What Power Amplifier Should I Buy?
I am looking to increase my system power. I currently am using a Bryston 2.5B cubed, which is specified at 135 Watts/CH. I am using Revel f208 speakers crossed over at 120 Hz to a 15" HSU sub. The f208 speakers have 88.5 dB sensitivity (Amir measured 88-89dB SPL at 1W into 8 ohms). I sit about 7.5 feet away from the speakers and listen up to 92 dB SPL, but mostly stay between 80-90 dB SPL at my listenin g location.
I have not had power issues. I've never seen a clipping light. I just want more oomph. I've never had a power amp with more power than the 2.5B cubed.
My budget is about $5K. I have been looking at some used 4b cubed amps.
My preamp is a vintage ML No. 38s. Digital from Bryston BDP-3/BDA-3 combo. Analog using Koetsu RS and Shelter 901 cartridges into an SUT (20x) followed by a very vintage Paragon System E used as a phono preamp (I have fully repaired this preamp, particularly the power supply).
I like the sound of the 2.5B cubed. I had a Cary 120 tube amp for some time, but grew tired of the heat and the continuous maintenance, including the insane prices for tubes. I did not experince that great "tube sound" that others rave about. I sold the Cary and went back to the 2.5B cubed.
Will the 4B cubed disappoint?
What other amps should I consifder, new or used?
Thanks for your help!
I've enjoyed this discussion. I have built my own full range speakers in the past. I understand how difficult a task it is. I can get one of the Hypex modules and check it out. Past that I really can't afford even one item you've recommended. Fixed income , yada, yada. I do wish I could grab the gear you've recommended, but I just can't. |
Oh, by the way, the Klipsch Cornwall is the most "civilized" of the classic Klipsch speakers, and in stock form has more or less flat response. The latest model is expensive, but there are lots and lots of beat-up old ones around (which are cheap), and modifying Klipsch is a cottage industry. Basically, you put in felt lining and fiberfill (or use NoRes automotive damping pads), reinforce the cabinet a little bit, and use better caps in the crossover. That’s it. All done. Way better than any speaker with a whizzer cone. And super efficient around 95~97 dB/meter/watt. I once owned the little brother, the Klipsch Forte, which has a 12" woofer and is about 2/3rd’s the size of the Cornwall, and that was pretty decent too, after I modified it with good caps. I was surprised how flat I got the Fortes after I twiddled with the crossover a bit. Since you’re into EQ, you might also be surprised what you get with an old Cornwall or Forte. By contrast, modifying classic Altec or JBL is a serious project that requires serious crossover mojo. Not for the faint of heart and definitely not for the beginner. Klipsch is way easier since they are basically simple speakers that respond positively to even minor upgrades. You might question the horns but the 12" or 15" woofers are the real deal. P.S. Beware of modifying Klipschorns, LaScala’s, or Heresies. Those have much more uneven responses and modifying them changes their basic character. I think Paul Klipsch wanted to try his hand at a mainstream "hifi" speaker, and he came pretty close with the Cornwall. In other words, they’re 80% there, and just need a little nudge to get to 90% to 95% there. |
Hi @lynn_olson Are you familiar with JBL 4430/4435? https://www.audioheritage.org/html/profiles/jbl/4430-35.htm They have a smooth sounding horn section compared to other vintage speakers. |
Sorry, not a JBL guy. "Smooth" is not the word that comes to mind when I think of JBL. They have their fans, I’m just not one of them. I prefer modern horns if possible ... see the Australian AH425 Azurahorn, which was designed by Bjorn Kolbrek using BEM computer simulation. The AH425 simulation became part of his Doctoral Thesis in Norway, and the physical horns were built in Perth, Australia by Martin Seddon. They were part of a project to design a modern successor to the Altec Model 19, which I have set aside, but the AH425 was a nice spin-off from the project. The other half of the project was an Altec/Great Plains Audio 416 woofer in a 4 cubic foot closed box with a crossover in the 640~800 Hz range. Going back to the OP, I still think, given his budget constraints, he should try a much more powerful amplifier (not just another 30 watts) and see if dynamics improve. I doubt it will, but I’m not the OP, and the experiment should be tried. In my experience, speakers usually limit the dynamic range of a system, not the amp. The true Theile/Small efficiency of the woofer typically sets overall speaker efficiency, and that in turn sets the overall system headroom. To a first approximation, 1% conversion efficiency in the T/S sense results in 92 dB/meter/watt efficiency for the bass driver, which is almost never attenuated in the crossover. |
From previous conversations, the T/S efficiency of the compact Revels appears to be in the 0.2% to 0.3% range. This would imply only 10 watts/channel are needed to reach 95 dB at a one meter distance. Allow another 2X for a 2 meter listening distance, and maybe we need 20 watts/channel. Anything more is just there for additional headroom, and to allow for the occasional transient peak. The fact that a 100 watt amplifier is falling short points to marginal amplifier design, or the speaker itself running out of steam. More likely it’s the speaker, if a 6.5" woofer is all we have to work with. Speaker manufacturers like to brag about "long excursion", but an old rule of thumb in the loudspeaker biz is: "If you can see the cone moving, it’s distorting". Still true today. One of the jokes we used to tell back when I did this for living was: "If the amp is bigger than the speaker, something ain't right". |
