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PostPosted: Tue Feb 13, 2018 1:55 pm 
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Often one hears about the main downside of a tube power amp being loose or flabby bass. But is this issue eliminated when one uses the pre-out from a pre-amp (vs high level or speaker-level connection from a power amp) to the subwoofer? In theory, the bass signal from the pre to the sub should not be affected by the causes of bass flabbiness when using a tube power amp. What about if the pre is tube based? I assume that roll off wouldnt be an issue. Thoughts?

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PostPosted: Tue Feb 13, 2018 2:14 pm 
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Tube amps do not have very good damping factor, so they can't control big woofers, especially when playing loud. They can move the woofer; they just can't stop it very quickly - thus the sloppiness in bass.
It's okay in really efficient speakers, but not in hard-to-drive speakers with big woofers....and subwoofers.


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PostPosted: Tue Feb 13, 2018 2:49 pm 
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There are as many variables in subwoofers as in tube amps, the vast majority of subwoofers sounding pretty bad for music and having terrible overtones in the 80-120Hz range. If your speaker is already efficient and accurate down to about 80Hz, that's the ideal match for a tube amp and sub system. And then look at something music-oriented like a REL T7i crossed over at 70Hz.

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PostPosted: Tue Feb 13, 2018 3:27 pm 
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planetofsound wrote:
There are as many variables in subwoofers as in tube amps, the vast majority of subwoofers sounding pretty bad for music and having terrible overtones in the 80-120Hz range. If your speaker is already efficient and accurate down to about 80Hz, that's the ideal match for a tube amp and sub system. And then look at something music-oriented like a REL T7i crossed over at 70Hz.


Yup thats pretty much my scenario. 97DbA, flat 10ohm load, spec'd to 29Hz but realistically to 40Hz. Thinking of one, or a pair of Rythmik servo 15 inchers crossed at 70Hz. I have a LARGE room.


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PostPosted: Tue Feb 13, 2018 4:11 pm 
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Ummm....since you are using the pre out on a preamp to drive the sub the tube amp doesn't even enter the equation. You could pull the amp and replace it with a jar of pickles and it wouldn't affect the sub.

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PostPosted: Tue Feb 13, 2018 4:36 pm 
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BinkyTheCat wrote:
Ummm....since you are using the pre out on a preamp to drive the sub the tube amp doesn't even enter the equation. You could pull the amp and replace it with a jar of pickles and it wouldn't affect the sub.


Yeah, already tried that. Sounded.....sour.


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PostPosted: Tue Feb 13, 2018 4:47 pm 
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dwolek wrote:
BinkyTheCat wrote:
Ummm....since you are using the pre out on a preamp to drive the sub the tube amp doesn't even enter the equation. You could pull the amp and replace it with a jar of pickles and it wouldn't affect the sub.


Yeah, already tried that. Sounded.....sour.



seriously tho, assuming the pre has 2 sets of pre outs, the signal going to the tube amp will have no effect on the signal going to the sub.

and vice versa...

as for a tubed pre, of the few I've owned, be it a 12at, au, ax7, 6922, 6sn7, none caused any flabby bass but that could be mfg and circuit dependent.

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PostPosted: Tue Feb 13, 2018 9:52 pm 
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Not eliminated without a high pass, either before the amp or speakers, just masked. Would still be sending full signal to main speakers. Most subs only have a low pass.

http://hsuresearch.com/products/high-pass-filter.html

There are passive ways to do this but that gets impedance dependant.


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PostPosted: Wed Feb 14, 2018 6:28 am 
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The nicest bass I have heard from my NOLA Metro Gold is when they were driven with tube amplifiers. Mac 3001 and Mastersound 300 B monos. articulate and tuneful.

Don't be mislead by reports of flabby bass from vintage tube gear. Modern tube design has sufficient dampening to reproduce bass in a very realistic fashion. Note how many great bass players use Ampeg bass amplifiers on stage.

J.


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PostPosted: Wed Feb 14, 2018 6:48 am 
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ngjockey wrote:
Not eliminated without a high pass, either before the amp or speakers, just masked. Would still be sending full signal to main speakers. Most subs only have a low pass.

http://hsuresearch.com/products/high-pass-filter.html

There are passive ways to do this but that gets impedance dependant.


Not sure how this pertains to the original post.

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PostPosted: Wed Feb 14, 2018 3:52 pm 
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The answer is, as it often is, it depends. It depends on the amp and the speakers and how they work together.
I've owned multiple tube amps and an integrated in the past and currently own 2 Audio Research amps. I would never call either bass shy. My old amp (still have it) was a VT100 and it has some wicked bass capabilities. The newer amp is a Ref75SE and it is awesome top to bottom.

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PostPosted: Wed Feb 14, 2018 4:20 pm 
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Transformer quality has a substantial influence on bass performance. It's usually the first place compromises occur because they're expensive!


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PostPosted: Wed Feb 14, 2018 4:31 pm 
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If the sub is active, why would the low DF of a tube amp even matter? DF is not an issue at 10kOhms....I don't think...

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PostPosted: Wed Feb 14, 2018 5:44 pm 
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Running the subs from the pre out will leave you with the phase lag factor of the output transformer as a large discrepancy in phase compounded by the angle changing with frequency . It is generally accepted that subs in a tube system derive their signal from the output of the tube amp .


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PostPosted: Wed Feb 14, 2018 6:21 pm 
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A speaker & its amplifier are a system.

Most modern subwoofers assume a low output impedance, a rarity in a tube amp. As well unless very special, the output transformer in a tube amp will start limiting the performance in the lowest frequencies. As well with a high output impedance amplifier the net frequency response of the system will have the speaker impedance convo.lved with the FR of the woofer (when measured with a low output impedance amp — which doesn’t car emuch about the impedance).

So usually something like a big Class D amp will do a better job with typical subwoofers. But if the woofer is designed with the output impedance and other characteristics of the tube amp (or other high output impedance amp) results can be superb.

And do not forget that this low your room dominates, so also has to be factored in.

So, it depends.

dave

-- 14 Feb 2018 18:23 --

ripblade wrote:
If the sub is active, why would the low DF of a tube amp even matter?


It doesn’t since the tube amp really has nothing to do with the sub.

dave

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