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Thread: Amp to drive hf horns and tweeters?

  1. #16
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    When using an amp directly coupled to a high sensitivity horndriver, what spec is most important to look at?
    Is it the Signal-to-Noise ratio?
    Which value is sufficient to keep it quiet? 90db a-weighted?

    Quote Originally Posted by Mr. Widget View Post
    I would go with a small Class A amp, vintage or new. There are numerous others as well.


    Widget
    Could you list the ones that are available new please?


    @ Pos & Bubbleboy:

    Does the THX AAA 789 really handle an 8ohm load of a compressiondriver? It looks like it is only specifid for 16ohms minimum...
    Have you driven these with serious spl levels yet? Or are these only suitable for moderate listening levels?




  2. #17
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by Dr.db View Post
    Could you list the ones that are available new please?
    The Pass Labs XA25 is likely one of the best amps ever made for this application.

    https://www.passlabs.com/amplifier/xa25

    https://www.stereophile.com/content/...ower-amplifier

    https://6moons.com/audioreviews2/passlabs3/1.html


    Widget

  3. #18
    Senior Member pos's Avatar
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    Quote Originally Posted by Dr.db View Post
    @ Pos & Bubbleboy:

    Does the THX AAA 789 really handle an 8ohm load of a compressiondriver? It looks like it is only specifid for 16ohms minimum...
    Have you driven these with serious spl levels yet? Or are these only suitable for moderate listening levels?
    8 ohm nominal (so around 6 ohm min for a typical JBL compression driver) is definitely too low for that amp.
    A LPUHP amp would be a better match.

    The THX is the perfect match for a 16 or 32 ohm compression driver, and will let you reach 105dB SPL/1m no problem after constant directivity equalization (on sinusoidal signals, and much more on real-world signals given the typical spectral power distribution of music).

  4. #19
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    Thanks

  5. #20
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    Quote Originally Posted by pos View Post
    8 ohm nominal (so around 6 ohm min for a typical JBL compression driver) is definitely too low for that amp.
    The JBL 2441 is rated 16ohms, but I think in reality itīs rather 8ohm or am I wrong? Would this work with this THX headamp?

  6. #21
    Senior Member pos's Avatar
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    16 ohm JBL compression drivers have a minimum impedance of around 12 ohm in the passband (Re might be lower, but is irrelevant here).

    Bubbleboy is running his 16 ohm 476Mg with the THX. I think he uses the SE output.

  7. #22
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    Thanks
    Sounds like it should be fine...

  8. #23
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    Today I have tested my two amps directly with my compressiondrivers.
    - NAD C275 (2*150w rms)
    - NAD C245 (4*35w rms)

    The Setup was as followed:
    - NAD C165 Pre-amp
    - NAD C275 or C245 amp
    - protection cap
    - JBL 2446 or 2405
    So there was no active crossover connected...

    Results NAD C275:
    I could here some subtle noise at 2 feet distance, with more distance it was dead silent.
    Than I used the variable input and put the gain with the level-meters of the amp completly down. This decreased the noise further, but just a little. I would have thought this to be of bigger impact.

    Results NAD C245:
    I could here noise until 7 feet distance, with more distance it was almost silent.
    The C245 hasnīt got any level-meters to adjust the gain.

    To sum this up, I was impressed by the much oversized NAD C275! At normal listening distances it was 100% silent, no noise at all. The C275 is an affordable amp, so this made me rather confident to find another silent amp for horns without spending big cash.
    But I was rather dissapointed with the NAD C245, as it was much more noisy. Actually I planed to use this 35watt amp for my horns, but itīs to noisy.

    .

    Now Iīm wondering if amplifiers or crossovers are the usual suspects with producing noise?
    In my understanding it all sums up, because itīs like a chain... But is it rather hard to find a silent amp or a silent crossover?
    Which device is more prone to produce noise

    .

    How about putting some resistors infront of the compression-drivers?
    This would reduce the sensitivy and therefor the vulnerability for picking up noise.
    But this would mean using more passive devices in an active system

    .

  9. #24
    Senior Member Ian Mackenzie's Avatar
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    Your on the right track.

    Noise masks resolving power.

    The issue with noise becomes increasingly more apparent with active EQ of horns by boosting high frequencies.

    Padding back a horn with an Lpad can be an effective means of improvement in the signal to noise ratio.

  10. #25
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    It looks like the C245 has 35 db of gain and the C275 only has 29 db of gain. That explains the difference in noise between the two.

    The C165 preamp has about 12 db of gain. That's probably high for efficient horn speakers. I prefer no gain/low gain (6 db) preamps with amplifiers in the 25-30 db of gain range, and high efficiency speakers. I like no system noise if possible.

  11. #26
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by rusty jefferson View Post
    I like no system noise if possible.




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  12. #27
    Senior Member pos's Avatar
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    Agreed, gain matching is very important, so you have to check both the gain of the amp and the level of your source/DAC.
    Ideally you will want a 0dBFS signal to produce the maximum level you will ever require, and always keep the attenuator of the amp at maximum position for better tracking between channels.
    You can use passive attenuators between your source and amp (xlr pads, etc.).

    For the record, the THX 789 amp has three gain settings: -10dB/0dB/+10dB for the single ended output, and -4dB/+6dB/+16dB for the differential one

  13. #28
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    Good to know, thanks for the backround.

    I have no quality active-crossover at the moment to try, just some noisy M553...
    Now Iīm wondering if amplifiers or active-crossovers are the usual suspects with producing noise?
    Which device is more prone to produce noise?

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