Tube Watts vs. Solid State Watts - Any credence?
For example, a 70 watt tube amp provides more power than a 140 watt solid state amp. Is there any credence to this or just sales talk and misguided listeners?it's just sales talk & misguided listeners. No credence to this statement. As Mapman & many others before have written: a watt is a watt tube or solid-state. Ralph Karsten of Atma-sphere has written a paper on power amplifier paradigms: http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php |
10-09-15: DjfstThe more expensive amp has a more robust power supply which most probably allows that power amp to double down with each halving of the load impedance. This means that the more expensive amp also has more current delivery capability which in turn means that it can power hard-to-drive speakers far more easily than the less expensive amp. This is based on the assumption the you are not comparing 2 very disparate brands i.e. both amps are of brands that have similar reputation & command similar prices in the marketplace. 10-10-15: Innathe above is an explanation for your question Inna. In this specific case the Gryphon doubles down all the way to 1 Ohms. One of the rather rare s.s. amps in the market & very expensive. My friend used to own the Antilleon Signature which was a 100W/ch amp but was 800W/ch into 1 Ohms. Beuatifully built amp - like a tank & almost no speaker could ruffle its feathers (but don't hook an ESL to this amp as it was not meant to drive an ESL). Current delivery into a speaker load is very important esp. when it comes to hard-to-drive speakers (which are characterized by having wild impedance & phase swings). |
Secondly, how can low powered tube amps sound so much better with some speakers that have amp recommendations much higher? Very few tubes get over 100 watts, yet are very prevalent even on some inefficient speakers. Any thoughts? Just trying to learn more.Atmasphere explained this quite clearly in his post above. Did you miss it? it's the distortion characteristic of tubes amps - when they're overdriven a little the distortion is more pleasing to the ear than a s.s amp that is overdriven the same amount. I know tubes have there own characteristics, but besides that, from a power standpoint, would it be better to go to KT120s to get more power to my speakers? Would the difference in wattage moving from EL34s to KT120s (15 watts increase in ultra linear, 5 watt increase in triode), be beneficial or even perceptible to my ears? Would this be better for the performance of the speaker, or at least the health of the speaker?in the end it really depends on what kind of sonics you prefer. Tube amps using ultra-linear mode of operation use a lot of global negative feedback to generate a higher wattage. These sort of amps have a very robust sound & trend to sound more like s.s. amps. And, behaviour-wise they also behave like constant-voltage sources (which most s.s. amps can be characterized). I've found that ultra-linear tube amps had more bass punch but their mids & highs do not have the delicacy that is often associated with tubes. Operating an EL34 in triode mode would be operating this tube in as linear a mode as is possible. Remember the EL34 is a pentode tube but in triode mode it operates like a tube with 3 units (sorry I could not think of a better word at this time!) - anode, cathode & 1 screen. You get much less wattage (as you have stated) but you get a beautiful tube sound that trends towards the type you hear from more traditional triode tubes such as 300B, 2A3, PX25, etc. At one point in time i used to own an AES Sixpac that had 6 EL34 per chassis & output 60W/ch in triode mode. It was a very addictive & beautiful sound. That amp drove my then-speakers with plenty of power - didnt have the bombastic bass of a s.s. amp but i did not care as I got much more from that amp that compensated for a less bass response. When I changed my speakers that amp had to go. Personally, I'd go for linearity hence triode mode. But like I wrote before - you might like you music delivered differently..... |
The manufacturer recommends 50-180 watts and received wisdom seems to be that the speakers respond better to solid state watts (what does that mean)?I've not looked at the Vienna Acoustics Kiss speaker impedance & phase plots but if this is the wisdom that has been imparted to you then it would mean that the VA Kiss has some wild impedances & phase angles in the bass region where the actual impedance is quite low where a tube amp would have difficulty sourcing large amounts of current to have a controlled bass response. In such a case a s.s. amp would do better esp. if it can double down for each halving of the load impedance. This would be an expensive s.s. amp since it would have a very robust power supply. Heavy chassis, heavy power xformer, large heatsinks, high cost but it would give you a tight bass response while a tube amp would give you flabby bass response unless you spent $$$ to get a large tube amp. |
10-09-15: DjfstI found your speaker measurements here: http://www.soundstagenetwork.com/index.php?option=com_content&view=article&id=1285:nrc-measurements-sonus-faber-olympica-iii-loudspeakers&catid=77:loudspeaker-measurements&Itemid=153 if you scroll down & look at the 2 plots "impedance magnitude variation" & "phase angle" you can see that this speaker has capacitive phase angles in the bass region to, oh, ~150Hz. The impedance is complex i.e. has a x+jy sort of form. So, the real part of the speaker impedance into the power amp is delivering current is not 4 Ohms as printed on the back of the speaker but less than 4 Ohms due to the capacitive (reactive) phase angle. So, any power amp would be asked to deliver more current than originally thought (since you are thinking it's a 4 Ohm speaker) & this can tax the power amp. When you connect your SF to the 8 Ohms tap, the power amp is being asked to deliver more current into the lower (4 Ohms) speaker impedance compared to when you have it connected to the 4 Ohms tap. The higher current delivered yields a better bass response. The plots show the speaker is mostly inductive in the 150Hz-2.5KHz. So, when high voltages are present in the mid-bass-to-mid-range little current is asked from the power amp due to this inductive impedance nature of this speaker in this region (the math omitted deliberately). And, in the high-freq even tho the speaker become capacitive there is not much energy in those frequencies so the power amp is not taxed much. So, it seems to make sense that this SF speaker would sound better on the 8 Ohms tap. |
All the "techno" BS aside, I recommend that the owner of the SFs and the Prima Luna gear should use the taps that sound best to his ears.I agree. In that post, given that the OP declared the 8 ohm tap was the best for his SF speakers, I tried to see if I could co-related his decision to the impedance & phase plots I found online. So, it was the other way around. I thought that was clear from my post since I quoted the OP before starting my reply but I guess not. Sorry if I lead you & others into thinking that one could read graphs & make a final decision which amp tap would be the best. I'm not even treading into the realm of "is 14dB too much global negative feedback?"!! ;-) |
10-10-15: Bifwynne Search & you shall find!!! (this is note to self) Look what I found: * an article in Stereophile where the late William Z Johnson was interviewed by John Atkinson. WZJ talks a wee bit about partial cathode coupling & gives the credit to QUAD as the initial inventor since QUAD used it in their Quad30 amp some 30 yrs prior to that interview. See para #3 from the top: http://cdn.stereophile.com/content/william-zane-johnson-1926%E2%80%932011#mX6ilT78dampubmG.97 * next, I found William Zane Johnson's patent application on the partial cathode coupling (must have been an enhancement of the Quad's version?). This is publication US3566236 A that was filed in 1968 & published in 1971. Yeah, you are correct - ARC has been using this for a long time in all their products. http://www.google.com/patents/US3566236 You can read this stuff but here is the crux (cut & pasted from the patent application) "Still another object of the invention is to provide an improved amplifier output stage coupling with partial cathode coupling, while maintaining classic tetrode operating parameters with substantially the same efficiency and drive requirements." hope this provides some more insight, Bifwynne. |
Ralph, thanks for pointing this out - you're right feedback & output power are not related. I should have written that sentence differently pointing out that output power depends on the topology of the tube - triode vs. ultra-linear vs. pentode with the output power going progressively higher as one moves from triode to pentode. |
10-11-15: Bifwynnewelcome Bifwynne. yeah, I figured it might be difficult to understand what was written in that patent application not only because of the material of the subject but also due to the fact that it was written in technical legal-ese that patent attorneys love! I believe that the basic premise of the partial cathode-coupling in the ARC output stage is to reduce output distortion while reducing impedance in the output stage circuit at the same time. This technique also allowed the ARC amps to have a "complex load driving ability" (written in his patent application) which in plain English means that they could drive tough speaker loads (the types that exhibit crazy phase angles that flip between capacitive & inductive over the audio spectrum). |
10-12-15: FrogmanI'm afraid that a watt is a watt & it is the distortion characteristic of a tube amp vs. that of a s.s. amp that appears to give the listener the impression that a tube watt is more powerful than a s.s. watt. It is not. I bought my first pair of Stax F-81 electrostats back in early '90's when mythis makes sense - an amp that is good for driving dynamic cone type loudspeakers (Thiel) & magnetic planners (Magnepan) cannot be assumed to be good enough to drive an electrostatic speaker. Electrostatic speakers are effectively a large capacitor to the power amp. This model of a capacitor for an electrostatic speaker comes from the fact that you have a stator on either side of the rotor/energized thin film that effectively creates 2 parallel plates of a capacitor where one is the top-plate & the other the bottom plate. Both stators create either the top-plate or the bottom plate. If the electrostatic loudspeaker looks like a large capacitor to the power amp, it also means that the impedance of such a speaker follows a 1/f profile i.e. speaker impedance is very high at low freq & very low at high freq. Just the opposite of a cone type speaker or even a magnetic planar. Since the electrostatic speaker's impedance is very high in the bass region, guess what?, the power amp has to pump current into a high impedance at the bass freq. Any s.s. or hybrid amp (which acts like a constant voltage source) will reduce its output with increasing speaker impedance. No wonder your NYAL Moscode 600 sounded horrible with an electrostatic & it was totally expected. A tube did much better because most tube amps act like constant power sources constantly adjusting their output current & output voltage to keep output power constant as the speaker impedance changes. This also means that a tube amp can give you relatively constant power (20% variation can be expected) over the 20Hz-20KHz range while a s.s. & hybrid amp will decrease its power into a higher impedance speaker load. it is no wonder that the Dynaco outdid your NYAL hybrid amp. Totally expected. You have to be very careful which amp you connect to an electrostatic speaker due to the speaker looking like a capacitor to the power amp. Most power amps oscillate & self-destruct when they have to drive large capacitive loads. It is no coincidence that SoundLab customers use tube amps almost exclusively (I think a lot of them use Atma-sphere amps) & that Sander Sound Labs makes a special s.s. amp for electrostatic speakers. |
10-12-15: BeavisSince Mapman has not answered till now & if I may be permitted to reply in his stead understanding what he is trying to say then......... no, he's not saying that s.s. & tube amps measure RMS differently. That simply cannot happen - RMS is RMS no matter which amp. i think he's saying the same thing Atma-sphere & I & others have already written which is: a watt is a watt but each amp reacts differently with each speaker. And, it is this interaction between amp-speaker that determines when & how much an amp will distort. This, in turn, will give the illusion in some cases that tube watts are more powerful than s.s. watts (they really are not). |
10-10-15: Djfstthere's a good explanation for it as stated in my earlier post. I guess you missed reading it?? Bifwynne, yeah LOL! ;-) @Bombaywalla ... do you understand the term "[o]utput stage coupling is a combination of “ultralinear” and Audio Research’s patented “partially cathode-coupled” topology ..."?? I have a rough understanding of ultralinear .... No clue about "partially cathode-coupled” topology. Any idea??well, this is a serious case of the blind leading the lame but I'll give it a shot. I hope that somebody who knows more steps in.... 'ultra-linear' is a global negative feedback technique where, in a tetrode (4 active electrodes) or a pentode (5 active electrodes), some part of the output (usually present on the anode or plate) is fed back to one of the screen grids of the tube. The amount of output signal fedback depends on the tube type (KT88, 6550, 6V6, etc). David Hafler has patent on this where he fed back 43% of the # of primary xformer turns to the screen grid to linearize his amplifier. What this global negative feedback did was reduce output distortion, reduce output impedance & raise the output power to near-pentode levels. 'cathode-coupled' is a tube amplifier topology where the input tube is cathode coupled to the next gain stage tube. here are some pix for you to look at (you can drag your mouse over the pix without any harm. Click on the pix at your own risk!) http://www.bing.com/images/search?q=cathode+coupled+amplifier&qpvt=cathode+coupled+amplifier&qpvt=cathode+coupled+amplifier&FORM=IGRE the 1st pix itself should be good enough to allow you to visualize what I wrote. In the pix the 2 tubes are strongly coupled as there is a deliberate connection between the 2 cathodes. The issue with this amp is that the cathode of the input tube is at a very different voltage than the cathode of the 2nd tube. So, this amplifier becomes very sensitive to power supply variations & noise. Thus, I'm *assuming* (you know this goes!! ;-) )that ARC has a patented technology where they partially couple the 2nd tube to the 1st tube so that they can make the cathodes of both tubes operate at nearly the same voltage while still transferring the input signal to the 2nd tube to amplify it. I could be out on a limb here..... |
