Cdc, IME and based on my readings, your questions are counter-intuitive and contradictory. I'll take the second question first.
IMO, based **solely** from an electrical compatibility perspective, a "perfect" Power Paradigm amp friendly speaker is one which has a totally flat impedance curve (say 8 ohms or higher) and a zero phase angle as a function of frequency. Such a speaker would be easy on a SS amp too, but the higher the impedance, the less current and correlatively the less power the SS amp could deliver.
As many of our knowledgeable techie members have said, one can call the manufacturer to ask whether the speaker in question was voiced to be driven by a solid state or tube amp. Some manufacturers (e.g., Revel) disclose the best amp to use for driving their speakers. Another clue is knowing whether the manufacturer used a SS or tube amp to showcase their speakers at audio shows.
Perhaps other members can weigh in on your first question, but I am not aware of a SS amp that functions like a Power Paradigm (tube) amp. OTOH, some tube amps can perform somewhat like a SS amp. Such tube amps have "low'ish" output impedances, "tight'ish" output voltage regulation, and moderate damping factors. However, some members might comment that tube amps that operate in the foregoing way use negative feedback which can degrade the sonics if used in excessive amounts and/or inappropriate ways.
I have exhausted these issues before. I suggest you look through some of my posts that discuss the topic. I raised questions similar to those asked in your OP and several of our tech savvy "EE-types" have provided comprehensive responses.
Happy Holidays,
Bruce |
Ctsooner, I'm not really looking to start another lengthy discussion about tube vs SS amps. I'll leave it this way. It is plausible that a speaker designer, a dealer sales rep and/or a customer could be indifferent to plugging a tube amp or a SS amp into a speaker if either (x) the speaker has extremely benign impedance and phase angle characteristics, or (y) the tube amp has very low output impedance.
As Al and Ralph Karsten (Atmasphere) have said on numerous occasions, a speaker's ultimate acoustic presentation will be affected to the extent an amp has a high'ish output impedance and the speaker was voiced (intentionally or not) to be driven by an amp that has a low output impedance. This is not my opinion -- it Ohm's Law.
It is my experience that when I drive my speakers off the 8 ohm taps of my amp, the speakers sound bright and detailed, maybe too much so at times. In contrast, when driving the speakers off the 4 ohm taps, bass is more extended and tighter, imaging less forward. Admittedly, I am conflicted about which acoustic presentation sounds better to my ears. It just depends.
This is no coincidence. The output impedance of my amp off the 4 ohm taps is about .55 ohms in the lower frequency bands; and about 1.1 ohms off the 8 ohms taps. It is similarly notable that the impedance curve of my speakers is roughly 4 ohms between 70 Hz and 700 Hz, rising sharply and peaking at 21-22 ohms at the 2.2K Hz crossover point, dropping again to about 5 or 6 ohms as frequency increases.
Let's put a sonic face (sic, an oxymoron) on what I just said. John Atkinson's bench test report of my amp states that output voltage regulation is +/- .4 db off the 4 ohm tap and about +/- .8 db off the 8 ohm tap. What this means in plain English is that my speakers should be about 1.6 db louder at the midrange highpoint of about 2.2K Hz as compared to the bass saddle of 70 to 700 Hz -- IF I use the 8 ohm taps. In contrast, the SPL delta off the 4 ohm taps should be about .8 ohms. Those stats cogently explain what I hear.
Oh ... the damping factor of my amp is also affected. Theoretically, about 7 ohms off the 8 ohm taps and about 14 ohms off the 4 ohm taps. Although with my speakers, those stats should be halved because my speaker's impedance is about 4 ohms in the critical parts of the bass frequencies. But those stats explain why I perceive bass to be more extended and tighter off the 4 ohm taps.
This is Ohm's Law, not my opinion. So, unless a dealer's sales rep explains in plain English what I just said above, he's either ignorant or scamming the customer. Of course, he could be honest and say even though a tube amp may be causing certain acoustic colorations, they sound good, in his/her opinion. Then it's on the customer to decide.
Al or Ralph, if you can simplify or clarify what I just said, I'm sure I and the other readers would appreciate your edits.
Regards,
Bruce |
Just one last thought. The OP doesn't ask about a speaker's phase angle characteristics. Definitely off topic.
Suffice to say that a speaker with highly negative (i.e., capacitive) phase angle and low impedance characteristics in the power spectrum (say 30 to 400 Hz ??) can really give a tube amp, even a SS amp, a bad day. That in part makes for a tough to drive speaker that calls for a "current" beast like a Bryston or Krell SS amp.
In my case, my tube amp has a large'ish power supply of 1040 joules. I surmise my amp's power supply reserve helps it to muscle its was through some pretty tough negative phase angles in the speaker's bass region.
Bruce |
Cdc, I believe that Pass amps are SS amps that use very low, or no, negative feedback. Even still, as a SS amp, I would expect it to be a constant voltage source. |
Shakey deal, your last comment is based on a very shaky foundation. LOL :) |
Tech guys -- let me put a face on the dynamic headroom discussion. My amp is a tube amp rated at 150 wpc, as measured off the 8 ohms taps into an 8 ohm load. The power supply is rated at 1040 joules. ARC couldn't fit another power supply cap into the chassis -- no more real estate. If relevant, the sensitivity rating of my speakers is 92 db. And yes, if I push the volume, I bleed out of ears. That is if my wife doesn't make me bleed from the top of my head with a rolling pin first. :)
So in plain English -- what does that mean? Is the 1040 joule stat even relevant? |
Will somebody out there please explain why I became a tax attorney when this EE stuff is just sooooo cool??? :) Ralph, if I went back to school to become a EE, would you hire me? |
This stuff is just soooo cool.
Tech guys, from a strictly intuitive and anecdotal perspective, I gather that the theory and formulas can take one just so far. That there's a "black box" aspect of synergy or a witch's brew of "X" factors going on in an amp that come together (or not) when driving a particular speaker.
To this point, I seem to recall that a while back Al may have posted something in another OP to the effect that the theory may help one identify a amp/speaker combo that MAY (??) work well and conversely MAY (??) not work well. But, and this is a big BUTT (sic), one will not know for sure until he/she tries out the particular amp/speaker combo of interest.
I recently posted an observation in the post running relating to amps and ESL speakers that speaks to the point made above. Based strictly on amp/speaker impedance matching theory, I surmise that my speakers should sound their best when driven off my amp's 4 ohms taps because voltage regulation is tighter, damping factor higher and output impedance lower.
But for some reason(s) that I can't explain, I keep coming back to the amp's 8 ohm taps. Maybe it's because the speaker's midrange band may be a little hotter (+ .8 db) and it works better in my furnished basement. Maybe it's because the 8 ohm taps punch out 2.5 db more gain that the 4 ohm taps. Maybe it's because there's a genie who lives in the output trannies. :) I just don't know. It just is -- to me.
So Ralph, what about hiring me if I go back to school to try my hand at becoming a EE??? ;-)
Best.
Bruce |
Thanks Al, Bombaywalla and Ralph. Obviously not being a EE tech, the only thing the joule power supply stat empirically and intuitively meant to me was that it helped the amp "muscle" its way through some tough speaker loads. But I didn't understand the current aspect.
My speakers present a 4 ohm impedance load and some highly capacitive phase angles in the bass region. Based on Bombaywalla's explanation, I gather that my amp not only performs "somewhat SS-like" because it has a somewhat "low'ish" output impedance, but the 10 amp and 2.92 second estimated stats (or perhaps less??) enables the amp to actually do what a real SS can do -- deliver some serious current into a speaker that presents a low impedance load and capacitive phase angles at low frequencies. Well ... at least to some degree. Cool!
Btw, ARC's new Ref 250 and Ref 750 mono amps have advertised power supplies of 900 and 1300 joules, respectively. And that's per channel.
Now I understand why it has been reported that a number of folks who own those amps are quoted as having cried out, "it's alive ... it's alive....," when cranking some serious volume. LOL :) Just kidding!
Best,
Bruce |
Al, Ralph and Bombaywalla -- I'm still confused. Are you saying that a tube amp that uses negative feedback is able to adjust the amp's voltage output to compensate for impedance swings in such a way that power (i.e., watts, or volts x amps) approximates the amount of power (watts) a true constant voltage source SS amp would make at a given reference impedance and frequency, assuming that the SS amp was operating within its specs.
If that is correct, then how should I interpret John Atkinson's bench specs of the Ref 150 when he says that output (???) regulation is +/- .4 db off the 4 ohm taps (output impedance being .55 ohms) and +/- .8 db off the 8 ohm taps (output impedance being about 1.1 ohms)??? Is he speaking about output voltage or output watts?? Based on Ralph's explanation, if JA is referring to watts, then presumably voltage must be swinging all over the place to match the power output of a voltage source amp.
Presumably, current output may also change as a function of voltage change, but power (watts) is power (watts), i.e., V x A. I'll re-read the article again. Here's s the URL link to JA's Ref 150 report (Graph 1 in particular):
http://www.stereophile.com/content/audio-research-reference-150-power-amplifier-measurements
I also assume that an amp's output impedance number may have much to do with the number of turns on the output trannies' secondary windings. But here again, I assume negative feedback is also at play, further reducing measured output impedance. If I am tracking here, I surmise the "constant voltage source" paradigm breaks down with tube amps because in the end, as Ralph has said many times, a speaker's SPL is a function of the power (in watts) being pushed into the speaker circuits at a given frequency. So, the NF servo circuit is telling the amp to do "ramming speed" (ala Ben Hur) with **voltage** in those cases where speaker impedance is low, and the opposite when speaker impedance is higher.
I hate to even broach the subject of damping factor in light of this discussion.
Thanks for the clarifications.
BIF
P.S. If I am finally starting to get it, does that mean that not all SS amps are true constant voltage sources if power doesn't double down if impedance halves, and the opposite being the case if impedance doubles?? If so, then even saying a speaker was voiced to be driven by a SS amp is a bit of a misnomer. If the SS amp used as the reference source by the speaker designer wasn't a true constant voltage source, then one will never be certain of which SS amp to match up with the speaker of choice.
Guess one has to just go with what sounds good. Huh, ... we're back to where we started. If it sounds good (to you, or me), then it is good. LOL :) |
Thanks Al. So what is JA measuring in the first graph?? Is it volts or watts? |
Thanks again Al. Well ... I'm back from where I started. It seems that one reason, among many others, that my Ref 150 tube amp does a nice job driving my S8s is because the 1040 joule power supply acts "somewhat" like a monster-current SS in its ability to deliver some serious juice when needed. One second, two or three, dunno. It just seems to work.
And Al, after reading the thread running about tube amps and ESLs, if you think I'm gonna climb onto the speaker "merry-go-round" -- forget it. As a practical matter, there are too few B&M stores in my area that would permit meaningful audition opportunities on like gear. In addition, after having read some reviews about so-called super "top-o-the-line" speakers that have stats that look less stellar than the stats for my speakers, I'm just not willing to drink the Kool-Aid.
Thanks as always.
Best
Bruce |
Hi Al,
Thanks for the link re the standard simulated speaker load used by JA. I've seen it before. It's a helpful tool which illustrates how an amp's output voltage (??) varies as a function of speaker frequency.
My non-tech anecdotal reaction is that while the simulated load presents roller-coaster impedance and phase angle curves, I surmise that the "simulated speaker" would not be terribly challenging to drive for a well engineered and made amp. This guess is based on a comparison of the companion functions at each attribute's saddle.
Specifically, the impedance load at the negative phase angle saddle between 70 and 150 Hz does not dip lower than 7 ohms. Also notably, the phase angles at the impedance saddle between 100 and 600 Hz ranges from mildly capacitive to mildly inductive.
As stated, I suspect that the simulated loads just described would not give a well designed and manufactured amp a bad day. Uuuhhmm, I wonder if JA would agree to swap my speakers for his simulated speakers. :) LOL
But as I said, I think the simulated speaker exercise is an illustrative and helpful tool that puts a face on the meaning of the numbers.
Cheers,
Bruce |
