You know it’s funny that we are now bringing the built-in powered subs into the equation. My ARC VT-100 MKII had an issue where it sounded like it was oscillating with my speakers at very low frequencies and I wondered then if the subs were causing that problem. The damn thing is that my old PL 400 Series 2 amps which only have skinny two prong power cords are quiet as a church mouse with my speakers.
The built-in powered subs never left the equation..... It's something I think of all the time because my speakers also have built-in subs. Unfortunately, with all the consumer protection that is imposed on designers these days we probably won't be allowed to have the nice skinny two prong power cords on amplifiers anymore.
If you put a 200 ohm resistor across the input of the subwoofer, you would short it out and the subs won't work. The output impedance of the amplifier has nothing to do with it.
Sorry, Gary, I would like to sort this out, you say:
Your loudspeakers, because it has a built-in subwoofer amplifier has a high-pass passive crossover to protect the midrange drivers from low-frequency energy. This combination results in a very high impedance (it can be up to 100k ohms) in the low frequencies (where the subwoofer is working).
which implies that the power amp is directly driving the relatively high impedance input of the subwoofer amp. Correct? If not, would you care to point to a circuit showing what is there.
If the subwoofer input is directly tied to the amp output then it most certainly will experience the output impedance of the amp. Also, the input impedance of an amplifier is not relevant to its operation, but on the ability of a source to drive it without distortion.
The PC from Krell showed up last night. I took it out of the box and let it "relax" all night as it was coiled up and stiff from being in the UPS truck. I plugged it in when I got home today and turned the KSA-250 on. The hum/buzz has been reduced to the point that you won't be able to hear it from the listening seat with no music playing. Really, you have to get pretty close to the speakers to hear it now. I'm going to try a MIT Z-Trap and see if that will have any further benefits.
I have never had a completely silent high-end system. It's usually a tube preamp that has some hiss or a tube phono section that has some hum-never a tube amp making racket. I have never had one of those systems where people claim they can turn their preamp gain all the way up with their 10,000 watt amps and they can place their ear on the tweeter and not hear a thing.
(...) I have never had a completely silent high-end system. It's usually a tube preamp that has some hiss or a tube phono section that has some hum-never a tube amp making racket. I have never had one of those systems where people claim they can turn their preamp gain all the way up with their 10,000 watt amps and they can place their ear on the tweeter and not hear a thing.[/QUOTE]
Mep,
If you use 83 dB/W speakers it will be much easier ...
Nice to know the PC cable solved your problems.
If the noise floor is now below your old tube system, that's a win. If you can get it even lower, even better. Then, of course there is the comfort and security of knowing you've bought yourself enough amplifier headroom to build a stable for Brontosauri .
I don't think anything else, other than the recording and the speakers, is quite as important as sufficient headroom. To say that yours is sufficient is an understatement. That's my story and I'm stickin' to it.
+1. With all that you've been through, you are more than deserving of gear that meets its expected level of performance and, most importantly, your musical peace of mind, body and soul.
There are 100s of good SS amps on the market. Pick one. Pass X250.5 for one. You just shouldn't have noise issues with SS amps, and while a PC is a nifty trick---that shouldn't be the solution imo.
Personally would feel the XA series from Pass is closer to the best in solid state than the AB version.
That said still feel Mark has a few options left before changing, such as PAT mains test with a very experienced/qualified regulations-compliance mains engineer (beyond standard electrician).
Appreciate preferences mean different things to each listener though.
Cheers
Orb
As for Pass Labs, I previously bought an X-250 and it didn't work in my system. The cyclops meter was always pegged while the output was never that loud. It didn't sound good. I sold it and the new owner was happy. I'm hoping the Z-Trap makes a difference for the good. Joe has shipped it to me and I should have it soon. Fed Ex is saying 6 Dec for delivery.
Meanwhile, the KSA-250 is simply a superb sounding amp. The amp just sounds like it has no limits in terms of power and frequency extension. The bass feels like it starts from somewhere in the center of the earth. The midrange sounds almost tube-like to these ears. Cymbals have a nice shimmer with plenty of air.
I still never heard from Steve or Orb if they ever heard any transformer noise from their KSA-250 amps and had any hum/buzz issues. The power transformer weighs more than lots of amps do. It's 85 lbs all by itself. More later.
It wasn't the KSA250 but smaller model and yeah it had some hum-noise but not buzz (nowhere near as much as the HiFinews review this year - that had been DIY'd in the past by various owners it seems)
A friend has the KSA250 (well selling it now), so will ask if he heard buzz and how much hum.
His was from new so it has never been modified by diyers - hopefully same is said of yours Mark as I would expect Krell to mention if it was changed.
Mark,
I will ping him next week and see what he says about the KSA250, and yeah appreciate it was not messed around with as Krell would had noticed on the repairs.
Having had a chance to listen to the Krell KBL and KSA-250 combo for close to two months now, I feel I have a handle on what the duo brings to the musical table. I can tell you without reservation that the Krell dynamic duo has elevated the sound quality of my system. There is a level of elegance and refinement that simply wasn’t there before. I find that aural description to be at odds with the physical presence of the KSA-250 by the way.
For those who have never heard Krell gear, I’m certain that they have heard of Krell gear and have formed some type of opinion about the Krell “sound” based on what they have read or heard people say. Krell has always had a reputation for building Class A amps that have great bass and can keep doubling down on the output power as the impedance is halved. If you have not heard these pieces before, I think you would be shocked at the sound you would hear vice the sound you thought you might expect to hear.
I feel that both the KBL and the KSA-250 are cut from the same sonic cloth from top to bottom. There is no “this kind of bass” and “that kind of midrange” and “this kind of treble” with all of the discontinuities that implies. Does the KSA-250 have great bass? Yes, it surely does. But, it doesn’t stick out like a sore thumb and distract from the whole sonic picture. An area where I find the bass to excel in comparison to other amps I have owned is how deep the bass goes and all of the room cues it brings to the table because of the information it is bringing you. Really low bass brings space. Those of you that have systems that are capable of cleanly reproducing the bottom octave know what I’m talking about.
The feeling I have when listening to the Krell duo is that I’m getting closer to master tape sound quality. That elegance and refinement that I spoke of before along with a naturalness that is accompanied by limitless power and authority is highly addicting to listen to. Take a listen to Laurence Hobgood’s “Left To My Own Devices.” In particular, listen to Kurt Elling singing “Back to Joe’s Bar.” Kurt Elling very much reminds me of Frank Sinatra in his singing style. This is a very sad song about a guy whose girl has left him. Everybody at Joe’s bar from the waiter, to the bartender, to the piano player knew the guy and his girlfriend as they were obviously regular customers. The guy still shows up every night at Joe’s Bar hoping his girlfriend will come back to him. The waiter still sets a place for the girl even though he knows she isn’t going to show, the bartender doesn’t mention her, and the piano player doesn’t play her favorite melody anymore. There is a palpable realness to the sound of Kurt Elling’s voice and you should hear the dynamic swells of his voice which are so effortlessly reproduced. You can almost imagine you are in the room with him as he is singing live. At the very end of the song, Kurt inhales and then exhales deeply in the form of a sigh. Mind you that this sigh is low in level and I wouldn’t be surprised that if I didn’t tell you it was there that some of you wouldn’t know it. I still wouldn’t be surprised if some of you still couldn’t hear it even after I told you it’s there. The sigh brings another element of humanness to the song and helps express his pain.
Back to the Krell “sound” for a minute…one of the reps that Krell has/had was of being “dark” sounding. I suppose that when people use that term that they mean the amp/preamp sounds closed-in on top and you aren’t hearing the top octave extension you are used to. I don’t find this to be true. I still hear all of the high frequency information that I know is in my recordings. I do think that because of the way the sound is more balanced that it could be perceived to be darker than what people are used to. And by that I mean lots of amps simply don’t reproduce the bottom two octaves with the power and cleanliness that the KSA-250 does. Ditto for the mid and upper bass. Because this information is now presented with the scale and authority that was encoded, it lends a greater weight to the bottom end than what lots of people are used to hearing which can skew your perceptions about the balance of the amp.
In summary, I am enchanted by the sound of the Krell gear. It has taken me to a whole new level of sound reproduction and it has not left me yearning to return to vacuum tubes. If you listen to the pieces I own in your system, you just might find there is more there *there.* I know I did.
Having had a chance to listen to the Krell KBL and KSA-250 combo for close to two months now, I feel I have a handle on what the duo brings to the musical table. I can tell you without reservation that the Krell dynamic duo has elevated the sound quality of my system. There is a level of elegance and refinement that simply wasn’t there before. In summary, I am enchanted by the sound of the Krell gear. It has taken me to a whole new level of sound reproduction and it has not left me yearning to return to vacuum tubes. If you listen to the pieces I own in your system, you just might find there is more there *there.* I know I did.
MEP - good for you! Fantastic read, and very happy to hear you are enjoying the Krell spell! FWIW, i have always admired the Krells in the generation of yours...truly great amp and really a strong statement about new not automatically being better...just newer. Enjoy!!!!
Congrats, Mark, hope this is "it" for a while! I never owned Krell but had several of their amps rotate through my system back in the day. At that time ML was the main high-end amp, and Krell was/is certainly in the same class.
. 
