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Luxman SQ-N150 Review (Tube Amplifier)

Rate this amplifier:

  • 1. Poor (headless panther)

    Votes: 224 76.7%
  • 2. Not terrible (postman panther)

    Votes: 48 16.4%
  • 3. Fine (happy panther)

    Votes: 8 2.7%
  • 4. Great (golfing panther)

    Votes: 12 4.1%

  • Total voters
    292

Bob from Florida

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Amirm - when you were testing this amp, was the baseline noise evaluated with inputs shorted? I ask because - assuming the schematic is accurate - it should be possible to easily find which section is the biggest contributor. Test for baseline noise with inputs shorted. Next, engage the mute and compare - this will show what the solid state buffer is contributing. Next, pull the input tubes and compare again - this will show if that section is source. Bad input tubes can be source. If noise is the same without input tubes we have the possibility of mismatched power tubes. Unequal bias currents will fail to cancel the 120 hz ripple on the B+ supply. Negative bias supply ripple, screen supply ripple, and ripple from preamp supplies require more invasive testing, but the above can be easily determined.
I realize you are extremely busy and it may not be practical to evaluate this with this particular amp, perhaps the next tube amp?
 

MAB

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Measurements are essential, but do no tell you all you will hear.
Agreed, you need to play music on it to actually hear the distortion this amp produces.

Sorry to be snarky, but this amp performs poorly on essential measurements, and is is really expensive. Whatever good qualities it has are masked by unacceptably poor performance.
 

levimax

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Amirm - when you were testing this amp, was the baseline noise evaluated with inputs shorted? I ask because - assuming the schematic is accurate - it should be possible to easily find which section is the biggest contributor. Test for baseline noise with inputs shorted. Next, engage the mute and compare - this will show what the solid state buffer is contributing. Next, pull the input tubes and compare again - this will show if that section is source. Bad input tubes can be source. If noise is the same without input tubes we have the possibility of mismatched power tubes. Unequal bias currents will fail to cancel the 120 hz ripple on the B+ supply. Negative bias supply ripple, screen supply ripple, and ripple from preamp supplies require more invasive testing, but the above can be easily determined.
I realize you are extremely busy and it may not be practical to evaluate this with this particular amp, perhaps the next tube amp?
This is Luxman's job before they release / ship a product not @amirm
 

Confused_by_tech

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Makes me wish for a unit with this kind of eye candy and 2022 performance (e.g. Hypex etc.) without a king's ransom for the price.
 

Ken Tajalli

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Makes me wish for a unit with this kind of eye candy and 2022 performance (e.g. Hypex etc.) without a king's ransom for the price.
Its like husbands and wives!
the eye candy ones don't have much substance, the ones with substance are not much of an eye candy.
usually !
 

SIY

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Would you say the phase-splitter/driver used, is most responsible for the high distortions figures? and then the feedback.
No, the phase splitter is a cathodyne (split load) which is intrinsically perfectly balanced when loads are equal and has essentially 100% feedback. So it is unlikely to be a major distortion source.

There's no component values shown, but the most likely issues (aside from poor output tube matching) are distortion from the input stage (plate load too low, without seeing it I'll guess 120k?) and yes, insufficient feedback because of lower-than-optimal open loop gain.
 

Doodski

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I like this one.

And it matches (kind of) my other Luxman amp.
No disputing they nailed the aesthetics and the bass and treble controls are a super addition but I'm more of a 300B tube aficionado.
parallax+p1.png
 

Inner Space

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I don't even have a legit use case for this amp, but I'd totally buy it.
I did buy it - at least, the previous version, or perhaps the previous-previous, about twelve years ago. I had a studio with a reception area where clients and visitors came in. There was a shelf behind the receptionist, and we put the amp on it, with its matching CD player, flanked by a beat-up pair of JBL 100s. We were expecting dignitaries from Sony Music, and we thought they might find it appealing.

Worst amp ever. Underpowered and audibly distorted, and also terrible for picking up local AM stations. Really, really bad in that respect. I was very surprised. Usually I find Luxman really good - e.g. right now I'm using a 509x with a D10x through JBL 4367s and loving it. The 150 sure is a strange anomaly.
 

watchnerd

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I did buy it - at least, the previous version, or perhaps the previous-previous, about twelve years ago. I had a studio with a reception area where clients and visitors came in. There was a shelf behind the receptionist, and we put the amp on it, with its matching CD player, flanked by a beat-up pair of JBL 100s. We were expecting dignitaries from Sony Music, and we thought they might find it appealing.

Worst amp ever. Underpowered and audibly distorted, and also terrible for picking up local AM stations. Really, really bad in that respect. I was very surprised. Usually I find Luxman really good - e.g. right now I'm using a 509x with a D10x through JBL 4367s and loving it. The 150 sure is a strange anomaly.

AM radio?

Really? ;)
 

captainbeefheart

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This amp could really only be used with very very efficient speakers so that you can let it hang at an average of less than 1 watt for adequate headroom.

The design isn't great and it's not because of Luxman using "tubes", it's the fact they don't take the time to pick better tubes with better operating points for open loop linearity. The other major problem is there isn't enough open loop gain for adequate feedback. Cathode bias with EL84's isn't going to get you a lot of power unless you cook the tubes hard which isn't advised unless you want to re-tube every year. You can get clean 20 watts from a pair of EL84's but it needs a proper design and fixed bias.

It's a copy of a budget tube circuit, one bottle preamp with common cathode gain stage and the other section split load phase inversion. The phase inverter is actually decent as mentioned but has it's problems when driving power tube grids nearing 0v. It would have been much better to add one more bottle per channel making it more of a Williamson style circuit with low rp driver tubes after the split load phase inverter driving the power tubes. This gives better performance near max power and also more open loop gain to be used for feedback. I don't get why anyone still uses the 12AX7 for hifi circuits. Active loads help linearize gain stages instead of the common resistor load.

It's amps like this that look great and cost a lot that give tube amps a bad rap. I have very efficient speakers and can get very nice clean and articulate sound from tubes, you just need to build them yourself or know what to purchase for good results. It's not sufficient to trust big names like Luxman or judge quality by price. Yes tubes will be more expensive vs SS due to higher parts cost but you do not need to spend this much for such poor quality. For around $700 in parts I can make a really nice performing tube amplifier, double it for a profit margin and you're still looking at half the price as this for much better sound.

The power supply needs a re-buff. The output stage doesn't need to be anything special as it has decent PSRR but better filtering should be provided to the 12AX7 as it has poor PSRR the way it's setup. Not sure what's going on with the 60Hz but either grounding or heater power needs to be investigated, possibly EMF from transformer also.

Overall poor attempt at a decent tube amplifier by Luxman. Now hang your heads in shame and go back to the drawing board.
 

captainbeefheart

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You say that like it's a bad thing.

As opposed to being the point of the design. ;)

I just mean that if you are going to gussy up an amplifier to the point where the chassis work needs to demand a hefty price tag at least stuff it with a decent circuit and not a 50's budget circuit. We had the Williamson circuit in the 40's which sounds good and tests much better than this, it really wouldn't add much to the cost of this amplifier to make it a solid performer to match the looks.
 

Angsty

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Obviously, because this is priced at the Luxman entry-level, we should expect poorer performance. Now if it were priced at $10,000 … well, of course, that would mean all things are sorted. /s
 
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