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While the KST-100 is not a 'pure' class A design, at the level you are running it the amp should maintain class A operation. |
I run my system under 85db and my speakers are 91 sens. With my Parasound A21 running the first 10 watts in class A, I'm in the same position. |
The Class A power level might depend on the impedance load. |
Perhaps you're wrong. For full range sound you need more power. It's only OK for 1kHz, but for the rest of frequencies especially in the crossover region, chances you're not in class A are high even at 85dB. |
I'm not sure on Runnin's speakers but my Vandersteens are fairly benign. Before I started playing with the Krell I was happy with a 35 watt Music Reference RM 10. The Krell is for playing but the Music Reference is a keeper. |
Ruunin and Digepix,
I think both of you are listening to class A power most of the time if your listening levels are usually in the mid 70-80s db range C weighted.You`re often using less power than you realize. |
Digepix, I understand that you consider class A better sounding, otherwise you wouldn't care. It should be better sounding if it is designed that way. Class AB has to use more of negative feedback to counteract nonlinear operation of output transistors. This negative feedback improves everything: THD, IMD, Bandwidth, Output impedance etc. but unfortunately can produce Transient Intermodulation (TIM) - basically overshoot of fast changing signals (signal fed back is late because amp introduces delay) that in frequency domain shows as addition of odd order harmonics. Since it can make sound unpleasantly bright designers try to keep amount of negative feedback to minimum. 30dB gain of power amp represent voltage gain of 30 but amplifier will most likely have gain of 300 in class A and 3000 in class AB before feedback that brought gain back to 30 was applied. Class AB needs more feedback (and therefore initial gain) not only to linearize non-linear operation of output transistors but also to reduce "gm doubling" effect. Gm doubling (trans-conductance doubling) is simply gain difference between two (class A) vs one (class AB) transistors operating at given moment.
Since your amp has both - nonlinear region of transistors and gm doubling it has to use more gain and "damage" was already done. This whole issue is very complicated and it was even shown that increasing bias in typical SS amp can actually increase THD distortions (overbias). I'm sure Krell engineers know what they're doing and this amp can sound better than class AB amp but it is not as good as equivalent class A amp at any loudness level.
I understand you need to know what you really got for your money but I would pay more attention to system synergy and overall sound and less to classes of operation, specifications etc. Often amp with poor specifications has wonderful sound. |
"Often amp with poor specifications has wonderful sound" so true. |
Kijanki-Wow!! Thanks for all the information. I'll be honest, the Krell was a freebie so it doesn't hurt my feeling one way or the other. It sounds good even though the KST series of Krell amps get no love. I'll tell you from a pure synergy perspective I haven't heard a better amp than my Music Reference RM-10 through my Vandersteens. Sure 35 watts won't tear the walls down but for me it plays loud enough. When Roger Modjeski designed this amp he used my Vandersteen's and a pair of old Quads to voice the amp with. I always loved el-84 amps, my first amp was my Dad's Harman Kardon Ballad integrated and ever since I've been hooked. I'm sure my amp doesn't offer the best specs but for me it offers the best sound. |
35W won't tear the walls but don't forget that 350W (that tears the wall) is only 2x louder. Also 3dB more sensitive speakers will give you same as doubling the amp power.
So, how your 35W amp compares with good 140W amp driving 3dB less efficient speakers? 140W amp will be only 22% louder.
People often ask if it is better to buy 200W or 100W amp. In spite of amp's power being useless specification IMHO, I would always choose 100W because for the same money I can buy better amp. |
Kijanki, there have been many threads which speak to the trade-offs of using NF. Certainly, Ralph (Atmasphere) has written quite a bit about NF.
Just curious, does it matter how the NF is applied: local or global. For example, my amp uses a form of local feedback. I believe ARC describes it as "partial cathode following," which in English relates in someway to the topology between the output tubes and the output trannies. |
Kijanki, I enjoy reading your contributions here, and as much as you are obviously speaking on your own behalf, I think that as a general rule your last sentence might not hold true for everyone in every circumstance. |
Used to have Quicksilver M60 to drive my Aerial 10t. Sounded great. Quickies were driving once owned Vandy 2ce. Still love these and regret selling.
Switched to Krell KAV300i sounded better.
Than switched to Sunfire 300 sounded even more better.
If I get Sunfire 600(devoted to them since), they will sound even more better.
Better bass, better imaging and presentation.
Bigger power brings bigger sound. Loudness is measured at 1khz, don't forget. Other frequencies will act different. My speakers can be brought to 25Hz FLAT with powerful amp. |
I suppose that's true. In my circumstance, I bought a 250 wpc Parasound amp, and as it turns out I don't like the volume above maybe 10 wpc with my speakers in my room! I could have bought a 100wpc amp instead. But on the other hand, I do occasionally crank it up on some passages and it's jaw dropping to hear a gorgeous vocal or cello.
Perhaps there's a benefit with having too much amp! |
Runnin, 250W would be nice if you can get it for the same price as 100W but if it is more money than perhaps getting better 100W (better design, better components) would bring more satisfying sound.
Bifwynne, Local feedbacks are better. Even emitter (or cathode) resistor is a form of NFB. SS amplifier, being voltage source, needs feedback at least for the output stage. Tube amps, being power source, most likely need less of it.
It is possible to design amplifier with negative feedback free of TIM. Since problem of TIM is caused by summing fed back delayed signal, during fast transition, it would be logical to prevent fast transitions and to eliminate delay. It comes to bandwidth limiting input stage before summing point and extremely fast output stage. High quality parts have to be used to achieve good initial linearity and wide bandwidth. NFB should be mostly local but also shallow just to bring THD distortions to about 0.5%. Bandwidth should be limited at the input to one that amp had before feedback was applied (since NFB widened bandwidth).
Such amp will have 0.5% THD and perhaps only 50kHz bandwitdh not to mention relatively high output impedance. THD distortion is not that audible, 50kHz bandwidth is passable and output impedance doesn't matter because inductor in series with the woofer is about 0.1 ohm (limitting DF to 80) while speaker impedance (being source impedance for back EMF) is mostly resistive.
Would you buy 100W amp with THD=0.5%, 20-50kHz, DF=50 when somebody else is selling 250W with THD=0.01%, 20-200kHz, DF=1000 ?
Specifications are useless - only sound matters. All comes to good design, quality (expensive) components and smart compromise. |
Kijanki, Could you translate the paragraph you wrote into English please, particularly the phrases framed with double astericks (**):
"Such amp will have 0.5% THD and perhaps only 50kHz bandwitdh not to mention **relatively high output impedance.** THD distortion is not that audible, 50kHz bandwidth is passable and **output impedance doesn't matter because inductor in series with the woofer is about 0.1 ohm (limitting DF to 80) while speaker impedance (being source impedance for back EMF) is mostly resistive.**
Thanks |
NFB lowers output impedance. If amp has 10x higher gain before applying of NFB then feedback will lower output impedance tenfold. We call it 20dB feedback. As a result deep NFB some amplifiers end up with output impedance of single milliohms. There is no need for that, since inductor in series with the woofer is about 0.1 ohm, while the fact that speaker's internal impedance is mostly resistive limits even more. When speaker's coil moves in response to signal it also generates response (back EMF) that works like brake that limits coil movement. This brake has damping effect on the membrane.
DF=1000 looks good on paper but it doesn't make big sound difference. Deep NFB used to achieve it, on the other hand does, making sound bright and unpleasant. Highly praised Atmasphere amps have output impedance in high ohms (DF=1).
Some speakers work well with low output impedance amps while others, (overdamped) sound great with tubes, but sane level of DF is perhaps 100.
It is very tempting to improve specifications with NFB because it doesn't cost anything. If you see fantastic spects in cheap amp you know that something has to give - it is sound. |
Kijanki,
Bravo! What you wrote has been confirmed by many who simply use their
ears. Those supposedly impressive specifications made possible with
increasing NFB don't result in high quality sound IMO. |
Charles1dad, Thank you. Atmasphere mentioned negative effects of NFB many times. I still believe that shallow NFB can be used but design has to start with good circuit and quality components. The best is perhaps not to even think of it and just to listen. |
I believe that most of us would agree that after a given point; a specific specs numbers can become irrelevant, academic, out of context or just marketing tools. On the other the other side of that given point; specific specs numbers can indicate appropriate or inappropriate system matching or just plain inferior design, manufacture or current operating status. And (the relevancy of) those given points of those specific spec numbers can change as the other spec points in the equation change. Before stating things as absolutes, I suggest we remember the context of the specific specs in the overall equation, when we can, and be mindful not to throw the baby out with the bathwater. |
Unsound,
Unquestionably measurements and specifications have their vital place and are needed for the reasons you state. What Kijanki and others recognize is the inadequacies of measurements to determine the most important aspect of audio components, their sound. Ironically the better some specifications become, the perceived sound quality diminishes, the converse has also been observed. |
While I don't believe specs can demonstrate all the qualities of sound that a component will provide, specs can offer a glimpse of what sound might be produced, especially when the specs of the surrounding components are known as well. |
My amp Sunfire 300 clearly demonstrates sound qualities per specified. It does use deep 22db NFB as most digital amps do. I can't tell exactly how many AB comparisons had been done so far swapping one amp vs. mine to just simply tell you that my amp was acquired according to specks that matched my other components and speakers and no other amp so far was able to proof its worthiness for the value. For JC sake how in the world can you beat $<1000 used 300wpc/8Ohm of continuous power stable to .5Ohm???.
Read more about audiophoolishness over the internet and do not buy neither digital amps or any other amps with NFB so they can be sold cheaper. |
I don't design audio but it would be quite easy to design an amp that would measure THD=0.001% IMD=0.001% BW=500kHz and DF=1000 with absolutely horrible sound. I suspect that if you find amp like that (plenty of them in 70s) IT WILL have horrible sound (and they had). Again, spects have nothing to do with the sound. Even power spects are so vague that amp listed as one with higher power might actually play softer. Price of the amp might be even better indicator of quality than spects.
Czarivey, 22dB is not a deep feedback. Most of digital amps don't use deep NFB because there is no need for that. PWM is quite linear while output has by definition low impedance to start with (since one Mosfet is always conducting to low impedance point - GND or VCC). |
^Maybe this proves your point:
http://www.stereophile.com/content/kr-enterprise-vt8000-mk-monoblock-power-amplifier-measurements
Then again, maybe not. |
I believe that example is classic in its representing the "major" discrepancy in actual sound performance vs lab measurements. If one were to judge the Kron amplifier on measured results alone it would be deemed an undeniable failure. Michael Fremer found it to be one of the very best,convincing, captivating and "realistic" music reproducing amps he`s ever heard! Thanks Unsound, that entire review and followup was quite interesting.Based on listening the review was an utter rave. |
^On the other hand, FWIW, though I've never heard the Krons (and the price(!) didn't exactly tempt me), when it came to other gear Fremer has opined about, well, let's just say we don't seem to share the same listening priorities. |
Unsound,
That you may have different listening preferences from Fremer, me or someone else is understood and a given. One could look at our two systems and conclude we likely hear things very differently and that`s perfectly ok in this subjective realm.
Given the very poor lab testing of the Kron you`d think no way could anyone find such an amplifier to sound even remotely decent,not to mention "captivating and among the very best". |
