[john1970]

Fellow VMPS Owners,

I will be receiving a pair of RM40s within the next 2-3 weeks and plan to biamp the bass section for better bass.  The ribbon mirange/tweeter array will run off a NAD C372 (which has an adjustable 2nd preamp out).  The amps that I am considering for the bass section include:

1) Adcom GFA 555 Mk III (Used ~$500) 325 W/channel @ 4 ohm
2) Odyssey Stratos (120000 uF upgrade) (Used ~$900) 260 W/channel @ 4 ohm  (New cost is ~$1.2 K so may even purchase new)
3) Bryston 3B-ST (Used ~$1K) 200 W/channel @ 4 ohm
4) NAD C272 (New ~$500) 160 W/channel @ 4 ohm (Identical amp to the C372.)

I think the Odyssey Stratos is the best buy, but unfortunately it does not fit into my equipment rack (TOO DEEP) so if I purchased the Odyssey I would have to set it next to the rack on the floor which does not look very good in a living room.

What I like about the Odyssey is the large capacitor bank.  It has the largest capacitor bank of the four amps!

Please recommend which of the above four you would use and add any amp (that cost <=$1K used) to your recommendations.

Thank you,

John

[zybar]

Fellow VMPS Owners,

I will be receiving a pair of RM40s within the next 2-3 weeks and plan to biamp the bass section for better bass.  The ribbon mirange/tweeter array will run off a NAD C372 (which has an adjustable 2nd preamp out).  The amps that I am considering for the bass section include:

1) Adcom GFA 555 Mk III (Used ~$500) 325 W/channel @ 4 ohm
2) Odyssey Stratos (120000 uF upgrade) (Used ~$900) 260 W/channel @ 4 ohm  (New cost is ~$1.2 K so may even purchase new)
3) Bryston 3B-ST (Used ~$1K ...

John,

I tried bi-amping a pair of RM 40's with the Adcom and wasn't pleased.  The problem with bi-amping the 40's is that the crossover is pretty high and you need a high quality amp to do the job.

George

[john1970]

George,

Of the four amps I've indicated do you think the Odyssey is the best choice?

Thanks,

John

[zybar]

John,

I am not familiar with the NAD, so I can only speak of the other three.

Out of those, yes I would go with the Stratos.

Personally, I would get a used Sunfire amp in the price range you are talking about.

George

[SWG255]

Bi-amping a speaker in the upper bass/lower midrange as you'll be doing with your RM40s is a tricky business as George has pointed out. It is more important that the two amps used match one another in sensitivity and sonic character than be of the utmost quality. In other words, the normally best sounding amp running fullrange might not be the best amp to use when bi-amping with a different make and model of amplifier. it is easy for two different amps to present two different sonic signatures and thus ruin the coherent presentation of the loudspeaker.

Are you actively crossing over? If so, which crossover and at what frequency and slope?

If you are passively bi-amping then the two amplifiers' sensitivity will be critical, and it can be a real task matching the amps.

I wish you good luck, but because of the foregoing, I'd consider getting the NAD amp.

Or even better, if you are passively bi-amping, run your current amp full-range for awhile until you get used to the RM40s. Then you might have a better idea of where you want them to improve sonically and this will help you choose the right amp to go with them. For example, you might decide on a different amp to run the ribbons.

John,

I am not familiar with the NAD, so I can only speak of the other three.

Out of those, yes I would go with the Stratos.

Personally, I would get a used Sunfire amp in the price range you are talking about.

George

[shokunin]

Ideally, veritcally bi-amping with the same amplifiers (2 NAD amps in this case) would be easiest and provide the best integration between the woofers and the panels.  If you play music through just the woofer section you'll notice quite a bit of midrange through the woofers, which is critical becuase the panels don't extend that low.  Most of the "body" of the vocals will come from the woofers so if you skimp out in the amp for the bass then you may not like the end-results.  

I tried a number of setups with my speakers and ended up going back to a single amp, just sounded better, easier, and cheaper.  If BRian tied the upper midwoofer to the panel section and kept the lower woofer on it's own amp and binding post then I suspect it'll be easier to bi-amp.

[john1970]

SWG255 and Zybar,

Yes I will be passively biamping the speakers.  I plan to use the the NAD C372 for the first few months until I get familar with the RM40s sonic characteristics.  After that I plan to biamp to give the bass a bit more current and more control.   If sensitivity and characteristics are difficult to match the NAD C272 is an easy (and very inexpensive choice @~$600 new).  

With biamping the NAD C372 and C272 I would have 320 W / channel continuous and 680 W / channel dynamic @ 4 ohm!  

Lastly, I will also check out Sunfire amps as well!

Thank you,

John

[opnly bafld]

John,
I have this amp NAD C272 and RM40s.
My opinion is that if you are happy with your NAD integrated when your speakers arrive, you will not benifit by adding a second NAD and if you are not happy with the NAD adding another won't make you happy.

As far as passive biamping is concerned I agree with the other posts emphisizing quality as well as current.
Having tried it myself, one combination(Eagle2 bass- NAD mid, treble) worked well because the bass amp had a little more gain which balanced the sound a little better with my original non CD versions.
Of course you have the ability to adjust output between your integrated and another amp.

[John Casler]

SWG255 and Zybar,

Yes I will be passively biamping the speakers.  I plan to use the the NAD C372 for the first few months until I get familar with the RM40s sonic characteristics.  After that I plan to biamp to give the bass a bit more current and more control.   If sensitivity and characteristics are difficult to match the NAD C272 is an easy (and very inexpensive choice @~$600 new).  

With biamping the NAD C372 and C272 I would have 320 W / channel continuous and 680 W / channel dynamic @ 4 ohm!  

Lastly, I will also check out Sunfire amps as well!

Thank you,

John

John,

I think your int/amp will actually "actively" biamp since each amp will have a volume control.  

So you will be actively, horizontally, biamping

Unless I misunderstand how this works in your Int/amp, you don't have to be as "particular" as to the sensitivty of the second amp, unless it is too low.

With a separate volume control (it reads like it has a separate control) actually onboard the preamp section of your integrated, you whould be able to "match" most amps and use the main volume for Unity Gain for both.

Forgive me if I am mistaken about the secondary volume control of the amp outs on your integrated.

The things to look for are, low distortion --- you want at least a point zero (.0) in front of the distortion spec as in .07%.  Point being (and as others have pointed out, the Midbass Driver of the RM40 comes in at over 200Hz, and requires an amp with enough finesse to handle that region and down.  Additionally the Mega-Woofered Bass System of the RM40, is very low distortion, so you want the amp to not add to that.

You want a high damping ratio, but that is not the most important number.

You want good signal to noise 95db or more.

You want high power and current.  A minimum of 200wpc @8 ohms, but 300+ highly recommended for truly awsome performance.  The amp should have a good stiff "Power Supply" and 4 ohm numbers should be close to "double" the 8 ohm stats.  This inidcates that the Power Supply is adequate to support large demands and power peaks.

These should always be RMS power ratings and not anything else, like "peak power" or IHF numbers since they are somewhat inflated and are not standardized.

[john1970]

john c,

you are correct that my integrated amp has an adjustable output (volume) on the second set of preouts.  From my understanding a maximum volume is 0 dB (equal to the other preamp outputs) and the minimum is -12 dB.

Thank you for your EXCELLENT advice (as always)!

John

[JoshK]

I think what others have said is good advice, but here is my $.02.

For biamping, I would get a used Crown K1 off ebay for around $600-650 that they are going for.  With the adjustable gain that the K1 allows you will find that matching with another amp will be much easier than the other "fixed" solutions.  K1 will make a badass bass amp.

[zybar]

I think what others have said is good advice, but here is my $.02.

For biamping, I would get a used Crown K1 off ebay for around $600-650 that they are going for.  With the adjustable gain that the K1 allows you will find that matching with another amp will be much easier than the other "fixed" solutions.  K1 will make a badass bass amp.

Josh,

IMHO the K1 or K2 aren't good enough amps to play as high as required in the RM 40.  

If you can stay 80Hz or below that is a very different story.

George

[John Casler]

I think what others have said is good advice, but here is my $.02.

For biamping, I would get a used Crown K1 off ebay for around $600-650 that they are going for.  With the adjustable gain that the K1 allows you will find that matching with another amp will be much easier than the other "fixed" solutions.  K1 will make a badass bass amp.

Hi Josh,

I think (and I could be wrong) that he already has "adjustable gain" from his Integreated amp.

It (as I understand it) is a highly unusual Integrated, that actually lends itself to "biamping applications" in that the secondary preamp outs have a "separate" volume adjustment" so that level matching can be done there, onboard.

This might suggest that a Power Amp only would be preferable so that we wouldn't be running the signal through 3 pots.

Maybe John can clarify, but I am under the impression that that is how this Integrated is set up.

I find it quite interesting, and if the on board preamp and the extra pot is of a good quality, it shouldn't sound too bad, with a good power amp running the bass section.

I can't comment either way for the bass quality of the Crowns from 80Hz to 200Hz, since I haven't spent time with any of them there, and haven't reviewed the specs to even have an idea.

That said, I do know that some have "raved" about using some of the Crown, Carver, and even QSC "pro" amps running full range with RM40s.  Hard for me to imagine, not having heard those specific amps in action myself.

[john1970]

John C,

As my previous post you are correct that the second preamp outs have a built-in volume control from -12 to 0 dB.  IMO NAD always does a good job making their integrated amps very expandable and inexpensive.

Thanks,

john

[JoshK]

John,

Your right, I read that about his integrated after I posted.  Even still, I'd recommend the K1 for this purpose.  It is pretty darn hard to beat for a bass amp, or even midbass amp.  

Jon Marsh had a lot to do with the K series design for Crown.  He suggested that it would be fine up to about 300hz, iirc.

[JoshK]

I think what others have said is good advice, but here is my $.02.

For biamping, I would get a used Crown K1 off ebay for around $600-650 that they are going for.  With the adjustable gain that the K1 allows you will find that matching with another amp will be much easier than the other "fixed" solutions.  K1 will make a badass bass amp.

Josh,

IMHO the K1 or K2 aren't good enough amps to play as high as required in the RM 40.  

If you can stay 80Hz or below that is a very different story.

George

We'll have to agree to disagree on that.

[warnerwh]

I found a Parasound HCA 1500A is excellent in the bass on my RM 40's.  I know a couple of people who did an amp shootout using RM 2's and they also felt the Parasound outstanding in this area.  For 500 bucks used they're a great buy imo.  I think gongos has one for sale in the for sale forum but am not sure.

Today I bought a tube amp to try a biamp set up and had planned on buying a 1500A for the bass(tube amp blew up after a minute).  These Parsounds  have pots to adjust level although it sounds like you wouldn't need them.

[dltonya]

I'm running an Acurus a250 for the bass part of my biamped RM40's.  This is an outstanding amp with plenty of power.  Actually, it has a scary amount of power.  It can be had on Audiogon for $450 or less all the times I've seen it listed.

[warnerwh]

I'm going to try a Rotel RB 991 on the bottom of my RM 40's with a Blue Circle BC 24 on top next week.  If I were going to spend more on the bass amp it would be with the Innersound(Coda) that I just sold.  The mids were very liquid on that amp but the low/mid bass was a hair softer than it should be in my room and in my opinion.

[john1970]

warnerwh,

Please let me know what you think of the Rotel amp.  Rotel amps like NAD are in my price range.

Thank you,

John