What Power Amplifier Should I Buy?

After all this discussion of power, I bought a Bryston BP-17 cubed preamp. I'll get it next week. This discussion has convinced me that I have enough power from my power amp. So I decided to see if the much newer BP-17-3 can outperform the aged Levinson #38s. I hope so.

@ditusa Thanks for showing me an alternate path. Could you explain how a second sub improves the imaging and sound stage?

Perhaps I used the wrong word. By "oomph" I meant more power for transients. I wasn't indicating that I needed more bass. I believe I have enough bass.

Oh, by the way, I use REW to calibrate and integrate the components. I aim for 1.5 dB/octave roll-off above 1KHz and 1.5dB rise from 200 Hz to 20Hz. I use a graphic equalizer to achieve an FR that's close to this.

Wow! So many great ideas.

I appreciate how these posts have recommended changes to other components, so much so that I thought I would discuss my system in a bit more detail.

The Paragon System E is used as a Phono pre only. It creates a beautiful bloom in the upper bass/ lower mids. Sometimes this works, other times not too much. I have other phono preamps I switch in from time to time.

I tried a Pass XP-12 preamp earlier this year. It was not a good experience. There was a lot of sibilance, no matter what I tried, even with a tube power amp. I did not enjoy the ergonomics, especially the grainy volume adjustment. I sent it back to the factory where Pass replaced the gain modules, but the sibilance remains. I sold it. I've tried some vintage preamps, such as the APt/Holman Preamps 1 and 2 and a 10 year old NAD. The lack of a remote (not the NAD), takes a bit of the fun away, although the APT preamps sound very good. I refurbished both with new caps.

I use a graphic EQ (dBx). I'd rather not have to use it, but need more room mode control than the passive absorbers can provide. I've experimented with analog parametrics, but found them very difficult to adjust. I've tried the miniDSP Flex, but I was underwhelmed. I'm able to do just as well with the GEQ. And the Flex has no control in the time domain (impulse response, group delay, etc...). I need Dirac for that.

The Bryston music server and D/A sound great. I'm very pleased.

My crossover is a Sublime Acoustic K231. This is a modern XO. I've tried XO frequencies from 75 Hz to 200 Hz. At 120 Hz, I get some help from room modes that are more apparent than with the sub. I have run the f208s full range, but was/am concerned about clipping the amp. This is one place where I need to continue experimenting.

The Revel f208 speakers are a keeper. They are the best sounding speakers I've ever had. I need to find an amp that will drive them well instead of getting more efficient speakers.

My main reason for getting a more powerful amp is to provide more headroom (which is why I use a sub). Perhaps I don't need more power. This thought has occurred to me. I could spend the money on something else.

To summarise, I feel very good about the sound from my system. However, I am always on the lookout for something else (better or just different?).

I need to update my system pics and description. I've changed a lot of components since the last photos.

I am still open to changing the preamp. I have already tried Pass, so that's out.

This continues to be a very informative discussion for me. Thanks for your participation!

@jbuhl Hi, see my system pics. Room dims are there.

@soix Hi, I can understand your frustration.

Please tell me how I can clarify. I would like to keep seeing your inputs to my questions, even if it is not complementary. I value what you have to say.

I cannot explain why this XP-12 was a failure in my system. I did swap out other preamps such a couple of vintage APT/Holman ones. I had no problems with either. I even sent the XP-12 back to the factory. I live 30 mins from the Pass facility, so I hand carried the preamp to them and explained directly to the tech what I heard. He did find a problem with the older gain modules. He replaced them with modern ones and retested OK.  However, when I put the XP-12 back in the system. the sibliance was still there, unlike all three of the other amps. So I just don't know why I had this experience with the XP-12. I did everything I could think of to make it work.

The suspicion that the 38s preamp is masking a different problem may have some traction. The problem with the XP-12 occurred with all inputs, two phono cartridges Koetsu RS and Shelter 901, the Paragon as Phono preamp and the SUT, one Technics SL-1200G TT, a re-aligned Sansui TU-X1 tuner, and the Bryston BDP-3/BDA-3 combo. I can't see how each of these could separately create the same sibilance.

I have looked at the Bryston BP-17 cubed before. Perhaps I should pick one up and give it a try.

@jimmy2615   @perazzi28 

I've talked to Bryston about bi-amping. They recomment against doing it because the speakers drop below 4 ohms at the xover to the highs (2.2 KHz), although they hedged saying I moght be OK because there's not much power/current needed at that frequency.

I'm not taking that chance.

Biamping will give me more power only if I use two outputs from the preamp. Not very many preamps have two (balanced) outputs. The ML 38s doesn't. But the Bryston BP-17 cubed does!

What's the word on this preamp? I've looked at it before thinking I would try it or the Benchmark LA-4. I wound up getting a Cary tube power amp. That didn't change the sound very much, so I went back to the Bryston amp.

@scm I deliberately crossover at 100-120Hz because of a nasty room resonance at 40Hz. This creates a big dip at 80Hz that can't be EQed away very effectively. This dip is very strong with the f208 speakers. It is much smaller with the sub. I've placed the XO frequency a reasonable distance from that resonance. I've used REW and other tools to guide me.

I've listened to sub only at 75, 100, and 120 Hz. I cannot hear voices at all. Frequencies below 200 Hz are radiated into a half sphere, with no dependence on angle. How can this muddy the sound?

Of course, I could be wrong. Could you explain how this higher XO frequency creates muddiness? Thanks.

Two subs may be the way to go.

@jaytor Yeah, I have always had concerns about the EQ. But some form of EQ is needed to help tame some of the FR variations from the room.

I have traps which are very effective. I don't need more, except for the floor to ceiling mode. But the "rules" prevent me from doing that. I have worked very hard at positioning the speakers and the sub to get the best FR, but there are still +/- 6 dB variations in the bass. I am restricted to near the present locations. I have tried a miniDSP Flex. It doesn't affect the time domain at all and is barely better than the analog EQ. I ditched that. And I enjoy the idea that I have an all analog signal path (except for the CD/DVD and music files).

So the dBx EQ is a somewhat "necessary" evil. I could live without it, but the engineer in me strives to have as perfect FR and TR (Temporal Response) as I can manage to obtain.

The XO does a very good job, far better than the Rane I once used. I don't like the idea of running the f208s full range and band limiting the woofer. However I haven't tried this in a while. Might be worth a shot.

Are you aware of any reviews on the Sublime XO?

Very helpful advice. Thanks.

I'm not sure if anyone is still paying attention, but...

My time with the BP-17 has come to an end. I could not get rid of the sibilance that drives me crazy. The ergonomics are OK, but nothing like the Levinson 38s. I've listed it, but not on Audiogon yet.

Now I use my old, old Paragon System E as a line preamp and a phono preamp. I still use the 38s, but now it is relegated to volume control because it has a remote. The Paragon does not.

This is the best sound I have gotten so far. I have rebuilt the Paragon PSU, replacing all components except the transformer, so it should be good for a while.

The Paragon is a tube preamp with six 12AX7 tubes. I've got new tubes (JJ). It was sold in the late 70s through the mid 80s. I bought mine new.

I'm finished with this quest. Although I have not found the Grail, I am quite pleased with the relics that I have. I've firmly decided I don't need an amp with more power output.

Gotta go buy some records. My gear search has ended.

@kennyc 

Thanks for reminding me about this. I've seen the impedance plot on ASR. There is a dip to 3.7 ohms at about 100 Hz and 3 KHz.

I also measured the voltage into the speakers while I had the SPL at the listening position using pink noise. I found that I needed about 3 V, which is about 1 W for 8 ohms and 2W for 4 ohms.

I concluded that I have enough headroom to allow for a little higher SPL and for the low impedance at the above frequencies (100 Hz goes to my self-powered sub).

@kennyc 

Just looked at Bryston's published spec. It is rated at 180 W into 4 ohms. So it is rated at 4 ohms. However, I was cautioned that if the impedance was below 4 ohms for a large part of the spectrum, especially in the midrange, there could be problems.

I have never seen any of the overload lights turn red, although maybe that doesn't mean much.

I really haven't experienced anything audible or measured any parameter with REW that would indicate problems.

Am I thinking properly here?

@erik_squires 

Moving the EQ to the sub path is a good idea. I do however, make adjustments to frequencies higher than the 120 Hz I now use as XO.

What kind of measurements are you referring to?

@lynn_olson 

I agree that another sub would help.

I'm confused by your statement about power requirements. Did you mean to say that any amp over 100 W will push the drivers into compression (does this mean non-linear?).  Therefore any amp over 100 W is not recommended for speakers that have the sensitivity that the Revel f208 does.

@erik_squires 

Thanks for the suggestions.

I use REW to characterize and help me improve my sound system. I have extensive traps from a company called "Real Traps". I know where the resonances are. I understand that dips in FR are hard to compensate electronically.

I normally test every component. First, electronic performance and second, in-room performance (listening).

My speakers don't sound any different close up.

What kinds of measurements am I not doing that you think would help me to further understand the performance of my system?

Thanks.

@lynn_olson 

@atmasphere 

My thanks to both of you. I agree with all that was said. I agree my speakers are mostly 4 ohms. My previous measurement indicated that even for the 4 ohm load, the voltage I measured at the speaker input terminals (pink noise input) was 3V. This is 9/4=2.25 W. The amp is rated to 180 W at 4 ohms. This is why I've given up the search for a new power amp.

I agree that higher efficiency speakers will provide more headroom.

The brands I think of are horrible choices: ZU Audio and Klipsch. I want a more neutral speaker, not these.

I've not based my speaker searches on efficiency, rather I chose a speaker that was neutral.

Can you suggest a brand that might be more neutral?

I have an FR curve from my last tuning. And I have just discovered what a pain it is to upload a jpg into this forum. So I won't. I'll attempt to describe it to you.

I tuned the FR to have a 1 dB/octave slope from 20-20K Hz (actual REW calc is 1.23 dB/octave). There are no big dips. Deviation from the 1 dB/octave slope is +/- 5 dB maximum throughout the spectrum. The phase plot indicates a problem (room resonance) near 300-400 Hz. But otherwise it is well behaved. I consider this a pretty good FR. I enjoy the sound. My measurements were done at about 85dB SPL, which is near the SPL I normally use for music. And I am evaluating the FR using the VAR filtering REW offers.

@lynn_olson 

Thanks for the recommendation.

Gee, those are some expensive speakers. My budget is $5K. I need to stay near that price.

What is your opinion of the Revel f208 speakers? I bought them mostly because I liked the small bookshelf speakers they make (now in the lo-fi TV system that my SO likes a lot) and by Amir's g;lowing review on ASR.

@lynn_olson 

@atmasphere 

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.

@lynn_olson 

I will probably buy the Buckeye Hypex NC502MP 2-Channel amp. Spec is 500W in to 4 ohms at 1% THD. I'm not happy with that way of specifying, but the power should be far more than the Bryston and should allow me to discover what more headroom will get me

I notice that in your last post, you seem to be implying that the amp may not be the problem. I've come to that conclusion. So the upcoming test will probably highlight any deficiencies in the Revels.

I am quite comfortable using REW. Is there a measurement in REW that will highlight the speaker non-linearities? Distortion perhaps?

@lynn_olson 

I forget if I had posted previously that I am running a single 15" HSU sub right now, 800W plate amp. I xover at 120 Hz using a K231 from Sublime Acoustic. The two channels are combined in the sub.That value is higher than most recommendations. I chose 120 Hz because it helped to minimize a big null in the Revels at 80Hz.

So the load on the Bryston is significantly reduced. I'm not sure how much, but probably less than 50%, more than 25%. I'm thinking about adding a second sub.

@lynn_olson 

I've dragged my Levinson no 27 Power Amp out of storage. It is now 30+ years old. I have had it for 20 years. A few months ago, I replaced all the big power supply caps (8 of 'em) with brand new ones and thoroughly cleaned it up. I broke the caps in with about 50 hours of music. But then I put it away. This amp is rated minimum 100W into 8 ohms and 200W into 4 ohms. No 4 ohm speaker limitations. It weighs about 90 lbs.

I've had about 1 hour listening, so maybe too fresh. My initial reactions were that voices were better articulated than the Bryston. Dynamics might be better. I need more listening time, but I am pleased with the change so far.