Dennis Had Inspire Amps

[Musica Amantem]

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.

[Bombadil]

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.

[Musica Amantem]

Originally Posted by Bombadil

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?

[Bombadil]

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.

[Musica Amantem]

Originally Posted by Bombadil

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.)?

[Bombadil]

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.

[Musica Amantem]

Originally Posted by Bombadil

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:

[FloridaBoy]

Originally Posted by Musica Amantem

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

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

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

[Bombadil]

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.

[Musica Amantem]

Originally Posted by FloridaBoy

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

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

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 ...