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Question about passive bi-amp and class A watts

Discussion in 'Audio Hardware' started by pdxway, Nov 27, 2019.

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  1. pdxway

    pdxway Forum Resident Thread Starter

    Location:
    Oregon, USA
    My Parasound amps are class a/ab.

    Parasound A23 stays in class A up to 3 watts, I believe.
    Parasound A21 stays in class A up to 10 watts.

    Lets say I am playing my speakers at a volume level that requires total of 10 watts. If I do passive biamp using Parasound a23 as amp for tweeter, would my a23 output 10 watts also (excess watts taken away by tweeter crossover?), or would it output less than that and stay in class A since tweeter power requirement is less?

    Thanks!
     
  2. F1nut

    F1nut Forum Resident

    Location:
    The Mars Hotel
    The power output will vary up and down with the music. It will not stay at a constant watts per channel. You would also have to level match the gain of the two different amplifiers.
     
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  3. pdxway

    pdxway Forum Resident Thread Starter

    Location:
    Oregon, USA
    Thanks for the reply. Both amps have same input sensitivity and input impedance. I do wonder if I need to play with amps gain level at all if that is the case.

    Yes, I understand power output will not remain the same. I was using 10 watts just as an example for a moment in time.

    My main question about passive bi-amp is this:
    At a moment of time, at any particular loudness level, would the tweeter amp always output the same watt as the woofer amp?
     
  4. PhilBiker

    PhilBiker sh.tv member number 666

    Location:
    Northern VA, USA
    Honestly - coming from a pro-audio POV where studio monitors, PA equipment, etc. are commonly biamped I don't understand what passive bi-amping on hifi is supposed to do. You're still sending a full range speaker signal into a passive crossover. What's the point?
     
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  5. pdxway

    pdxway Forum Resident Thread Starter

    Location:
    Oregon, USA
    The point is for tweeter to get class A watt more often than using single amp.

    My understanding is that although tweeter amp still sending full range signal, only the high frequency would take the current. In that case, since tweeter uses less watts than woofer, there is a possibility that tweeter amp would stay in class A watts more often, regardless of what woofer does. Is my assumption correct?
     
  6. CoolJazz

    CoolJazz Forum Resident

    Location:
    Eastern Tennessee
    The output stage is unloaded by the crossover and therefore doesn't create the same distortion levels. Much, much of the sound of an amp is created in that output stage and the load created by the speaker/crossover. Also created by the amps topology design, which is why the overall mission to get class A watts out of a typical push-pull amp, even if it's still in class A, is kind of a empty mission.

    CJ
     
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  7. pdxway

    pdxway Forum Resident Thread Starter

    Location:
    Oregon, USA
    Are you saying passive bi-amp potentially have less distortion? The a23 has better THD number than the a21, would that also help with overall distortion level?
     
  8. CoolJazz

    CoolJazz Forum Resident

    Location:
    Eastern Tennessee
    Yes.

    THD is a worthless spec to worry about. It's not nearly descriptive enough.

    Sound from bi-amped speaker isn't all about the total watts being used. It's also about that less disoriented possible from the output stage not having to try to drive the current at all frequencies.

    CJ
     
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  9. harby

    harby Forum Resident

    Location:
    Portland, OR, USA
    The voltage swings and signal produced by the amplifier at the terminals will be the same at a particular setting of the volume knob, regardless of what it is hooked up to. It still goes "class AB" even if a passive crossover is blocking the musical transient's current, or even if you left the speaker disconnected.

    For example, if there's a bass note that drives the amplifier +5V/- 5V (or +9V/-1V on a biased output stage) the amp still has the same zero crossing point where "push" turns into "pull" even if you unhook the LF speaker terminal.

    The "watts" wouldn't be the same, as the bass current is blocked (and shunted) by the tweeter crossover's filter components. Watts is voltage (like water pressure) multiplied by current (the amount of water flow), to obtain the rate of work done. As I explained, the watts don't affect the "class".

    Two amps in biamp may have more power capability in total, but in real life, maximum power is used by transients like a kick drum or cymbal crash that would utilize just one amp's frequency range; a large amp & a small amp may actually restrict some types of musical dynamics.

    I wouldn't fret about it too much, as any problem in the amp design would demonstrate itself in the distortion spec sheet.
     
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  10. pdxway

    pdxway Forum Resident Thread Starter

    Location:
    Oregon, USA
    Thanks! That is what I am looking for. So, to let the tweeter amp stays in class A, I will have to do active bi-amp, am I correct? May be usng a minidsp HD to do the signal split?
     
  11. pdxway

    pdxway Forum Resident Thread Starter

    Location:
    Oregon, USA
    I ordered a minidsp 2x4 HD from partexpress due to the 15% off black Friday sales. I will use it to limit the frequency range for both amps to do active bi-amp. Parasound customer support said they tried it before and the benefits outweigh the negatives of using dsp.


    If any of you have better suggestions, please let me know. Thanks!
     
  12. F1nut

    F1nut Forum Resident

    Location:
    The Mars Hotel
  13. pdxway

    pdxway Forum Resident Thread Starter

    Location:
    Oregon, USA
  14. F1nut

    F1nut Forum Resident

    Location:
    The Mars Hotel
    No, not worth the effort or cost.

    I hope now you realize that minidsp you bought is not the type of electronic crossover used for bi-amping.
     
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  15. pdxway

    pdxway Forum Resident Thread Starter

    Location:
    Oregon, USA
    Care to explain more why minidsp HD won't work?
     
  16. F1nut

    F1nut Forum Resident

    Location:
    The Mars Hotel
    Line level active crossovers are used between preamp and power amp. That minidsp is used between the source and pre amp.
     
  17. pdxway

    pdxway Forum Resident Thread Starter

    Location:
    Oregon, USA
    I see. Actually, the minidsp have line level RCA in and RCA out. Its primary function is to do DSP between preamp and power amp. That is why those are great between AVR sub preout and subs.
     
  18. F1nut

    F1nut Forum Resident

    Location:
    The Mars Hotel
    Ah, I obviously misunderstood the position of that unit.

    That said, there is the issue of using a digital vs. analog active crossover. The digital type converts the analog signal to digital, which is then filtered through the DSP, then the filtered digital signal is converted back to analog. So, you have 2 extra conversions. A pure analog active crossover passes the signal unmolested. In my book, the less messing with the signal the better.
     
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  19. F1nut

    F1nut Forum Resident

    Location:
    The Mars Hotel
    Having helped a friend play around with bi-amping his speakers I can say it took a lot of time tweaking, listening, tweaking, listening.....and in the end neither of us thought it was worth it. However, by all means try it yourself, but be aware that it's not just 1, 2, 3, done.
     
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  20. pdxway

    pdxway Forum Resident Thread Starter

    Location:
    Oregon, USA
    2 extra conversions is my concern as well. But Parasound support said it is still worth trying. The benefits might outweigh the negatives. I guess I will find out soon. :)
     
    Last edited: Dec 1, 2019
  21. F1nut

    F1nut Forum Resident

    Location:
    The Mars Hotel
    I'll be interested in your impressions.
     
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  22. pdxway

    pdxway Forum Resident Thread Starter

    Location:
    Oregon, USA
    I got the minidsp HD last Thursday. First couple hours of listening impression was not good. I decided to let it burns in (just in case) for a few days, watching TV and movies. I tried music listening again this morning and still don't really like the sound. It seems like the "magic" is gone. Bass guitar sounded off. Music playback got a slight veil to it. :cry:
    Will get back to using single amp soon and see if I can get the "magic" back....
     
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  23. F1nut

    F1nut Forum Resident

    Location:
    The Mars Hotel
    Thanks for posting your experience.
     
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