Adding tubes to SS system-Tube Preamp Amp or Int?

Nnck,

All of the subject areas you touch on are complex, so, at best I can offer only some very general advice.

I would start with looking for speakers. By far, speakers define the basic sound of the system. Find what you like and then look for a compatible amplifier. Because of compatibility issues, certain choices of speaker will eliminate certain amplifiers as contenders, so it makes little sense to choose the amplifier first. This is particularly the case with tube amplifiers which tend to have more limited ranges of compatibility.

Speaker efficiency and impedance characteristics MAY determine what is compatible. A lower efficiency speaker will mean a greater need for power. A speaker with a low nominal impedance (e.g., a 4 ohm rated speaker) MAY mean it presents a difficult load (again a bigger issue with tube gear than solid state). But, such a single number hardly tells it all. I would suggest looking at a Stereophile magazine test report on speakers. One of the first charts shown shows how the impedance changes with frequency. Even an 8 ohm rated speaker will have certain frequencies where impedance dips well below that number. Not only is how low that points important, but WHERE that dip occurs. If it occurs at around 60-150 hz (it is a bigger deal than if it occurs elsewhere because there is a lot of musical energy in that frequency range. The graph also shows another plot of "phase angle." Because of the characteristic of the load (the speaker) delivery of power and current do not go up and down in lock step so they end up being out of phase with respect to one another. A high phase angle, combined with a low impedance at a particular frequency, would make for a "difficult" load. I know this sounds very complex, but, at least Stereophile technical reports do give a subjective analysis of how difficult a load is a particular speaker under test.

For all of the technical arguments, ultimately, it does come down to personal trial. Whether or not you will "need" high power or a solid state amp to handle a difficult load will depend on personal practice (how loud you play the system, how big is the listening room) and personal priorities (compared to comparably priced solid state amps, tube amps rarely do bass with as much impact or tightness, but whether that is important is purely subjective).

When trying out different amps with the speakers that you like, don't overlook combinations that may seem incompatible. A lot of people, including dealers, overestimate the amount of power that is needed for a particular speaker. Often, a lower powered amp can deliver adequate power while also delivering qualities that a higher powered amp cannot. I know a local dealer that sells mostly low-powered tube gear that has several high-powered solid state amps to use for comparisons. Often, customers comment that the low-powered tube amp sound more powerful than the solid state amps. That is not really the case, but, what the listener is hearing is how good the sound can be at LOWER volumes when the amp sounds good. I know that my system is moving in the right direction when I find myself listening at lower, not higher volume.

I generally don't like the sound of most higher-powered tube amps (more than about 60 watts or so). If I truly needed that kind of power I would concentrate my search on solid state amps. The one notable exception is OTL (output transformerless) design. I like the sound of OTL amps for both high and lower-powered use. So, if I needed more power I would look first at OTL amps, then solid state designs (OTLs put out a lot of heat and have other operational issues that may rule them out).

I think that in most home listening rooms, and if listening levels are not too high, there are very few speakers that truly demand an amp bigger than 60 watts. In short, don't rule out lower-powered tube amps. I find that many otherwise fine audiophile-approved speakers suffer from being somewhat lifeless and dull sounding (particularly in comparison with horn and single-driver systems). To compensate, a lot of people play their systems quite loud. In that case, one may profit by not increasing power, but going with tube amplification, which tends to sound more lively at any given output. This is particularly the case with OTL amps.

Tube power amp is "tubiest". You have to make sure your speakers are tube friendly for this to work optimally though.

I use a tube pre-amp. That introduced a healthy dose of positive tube attributes without sounding overtly "tubey". That is good because I want my music to sound natural, whatever that means, not like the technology used. I'm sure different tube pre-amps will sound significantly different from each other and not all present the same results, especially if compared by swapping into the same system.

If you use a tube pre-amp, impedance matching to an appropriate power amp is important to optimize results, especially if a SS power amp is used.

I also have and use both SS and tube DACs. The tube DAC can also provide an audible dose of tube like sound. It can vary to quite SS like to distinctly "tubey" depending on the specific tube used and teh rest of the system, so tube rolling can be done to tweak the sound significantly in some cases.

I've used different tube makes in the pre-amp and have heard little difference in the sound there to-date from one type to another, other than background noise perhaps which can vary greatly from tube to tube, depending on health and quality.

For a tube integrated, again the main thing is to make sure the speakers are tube friendly and that the amp has enough power to truly drive them well.

Also, expect with a tube amp that is well matched to speakers that less power may suffice to deliver good sound at higher volumes than with SS amps. The reason for this is that tube amps tend towards soft clipping while SS amps tend towards hard clipping.

Larryi and Mapman-

Thanks for that info. More things slowly starting to make sense here. I'd like to go over a couple of specific examples if possible to explain further.

I should just start with my current speakers - the Vandersteen 2Ce. Specifications pulled from the manufacturers website (http://www.vandersteen.com/2cesigii_specifications.pdf) show the following:

IMPEDANCE: 7 ohms nominal 4 ohms minimum.
SENSITIVITY: 86dB with 2.83 volts of pink noise input at 1
meter on axis.
RECOMMENDED AMPLIFICATION: 40 to 160 watts per channel into 8 ohms.
FREQUENCY RESPONSE:
29Hz to 29kHz 3dB
32Hz to 21kHz 1.5dB
By FFT step function.
DISPERSION: 29Hz to 16kHz 3dB 30 degrees off axis.

The first page of the Stereophile measurements (http://stereophile.com/content/vandersteen-audio-2ce-loudspeaker-sidebar-3-measurements) show the graph I believe you are referring to. I cant say I understand everything completely here. But I think the set of curves that is generally lower might be the impedance since it tends to stick around 6 or 7 and then falls to around 4. Both sets of curves fluctuate wildly at the lowest frequencies, and then stabilize somewhat before gradually drifting up (phase) or down (impedance). I hope I got that much right. But other than that I cant say much about anything that would need to be addressed in terms of the amp needed to power these. As you say, the reviewer does indicate that this would be an easy speaker to drive.

Now on to the Dali Helicon 800 since this is one of my top choices for a replacement pair. Manufacturers website (http://dali-speakers.com/display_content.php/USA/speakers.html/179/1061) indicates the following:

Frequency range (+/- 3dB) [Hz]: 31 - 27,000
Sensitivity (2,83 V/1 m) [dB]: 89.5
Nominal impedance [ohms]: 4
Maximum SPL [dB]: 113
Recommended amplifier power [W]: 50 - 400

I unfortunately cant find the Helicon 800 impedance graphs. But just to use the Dali Helicon 400 review from Stereophile instead (http://stereophile.com/content/dali-helicon-400-mk2-loudspeaker-measurements) There may or may not be much correlation between these 2. But the impedance fluctuates wildly again at the lowest frequencies and then stabilizes and drifts between 4 and 6 or so. The reviewer again says they are easy to drive. Anything else to note?

And now Monitor Audio PL300. Again from the manufacturers website (http://www.monitoraudiousa.com/products/platinum/pl300/specification):

Frequency Response: 28 Hz - 100 KHz
Sensitivity (1W@1M): 90 dB
Nominal Impedance: 4 Ohms
Maximum S.P.L(Per pair in room): 118.6 dBA
Power Handling (RMS): 300 W
Recommended Amplifier Requirements (RMS): 100 - 300 W

Again no graphs at Stereophile, but for the PL200 (http://stereophile.com/content/monitor-audio-platinum-pl200-loudspeaker-measurements) the impedance fluctuates MUCH MORE throughout the frequency range. But also with a VERY high sensitivity. I dont know how this would differ in terms of the tube amp you might want to choose?

I just want to use these examples for the sake of discussion about what sort of ratings in a tube amp you might want with my current speakers and some of my options for new ones. I can go through several other speakers on my own to see how they compare as well.

And so far, my favorite contender for an integrated tube amp is something like the Cayin A100T. Mainly because I like the option it has of using the full integrated tube amp vs using the pre-in input terminals on this component, that would allow me to use this as a stand-alone power-amp with my Parasound JC2 as the pre. And for the sake of completeness, the specs on the Cayin are as follows:

Frequency response: 10Hz - 65kHz
Total harmonic distortion (THD): 1% (1kHz)
Signal-to-noise ratio: 89dB
Input Impedance: > 100 Kohm (RCA)
Vacuum tube: KT88 × 8, 12AU7 × 2, 6CG7 × 2, 12AX7 × 1
Input Terminals: Aux, Tuner, CD, pre-in
Circiut: Class AB PP
Sensitivity: 480mV, 900mV (pre in)
Output Impedance: 4 Ohm, 8 Ohm
Power Output: 50w Triode - 100w Ultralinear
Consumption: 280 W

I know this is a lot of reading. Thanks for following along and helping me out here. :)

NNck,

It really isn't possible to say what works just from numbers; even looking at the published curves only gives one an inkling of what may be troublesome, but, even then, actual experience often contradicts the measured statistics. Still, to read the curves, the most important thing is the lowest point on the impedance curve (the solid line in Stereophile). At that particular frequency, look to see where the other curve lies. On the right hand vertical axis, you will see the phase angle that that point represents. If it is plus or minus 30 degrees or more, that would be a difficult combination of low impedance and high phase angle.

Several years ago, I got to help someone with Wilson WP 7 speakers. These were reported to be easy to drive, and the manufacturer claimed something like 95 db/w efficiency. In fact, the manufacturer would show them being run by an ipod feeding a really cheap amp to demonstrate the primacy of speakers in the selection process. In a really high end system, I found this speaker to actually be a "difficult" load to work with tubes. Sure, it is pretty efficient, but, it must otherwise be difficult to drive because it did not work well with a lot of tube amps, though even low-powered solid state worked well with the speaker. In the end, a Hovland (medium-powered solid state amp) was employed to drive the speaker.

I am not familiar with the particular speakers you mentioned above, but, their stats suggest that they are not tube gear friendly speakers. Even so, tube gear, even medium powered tube gear, could be used with such speakers as long as you can accept certain limitations -- cannot be played at head-banger level, might be somewhat challenged in bass response.

I have only limited experience with Cayin amps (I believe it was a KT88 model). For the money, I thought it was a very good sounding amp and I was surprised to see how well constructed the amp appears to be (neat soldering, decent parts). The Prologue amps, also from China, are another decent sounding alternative that is not a bank breaker. If you can spring for more, I think that the integrated amps from Ayon sound decent.

For something completely different look at OTL amps from Atmasphere or Joule. These are power amps, not integrated amps, but, they offer speed and immediacy that will make you sit up in your chair like no other kind of amps. These are sort of the antithesis of what some people think of as tube sound (not as warm, lush and relaxed sounding), but everyone should experience OTLs.

Agree with larryi in general.

I would not assume any of those are "tube friendly".

That's not to say they might not sound perfectly good to you running off a tube amp.

The thing is that at least on paper, which as said is only an indicator, I would expect tonal colorations at certain frequencies and possibly challenges with dynamics and loudness as well with the less efficient models.

The end results may still sound very nice or even quite good, but I would be willing to bet not optimal and that a better matching for better balance, dynamics and ability to go loud is possible at the same price poit.

You might want to start a thread to ask specifically about user experience with Vandersteen speakers and tube amps. I am not very familiar with that combo so I cannot comment. I would expect challenges with dynamics and loudness and perhaps some coloration due to impedance related issues however off the cuff based on specs. I think Vandys and SS are a common pairing and I would personally probably lean that way.

Also keep in mind that the down side off tubes is that power amps in particular require some maintenance of the tubes over time. Poorly performing tubes can be a pain in the but, especially when there are a lot of them. I like the sound of the half dozxen or so tubes I use in my pre-amp and DAC, but even this results in time spent making sure things are in good working order that I would not have to deal with if all SS.