    Am I missing something here? Does this mean I could attenuate 25% less?

    thank you
     
  10. mattkhan

    mattkhan
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    pretty close but you are mixing balanced and unbalanced sensitivity there, if you stick to unbalanced I think you get this

    Classe
    100W into 8ohm in volts is sqrt(100*8) = 28.284V
    0.5V to 28.284V is 20 × log (28.284/0.5)dB = ~35dB

    ATI
    300W into 8ohm in volts is sqrt(300*8) = 48.99V
    0.975V to 48.99V is 20 x log (48.99/0.975)dB = ~34dB

    so 0.5V raised by 34dB is 10^(34/20)*0.5 = ~25.05V
    in power terms at 8 ohms is (25.05^2)/8 ~= 78W

    the difference between the 2 powers is 10 x log(100/78) = ~1dB
    the difference between the 2 voltages is 20 x log(28.284/25.05) = ~1dB

    tiny difference basically
     
  11. TB303

    TB303
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    and if we are talking balanced, does it make a difference?
    Thanks
     
  12. mattkhan

    mattkhan
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    no

    sensitivity is reduced by the same amount as the gain is reduced, the output is the same
     
  13. TB303

    TB303
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    I'm not sure I understand, I must admit math was never a strong point for me...

    Thank you anyway...
     
  14. TomScrut

    TomScrut
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    This is basically your problem IF the CA2100 amp has a gain of 29dB. I thought you (@TB303) had found a review somewhere showing a really high (circa 40dB) gain for power amp mode?

    I don't see what your issue with using a volume control in JRiver is. You have to attenuate the signal somehow whatever amp you use (unless it has a pathetic gain), if its digital done properly how (is JRiver, DAC with volume) doesn't matter. If analogue then you need a pre amp or a passive volume control.
     
  15. TB303

    TB303
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    True,
    i'm hoping to have to attenuate less in Jriver, because you are 'losing bits'...

    I thought that if I'm replacing my amp I might focus one one that fits the way I listen to music...
     
  16. mattkhan

    mattkhan
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    this was covered in that thread over on interact, you're not losing anything. The only possible issue is if you're attenuating substantially and have a 16bit output (and even then it was pretty questionable whether you'd hear the difference, you'd probably have to crank up the gain afterwards to hear it or use headphones but you're not doing that).
     
  17. mattkhan

    mattkhan
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    basically it takes 0.975V in single ended, converts it to balanced internally which doubles the voltage (6dB of gain added) and amplifies it as normal
     
  18. sounddog

    sounddog
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    Have you considered a simple passive pre-amp. IIRC Schiit have one you could consider.

    Use the passive for rough level matching then day to day use the JRiver volume.
     
  19. TB303

    TB303
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    Thanks guys - that's probably the best solution. Is there a passive volume control with balanced connections? And doesn't it impact the sound quality?
     
  20. dazed&confused

    dazed&confused
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    Music First passives have balanced connections but they are very expensive. I did see one model sell second hand relatively cheap recently, about £1200 or £1500 I think. I think Django passives might also have balanced connections.

    Where are you located? If you are not too far away from me, you would be welcome to try out my Townshend Allegri. These retail at about £1900. I also have a Townsend Fractal F1 interconnect.

    I cant see a balanced connection between the passive and power amp making any notable difference. Neither can I imagine a good passive degrading the sound. They are totally free of noise and any electronic grain or Hash and appear completely transparent from the very bottom to the very top of the frequency range. what you hear is what is on the CD (audio file) as they say - no added colour or characteristics or sound signature.

    Some people feel that passives lack drive but I haven't really experienced this problem.

    All the passives I have mentioned are transformer preamps. A cheaper alternative is one made from vishay foil resistors.
     
  21. stephenbarnes

    stephenbarnes
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  22. TB303

    TB303
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    Thanks Guy,
    The reason I'm trying to avoid a preamp is that I only have one source (a DAC).

    I'm too familiar with Max's work (already have his speaker cables, fractal ICs and the amazing isolation bars for the speakers and sub).

    I really need to attenuate the signal by about 12dB in the clearest way I can then control the volume via Jriver...

    So a passive preamp is an expensive iotiknedpeiclalga s I don't need multiple inputs or indeed a flexible volume control.

    I know this looks awkward but to me that's the next sound... One day all system will be like that ;)
     
  23. dazed&confused

    dazed&confused
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    Maybe it would be worth telephoning Max, to ask if he could make you a pair of in line attenuators. Normally his wife answers the phone and she will put you straight through to him. Ring over lunch time when he's eating his sandwiches and he'll be happy to chat away with ideas ;-). Then let us all know what he says.
     
  24. TB303

    TB303
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    I might do that, partly because I'll be switching my interconnects from single ended to balanced...

    Presumably passive in line attenuators are the best interns of transparency? I thought I saw somewhere they do have a detrimental effect on the input impedance?
     
  25. dazed&confused

    dazed&confused
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    I think it would depend on the materials used and how the solution is implemented. Maybe Max will be able to offer a custom solution that goes from single ended to balanced and include a fixed level of in line attenuation that you specify. He may try to dissuade you though – I have vague recollections of reading and article in which he expressed a preference for single ended connection.

    If I were you I think I would consider selling my integrated amp and finding a suitable Power Amp with trims that enable you to adjust the input voltage.

    By the way I have a question as I interested in a new transport. Does your Rasberry thingy with J river have a remote control for volume?
     
  26. TomScrut

    TomScrut
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    I found one that I could get made reasonably cheap. Will PM you the details when I get chance. Remind me if I haven't sent in a day or so.
     
  27. TB303

    TB303
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    You're opening a can of worms with Jrivers volume control but I just use the app it's brilliant on iOS (Jremote) and there's another for Anderoid that's equally good whose name escapes me.

    Yes this is why it looks like I'm replacing the Classe in the ATI
     
  28. dazed&confused

    dazed&confused
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    Okay, thanks. My brother is a computer guy so maybe I'll ask him to sort me out with Rasberry and the software.

    Does the ATI have trims on the inputs? Any info out there on the web regarding whether or not they degrade sound quality?
     
  29. TB303

    TB303
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    Hey,
    Getting the Pi to work isn't rocket science but also not trivial - theres a very good Jriver forum that will help you.

    Depending on your set up you'll also need doughtier board called hifiberry - I went for the Digi+ which gives you optical and coax outputs.

    The ATI doesn't have trims but does have glowing reviews.

    I was hoping that because it has different input sensitive and output power it'll actually play quieter with the same voltage compared to the classe (0.5v vs1.95v input voltage, 100w vs 300w) - but apparently that won't make any dramatic change...

    So I'm upgrading the amp simply because it's much better quality, fits the way I use it (no pre-amp) and isn't a penny of 'hifi jewellery'... ;) So I'm looking at it as a better location of my budget (I'll sell the classe). My wife looks at his differently... ;-)
     
  30. TB303

    TB303
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    BTW
    I did have a chat with max about balanced IC - he feels that balanced equipment in general is less efficient and transparent, but as it happened I'll soon have a 'fully fully balanced' DAC and am - in which case balanced make sense.
     

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