Solid-State Power Amp Adventures

Discussion in 'Power Amps' started by purr1n, Jan 24, 2017.

  1. uncola

    uncola Friend

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    did you ask them to bias it into full class A? the aliexpress ad says it does 180 watts into 8 ohms. The 800va plitron transformer is certainly a nice part for the price of the amp
     
  2. Peter

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    No, I did not ask them to do that. I think the heat sinks are too small and there is not enough ventilation to bias it farther into class A than it already is. I know it idles at around 120W which I believe is only enough for about 20 Watts class A. It does get pretty hot, so I would not want any more than that.

    You may be referring to a different amp than the one I got. According to aliexpress mine is: "150W*2/8Ohms ; 300W*2/4Ohms , push all speakers easily"

    https://www.aliexpress.com/item/QUE...32816534722.html?spm=a2g0s.9042311.0.0.DaEABA

    I think that transformer is very good. There is a slight hum, but it is only audible if you are very close to the amplifier.
     
  3. Priidik

    Priidik MOT: Estelon

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    Unlike mosfet amps, BJT complementary AB amps can be optimally biased, where crossover distortion is minimal.
    That is for the case of actually using it out of class A region.
    More bias will result in more crossover distortion due to Gm doubling past the optimal value.

    It's not good idea to blindly increase bias even when the transformer and heatsinks can take it.
    At least in the cases where one can trust the designer knew what the hell he/she was doing.
     
  4. Hrodulf

    Hrodulf Prohibited from acting as an MOT until year 2050

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    So are the counterfeits.
     
  5. Peter

    Peter New

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    Thank you, great post. I actually learned something and that does not happen to me every day on internet forums.
     
  6. yotacowboy

    yotacowboy McRibs Kind of Guy

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    Following up on the Nuforce/Underpowered JOB, amazon delivers...

    Initial impressions compared to PP El34 Cayin TA-30 I've been living with for the better part of 10 years (essentially a Prima Luna minus the auto-bias): Much better macrodynamics, slighly better microdynamics/inner detail, better extension at both ends of the frequency spectrum. Soundstage is comparable, less front-to-back, but better instrument separation/delineation. But nothing's "jumping outside the speakers like it's coming from the next room". Better air, likely due to better/more extended HF response. Once I get some hours on it I'll do some more "critical" listening, likely this weekend. For now it'll be relegated to background NPR. It does sound like it needs some hours to open up a little. This definitely sounds better than any $500 amp I've heard (even considering it's on regular blowout/discount at nearly $700-off MSRP).

    I'm running it sans pre-amp through Roon - Will be adding Freya soon. So, caveats.

    Edit - just within the last 30 minutes, it's opened up a good bit, and that's only with an hour or two on it, so this might have some good potential.
     
  7. msommers

    msommers High on Epipens

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    Likely more about reaching proper operating temps than "opening up" and if it's brand new the caps will need at least 100 hours on them. But overall sounds positive and the reviews on Amazon are also encouraging.

    What other gear is in your chain?
     
  8. yotacowboy

    yotacowboy McRibs Kind of Guy

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    Yeah, just wanted to see how awful it could sound, fresh out of the box.

    Rest of the chain: Roon, RPi, HifiBerry Digi+ Pro Coax to Bifrost Multibit, Audio Note AZ-Two. Prior sub-$1k amps I've had are: ubiquitous NAD C325BEE (boring), Marantz PM-8003 (different than the Cayin, but not better; flat sounding).

    Trying not to go head over heels and pick up a Gungnir Multibit when I order the Freya in a bit. Need to be patient.
     
    Last edited: Nov 29, 2017
  9. yotacowboy

    yotacowboy McRibs Kind of Guy

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    OK - so a little check in after another 24-ish hours of burn in on the NuForce STA200. Treble has settled down a bit, but this amp is pretty fast sounding without being fake-detailed or over emphasizing transients. Just great microdynamics and macrodynamics - trails from cymbals from the initial strike and SPLASH just go on and on and on, which really jumped out at me. Things pop out of a relatively low background with better convinceability than my old Cayin/Spark. Not going with "veils lifted" or any of that BS.

    No real pre-amp yet (caveats...), but running it thru Magni2U simply as volume pot. And to be quite honest, for a single input system, for $600 plus speakers, this would be pretty f'ing sweet... Anyhow, liking very much what I'm hearing so far. I know i just picked up Andro recently (and obvs, IEM to speaker based comparisons are weak at best), BUT the confident but detailed upper freqs remind me a lot of the Andro. Andro vibrancy (not stridency) with actual soundstage/layering versus headstage. I know the "effortless" thing is kinda audiophile blah blah similar to "neutral" but there's a speed to the sound that make things bouncy and quick. I won't say PRAT-something-or-other... but bass is taught, a little tiny bit over emphasized in the 80-100hz range, but only by a couple dB. That could be entirely due to the my speakers and a little weird impedance/higher than normal sensitivity. Still farting around with sub levels and x-over points, but good punch with the subs removed completely.

    If this seems like noise, just let me know and I'll wait until the set up is more properly baked to post thoughts.
     
  10. Peter

    Peter New

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    I suspect that amp ^ is one of the best things NuForce has ever made. Their products have had mixed assessments over the years, but this seems to be a solid, no nonsense amplifier. A great choice if you have medium to high efficiency speakers. Looking forward to hear more.

    I am currently enjoying my Chi Fi power amp. The house is quiet and I am listening at pretty much the lowest possible level. Still sounds beautiful, 3 dimensional and musical.
     
  11. yotacowboy

    yotacowboy McRibs Kind of Guy

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    if I had read anywhere that the STA200 sounded anything like their other gear I'd have stayed far far away. internally, it's exactly like the Job/Goldmund, with fewer output transistors, based on pictures. I might pop it open to take a look/confirm.
     
  12. msommers

    msommers High on Epipens

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  13. Peter

    Peter New

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  14. msommers

    msommers High on Epipens

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    Glossed over your previous post, apologizes.
     
  15. bengo

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    What about Saga plus Gungnir Multibit instead? Saga is, according to those who heard it here, more transparent in tube mode. Unless your power amp is a special topology like Ragnarok which really benefits, it's not worth worrying too much about balanced. Read Marvey's thread on the topic
     
  16. yotacowboy

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    well, I need the input switching (3 inputs, digital, tuner, and TT) and I figure if I run passive, it's probably pretty close. But I'll read marv's thread. I could be wrong!

    Edit: ran through the thread, and I appreciate you linking that one. but yeah, balanced isn't the driver for freya purchase, it's more about input flexibility in the long run.

    edit, edit: why did i think Saga only had two inputs? fawk me i'm retarded. hrrrm. whatamigonnadowithmy2matchedpairsofRCA5692snow?

    edit, edit, edit: so, does either saga or freya have any DC leakage on the outputs? I'd imagine Jason wouldn't let DC pass. Further reading on the goldmund topology sez it doesn't have a DC servo.
     
    Last edited: Nov 30, 2017
  17. yotacowboy

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    So, some more listening. This thing is getting better with pitch definition and lower frequency detail.

    Listening to kieran hebden's latest, on the track LA Trance, there's a bass hit that so far on every setup I've heard in the first 20 seconds, sounds like 808-farts, all three hit about the same, but kinda flobble into low frequency mumbles because they're low level. Only, with this amp did the bass hits come across as three distinct tones separated by an octave each. IOW, the fundamentals came thru much more so than the harmonics.
     
  18. Kolohe

    Kolohe Facebook Friend

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    Somebody already popped them both open, here.
     
  19. Purastikku

    Purastikku New

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    Good to see Nuforce moving away from Class D, I had a brief stint with the STA-100 and while plenty powerful given its size, the overdone warmth and bloated bass did not win me over. Plus a constant background noise/ hiss, even without any input, loud enough to be noticed 2 meters away (with low-sensitivity speakers, 86dbm). It was apparently a widespread issue in Nuforce amps at the time, and a real shame given the size/ power/ price ratio was great.
     
  20. yotacowboy

    yotacowboy McRibs Kind of Guy

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    From what I've gathered on the innernets, Nuforce did some restructuring/rebranding where the core of the company sold off the lower-end products and did a restart on the higher-end, branding-wise, rebranded as Nuforce Prime (NuPrime). the company that bought the rights to the lower end gear is Optoma, who does mostly projector/HT stuff. IOW, the STA200 amp seems to be a bit of an outlier.
     
    Last edited: Dec 1, 2017

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