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

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.

Thanks again guys. I am understanding the graphs much better now.

My question now is concerning both of your comments that the impedance and phase shift graphs or specs I choose as examples are maybe not "tube gear friendly speakers". I understand what you are saying about only using the measurements and numbers as guidance and not the end-all answer, but if you see things in the graphs or specs that specifically lead you to believe this, I'm interested in what it is. In at least 2 of those 3 examples, the reviewer actually commented the the speaker would be an easy load to drive. So if there are things that are not tube-friendly, I'd like to know more about it.

Larryi- Thanks for the mention of the Prima Luna. That looks like another nice piece of equipment. And it also has an HT bypass that looks like it would give me the same option of using my SS preamp with just the tube amp in the circuitry. The only concern is for roughly the same price point the Cayin A100T has alsot double the power, uses similar tubes (but more of them) and had many of the same functions (although the Prima Luna has an auto-biasing) function that the Cayin does not). I was looking at the Ayon earlier this week, and it looks excellent too. There dont seem to be many reviews online though.

Mapman- Could you also offer a little bit of info about tube maintenance. It is one thing I have not considered at all yet. Approximately how often will the power amp tubes need replacing (roughly speaking)? What is an approximate cost for similar tubes? If one tube goes out, do thay all need to be replaced? Thanks again.

I am not a power tube guru so will defer to others for details of tube maintenance.

I think it safe to say power tubes tend to be the most shot lived and must be replaced periodically.

I do not believe one tube going bad requires others be replaced in general, but finding the bad or lesser performing tubes can be a challenge without the right equipment and know how and desire. That is always the key.

Personally, I am used to dead quiet background noise and maintaining this with tubes just n the pre-amp can be a challenge a times.

Also, replacing tubes, particularly larger power tubes, is not an inexpensive endeavor these days like it once was in their heyday.