• http://www.6moons.com/audioreviews/firstwatt/firstwatt.html

Two quotes from the article, I hope they don't mind my lifting the text directly.

Quote 1 :

"His whole optimization scheme for the single-driver speaker/amp interface hinges on external compensation networks which are specific to each loudspeaker. Indeed, what speaker would I be using? Terry Cain of Cain & Cain and Louis Chochos of Omega Loudspeakers to the rescue. To enable Nelson to include optimized networks with the review amp, Terry Cain personally delivered a pair of Abbys to Nelson's California digs while Louis shipped his pair instead. Using on-site acoustical measurements of either speaker's frequency response allowed Nelson to tailor the compensation networks in conjunction with his F-1 amplifier and the actual speakers."

Sounds just like what I have been doing for several years. Maybe Mr. Pass's circuit is implemented differently, probably a lot more elegantly then mine, but I bet the concept and results are very similar.

Quote 2 :

"Tube amplifiers seem to bring out the best from such drivers. They have more bottom end, a warmer mellower mid- and upper mid-range and often more top octave. By comparison, the 'best' solid-state amplifiers make them sound more like transistor radios - less bottom end and an occasionally strident upper midrange. If you are a solid-state kind of guy like me, you start wondering how that could be. If you are a tube aficionado, you smirk and say, "I told you so." The solid-state guy probably starts fixing the response with a parametric equalizer and the tube guy enjoys his music with a nice glass of wine."

This is the damping factor impact that I have also been talking about for a couple of years. A low damping factor tube amp will work with a low Qts Fostex or Lowther drivers without much compensation beyond the cable and connection resistances. The Abby is a good example. The tube amp can have several ohms of internal series resistance.

The high damping factor SS amp will probably sound terrible with the an uncompensated Fostex or Lowther driver (I know this for a fact). The Abby will not sound its best with a SS amp. Add a compensation circuit to the Fostex or Lowther driver and the SS amp will sound great and the tube amp will sound booming and underdamped. No magic here.

I personally believe tha damping factor issue is the major source of the differences reported in the tube and SS amps. The odd or even distortion stuff is much less of an impact. The warmth and bass output generally associated with a tube amp is due to the internal series resistance not present in SS amps. Low Qts big magnet full range drivers will sound better with a tube amp if no compensation circuit is used.

Conclusion : You need to design the speakers for the type of amp being used. I think both a tube amp and a SS amp can work well with Fostex or Lowther drivers. But you cannot design a single speaker that works well with both without some form of compensation or adjustment.

Does that make any sense?

Martin

So my conclusion is it doesn;t seem like this new amp is anything radical at all, just an application of well known theory (i mean damping factor on loads) with a marketing twist!(not that i'm decrying it or anything). It seems that 6moons is marketing (reviewing) it with a vengeance.

I'm not sure about the relative impacts of damping factr sensitivty versus the even order distortion on perceived euphonia. That would require some research...it seems you have more empirical data here than i do. However, i will offer that in order to understand why tube amps sound different from ss, we may need to start with a list of factors, two of which would undoubtedly be DF & Distortion. there may be other factors too, such as pshoacoustical factors, and then the other factors that may not have been quantified yet (the elusive "tone").

Anyways, nice post. thanx
-akhilesh

A couple of more thoughts tossed out in no particular order.

1) Ever heard somebody say "All amps sound the same." Obvious;y this is not true but the differences in solid state amps can be subtle. However, the differences in tube amps are reported to be significant and obviously the differemce in tube and solid state are large. If I adjust my variable BSC resistor by 1 ohm the sound of the Lowthers can change very audibly. Swapping SS amps in a system probably does not change the damping factor very much and the differences in the system performance are small. Changing tube amps in a system can change the damping factor, meaning the series resistance, significantly and thus the sound of the system is dramatically changed.

2) I doubt that many tube amp designers want audible distortion. I bet that the design goal is to minimize distortion and all audible artifacts in any amp. Obviously nothing is perfect and maybe a tube amp has more of some audible artifact then a SS (or the other way around) but I have to believe that this is not an intentional design goal.

3) If you design your speakers, keeping in mind the amp to be used, I think either type of amp can be made to work very well with a full range driver. In general I believe that speakers designed for SS will not perform well with a lot of tube amps, the opposite is also true in my opinion.

4) The reason I stay with SS is that having essentually unlimited power (>100 watts vs. 2-3 watts) allows me to do anything with a filter or box and still have a working speaker design. Power is not a limitation driving decisions in the design of my speaker system. The amp for all practical purposes is removed from the design. Taking my speakers to somebody else's house (assuming SS amp) produces an expected almost consistent result.

5) If you keep in mind what I have said, you don't have to believe it at all, and go over to AA and read through the High Efficiency and SET forums where people are describing their speaker's performance I think that you will begin to see a trend. The strengths and weaknesses they describe seem to support my observations. How else can changing a tube amp in the system have such a dramatic impact?

Food for thought,

Martin

What do you think?

-akhilesh

"Given that tube amps will work well with some speakers and SS with other speakers, maybe it's the SPeaker/amp COMBO that makes the difference. In other words, the interaction effects between tube amps' low damping and the highish sensitivities and flat impedances of the speakers that work with them as a COMBINATION may produce better (meaning more realistic) sound than the SS amps / high Q speakers combo. In general that is.

What do you think?"

I agree that the COMBO is the key. Lets look at three speaker/amp combination examples.

1) A SS friendly speaker with an efficiency of 88dB, Re = 8 ohms, and a Qtc (~ Qec) of about 0.7. The SS amp adds essentially no series resistance so the result is a maximally flat 88 dB response. But if a SET amp with an output impedance of 3 or 4 ohms is used, then the system Qtc rises to approximately (0.7 x 12 / 8) 1.05 which is an underdamped response. The efficiency also drops so the amp runs out of steam on loud passages. Not a good combination.

2) A tube friendly speaker with an efficiency of 100 dB, Re = 8 ohms, and a Qtc (~ Qec) of about 0.3. The SS amp adds essentially no series resistance so the result is a very rolled off overdamped low end, screaming and shouty mid range, and an efficiency of 100 dB. But if a SET amp with an output impedance of 3 or 4 ohms is used, then the system Qtc rises to approximately (0.3 x 12 / 8) 0.45 which is almost a critically damped response. Add some cable resistance and it only get better. The efficiency also drops a little but probably is still near 95 dB so the low power amp is not such a concern. The tube amp is a good combination.

3) A tube friendly speaker with an efficiency of 100 dB, Re = 8 ohms, and a Qtc (~ Qec) of about 0.3. The SS amp adds essentially no series resistance so a correction circuit is used in sereis with the driver. Much better result. The efficiency drops, but this is not a concern. The circuit allows adjustability, this is a nice advantage. I think that this is also a good combination and the path I have followed.

After reading Nelson Pass's write up on his F1 amp, I think he is doing something similar to system 3, but if I understand correctly his current amp requires the correction circuit to be in parallel with the driver. So his individual circuit components play the opposite roll of the components used in my series correction circuit approach. This means that while in my series circuit the signal passes throught the inductor at low frequencies, in the F1 configuration the inductor passes the high frequencies. I would not want to rely on an inductor at high frequencies. When I measure the impedance of inductors using LAUD I find that at high frequencies they become their own resonant LCR circuit due to capacitance build up between the turns. Maybe he has already though of this and addressed it, or maybe his smaller inductors are not prone to this at audio frequencies. But I like his approach and do find it interesting and amusing that suddenly the AA HE forum seems to like this better then the circuits I have been proposing for a few years. Even Terry Cain seems to be excited!

Martin

Great points! One last question, have you ever done a listen-off between a SET and an SS on any of your speakers? If they sound essentially indistinguishable (with proper compoensations applied in each case) then you are totally right. It would be interesting to do such a listen-off. You know, take a pair of speakers, and put the relevant amp/network combos in fornt of them.

Also, the whole 1 watt amp thing...to me it's just the usual audio hype. The fact that some vendors are "excited" about this and call it a "breakthrough"...well... i can tell you what i think they are excited about, and it begins with a D----- and is colored green.
-akhilesh

==Amusing no doubt.

Totally different approach AND results. They could not be more dissimilar.

Notice in NP's design, ANY of his designs he never uses a passive element in the final output circuit (in series). The whole reason for his current source amp is to eliminate the negative electrical effects of these (passive) devices on the sound. Even his 4-way spkr uses 4 amps to deliver direct amp loop circuits with the voice coil, never to be damaged by extraneous compensation. He can hear the detrimental effects these have.

You cannot push clarity through a resistor, although you can push a flat signal.

That's also why he builds one of the worlds most elaborate and expensive active crossovers, because you cannot mess with an output circuit of a conventional amp and maintain ultimate clarity.

In his circuits the compensation affects the output yes, but only in the frequency current domain entirely without affecting back electromotive force (emf) into the amp circuit as do other circuits. And without any kind of the signal clouding effects of the ceramic resistor media needed to balance a hi Q driver as in example #3 which NP and myself agree would be detrimental to clarity

Once an output signal sees the ceramic matrix, it is split into smithreans never to be assembled correctly again. Far far better to adjust the circuit ANYWHERE buut the final output circuit like before the amp (actively).

So yes it's the same game of adding RLC to tailor response. Only he has changed the rules to maintain absolute clarity. Something passive circuits with conventional amps both tube and SS cannot do.

>>Even Terry Cain seems to be excited!

>> I get excited when I hear good sound. Especially sound so good that it *IS* exciting.

Will I dump my SET collection? Not a chance. They are exciting too.

TC

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