They don't seem to help if the impedance of the speaker is already eight ohms or more.
That's kind of my point- the move to four ohm speakers which seemed to really gain steam in the 70s seems like it was not such a great idea after all.
Labtec, I thought of Mac almost as soon as I saw the email from Steve to Paul Speltz. Not such a bad idea after all... |
Under what circumstances would using ZEROs not be a good idea? |
Atmasphere,
Not sure if your reference is to Steve McCormack (ie. mfg of transister amps), but I know he also recently tried the autoformers to very good success. I think he is going to use them at CES and promote their use on his website, so I don't think it's any "secret" I'm disclosing.
My two cents is worth far less, but I can also vouch that the difference you referred to can be quite significant.
It's probably fair to throw some kudos to McIntosh for implementing this long ago with SS designs. |
Pubul57 and Phaelon, my comments about 4 ohms has little to do with the tube amp in question. 4 ohm taps on output transformers in general have less performance than the higher impedance taps, regardless of the size of the output transformer. Its *easy* to demonstrate!
IOW a simple way to get a speaker to appear to be more transparent is to keep the impedance high. The speaker won't sound any different, but the tube amp driving it (regardless of the amp) certainly will.
If you could switch a speaker from 4 ohms to 16 ohms and keep all the other variables equal, the result is that the tube amplifier will make less distortion, have more bandwidth and exhibit slightly more power. Right now the only way to demonstrate that is by using a set of ZEROs to accomplish the conversion from a 4 ohm speaker to 16. But if the speaker were 16 to start with, things would be even better.
Over the holiday weekend, I found out that at least one major manufacturer of transistor amplifiers also found out that higher impedances helps transistors sound better too- not because of limited current availability, but due to the aspects of the way the transistors work in the first place.
He used a set of ZEROs to discover this.
The evidence suggests that there is not really a good argument for 4 ohms regardless of tube or transistor, although the reasons are different depending on the amplifier. |
Not quite. But in speaking with your amp and speaker folks, you should be able to see if there are any red flags that would be obvious to them; if they are honest, then at that point you should not end up with any grave mismatch, and then it is up to you and your taste - there will never be one choice that works best for everyone.... |
OK, you guys are making me feel pretty inferior here. Are you telling me that I should be able to listen to a specific speaker/amp combo and then determine that somewhere around say 180hz there is an impedance mismatch of 2ohms. Please don't tell me you're telling me that,LOL.
Regards, |
I agree with you, and when you do hear an good match between pre/amp/speaker it suddenly becomes obvious that something good is happening, a sense of balance from highs to lows. One advantage to well designed integrateds. |
Pubul57 - I would have no problem agreeeing with your comments about PP/SET amps interaction with speakers with a flat(ish) impedence curve, and there is no reason that a quality amp can't handle moderate speaker impedence dips, BUT one of the problems is that amps have varible output impedence to deal with that can be as problematic as speaker impedence (one of mine has a rise to 3.5ohms in the mid bass) so its important, at least on paper, to match the amps varying output impedence with the speakers varying impedence. Not a walk in the park if your looking for anything approaching ideal matching of amps and speakers without listening. FWIW. |
I do have a tube amp (CAT JL2)that can handle low impedances, but it is expesnive and requires large transformers (the amp weighs 180 lbs!)and Atmasphere obviously uses a different approach. But nevertheless a higher impedance is always better for tubes and a smooth, linear impedance curve is important. I would think even a 4ohm nominal impedance would be ok, as long as the impedance curve was smooth, without large peaks and valleys at various frequencies - I think they call it impedance phase(?) or something. A discussion with your amp and speaker mfg always helps. I never understood much about the subject till Bobby at Merlin (speakers) explained some of this stuff to me and Atmaspheres contribution on the subject have always helped. The speaker in question seems to offer challenges to tube amps, even if they worked, they would "work" the tubes hard. |
"Keep in mind that if you are investing in tube power, your investment dollar will be better served by a speaker that is 8 ohms or more (particularly in the woofer region) than a speaker that is 4 ohms."
Hi Atmasphere,
I've always understood this to be true of OTLs but how significant is the high impedance issue with push-pull or SET amps. This has always been a little confusing to me because it seems that while almost all speakers are classified as either 4 or 8 ohm, impedance charts can show quite a bit of fluctuation. I would like to try an OTL with my 8 ohm Mini Utopias but I believe they dip to 4 ohm and I don't know where.
Regards |
There are tube amps that do a great job with extremely difficult speaker loads (SoundLab electrostatics) such as Wolcott. Unfortunately these amps are not well known due to a lack of advertising. Furthermore, Wolcott amps are extremely easy to maintain, due to auto biasing. Henry Wolcott's patents have prevented other manufacturers from copying his circuits. I have a pair which are going on 8,000 hours with only two tube failures. In each case, a LED indicated which tube needed replacement. Simply a matter of inserting a new one. These amps do a superb job from bass to treble. I also own Halo JC-1's which do a great job, but I prefer tubes! |
Agree on SS for these speakers. How much are you willing to spend to upgrade from the Rotel? |
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Pay close to attention to Rlawry and Atmasphere's comments, a tube amplifier must be well mated to the speakers. Certain speakers need to have SS amplification if they do not have linear impedance (one might argue these are not particularly well desgined speakers, but that is another issue), but if you have "tube friendly" (your dealer should be able to help, or the speaker mfg)speakers, I think you will go to tube amps and never come back. |
Darkmoebius: In response to your questions.... I generally listen to jazz at moderate levels. My ears value a balance integrated sound which reproduces a live performance. An overly bright tremble or heavy bass is not desirable to me. I am leaning toward the Paradigm Reference Studio 100 main speakers with the Rogue Perseus tube preamp & Rotel RC 1080 S/S power amp.
Thanks, everyone, for guiding me through the myriad of available choices.
Also, if I can dovetail my own thread here....what are the main maintenance issues with tubes? How often to replace? |
*In general* If you go with a tube amplifier you will find it smoother and more detailed than the best of transistors, if the speaker is compatible with the tube amplifier. This is because tubes obey the rules of human hearing to a much greater degree than transistors do (although this is not to say that that couldn't change in the future).
You've already heard how this works with preamps- its the same with power amplifiers.
Keep in mind that if you are investing in tube power, your investment dollar will be better served by a speaker that is 8 ohms or more (particularly in the woofer region) than a speaker that is 4 ohms. |
Hi Kitjv:
I've recently listened to a Rogue Perseus through a Rogue Stereo 90. At that time I had a Rogue Cronus integrated, which was great. Rather than buy a new Perseus and 90, I found a used Rogue 99 preamp and a 90. The 99 is remarkable. Better detail and soundstage than the Perseus. For $2500 I got both units vs. $4k for new Perseus and 90. Rogue is a great company to work with too. I've been to their factory twice. If you want to upgrade tubes, get them from Rogue directly, they can guide your choices. |
Kitjv,
I owned a Rotel 980BX amp and RC960(?) preamp about 6 or 7 years ago. While a great value for their price, Rotel definitely errs on the lean side of accurate. Most of the problem was in the preamp stage, I thought.
But, in my audio journey since those early days, I've found there are lot more lifelike and rich components out there, both ss and tube.
Rogue definitely makes great, dependable, equipment which holds it's value well. But, selecting tube components is a highly subjective and personal experience.
How about letting us know what type of music you listen to and at what volumes. Also, what are the musical traits you value the most - dynamics, bass, midrange, scale, etc.
Rogue, Antique Sound Labs, Quicksilver - all worth checking out. |
I've got a tube integrated (preamp plus amp), tube cd player and tube phone stage. Can't get enough tube :) Seriously, at least to my ear, solid state is just for office and bedroom systems.
In my experience, if I had to put tubes in one component, it would be the preamp hands down.
Art |
My take on tube equipment is to use it where it makes sense, since tubes won't work well in every application. Certainly, the best use for tubes is in voltage amplification applications such as in preamps, input and driver stages of power amps, phono stages, CD players, D/A converters, and the like. Where solid-state equipment has an advantage is in output stages of power amps where semiconductors have a much lower output impendance and work better for current amplification. Now if your speakers are a relatively benign load tubes will probably work well and give you what Cyclonicman and Newbee say they will. But if your speakers have a difficult impedance curve, not only will your tube amps not provide a sonic improvement, they may be prone to outright failure. It has happened to me in the past. The other issue is maintenance of tubes and tube amps, so if you don't like turning dials or adjustment screws, I would stick to solid state power amps and tubes for everything else. There is something magical about the little glowing glass bottles. |
Hi KIt,
Newbie is right on target, you have to weigh all of the possibilities, especially price, which is the biggest factor for most of us. I can vouch for the Rogue 90 power amp whioh I owned for about 4 years before selling it last year. It is a tube amp with 90WPC in ultralinear mode or about 55WPC in Triode mode. It was very musical, good soundstage and dynamics. It's versatile enough that you can roll the tubes to 6550, KT88, or even KT90 and it has a built in biasing control which is the simplest that I have ever used. It is fairly priced about $2,200 new and is built like a tank. I've seen used ones on Audiogon in the $1,200 - $1,500 range. In my opinion, besides the sound quality, tubed equipment offers a dimension of fun and appreciation in this hobby that places it in another world when compared to solid state equipment. Good Luck! |
(1) A vast difference in a gain of a sense of dimmension and fluidity. I wouldn't be without one - I think I could skip a tube pre-amp, or any pre-amp at all before I'd lose a tube amp. (In fact in one system I have now done just that!)
I'll pass on 2) and 3) as I have no knowledge the Rogues and there are just too many possibilities for 3) and the right one depends on many things personal to your specific needs, including budget, flexibility, and features. |
