Bombadil wrote:

"Wish my speakers were 95dB. That would make my 17 wpc Inspire sound the equivalent of a 40 wpc amp with my 91dB speakers. I suspect you have a 12 wpc Inspire, that is the standard model. Still a 12wpc with a 95dB speaker will be louder than my 17wpc - 91dB combo.

As discussed here several times, you can get more out of these amps if you use a powered subwoofer ... "

My Inspire amp is Triode-strapped and features the oversize 20 Watt output trannies. I never miss SPL when listening to jazz or vocals in my near-field setup. The only caveat is its limitations to reproduce the range between low volume passages and climactic peaks typical of orchestral classical music, much larger and faster-changing than jazz ever demands. Those cues are essential in classical music and the Inspire simply lacks that much headroom.

I also use a powered SUB, with it exclusively handling the lowest 100 Hz, which really helps. My two favorites output tubes are Gold Lion, the KT-77, followed by the KT-88. My quest for setting up a classical music configuration is facing a crossroad decision, between a sand amp or going to 104+ sensitivity speakers for a classical-friendly system.

Running KT77s in triode mode will produce, what, about 6 to 7 wpc? That's not going to get you concert levels on anything less than 100+dB speaker.

In my system, getting to concert-equivalent levels requires a pretty powerful SS amp. I've twice driven my 260 wpc SS amp into clipping on classical music.

6 watts into a 100dB speaker is equivalent to approx 50 wpc into 91dB. IMHO, that's not nearly enough for full scale classical.

So, which approach would you suggest in my case for decent classical music reproduction, a large SS amp or 104+ dB/W/M speakers?

I would go with a high quality SS amp paired with your speakers, unless you found ultra high efficiency speakers which sound wonderful to your ears.

As much as I love my Inspire SE playing a number of music genres, to my ears and within my system, it comes up short on some types of music. Including large scale classical, progressive rock (Yes, Pink Floyd), and when I crank it up for bands like Steely Dan, Dire Straits. The dynamics and ability to tightly control & define, along with the power demands, just aren't there ... to my ears. Put on Holly Cole, Norah Jones, or Yo Yo Ma & his cello, and it is pure magic.

Here's an interesting video demonstrating how much amplifier power is needed for certain types of music and when using less efficient speakers. In this case speakers by Harbeth, which I find to be quite good. Watching this I better understood just how it was that I've clipped my 260 wpc amp a couple of times, well, badly clipped. Who knows how many times I've softly clipped it? I bet I've clipped my Inspire amp, on quick transients, many, many times.
https://www.youtube.com/watch?v=bRMR9JZ1m0s

These are Harbeth 40.1 speakers, 85dB efficiency. If your speakers are truly 95dB, you'd need 1/10th the power, which would still hit peaks of 75 watts if used as shown in the video. My 91dB speakers would draw up to 188 watts.

The power handling spec on my speakers is 200 watts. This means I would require an amp with a continuous max power of 200 watts to make sure I don't melt the coil material in those speakers by applying a higher continuous wattage. This would also ensure I'm taking maximum advantage of the rated power capacity of my loudspeakers. Both devices (SS amp and loudspeakers) should be able to handle the short-term energy bursts stemming from the music's dynamics. This would also be theoretically equivalent to having my Inspire amp running speakers rated at 110 dB /W/M at 8 Ohms (which would essentially be heavily horn-based).

Does this sound right? Can I use my current Inspire LP-27a preamp with such an SS amp (input impedances, etc.)?

You could easily exceed that 200W "limit" on peaks with good, clean power ... i.e. not clipping. Those Harbeths in the video have a spec of 50W-200W and they were handling 750W peaks. The key is not clipping. So you could go with an amp of 200, 300, 500W.

Lets see, 200 wpc into 95dB speakers is roughly equivalent to 6.25 wpc into 110db, so you are correct.

I know people running Klipschorns with 300wpc amps. I think those measure at 104dB. They feel they need that much power to get optimal micro and macro dynamics

I don't know the specs of the LP-27a. What is the output impedance? You should be in good shape as long as the SS amp has a high input impedance. Many of them are up around 100K, but you can run lower. I have two tube preamps and both work fine into my power amp, which has a 33K impedance. The general rule of thumb is the 10X rule, where the input impedance of the power amp is at least 10 times higher than the output impedance of the preamp.

I believe a nominal 200 Watt RMS amp is capable of serving short bursts of peak power demands up to 75-100 % (350-400 watts) of nominal power, so that ought to be enough for classical music dynamics. The key here is the time of the involved peak. This means, running 300 or 500 watts continuous RMS on a 200 Watt-capable speaker is dangerous as you would need to make sure you don't go beyond the nominal speaker capacity. The 750W example you mentioned is just short-term, which do not damage anything. Both clipping and a nominal power much above the speaker power handling spec are potentially damaging to the speaker.

In any event, as you pointed out, it would be easier to get an amp rated at 200 W RMS to do the trick than to find an affordable pair of speakers rated at 110 dB sensitivity. I may have to look at Parasound and the likes ... scratch2:

The chicken or the egg. With your present speakers 100 watts should be plenty. Does it ever end? :scratch2:

I still wonder about a PSE but think I'll do a sub and the red filters.

100 wpc will give you another 12dB of headroom over your Inspire. That certainly is a lot.

Here's an in-room SPL calculator. With your present amp, and estimating that you sit about 8' from your speakers, it estimates that your max volume level now is 98dB (or 101dB if you have your speakers near the wall). This is no where near "concert level," which, believe it or not, is close to 120dB on peaks.

http://myhometheater.homestead.com/splcalculator.html

Now I'm not an advocate of being able to hit 120dB in my living room, but that is what they hit at both rock and classical concerts from time to time. That's way too loud for my ears. But it does illustrate that a LOT of power is needed to approach those levels.

The estimator above shows that with 100wpc a pair of 95dB speakers should hit something around 110dB (113dB if near wall). That's a realistic goal to shoot for, although if I could find a deal & could afford 200wpc, I'd probably go for it. There are some really good 100-135wpc SS amps around.

I know, but in true fairness, I have not been able to enjoy orchestral classical music with the Inspire near as much as I do enjoy it with acoustic jazz. Two quite different demands. I don't need more SPL or any other attributes for Jazz with my current Inspire so the PSE really does not represent an advantage.

Do the SUB and the RED MOD filtering. No brainers ...

Bombadil wrote: "The estimator above shows that with 100wpc a pair of 95dB speakers should hit something around 110dB (113dB if near wall). That's a realistic goal to shoot for, although if I could find a deal & could afford 200wpc, I'd probably go for it. There are some really good 100-135wpc SS amps around."

I'm hoping, if I do this, to get a good-sounding 200 watt power amp (not an integrated) for decent money. Not because of the nominal high SPL ceiling but because of its healthy headroom reserves to offer that "oomph" factor, when required. If not, I'll have to settle with a more modestly powered alternative in the hopes it would still make the trick. Any suggestions?

Hard to pick something for someone else. There's the Parasound A21, which can be had used in the $1500-$1800 range. Built like a tank. 250wpc. Has only been out for about 10 years, so none of them are very old. Still in production, so you can find them just 2 or 3 years old. Conrad Johnson 2550 is very nice. Their 2275SE is just 135 watts but filled with high-end Teflon caps, said to be very good. There's also a 2550SE but pricier.

Bryston 4B-SST's can be had for reasonable prices. They made a 4B-NRB, 4B-ST, 4B-SST, 4B-SST2 and 4B-Cubed (current model). The NRB's are pretty old now. They all came with a 20 year transferable warranty, no receipt required. So if you find one with a 2005 build date, it still has 8 years of warranty remaining.

There's the Cary SA-200 and a 200.2. This amp is well regarded and you could stay in the Dennis Had family of products. http://www.positive-feedback.com/Issue61/cary200.2.htm I've seen them selling used in the low 2K range.

Lots of others out there, these are just a few.

I'd love to find a real 97-98dB speaker which connected with me. That would make my 17wpc Inspire act like a 75watt amp, as compared to with my 91dB speakers. That would be nice. I bet your triode Inspire makes a glorious 6 watts.

Thanks for the pointers. Interesting stuff.

When I got my current speakers over two years back, I was looking for that type of sensitivity and I don't regret it (be it 98 dB theoretical, which I deem more like 95 dB in real conditions), as they sound nice, with plenty of detail and transparency, sound-stage, etc. The perfect Inspire system match for acoustic jazz. These also sound great with quartets, trios, sonatas, and other chamber music, with the right timbres, etc.

Man, I thought I was settled already ... :sigh:

If there is a Klipsch dealer near you consider bringing your Inspire in and have a listen.

I have listened to Klipsch's many times, including the Klipschorn, La Scala, and Cornwall. They are not my cup of tea at all.

Good quality at reasonably prices, 95 dB or higher: Tekton Designs and Omega Loudspeakers (make sure you upgrade stock Caps)

Yes, I am familiar with these too. Tekton consistently tests at 92dB. Omega is okay for what they are. Neither of these lines are close to what I already own. It would be difficult for me to step so far backwards in overall sound quality in order to gain a few dB in efficiency.

I know there have been some people testing the Tekton Lore's in some forums with some arguments on both sides ... Is that what you mean with these being consistently 92 dBs?

I can't really believe there is such a difference between the marketed 98 dB and the 92 you cited. Maybe different model speakers?

I own a number of medium to high efficiency speakers. What are you using right now?

There are two issues with stated efficiency:

1. Credibility of the source. We are required to trust the manufacturer's stated efficiency on its face. That is fine for those who are honest about their efficiency ratings, but for manufacturers who like to stretch the truth they can make any assertion they like.

2. Conditions under which the stated efficiency is measured. Sadly, most manufacturers do not couch their efficiency figures in standard terms. That means providing both the frequency range and bandwidth (e.g., +- 3dB). One speaker I own is rated for 94dB efficiency and 8 ohms impedance. However, in reality this speaker is only 94dB efficient from 500hz to 5,000hz. If we were to require it to be measured from 100hz to 10,000hz the actual efficiency would be closer to 90dB -0dB +4dB.

Your Tektons may be 98dB efficient over some point in their frequency range, but probably are less efficiency over the frequency range most of us would consider "full range"

Yes, I'm aware of that, and thanks for your thoughts, but based on my familiarity with them, I do not believe the difference is 6 dB. After all, that would imply doubling power requirements twice in a row (binomial exponential). No marketing scheme could mask that reality. Tekton's niche is with medium-powered amps (at least those speakers rated at 98/1W/1M @ 8 Ohms). Based on another pair of speakers I use alternately, my best guess is my Tektons have a net avg sensitivity of 95 dB.

I'm referring to bench tests of Tekton's speakers. For example in this Stereophile bench tests, a Tekton Enzo XL, spec'ed at 96.5dB, was measured to be just 90.6dB.
https://www.stereophile.com/content/...r-measurements

Same has been true in other bench tests of Tekton speakers, consistently measuring at 5.5 to 6.0 dB under the specs that Tekton claims.

No one polices loudspeaker specs. Manufacturers can claim pretty much whatever they want to. Tekton uses an Eminence B102 woofer/midrange in several of their speakers. Eminence specs this driver at 92dB. But when Tekton puts it into a speaker, they still spec the speaker at 97 to 98dB. Zu does the same thing, using the exact same driver.

Well, so be it. It's all a moot point anyway as my Inspire make them sing in my setup with small ensembles and acoustic Jazz. The point is, classical orchestral music requires either a much more powerful amp, or true 110 dB sensitivity speakers.

Let's look at a group of five speakers.

Paradigm 95F spec'ed at 91dB
Tekton Enzo XL spec'ed at 96.5dB
Zu Soul Supreme spec'ed at 97dB
DeVore Orangutan O/96 spec'ed at 96dB
Goldenear Triton Five spec'ed at 90dB

Someone looking for a higher efficiency speaker would cut the list down to the Tekton, Zu, and DeVore. But how do they really measure?

Paradigm 95F - 92.0dB
Tekton Enzo XL - 90.6dB
Zu Soul Supreme - 91.5dB
Devore Orangutan - 90.6dB
Goldenear Triton Five - 90.8dB

We see that they are all very close to being equally efficient, with the Paradigm actually being the most efficient. With Paradigm and Goldenear slightly understating their efficiency, while Zu, DeVore, and Tekton significantly exaggerating their efficiency.

I am using a custom modified Von Schweikert tower. It started life as a model VR-4, but was upgraded by the speaker designer himself to a model VR-7. It is very similar - 4 drivers are the same, one was slightly modified, the crossover was tweaked (mine has the V-Cap, Hovland, Analyst Plus wiring & nearly all of the stuff described in this review) and the cabinet is slightly different - but mine is much uglier, to what became the VR-5 Anniversary speaker, which sold for $27,000 and was reviewed here:
http://www.positive-feedback.com/Iss...nniversary.htm

When the designer upgraded mine, he took them into their sound chamber and tweaked it himself until he thought it was perfect. He owed me a favor and this was his way of repaying me. A favor which is still repaying me.

In the end, it is not quite up to the standards of the VR-5 Anniversary, but it is satisfyingly close.

Well, unless the speakers are horn-laden I wouldn't trust any as truly high sensitive (i.e., 98 dB and upwards), in spite of their claimed specs. Given current speaker prices, I rather invest in a good high-power amp. Then, I would have a great setup for each music genre.

For you, more watts is the answer. :thumbsup:

Something to consider for those wanting to stay with their Inspire amps and run efficient speakers.

https://greatplainsaudio.com/wp-cont...604_8H_III.pdf

Dennis has engineered a crossover for the Altec 604-8G that sounds fantastic and should also work well with the GPA 604-8H. I don't know what you all are spending on speakers, but I believe a pair of these run $2K a pair or so.

Mighty fine speakers! Cabinets?

I agree and was wondering the same about cabinets. I like the Great Plains Audio web site. There is a page called Enclosures where they say:

Great Plains Audio has partnered with Speakers on Steroids in Atlanta, Georgia, to offer custom cabinetry and complete vintage Altec-Lansing loudspeaker systems. Whether you’re looking for a set of new Model 19 cabinets, a complete Model 19, or something custom, we can provide it.

In the "everything I know is wrong" category, I'm pleasantly surprised at how well my alleged 91db speakers work with my HO (12 watts or maybe 17 watts…jury is out on output)…I listen to a wide range of music including modern jazz, orchestral stuff, things that rock, etc., and my listening space is around 18 by 20 with the ceiling going from maybe 8 to 20 feet sloping up from the gear heap. My main speakers are maybe 8 feet or so from my earballs and can be enjoyed to seriously loud levels with no apparent distortion…easy to see where that distortion shows up by simply turning it up until it goes into overload, but it's loud enough to not have to go near that area. 2 subs reinforce things, but dynamic classical and everything else doesn't seem challenged at all…I might be lucky.

I don't think Dennis has built very many 17wpc Inspires. I think I've only seen one of them for sale on eBay. This design pushes the standard KT88 tubes pretty hard and may not be his preferred model in terms of producing a sweet SE sound.

If I'm not mistaken the lam stack on the OPTs is significantly thicker on the 17w units. The standard having adout 1" thickness and the higher watt units being closer to 2". I top view picture should tell the tale.

What is the lam stack? This is what my amp looks like:

Regardless of the capability of the OPT, I'm not convinced driving the snot out of the output tubes gives the best sound. I own a [15 watt opt] KT88HO and a PSE. In both cases I find my best sound is with tube combinations that give less power than I could get by going with the 5AR4/KT88 combination. In my system and to my ears I find my KT88HO sounds best with a 5U4/6V6GT combination and my PSE sounds best with KT77'. Neither combination was chosen to give more power.

My opinion is that if you need the extra power you get going from a 12wpc KT88 to a 17wpc KT88 amp you really need to step up to the PSE. That being said, the larger OPT's on the 17wpc amp may provide better bass response even at lower power, though there may be a tradeoff. I have not listened to a 17wpc amp so cannot offer my direct opinion.

Does anyone know for a fact if these amps can be bridged to mono without detriment to the sound quality? If so, can a single preamp (Lp-27a) feed both monoblocks by bridging the selector for the two pairs of outputs (to avoid splitting a single output pair's signal)?

The lam stack is where DH puts his Inspire label. At the angle of the photo it looks like you have the higher watt version but it is hard to see clearly. Attachment 51535

These are the 15W opts.

Yeah looks like I have the higher watt version:

I am not certain if having the 20W output transformers is a guarantee that one has the 17 wpc version. It depends upon the voltages in the circuit. Perhaps Dennis always used the 15W OTs with the 12 wpc designs?

As to driving the tubes hard, Dennis has previously stated that he feels the amps sound better when they are not driven to maximum. When he released the PSE amps, he said that they would produce something like 22-24 watts with two KT88s per channel, not overdriving them because he felt this was where they sounded best.

I purchased the 17 watt version, used, for a price below the 12 watt new. I felt I needed every watt I could get as even with my SS amp - spec'ed at 180wpc with dual external power supplies and which has been measured to get to 260 before clipping - I have clipped it a few times.

Going to a PSE would buy me what, 1 more decibel? But then maybe more magic in every watt.

I am content with using my Inspire for moderate volume levels, which is where I listen the vast majority of the time. The SS amp is there for when I want to crank it up.

Would I love a 60wpc tube amp with the magical sound of an Inspire? Sure! But I have no idea if such an amp exists. Right now I am pondering the purchase of a pair of 450wpc monoblocks! Not because I need 450, but because they would provide essentially limitless clean power and there is something to be said about having even the most fleeting transient reproduced with no strain.

Agreed. In my case, only an SS amp would give me the extra "oomph" I need for some classical music selections. The rest can be played at excellent SPLs with extraordinary sound quality through the Inspire HO / LP-27a combo, and even with the amp by itself along with the balanced-fed ZBit (great sound!). Therefore, IMO a PSE would not add much to the equation. Assuming it is feasible, bridging the Inspire amp and buying another unit would probably not be enough either.

The only other possibility is to find an affordable 110+ dB/W/M pair of speakers ... a much more difficult proposition!