Question about tubes?

[JJkizak]

It would be nice to see charts comparing the two different amps into a resistive load at the same power output.

JJK

[Ski Bum]

It's on this Ebay page:

http://tinyurl.com/3j5n5l5

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It's at the question and answer part at the bottom. Obviously, lacks objectivity when ones trying to sell something. I don't know the guy in any way. Looks like a nice unit but I would never bid on something that will obviously go very high just on the seller's reputation.

Well, no wonder. That's Bob Carver, of Carver/Sunfire/etc. Bob's amps always get bid up to ridiculous prices. I admire his passion and commitment to audio, but he also happens to be an extremely adept marketer as well. That particular amp looks pretty crude and utilitarian compared to most of what he does, but I expect that with his smooth talking and name recognition it will ultimately sell for a huge premium.

You can find less expensive amps that would perform just as adequately. You can even find them with a 'lifetime warranty' as Bob is offering (some boutique builders do this, and they also have return policies and such, which I'm not sure Bob is offering). If I had a wad of cash burning a hole in my pocket, I'd probably contact Craig (NOSvalves) and order up some VRD monos before bidding on one of Bob's amps.

Also, I have to agree with artto's post. We went to the symphony last night (at home), and 5 watt SETs just ain't enough for Berlioz at reference levels. If you do go with low power, be sure to keep a big amp around for such events.

[Don Richard]

It would be nice to see charts comparing the two different amps into a resistive load at the same power output.

The last paragraph of the Wiki article gives the answer:

Because no ideal sources of either variety exist (all real-world examples have finite and non-zero source impedance), any current source can be considered as a voltage source with the same source impedance and vice versa. These concepts are dealt with by Norton's and Thévenin's theorems.

Resistance is constant, impedance varies with frequency. The two types of amplifiers would behave similarly into a resistance. The difference becomes apparent when the amplifiers are connected to a loudspeaker, because of the varying impedance of that sort of load.

[JL Sargent]

The difference becomes apparent when the amplifiers are connected to a loudspeaker, because of the varying impedance of that sort of load.

That's really interesting stuff. Makes sense too.

[Don Richard]

A voltage source amplifier can be made to behave much like a current source amplifier by adding a non inductive resistor in series with the loudspeaker. You have made a voltage divider with a constant resistance and a varying impedance. This chart shows the effect on the acoustic output of a loudspeaker with a 0 ohm resistor added in black, 1 ohm in green, and 2 ohms in red:

[gnatnoop]

i'm running 30 (tube triode) watts to my khorns, it's perfect for my neighborhood...

[gnatnoop]

i've noticed this is the technical forum...and that my previous post was not technical in nature.

i'm getting 105 db with 30 watts rms at two lots over....

[Ski Bum]

Don- thanks for posting that graph. It looks like that shows 3-5db boost in the bass and treble areas, which seems to me to be just a 'smiley' eq curve. I was always told that high output impedance amps would have frequency aberrations where impedance peaks occur, i.e. at driver resonance frequencies. My ears never really bought this, as my tubed/Klipsch system sounds remarkably similar to another, more conventional, SS based, engineer approved system. I expected greater freq. aberrations, particularly when using a SET with an output impedance of around 3 ohms.

I've tried to replicate the tube amp sound using tubed pre-amps, tube line stages, and an assortment of eq/processors, and nothing sounds quite like tube amps driving speakers. It does not seem to me that what I'm hearing is just a smiley curve. The PP tubes I tried certainly sounded like SS, only richer, which appears to correspond nicely with your graph, but the SET's I've tried all have distinctly clearer low level detail retrieval, a peculiar dynamic contrastyness which gives music a more emotional impact (vocal inflections, the ability to pick apart every single note, etc.), not to mention the effect of expanding the sonic image in striking, 3-D ways. The only measurable thing which seems to correlate to this is high order but very low level harmonic information, and by all availble evidence such low level information should be below the threshold of audibility.

Perhaps related, when hooked up to a scope, my SETs don't produce harmonics above the tenth or eleventh unless grossly overdriven; ss and pp amps do (again, as long as not driven into gross clipping, the harmonic info should be so low as to be inaudible). At low levels (<1w), the SETs have very little harmonic information, and whats there is 2nd and 3rd order, which are typically perceptually masked by their proximity to the fundamental. There is a range between 3-6 watts where the harmonics increase (even and odd) up to about the 10th or so. Within certain limits, the harmonics from 4th up to 10th or 11th add body and bite to the sound without becoming objectionable (probably 5% THD at that point). The amps actual electrical output starts to top off past 5 watts, but the harmonic content is increasing within that range, giving the subjective impression of increased loudness. Of course, at some point the distortion becomes objectionable. But before that, the SET amp acts as an ideal compressor.

It is my opinion that the low level contrastyness you get with SETs happens to be very copasetic with horn speakers, which are adept at elucidating such delicate dynamic contrasts. No other amps I've tried with my Klipsch produce the same depth of image, where the music is dissociated from the speakers physical location, and isn't that a big part of what we're after? At the other end, when the SETs are at their limits, you get the harmonic 'bloom' and added subjective loudness without the chochlea shredding spl you would get were a proper, headroom-unlimited amp being used.

Perhaps I'm the victim of placebe effects, but I don't think I'm imagining things here. I may be completely off in trying to correlate the crude measurements I've seen and my subjective impressions. Despite their technical flaws, SET sound is distinctly pleasant, and addictive.

I actually go through SET withdrawal when I travel, and can't wait to bask in the glorious sonorities of SET driven Klipsch sound upon my return.

Gagelle, hope this info helps you in your tube search. I just shared about a decade of my personal tube experimentation with you.

As an experiment, I went back to the symphony again last night, using low power SET amps exlusively. Here are a few things I noticed:

-From the prior evenings session with SS, dynamic range for the concert I was listening to was from ~65db up to >105db, pretty close to reference levels. It never runs out of steam. The sound is big and bold, but kind of two-dimentional, like an IMAX presentation for the ears if you will. It was like drowning in loudness, a body encompassing experience of sheer power that the SETs just don't do.

-With SETs, had to turn it down a bit, so dynamic range was shifted down from ~60db up to ~100db, which is about the top limit of my particular SETs (and about as loud as I ever subject myself to, and then only for very brief periods). Low level detail you wouldn't know was missing was suddenly apparent. During quiet passages, I could hear members of the orchestra shuffling their feet and such, and so real sounding I almost wanted to tell them to "pipe down over there!" The big yet flat IMAX-ish presentation gave way to a sense of the recorded space. Close the eyes and I'm transported into a much larger venue as the walls fall away. Open them back up and the illusion is so compelling that it persists. (I am blessed with a really good room, by the way, which is 98% of the battle.) The sonic image is distinctly expanded, and it grabs your attention. The freq balance seems subjectively brighter, but simultaneously less edgy, and the sheer attack of some instruments is literally striking. Tympany drums kick major butt on the SETs. Despite these pleasantries, the image is kind of whispy and ethereal compared to big SS power.

That was with some Berlioz and Mahler, about the most demanding things I have to throw at the SETs. The SET's do things for vocals that I've never heard any pp tube or ss amp replicate. Next up was some Bach, with both solo and full choir vocals, on an excellent recording. The dynamic contrastyness of the SETs really plays well with vocals, resulting in almost an almost unavoidable emotional connection. It can be quite moving, even when you least expect it.

Sorry I don't have more technical data to support this, but for that matter I don't think technical data would support the use of SET amps, ever. Even calling them 'amplifiers' is being generous, since they don't really do that task very well. But, holy cow, do they sound sweet.

[Marvel]

SB,

thanks for the entertaining review of the MAGIC! SETs do it in spades, as far as I am concerned. So far, they are the only thing that can carry me to another time and place.

I appreciate the timeit took to get this down.

Bruce

[tube fanatic]

I've tried to replicate the tube amp sound using tubed pre-amps, tube line stages, and an assortment of eq/processors, and nothing sounds quite like tube amps driving speakers. It does not seem to me that what I'm hearing is just a smiley curve. The PP tubes I tried certainly sounded like SS, only richer, which appears to correspond nicely with your graph, but the SET's I've tried all have distinctly clearer low level detail retrieval, a peculiar dynamic contrastyness which gives music a more emotional impact (vocal inflections, the ability to pick apart every single note, etc.), not to mention the effect of expanding the sonic image in striking, 3-D ways. The only measurable thing which seems to correlate to this is high order but very low level harmonic information, and by all availble evidence such low level information should be below the threshold of audibility.

I told myself that I'd stay out of this discussion, but what the heck! Your observations about SETs vs PP tubes, etc., are valid and duplicatable (from the usual subjective standpoint). One factor which is contributing to the difference is that virtually all pentode based amps (whether single ended or PP) use some degree of negative feedback (degeneration) to extend the bandwidth, decrease distortion, and also as a means of taming the usual runaway high frequency harshness and abrasiveness. In my own observations, as well as in listening done with fellow audio nuts, as the degeneration in pentode amps is increased, there's a very discernable decrease in low level detail retrieval as well as a shallower and narrower sound stage. So, the advantage of going the SET route could be in part related to the fact that degeneration is not used in most designs of that type. I have yet to be able to duplicate the 3D, almost holographic soundstage of SET amps in any of my pentode designs. Close, yes, but as good never!

[gagelle]

Seems the same with solid state. I'm running a relatively low powered Sansui and I don't even have to turn the volume up much. The sound is so full and rich that I enjoy it at lower volumes.

[JJkizak]

I believe my receiver is corn fed. (I borrowed this from Jacksonbart)

JJK

[tube fanatic]

Seems the same with solid state. I'm running a relatively low powered Sansui and I don't even have to turn the volume up much. The sound is so full and rich that I enjoy it at lower volumes.

Keep in mind also that the position of the volume control does not equate to the amount of power the amp is putting out. Depending on the taper used (i.e. the amount of resistance change for a given amount of turn), and the resistance of the control itself, the amp's output can ramp up very quickly or very slowly. Years ago some commercial amp manufacturers used a taper which allowed the amp to ramp up power with very little turning of the control. It gave the illusion of an extremely powerful amp. Psychologically, if you had to turn the control to 12 o/c, instead of say 8 o/c, to achieve the same volume level you might think the amp less powerful than it actually is.

[gagelle]

The volume control on my Sansui AU-717 is suberb. It actually has notches and the output rises very gradually. It's rated at 85 watts per channel with both channels driven and like all Sansuis from the 70s, tests much higher. I haven't been able to turn the volume much without it getting extremely loud but I'm driving very efficient KLF 30s. The owner of a record store I know is running a Sansui 9090DB which is rated 125 watts. He has some inefficient KLH speakers and has to turn the volume about 1/3 of the way to really get loud. I hear what you're saying about the position of the volume control not directly cooresponding with power output, but mine is so silky smooth and graduated it's a pleasure to use.

[JohnA]

................... Tube watts are different than solid state watts. ..............

Absurd and very wrong. A watt is 1 volt x 1 ampere. Any amp producing 1V and 1A at the same time is producing 1 watt. It matters not what the topology of the amp is.

Most humans will tolerate much higher distortion and clipping vrom a tube amp than they will from a solid state amp because the distortions are even order and seem to sound more musical. So, lots of tube owners regularly losten to clipped output and think their amp is more powerful than it really is because they like the distortion.

[Chris A]

...Most humans will tolerate much higher distortion and clipping from a tube amp than they will from a solid state amp because the distortions are even order...

Discussion on this subject can be found here:

http://en.wikipedia.org/wiki/Tube_sound

I prefer my music without added "sonic enhancement". I use Crown D-75As to bi-amp my Jubs/TADs: they sound clean and neutral.

PWK made his living (after about age 45) providing low-distortion loudspeakers to those that appreciated them and were willing to pay the price differential. When good SS amps came out after years of living with tube amps - he switched to SS (i.e., the Crown D60).

Chris

[Ski Bum]

John-

While I agree with your first point, you make an incorrect generalization about the distortion components. The low power SET amps I've seen on a scope (only a handful, mind you), were not characterized by even order harmonics, but low order harmonics, both even and odd, that diminish rapidly in an evenly descending pattern. I think Nelson Pass has engineered some of his amps to emphasize even order harmonics over the years.

It is a fact that as sound propagates through air, low order distortion increases over distance. Do you think human perception may have evolved to notice such things? How far away is that lion roar, anyway?

Is it purely coincidental that SET amps, which closely mimic this naturally occuring phenomenon, are so revered for their 'vibrancy, liveliness and holographic imaging'?

A little distortion may be more like real life after all.

Believe it! (Or just kick back and enjoy the music, however you like it.)

[lighting guy]

I may drive to the Bay area to listen to a good tube setup at a high end shop.

Gagelle, let me know when you come to the Bay Area. If I'm around, you're welcome to come by to hear (IMHO) a couple of nice-sounding tube setups on Klipsch heritage.

D

[Chris A]

It is a fact that as sound propagates through air, low order distortion increases over distance.

I assume that you are referring to large distances (relative to the wavelength) and high intensities--like in the throat of a horn loudspeaker--to be significant/audible, right?

Chris

[Don Richard]

It is a fact that as sound propagates through air, low order distortion increases over distance

Only inside a horn waveguide, or at high (145 dB+) SPLs, and long distances. Concert sound system arrays are most affected by this issue.