Luxman SQ-N150 Review (Tube Amplifier)

[DonH56]

This is just the amp for your summer cabin or your boat.

I remember when overweight, underperforming amplifiers were referred to as "boat anchors".

 

[watchnerd]

I remember when overweight, underperforming amplifiers were referred to as "boat anchors".

Hey, it's only 12 kg.

It's barely even chubby.

 

[DonH56]

Hey, it's only 12 kg.

It's barely even chubby.

Wait, so it's not even a good boat anchor? Knew I should have kept my Blaze Linear, though it wasn't all that heavy...

 

[watchnerd]

Wait, so it's not even a good boat anchor? Knew I should have kept my Blaze Linear, though it wasn't all that heavy...

It would be perfect for anchoring my single man crewing scull shell, though.

Or maybe just keep it in the boat house.

 

[SIY]

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.

SCA-35 is one of the best selling tube amps of all time, and Dynaco managed 17.5W from cathode biased 6BQ5. And tube lifetime was excellent. So it CAN be done, it just wasn't here.

Honestly, if they had done the output stage a bit better and used a better tube for the input stage (my amp used an ECC81, the Dynaco used a 7199) to increase feedback, this coulda been a contender.

 

[pseudoid]

Wut da....?
I spent many a romantic night with a Luxman T2 tuner but this one has got to be a bastard-child from another father!
Shame on you Lucksman!

 

[Ken Tajalli]

SCA-35 is one of the best selling tube amps of all time, and Dynaco managed 17.5W from cathode biased 6BQ5. And tube lifetime was excellent. So it CAN be done, it just wasn't here.

Honestly, if they had done the output stage a bit better and used a better tube for the input stage (my amp used an ECC81, the Dynaco used a 7199) to increase feedback, this coulda been a contender.

This amp is not cathode biased - it is fixed bias!
Just look closely at -C1 voltage, and trimmers.
I have built a similar amp to this, EL84's and ECC81's, matched tubes, better powersupply, running it in triode mode, getting about 5 or 6 watts.
Good enough to fill my office! Dead quiet when not playing! with ears to the speakers!

 

[MakeMineVinyl]

SCA-35 is one of the best selling tube amps of all time, and Dynaco managed 17.5W from cathode biased 6BQ5. And tube lifetime was excellent. So it CAN be done, it just wasn't here.

Honestly, if they had done the output stage a bit better and used a better tube for the input stage (my amp used an ECC81, the Dynaco used a 7199) to increase feedback, this coulda been a contender.

The SCA-35 amp I tested in this thread used a 6GH8 instead of the 7199 (The 6GH8 is a popular replacement although it isn't a direct pin for pin drop in replacement). I measured no real performance differences with this tube vs the 7199.

 

[Ken Tajalli]

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.

You can get clean 20 watts from a pair of EL84's but it needs a proper design and fixed bias.

How?
20 clean watts?

 

[Bob from Florida]

This is Luxman's job before they release / ship a product not @amirm

A big problem with tubes is they can create all kinds of noise problems. The good thing is they are easy to replace if they get noisy. All I was asking was to consider adding a couple of quick tests to see if some bad or mismatched tubes were impacting the results. As I understand it the amp came from a member not Luxman. Given the experience I have had with my Luxman solid state integrated it seems odd they would offer this product without doing a good job.

 

[SIY]

How?
20 clean watts?

I get 25, and Roger Modjeski got 40.

 

[SIY]

This amp is not cathode biased - it is fixed bias!
Just look closely at -C1 voltage, and trimmers.
I have built a similar amp to this, EL84's and ECC81's, matched tubes, better powersupply, running it in triode mode, getting about 5 or 6 watts.
Good enough to fill my office! Dead quiet when not playing! with ears to the speakers!

The Luxman is fixed bias. The Dynaco SCA-35 is cathode bias. And still gets 17+ clean watts.

 

[Xyrium]

I'd love to gut the thing and place a pair of Hypex modules in it...keep the tubes glowing in the meantime.

That said, I love Luxman stuff....I had a very old solid state receiver of theirs back in the late 80s. I bought it used (but pristine) along with a pair of Signet speakers and a Rotel CDP for less than $2k. Perhaps it's merely nostalgia, but I loved that kit. It was essentially my intro to Audiophilia....ugh.

 

[captainbeefheart]

CA-35 is one of the best selling tube amps of all time, and Dynaco managed 17.5W from cathode biased 6BQ5. And tube lifetime was excellent. So it CAN be done, it just wasn't here.

I attribute the tubes living so long in these amps are because the power tubes were much better than current production tubes in regard to lifespan and high dissipation. Today's modern production amps should be designed around the limits of the tubes being made today. Correct me if I'm wrong but I remember lots of these amps coming with RCA or GE 7189a types which can handle the higher dissipation. I remember EL84's in these amps dissipating well past the 12 watts max dissipation rating of a standard 6BQ5.

Vp = 365

Vg-k = -16

Vk = +16

Rk = 95 ohms

16 / 95 = .168 or 168mA

168 / 4 = 42mA

deduct a couple mA for the screen

365 - 16 = 349

.04 * 349 = 13.96 watts

This was just pulled from the service manual which jives with what I remember with these amps running the tubes pretty hard. Even a standard 6BQ5 or Mullard EL84 can probably handle this and last long enough but our modern run of the mill EL84 will red plate and have a shortened life span. The Sovtek EL84M is decent and will most likely be fine in this circuit. If Luxman uses this EL84M then yes they could get the 17.5 watts with cathode bias. I was just thinking that people love to "tube roll" and so a modern design with current production tubes would benefit from fixed bias so there is a broader tube selection for people to play with. There are some reproduction guitar amps like the Marshall 18 watt amp and it also is very hard on tubes due to cathode bias. I'll only install EL84M or vintage types that don't show any redness on the plates, I mean if a the amp owner really wants a standard 12 watt current production type I'll pop em in but I'll explain to them that they might want to replace them every year at least if you play a lot. Those amps have very high power tube failure rates and sometimes takes the output transformer along with the tube. Great design when Mullard was making the EL84 but now a pair of real Mullards is just too expensive.

The Luxman is fixed bias

Holy crap batman I just had another look at the block diagram and you are 100% correct. Has anyone had this amp on their bench? Curious if they are running low plate voltage and high bias current to keep it in Class A hence the lower power?

How?
20 clean watts?

Colder bias and high plate voltage Class B operation. You can squeak 35 watts from two EL84's like Roger Modjeski. I tend to think they sound their best around 20 watts per push pull pair, think Scott 299a, those amps sound great. Start running too deep into Class B for higher power and I just don't think it sounds as good.

 

[Ken Tajalli]

The Luxman is fixed bias. The Dynaco SCA-35 is cathode bias. And still gets 17+ clean watts.

17 watts, OK! anymore is class B operation.
Best subjective sound I could get out of mine was in class A triode mode, about 6W.
In pentode mode, sounded punchy and muffled.
Not for classical music.

 

[SIY]

17 watts, OK! anymore is class B operation.
Best subjective sound I could get out of mine was in class A triode mode, about 6W.
In pentode mode, sounded punchy and muffled.
Not for classical music.

By "subjective," you mean "evaluated without basic ears-only controls"?

Assuming you still had the feedback in place, there's likely not much difference between the two modes other than power. Pentode has a higher source impedance but higher gain, so the feedback will even things out. Ditto distortion. The only common difference between the modes is a reduction in top octave response with triode because of the combination of grid capacitance and reduced open loop gain, but that's not what you're describing here.

 

[SIY]

I attribute the tubes living so long in these amps are because the power tubes were much better than current production tubes in regard to lifespan and high dissipation. Today's modern production amps should be designed around the limits of the tubes being made today. Correct me if I'm wrong but I remember lots of these amps coming with RCA or GE 7189a types which can handle the higher dissipation. I remember EL84's in these amps dissipating well past the 12 watts max dissipation rating of a standard 6BQ5.

Anecdote: I ran JJ EL84 in my Red Light District amp at 13.75W plate + screen dissipation for a decade before replacing them. They were still working so it was really more of PM.

7189 is not pin compatible and is somewhat different in terms of required grid drive and optimal plate load, but is a great tube for this power class. Ditto 6CZ5. Another fun tube to use there (and likely will be in my next small tube amp) is the 6360 (or Euro equivalent QQE 03/12). Dual pentode, but with paralleled sections can hit 20 watts in push pull pentode with ease. Jan Didden picked up a bunch of them for me at a really attractive price, a major advantage of using tubes outside of the conventional "audio" tubes.

 

[Ken Tajalli]

By "subjective," you mean "evaluated without basic ears-only controls"?

Absolutely! always.
Don't do quick A/B comparison.
It is possible I did not readjust feedback in pentode mode, and that had something to do with it, was a while ago.

Assuming you still had the feedback in place, there's likely not much difference between the two modes other than power. Pentode has a higher source impedance but higher gain, so the feedback will even things out. Ditto distortion. The only common difference between the modes is a reduction in top octave response with triode because of the combination of grid capacitance and reduced open loop gain, but that's not what you're describing here.

I did check FR in triode mode, with correct feedback, it was pretty flat, rising slightly past 17kHz or so, before dropping past 40K.(on a scope)
Still sounds good! for background music. Very black background noise, buzz, nothing.

 

[Mnyb]

A bit sad that many modern tube amps are so badly implemented, I bet even lux themself made better ones in the past .

As described by our tube fellows on this forums , it seems that you just have to apply some well known facts to make a more suitable solution, would not cost more in parts . Not even an expensive development project as it seems to be possible to just read some engineering textbooks and the solutions are so old so there is no ip or patents to infringe upon ?

All audio products does not have to be super rational all the time , you can have some tube fun i’ll bet .

But the expectation is that Luxman makes this as good as it can be with the choosen technology, they have not done this.

 

[SIY]

A bit sad that many modern tube amps are so badly implemented, I bet even lux themself made better ones in the past .

The Luxman MB3045 was a brilliant design, mostly based on the McIntosh topologies. It was handicapped a bit by the choice of proprietary tubes, but the performance was outstanding.