how many watts of Luxman R-115 receiver are Class A?

Discussion in 'Audio Hardware' started by CraigVC, Mar 22, 2024.

  1. CraigVC

    CraigVC Senior Member Thread Starter

    Location:
    Portland, OR
    I've had this Luxman R-115 receiver (circa 1987) for a couple of months now, and I've really been enjoying it.

    It's part of a budget system (under $1,000) including WiiM Pro Plus streamer (streaming Qobuz, and occasionally TIDAL) and Pioneer SP-FS52 (Andrew Jones) tower speakers. I have the speakers positioned fairly close to what I think is called "golden triangle" (??; in other words, an equilateral triangle among the speakers and my listening position).

    At lower volumes (according to my phone's "Sound Meter" app, around 50dB with phone held about 1 meter from speaker), the sound is warm, dynamic, and creamy tube-ish goodness especially in the bass notes, with plenty of little micro-details in the soundstage, and a lovely midrange for realistic vocals. A total joy to listen to for hours.

    However, when I turn it up, the highs get thinner and harsh, the bass seems to substantially disappear into the room (less so if I close the curtains of the glass windows behind the speakers, so room treatment would likely help with this), and overall the sound quality declines.

    I'm wondering if I might - at least in part - be hearing the difference between Class A at lower volume/watts, and switching to Class B at higher volume.

    So I asked Microsoft's Co-Pilot AI (yes, I know it's sometimes wrong; it's early days yet for this technology), and it offered that up to 20 watts of this 70 watt (at 8 ohm; my speakers are 6 ohm) are Class A. That seems kinda high to me, but I dunno.

    Would the difference between Class A and Class B watts account for the noticeable difference in what I'm hearing - the truly outstanding sound quality at lower volumes, versus the less outstanding sound quality as the volume increases?

    "Pics for Attention" :p

    [​IMG]
    [​IMG]
    [​IMG]
     
    arisinwind likes this.
  2. Black Elk

    Black Elk Music Lover

    Location:
    Bay Area, U.S.A.
    That does not strike me as correct.

    The efficiency of a Class A amplifier is a measure of how much of the supplied power is actually transferred to the load. If the Luxman has an efficiency of 30%, it means only 30% of the supplied power can be used. So, the amplifier can supply 233 W, of which 233 - 70 = 163 W are dissipated as heat. This assumes Class A operation all the time.

    If the amp switches to AB (or other) operation at some point, the efficiency then changes, so the supplied power will be less, and less heat will be dissipated.

    One would need to know from the published spec. at what point the switch takes place.
     
  3. vinylkid58

    vinylkid58 Forum Resident

    Location:
    Victoria, B.C.
    I skimmed thru a review of the R-115, and there's no mention of any Class A output, so not sure where you got this from.

    jeff
     
  4. CraigVC

    CraigVC Senior Member Thread Starter

    Location:
    Portland, OR
    Is there any way to tell what amplifier topology Class the Luxman R-11x receivers utilized, from this part of a Luxman brochure?

    It talks about "Duo-Beta circuitry, STAR circuit patterns and LED bias circuitry" ... but I don't know how those attributes translate, if at all, to whether this receiver is Class A, B, AB, etc.

    [​IMG]
     
  5. CraigVC

    CraigVC Senior Member Thread Starter

    Location:
    Portland, OR
    Hmmm, I found this reference to the "Duo-Beta" Luxman amplifiers operating in Class A for the first 15 watts...

    Source: NFB and load characteristics | Page 2 | diyAudio
     
  6. CraigVC

    CraigVC Senior Member Thread Starter

    Location:
    Portland, OR
    This is an excerpt from the Luxman R-115 receiver's owners manual. "Push-pull" indicates Class B or Class AB, right?

    [​IMG]
     
    Old Rusty likes this.
  7. I've had the Lux R-113, 114 & 115 at different times & their circuit design delivered the polar-opposite to what you describe -ie- they sounded better the louder you played them. Headroom to spare, ya dig? But being 30+ years-old that amp might need a 'recap'. Just sayin'...
     
  8. CKDC

    CKDC Forum Resident

    Location:
    Washington, DC
    Have you tried measuring the listening volume?

    That would be an indication of whether you are headed into class B amplification.

    I think, as Old Rusty pointed out, what you are hearing is probably a sign that the receiver needs some attention.
     
  9. Teraphoto

    Teraphoto Forum Resident

    Location:
    Italy
    May be your loudspekers which increase distorsion turning up volume, much larger effect than passing from A to A/B class in such an amplifier.
    The negative effects of the room are volume dependent too.
    Regards
    Paolo
     
    Apesbrain likes this.
  10. CraigVC

    CraigVC Senior Member Thread Starter

    Location:
    Portland, OR
    I did have the receiver bench-tested by a local technician with several decades of experience, after I bought it, because the volume/balance knobs were scratchy. He said everything tested well and he didn't see anything that needed additional work. However, I realize that's just one technician's assessment and maybe he just missed something.

    The room being a factor is starting to become more plausible as this conversation progresses. Other than the curtains, an upholstered couch (my listening seat) opposite the speakers, and the two upholstered chairs on either side of the speakers, everything else in the room is hard surfaces - hardwood floor, walls, ceiling, coffee table, side tables, etc.

    I think now I will research the best balance of 'most effective + least intrusive' room treatment methods ... as well as research how to "measure the listening volume" as @CKDC suggests.

    I'm probably only here in this house (I'm visiting) for another month or so -- this limits what I can do in short term -- but I will be returning again periodically in the future, so doing what I reasonably can to improve the sound quality is definitely something I'm interested in.

    Maybe I'll ask the technician (or find a different one) to take a closer look at the capacitors and other internal components that tend to wear out over time. I could see if they would mind if I left it with them for a couple of months until I return for my next visit, so they can take their time with it and insure it's effectively performing at its full potential.
     
    Old Rusty likes this.
  11. CraigVC

    CraigVC Senior Member Thread Starter

    Location:
    Portland, OR
    This "negative effects of the room" comment seems to be another "vote" in favor of me exploring room treatments, experiment with alternative speaker placements, etc.

    The cabinet between the two speakers in the last photo I shared is actually an old Sears tubed console stereo system from the 70s. Same location in the room after all these decades. Back in the 80s, I used to crank it up really loudly when my parents weren't home (I have a specific memory of playing Yes Tormato LP loud enough that neighborhood kids walked down the street to investigate, and laughed at the weird music I was playing).

    I recall that the bass from those built-in-cabinet speakers had plenty of bass the louder I turned it up ... but back then the room was also carpeted on top of the hardwood floor, so maybe the carpet was an effective room treatment back then?

    I wonder how I can determine whether these speakers are distorting at the higher volumes. Hmmm?

    Specs of Pioneer SP-FS52 (Andrew Jones) tower speakers from the manual:
    Enclosure: Bass-reflex Floorstanding
    Configuration: 3-way
    Frequency Range: 40 Hz - 20 kHz
    Nominal Impedance: 6 Ohms
    Sensitivity (2.83 V): 87 dB
    Maximum Input Power: 130 W
    Cross-Over Frequency: 250 Hz & 3 kHz
    Magnetically Shielded: No​
     
  12. Benzion

    Benzion "Cogito, ergo sum" Forum Resident

    Location:
    Brooklyn, NY
    IIRC, in SS "push-pull" does mean A/B.
     
  13. Apesbrain

    Apesbrain Forum Resident

    Location:
    East Coast, USA
    If you intend to regularly use the room for listening at louder levels, this is the first problem to solve. Put down an area rug/carpet pad at least as wide as the distance between the speakers.

    There are other things -- maybe more difficult to manage -- that should also help:
    1. Get rid of the old console. There are so many things inside of it that are going to vibrate at higher levels. The large drivers will suck bass out of the room. (Alternatively, use it! Some of those old console systems still sound pretty good.)
    2. If you (or your parents) don't like this idea, move the Pioneer speakers out in front of the leading edge of the console and push those armchairs further to the sides out of the way of your tweeter dispersion.
    3. Take that clock off of the right speaker and put it on the console. Why have a piece of plastic in the room buzzing any more than necessary?
     
    CraigVC likes this.
  14. CraigVC

    CraigVC Senior Member Thread Starter

    Location:
    Portland, OR
    Thanks for these ideas!

    Just Mom is left here (Dad died 2 years ago), and she's moving into an assisted living apartment next weekend. That means eventually I will be able to move things around more in here to experiment ... but I'll probably hold off on major changes because I plan to bring Mom back over here to her house sometimes whenever I'm back in town for a visit, and I don't want her to be disoriented or upset if things look a lot different than she remembered them.

    I might be able to get away with swapping out the hard coffee table with an area rug and an upholstered ottoman for me to prop my feet up while listening to music.

    I definitely understand what you mean about the console vibrations, etc. I even wonder about the magnets inside the Pioneer speakers (un-shielded) somehow interacting adversely with the magnets inside the console speakers less than a foot away from each other ... but I see so many people online who have multiple tower speakers flush next to and/or on top of each other ... those configurations always looked visually bonkers to me, but I wonder if sonically they're bonkers as well?

    I really would like to move that console over to the side of the room ... but Mom loves having a place to put those two lamps ... I guess I could move the console and find two small matching end-tables of comparable height to put those lamps on.

    Finally, the clock on top of the speaker was Mom's action, soon after I put the speakers there. (The "ooh, there's a surface, I'll put something on it" pattern so many of us are familiar with. :) ) I doubt it's causing any adverse sonic effects, certainly not compared to the other points you've brought up that could be substantially more affecting, so in the practice of "do least harm" I'll leave it there for her.
     
  15. avanti1960

    avanti1960 Forum Resident

    Location:
    Chicago metro, USA
    Your amp is running out of steam and clipping at higher volume levels. Bass is the first thing to drop off. Realistically it is a 70 watt amp that weighs 25 lbs. Weight is an indicator of power supply capability FYI.
    A re-cap might help your issue but what you are hearing is typical for an amp of that spec.
    I had an 80 watt per channel NAD amp that had similar weight as your Lux and it did the same thing at higher volume levels even when new. I sold it and bought a 150 Watt NAD amp and the sound was so much more powerful and the bass kept up at higher volume with no harshness.

    I suggest a new or used amp of higher power to fix your issue.
     
    Old Rusty and McLover like this.
  16. CraigVC

    CraigVC Senior Member Thread Starter

    Location:
    Portland, OR
    The room dimensions are 12 feet deep (measuring the dimension spanning from my listening seat to the speakers) by 20 feet wide by 7 feet tall ceiling. there is an opening to the right (when sitting and facing the speakers) that is 25% bookshelf, and 75% open space into the adjacent dining room, which is perhaps 12' x 12' or so.

    When the sound is outstanding, the decibels are measuring around 50 dB at approx. 1 meter from a speaker. For me, "loud" (when the sound gets relatively less outstanding) means getting up to more like 70 dB.

    Given that this receiver offers 3 dB headroom (owners manual also indicates: "Dynamic Power Output 1( kHz, 20ms).. 150W x 2 (8 Ohms) ... 210W x 2 (4 Ohms)"), are this room's dimensions still too much for this Luxman receiver to deliver more than 50 dBs of quality sound into the room?

    Lots of interesting ideas and perspectives being offered so far -- thanks!!
     
  17. CKDC

    CKDC Forum Resident

    Location:
    Washington, DC

    By way of your thinking, shouldn’t the OP buy a heavier amp???
     
  18. CKDC

    CKDC Forum Resident

    Location:
    Washington, DC
    I suggest that you don’t need to buy an expensive dB meter. Just download an app to a smartphone.

    Find the volume level you like and hold the phone a meter from a speaker and let us know what you see.

    You might also want to try borrowing another amp and see how it plays in the same system (and volume level.) This will help further define the problem.

    I had an R115 and it had plenty of power… for my needs at least. (As far as I know, it is still in service.) But, your receiver is possibly getting to a point that it needs servicing.
     
  19. Angry_Panda

    Angry_Panda Pipe as shown, slippers not pictured

    On the initial question - it's my understanding that any Class A/B amp operates in Class A at low power levels - if it didn't, it would be a straight Class B amp. As to the point at which it crosses over into Class B (0.1W? 1W? 10W?), that's going to be hard to answer unless you can find something in a manual. I'm a bit skeptical that the transition point is what's causing your change in presentation, however.

    Based on what you've said above, I would be more inclined to attribute that change at higher volumes to the speakers. They appear to be intended for home theater, and I wonder if you could get better results with something more aimed at traditional stereo setups. If you know someone who can lend you a pair of 90+dB 8 ohm hi-fi floorstanders (I would personally avoid lower impedance with any 70's or 80's SS integrated lacking separate taps for those impedances), I would think it would be worth trying those out to see if they flatten out response at higher volumes. Certainly the room is also playing into this, but there are enough soft surfaces around the area I don't suspect that's the primary culprit at this point.
     
  20. Ingenieur

    Ingenieur Just a dog looking for a home...

    Location:
    Back in PA
    A Class A amp can be a push-pull configuration

    Luxman Class A 590
    [​IMG]
     
    Triffid likes this.
  21. avanti1960

    avanti1960 Forum Resident

    Location:
    Chicago metro, USA
    With more power and quality - e.g. power supply transformer and capacitor banks- comes more weight. Unless we are discussing Class D amplifiers. My experiences over the years tells me this rings true.
     
  22. Simoon

    Simoon Forum Resident

    Location:
    Los Angeles
    Wait a second...

    Aren't ALL class AB amplifiers biased class A for some portion of their output?

    Isn't that what the "A" in class AB means?
     
  23. avanti1960

    avanti1960 Forum Resident

    Location:
    Chicago metro, USA
    Here are the specs of my NAD amplifier and its headroom. Very similar to your amp and I had the same issues at higher volumes. My room is larger but yours is connected to open area. My listening spot with that system was about 8 feet away from the speakers. Also my speakers were slightly more efficient (89db PSB towers).
    Your amp is clipping and the midrange treble output is louder but not bass.
    I have measured speaker output in my room with RTA software and it clearly shows this issue. After a certain volume level the bass remains the same but everything else can get louder.
    Technical specifications:

    • 2 x 80 watts minimum continuous power into 4 or 8 ohms.
    • 145 watts, 220 watts, 290 watts dynamic power into 8, 4, 2 ohms
     
  24. Ingenieur

    Ingenieur Just a dog looking for a home...

    Location:
    Back in PA
    Bingo
    If not it is a Class B
     
    Glmoneydawg likes this.
  25. avanti1960

    avanti1960 Forum Resident

    Location:
    Chicago metro, USA
    Correct but if they do not mention where the transition power is chances are it is not a selling point and it happens at a very low power level- could be a watt or two.
     

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