A n00b with questions

johnjen · « **on:** 4 Nov 2009, 07:34 am »

Ok so I've been hip deep in the audio-filic world for a while now but I'm new to VMPS and I'm doing some preliminary research.

I have a small house and I am considering one flavor or the other of RM30's. I will probably spring for the combo deal with a bunch of the tweaks that are offered.

But my question really revolves around what to power them with. I don't really need LOTS of power due to the small listening room but I also don't want the amp to 'work hard' just playing at 'normal' (slightly elevated) levels either.

I have been intrigued with the design of the ARCAM AVR600's power amplifier section. Has anyone tried this combination? Of course the rest of the do-dads will be turned off since I have no need for them. And thus far it appears that the power amp section has not been cleaved out of the 600 and made available as a separate power amp, yet.

Any thoughts good or bad?

I am familiar with tubes (their +'s and -'s) but trying to get at least 150 real watts (or more) out of tubes, while possible is an expensive proposition, not only in initial cost, but in maintenance as well. Buying sets of 8 (or more) matched output tubes can take a big bite out of ones wallet. But the sound is definable preferable to most of the SS designs (thus my intrigue with the AVR600's amps)

Thanks for any and all insights and suggestions.

JJ

JLM · « **Reply #1 on:** 4 Nov 2009, 01:09 pm »

It's important to have enough watts, so that the amp has a commanding grip on the speakers. Here's how to roughly calculate what you need:

Start with the rated speaker efficiency, say 88 dB/w/m.

Next estimate room gain/loss. In a 2,000 cu. ft. room it's pretty much a wash (assuming two channels). Tiny rooms could add 3 dB, huge residential rooms could subtract say 6 dB. Let's figure your room is a 0 dB gain.

Then target the type of music you're most interested in and the typical peak sound pressure (volume) levels. Most experts/sources would use Classical and Jazz peaks run up to 105 dB and rock is a more constant 110 dB. Note that permanent hearing loss/pain starts with extended exposure of 85 dB, so 105 - 110 dB is very loud. Most audiophile gatherings I've been around do their critical listening around 85 - 90 dB. But it's best to oversize than undersize as a speaker can handle a clean load beyond it's rating much better than a distorted signal (from an overloaded amp) within it's rating. To be safe lets use rock and 110 dB.

So subtract the music from the speaker efficiency and add room gain: 110 - 88 + 0 = 22 dB

This means you would need to add 22 dB of gain. The relation between watts and dB's:

1 watt = 0 dB of gain
10 watts = 10 dB of gain
20 watts = 13 dB of gain
50 watts = 16 dB of gain
100 watts = 20 dB of gain
1,000 watts = 30 dB of gain, hopefully you get the idea

So in this case it would take about 165 watts/channel.

Tube amps clip (temporarily exceed rated output) much more graciously than solid state, which is why you can "cheat" the above calculations with tubes.

I'd contact various VMPS dealers or even PM Brian Cheney himself for amp advice.

Zheeeem · « **Reply #2 on:** 4 Nov 2009, 01:46 pm »

I have a pair of RM30Ms in an 11x14 room, and 130 WPC is more power than I'll ever need. I'm currently using a Van Alstine Fet-Valve 350 EXR hybrid. I have been looking at a 60 WPC tube amp as an upgrade (well, lateral really). I think 60 WPC is all I'll ever need in a small room.

Most of my listening is classical/world/jazz - about 60/30/10. I don't listen at headbanging levels, but every so often it can get pretty loud with symphonic or organ music. I've never gotten close to clipping - even demoing to friends.

FWIW, the RM30 is a great speaker.

BobRex · « **Reply #3 on:** 4 Nov 2009, 04:54 pm »

I'm going to give you a slightly different view on RM30 power needs. I have RM30Ms with all of the mods, including the BPS mounted in the outboard crossover. I only need an amp for the mid panels up (from 280 Hz to infinity.) Given that most of the power is needed for bass, and given that the mid sensitivity is 93dB, I can get by with a small tube amp for the mids and tweeter. In fact, I run a 2A3 SET amp (3.5, maybe 4, watts) and for most of my music (classical, jazz, folk, and prog rock), most of the time, it sounds incredible. For reference, my room is 21x17x16 (cathedral ceiling) with wall-to-wall and large furniture.

Now I'll admit, I have considered changing the amp out for some more power. I'm thinking about an Atmasphere S30 (30 watts), or maybe Roger M's EM7 monos (12 watts), or even his OTL (15 watts?) (if he ever releases it), or maybe an Almarro 318B (16 watts.) But at this point, I'm not in any hurry.

Bottom line, you may not need as much power as you think. If you use JLM's numbers and substitute 93dB for the speaker sensitivity (which is the published sensitivity of the RM30s), you will see that 50 watts is more than sufficient. If you drop 10 dB from your max level (and really, 110dB can be painful in a small room) you can be successful with 5 watts. So a nice 30 watt tube amp would be fantastic. In fact, if you read Roger Gordon's RM30 review in Positive Feedback you will see that he uses a 30 watt SET amp and is very happy.

woodsyi · « **Reply #4 on:** 4 Nov 2009, 05:32 pm »

As a point of reference, 8 watts of SET was not enough for both the mids and the twitter. 20 watts SS Class A was not enough for listening loud either, which I would think means lack of head room. 80 push-pull tube watts are more than enough on the ribbons. This, BTW, is on a pair of 40s.

Scottdazzle · « **Reply #5 on:** 4 Nov 2009, 06:04 pm »

I have run my RM30M speakers with a Music Reference RM-200 with no hint of trouble. My room is small and I never listen at 100dB.

JLM · « **Reply #6 on:** 4 Nov 2009, 06:23 pm »

In a 2,000 cu. ft. room I tried 7 wpc into 90 dB/w/m speakers for mostly jazz/classical (and I'm no headbanger). I knew this wasn't enough by the numbers (that was 35 watts), but was fascinated with the amp. Then I moved to 40 wpc, wow! My polite dinner guests (speakers) turned into NFL linebackers in tuxedos. Better detail, imaging, and dynamics. Plus more bass.

So, can you get by with less? Sure, but what will you be missing? Note that classical has 30 dB peaks (that's like going from 5 to 5,000 watts).

BobRex · « **Reply #7 on:** 4 Nov 2009, 07:44 pm »

JLM - I assume you were running your flea amp full range. If that's the case, then I agree that you'd need more power - and said as much in my initial message. But, I'm not running full range; taking the bass out of the picture makes a big difference.

The OP was apparently considering 150 watt tube amps. I wanted to point out that you can be successful with much less. Hence my recommendation of 30 watts.

JLM · « **Reply #8 on:** 4 Nov 2009, 08:45 pm »

You're right BobRex, once the heavy lifting (bass) is out of the equation, the amp's job is much, much easier. But my mistake was assuming that I don't listen much above 90 dB, even with peaks, so I could skimp on wattage. That was a mistake. Now I follow my own advice. The commanding grip that 40 watts, with substanial power supplies, provides really makes a difference. Kinda like driving a BMW with really skinny tires versus nice fat tires on a curvy track.

johnjen · « **Reply #9 on:** 6 Nov 2009, 05:29 am »

Thanks everyone for your input. The reason I was figuring ≈ 150 watts is I'm planning on (initially) using just one amp and bi-wiring and not wanting to 'tax' it while going for the bottom end.

Also I noticed that the AVR600 is a relative unknown, which doesn't surprise me since its rather obscure and aimed at a non audiophile niche market. But the review done by Moncrief at IAR was nothing short of superlative. So I was looking to see if anyone had some real world experience with this semi-new class of power amp.

Oh yeah the reason that 150W is a 'target' is due to the dynamic range of peaks (especially bass), rather than the relatively low power needed for mids and highs.

JJ

woodsyi · « **Reply #10 on:** 6 Nov 2009, 02:49 pm »

200 Watts in pentode did good enough job running my 40s. You wouldn't know what you would be missing until you go active and run the woofers with 1000W ICE amps. Then you know that the bass can be so much tighter. I am not fond of class G amps but Arcam may have found a way to tame the harshness. Even big ass tube amps have low damping power for woofers (compared especially to switching amps which I think are perfect amps for large woofers and not much more). I would only use tubes on the ribbons on RM series if I am biamping. I would go with a big and refined class A/AB (and probably expensive) SS amp if I am driving the whole speaker.

Just my 2 cents.

BobRex · « **Reply #11 on:** 6 Nov 2009, 04:43 pm »

JohnJen - I'm still not sure that you are going to need 150 watts. That's roughly 22dB of gain; add that to the 93dB sensitivity of the RM30s and you can get a maximum output of 115dB. That's damned loud!

Now, as far as "taxing" the amp is concerned. Get on the Stereophile site and take a look at the distortion graphs of amplifiers under review. For reference, I'm looking at the Chord SPM650 (130 watts) right now (March 2009 issue). If you look at the THD graph you'll see that the minimum distortion levels out between 30 and 130 watts, with the THD taking off as the amp clips. The distortion levels start at 0.1% at a 10th of a watt, drop to 0.04% at 1 watt and ultimately level out at .009% at 30 watts. This is common behavior for a well designed SS amp. Most listening with RM30s is going to be under 30 watts, and if your average levels are around 80-85dB - under 1 watt. So in reality, your 150 watt amp is going to be "working" (meaning generating more distortion) harder at the lower power levels than it would at max rated output. Now, in reality these distortion figures may below perception, and THD isn't the only distortion that's critical, but this measurement goes a long way to disabuse the idea of an amplifier working hard with a benign load.

Look, all I'm saying is there are other factors to consider beyond power, even in the bass.

doug s. · « **Reply #12 on:** 7 Nov 2009, 06:38 am »

you definitely want to go active bi-amping, w/a powerful (doesn't need to be expensive) s/s amp on the woofers, and a nice tube amp on the upper range. if your room is small, you should have more than enough power with even 15wpc. fwiw, i took my 40wpc set tube monoblocs over to woodsyi's, and they drove his rm40's as loud as necessary, imo, in his decent-sized room, w/his ice-power amps handling the low frequencies...

doug s.

Hipper · « **Reply #13 on:** 7 Nov 2009, 10:22 am »

I have RM30Ms with internal crossovers in a 13' x 8' x 8' high room. I use one Son of Ampzilla amp biwired. My set up is at the link:

http://www.audiocircle.com/index.php?action=systems&sa=view&sys_id=783

There are also some pictures in the gallery here:

http://www.audiocircle.com/index.php?action=gallery;area=browse;album=1085

My set up is for 'nearfield' listening with my typical listening levels being around 75dB, mostly folk or folk rock type music.

The SoA, whilst solid state, is said to have some tube characteristics. All I can say is that I love the combination.

JLM · « **Reply #14 on:** 7 Nov 2009, 10:37 am »

Years ago I had a chance to listen to active versus passive versions of the same speaker (Paradigm Studio/Active 20s, small 2-way standmounts). No contest. Flatter frequency response, much more dynamic, and gobs of deep bass. Bystanders were slack jawed. After 35 years into audio, one of handful of epiphanies for me. Unfortunately audiophiles are driven to buy as many components separately as possible rather than give up the equipment hunt.

So start with the cheaper, big solid state amp that can eventually be your bass amp.

johnjen · « **Reply #15 on:** 8 Nov 2009, 06:49 am »

JLM
I'm confused on your last post.. Are you saying that passive approach (less complication, fewer components) was the better approach?

JJ

JLM · « **Reply #16 on:** 8 Nov 2009, 10:08 am »

Thanks for reading my post.

Yes, less complicated is best (I run single driver speakers so no crossovers with monoblocks and no pre-amp in a single source system). Actives provide for less complication for the overall system (and they kick b*tt!). The secret is allowing the amp to directly "sense" the driver load and so "react" better to it without the masking of the crossover and complication of multiple drivers. You're also letting the speaker designer pick the amp and eliminating the speaker cable. This effect is far more amazing than most could ever imagine (there's an AC thread ongoing regarding Audio Engine A2 and A5 active speakers in the Cheap and Cheerful circle above to give you an idea).

Theoretically an external crossover would be subject to less microphonic distortions (not getting rattled by the higher pressures inside the cabinet). But that factor is way, way down on the list of what makes good speaker design/performance. The same argument gets made for having the power amp attached or internal to the speaker cabinet as active designs do. But PA speakers, with their very high sound pressure (volume) levels all do it with no apparent problems. Those who argument this point have never done the active/passive comparison like I did years ago.

johnjen · « **Reply #17 on:** 10 Nov 2009, 06:44 am »

And in that same vein I long ago learned that a simplier system, ie. fewer active and passive components make better music, providing the components in use are complimentary to each other and to the system as a whole. This 'dynamic' compensation of the strengths and weaknesses of all of the parts if/when achieved can startle and amaze.

Having stumbled upon this only a few times in my 45+ years of audio involvement, it remains my goal to achieve and then hang onto it yet again.

JJ

JLM · « **Reply #18 on:** 10 Nov 2009, 10:33 am »

One reason why I like VMPS (espcially the 626) is the use of extended midrange ribbons, it adds coherence across the heart of the frequency spectrum.

With simpler systems you're cooking with less spices to disguise or cover for poor quality ingredients.

Hipper · « **Reply #19 on:** 10 Nov 2009, 11:08 am »

I had a trial of Cain and Cain's Abby (single driver) speakers in my 13' x 8' x 8' room and no matter how I placed it the sound suffered the same problems as for other speakers I trialled, namely far too boomy bass.

This wasn't the fault of any equipment or the speakers but of the room. This was my epiphineous (!) moment, namely I should address the problem of speaker and room (and room contents) interaction before improving anything else. I did this with the use of acoustic foam and a digital equalizer. I had already discovered the benefits of nearfield listening.

Once I'd done this, I gambled on VMPS speakers - I couldn't trial them. The gamble paid off! I've no idea how the Abby speakers would work under my new conditions and feel no need to find out. The difference the foam and equalizer has made is more significant then any other alteration, be it equipment, cables or support.

So to summarize, without the perfect room, I would not be without acoustic treatment and a digital equalizer, whatever equipment I used.