the best amp to run the bass of infinity RS-1b's

I have a pair of infinity rs 1b's and am running them with a pair of bryston 4b-st's. I have a nakamichi dragon 3 piece cd setup with a nakamichi CA7A pre-amp to the brystons. I have 2 pairs of mit MH-750 CVTerminator II cables to the speakers. I am looking at a pair of Bryston 7b's at 500/ch at 8ohms, 800/ch at 4ohms. Classe Ca-400 400/ch at 8ohms, 800/ch at 4ohms. Mcintosh mc2500 500/ch at 8ohms. Perreaux 5150b at 500/ch 8ohms. I like rock,jazz country and classical. All the amps are for sale in my area and I am wondering which would give me the best punch and sound for the type of music i listen to.

Thanks for the help
Judging from past experiences, i would consider the Classe' and Perreaux long before either of the others. A Sunfire Signature with their factory "low impedance mods" aka "Apogee mods" would also be a good candidate. These are rated at 600 wpc @ 8, 1200 @ 4, etc... Actual clipping power on mine was 780 wpc @ 8 and 1480 wpc @ 4.

As a side note, you better have a healthy AC system if you want any of these amps to work optimally. Any of them will be able to suck a 20 amp circuit dry on momentary peaks if you are standing on them at low impedances. As such, if you haven't already done so, you should get your AC system straightened out first before spending more money on something that you might not necessarily need. My guess is that you probably do need more amplifier than what you have, but assuring consistent power feed to the amps that you already have might be enough to make you think twice about needing an upgrade. Sean
Hi Darin....I have the same speakers you have! Listen to Sean...he has helped me out quite a bit! I also had Bryston 4B's but went with a Perreaux 2150B because it had a warmer sound that mated well with my set up.
The desire for a more powerful amp led me to the 3150B (Sean's suggestion) and I got it. Although I am in the mist of trying to slove a few problems (hum and funny noises), the amp is quite powerful but still retains the warmth and overall synergy with my tube amps on top.

I will watch this thread closly. Good luck

Hi there,

Oke I didn't listen to this amp myzelf(jet) but I hear great things about this amp.

The Crown Audio K2 it's 500w 8 ohm and goes all the way down

I'ts price is about 1300/1400 dollars on internet and damping factor is < 3000 Stereo Times had a great review on this amp. I'm gonna use it on the low of my IRS Beta's

It has a better slam than the Krell kma 200 ect...
This of a friend of mine that sold the Krell after listening to the K2

let me know what you gonna do.


I purchased a Pereaux 5150b, and suposibly in shipping it was damaged. I hooked every thing up and just got a buzz niose from the speakers. If I turn the pre-amp up to just about full volume the buzz would stay the same but I could just hear the music, maybe only a couple of watts of out put. So I have taken it to a shop and hope they can find the problem. I will let you guys know how things turn out.
A friend runs his RS1b's with a pair of older Krell monoblocks on the bass towers, sorry I don't remember the model, and an ARC D250 on the panels. He dispensed with the trouble prone Infinity crossover and uses a Dahlquist active crossover.

Hi Brian, I have also heard some folks doing away with the Infinity crossover. It gives me a little scare to do that although I get tempted now and then. I believe if you use another crossover (bryston, Dahlquist, Merchant) it negates the servo control on the woofers. Some say it sounds better and some say it does not. The Krell amp that a friend of mine has on his woofer towers are the 150 mono's. He retains the infinity crossover.
As to an update on my newer Perreaux that I have had it for a few is wonderful......plenty of power and control!!
Hello again

I finally got my perreaux 5150b back and hooked it up to the woo+ffers of my RS-1b's and I sware you can hear the vioce of GOD! threw them. The system has such a massive amount if impact it makes you laugh. Good live recorded CD's at even moderate sound levels have the same punch that you feel against your body at a rock concert. The sound is so tight and accurat on jazz and country music it's just amazing.
The guys that fixed my amp made a joke and said "OH your the guy that owns the welder" they were taken by it huge power supply, the technition said it hase endless power.

So I am going to play with it for a while and enjoy the beast. I had a second power outlet with a 20 amp breaker allready in the wall for just for my brystons so I sould have plenty for this amp.

Thanks for all your help,

I took the lid off and was inpressed about how have the amp was biult. It has 24 Hatatchi transistors and a massive transformer that weighs about 40lbs by it's self. It has 8 caps that measure about 6" tall and 3" in diamitor. Its just impressive
Help!! I am looking for a pair of 1b's I owned a pair about 15 years ago, got hitched and out they went. Now out went the wife in comes the new system. I just bought a pair of vincent 991 monos but I need speakers. Can anyone help?
Darinkperih: Glad that things worked out for you. I somehow missed both your original and follow-up posts to this thread. Not only am i glad that you were able to get the Perreaux working again, i'm glad that you were at least initially happy with the results. After having the Perreaux 5150 up and running for almost a year now, i'm wondering what your thoughts are now that you've had a good amount of time with this unit. Is it still shaking the foundation of your building or have you moved onto something else? Sean
P.S. On a follow-up to my original post dated 10/25/03 my original 3150B WAS not working as properly as I expected. I tried to eleminate the hum but could not. However, I was fortunate to find another on (here as a matter of fact) that runs and is running beautifully. I keep an eye out for the 5150B however!!
I am very happy with the amp. I took the front face plate and handles off and had it plated a copper black and then epoxyed clear coated. I changed the power Led to an intence liquid red. I have a pair of Conrad Johnson Premier 5's vac tube amps that I had solar copper 5/8 thick glass face plates made up with beveled edges and the CJ logo engraved in the glass in the same font as factory. Now I can see the warm glow of the tubes. The three pieces look awsome now.

I am now tring to decide on what cable to use my RS 1bs, I have Mit MH-750CVT series II and Monster M1.5's. I am looking at PS Audio 12' lab cables or thier 12' Statement cables or may be Mit tube cables, so I am putting up a thread asking about cables

Thanks for your help guys
Darin: Sounds like you've not only got a very nice sounding system, but one that is also quite eye-catching too. I'll keep an eye out for your next thread as i'll be interested to see where you go with cables. Sean
I have an old friend,who is quite an experienced hobbyist,and,record collector.He runs his RS-1b's with Krell on bottom and CJ PREMIER 8's on top.Believe it or not,he is using PHOENIX GOLD speaker cabling throughout.This is really cheap stuff.I auditioned it in a friend's set-up consisting of Rowland driving Kharma's.It was unacceptable in that set-up.However in the Infinity set up it is like the laws of the universe don't apply.UNBELIEVEABLE sound!You may want to check the stuff out.I'm talking about cables that go for about ten dollars for an 8 ft. run.Good luck.
I have two sets of RS-1b's and I want to use one amp to run 4 bass towers with one pair of high end panels..
Anyone know how to do this and what amp could run that type of low impedance load on the bottom?

For the record with my Older RS1'a (RS1a's) I used 2 bryston 4b's which were a bit bright. Also since they don't double wattage as impedance drops I think the Bryston 4b's run out of current.
I have tried driving the low end,bass section of my speakers with a number of amps,most of them disappointed me.The worst were the Classe mono I think model was 350,(cannot remember)second worst were the Bryston 7 monos,third were the YBA Passion 1000 monos(excellent for mid and high frequencies,Acoustic Reality 1000 monos(ICE amps) were pretty good,but better were the Innersound 1KW amps monos, and THE best are the Electrocompanient NEMO monos.The bass speakers in my system have an impedance of 4ohms. The latter amps are currently in my system.
JM Labs Utopia in the Bedroom Ramy ...... You dah man !!!!

Ramy MANY THANKS! I was considering using newer Bryston 4b SST, and also Classe CA-400 or 350..thanks for eliminating the 7 monos,

I met Innersounds 1 man show and I believe him to be an honest fellow- one I would like to support with my purchase.

The Bryston 7b is a bridged design which can not be used with the Infinity Rs1b crossover though.. and looking inside the Electrocompanient Nemo mono

it looks also to be a bridged design (I see two identical chassis components and a bridge wire...... you can not us bridged amps with the bass section of the RS1b's because they will go into positive oscillation. (very loud painful and costly)

In your RS1'bs ..Did you use a different crossover arrangement? I am using the stock crossover. Or are you using different speakers? I checked your system page and did not see RS1'bs, but greatly appreciate your advice anyhow.
Has anyone used a Classe CA-2300 amplifier for the bass on the RS1b's? The rest are driven by Manley Neo-Classic 250's via a Steelhead. As I've never had the desire to change the RS1b's so I want to see them operating for many years to come.
I was happy to find this discussion.  I have a pair of Infinity Betas with CJ Premier 8 on top, and Adcom GFA-565's on the bottom.

Couple of years ago the Adcoms blew (leaking caps) and I fixed them.  They just blew again, and they're going out the door.

So I'm shopping for bass amps.   On my shopping list so far are Bryston, Classe, Ayre, Krell.   Any recommendations?

I never, ever, want to deal with the problem of amps blowing up and potentially smoking my speakers on the way out.


Day Radebaugh
Hello dayradebaugh

are you able to demo the Ayre, Bryston, Classe' or Krell?
For sheer high power- Bryston and Krell will be a sonic match for the Infinity speakers.  Happy Listening!
The better Class D amps can work well on the bottom. Just food for thought...

Bill Watkins Sr, inventor of the Infinity Watkins Dual-Drive woofer (the predecessor to the Infinity woofer used in the IRS Beta) once told me he preferred Threshold amps with the big Infinities.

The Threshold S500 Series II Class A amps with optical bias were a popular choice, with ARC tubes driving the mid/tweeter panels.
A Bryston 4B will work wonders on those woofer towers.
Thanks.  Hadn't considered Threshold, but will put them on the list.  Has anyone heard Spectral driving the woofers?

By the way, I had the woofers rebuilt by Watkins several years ago.  Did a fine job.
Depending on budget, if you’re looking for keepers, i’d look at the PS Audio BHK tube hybrid mono’s or BHK stereo amp. Arnie Nudell said they were the first amps that changed his mind about running pure tube amps on his IRS-V’s. That would allow you to drive the bass & mid/tweeter panels with one pair of amps since they’ll give you some tube goodness.
Good suggestion, hadn't thought of that.  They're out in Colorado, and would be worth a trip from here in Kansas.  Have you followed the discussions and videos from Paul McGowan as he set up his IRS V's?
Hi Day,

Ran across this when looking through the amps-for-sale section:

The Coda guys are ex-Threshold. Their amps have a very good reputation. A very powerful amp that doubles down. Worth consideration.

No affiliation of course.


Thx for the reference.  The Coda is a stereo amp, and I'm limited, in practical terms, to a pair of monos.  

Here's a picture of the system:

This will make you cringe, but the room through the doorway is a dining room, and there's no getting around the issue of having a break in the wall behind the speakers.  I had to run my cables from the crossover (seen in rack at right) into the wall behind it, down in the basement, then up again in the wall cavities behind the speakers with special receps.  It's pretty goofy, but wife would not tolerate cables in the walkway between speakers, so there it is.

Thus I'm constrained to placing amps directly behind speaker towers.  No big deal in the long run.
dayradebaugh4 posts01-18-2017 12:39amGood suggestion, hadn't thought of that.  They're out in Colorado, and would be worth a trip from here in Kansas.  Have you followed the discussions and videos from Paul McGowan as he set up his IRS V's?
I have watched Paul's videos of setting up his IRS-V's. It was quite fascinating. I first heard the IRS-V's back in 1991 & was blown away by their dynamics, awesome bass & ethereal "reach out and touch it' imaging. To this day, they are still the best sounding loudspeakers i've ever heard, but I haven't heard them all. And my Magico S5 Mk2's are still breaking in.
You do have an incredible system- melbguy1

Happy Listening!
Thanks.  The rest of it is CJ 14 and 15, MR-78 tuner, and an old Philips CD-80.  The CD player will be the upgrade after the bass amps are replaced.  If you hear of any IRS-V's for sale, I'd like to know.

I had the Adcom GFA-565's rebuilt 3 yrs ago by a place called Big Sky Audio, Rick Krzemien.  He replaced all the caps.  We've agreed I'll send them back and he'll look them over.  I'd like to fix them, and send them elsewhere as usable monoblocks.  I won't have them back in my system.  I don't expect they have a lot of value, and I don't expect to make much money here, but I also don't want to just take them to the junkyard.  They're cosmetically perfect.

I've looked at the Perreaux Prisma 750.  As Dave said above, I believe one needs an amp that "doubles down".  The Perreaux seems to be a good candidate in that respect.  I'm also looking for an amp that offers DC output protection, and that would include the Classe, Perreaux, and Spectral, and perhaps others that I don't know about yet.  

Although the Perreaux seems to nominally fill the bill, I'm reluctant for a couple of reasons.  First, they don't have much presence in the USA.  Second, I need some amps that will work well with speakers I might buy in the future.  I tend to favor established brands, even at the sacrifice of perhaps some ultimate audio quality, in the hope that 10 years or so down the line such amps would have some value, and also could be repaired if necessary.

It's been so many years since I was intimately conversant with the requirements of the Betas, but are the woofer towers the ones whose impedance drops very low, and require the current levels that these "welder amps" such as Perreaux offer?

Thanks for your input.

5,368 posts
01-20-2017 9:12am
You do have an incredible system- melbguy1

Happy Listening!
Cheers Jafant!
Still looking for bass amps for Betas, but have narrowed down the field.  

Have rejected Spectral, because you cannot connect them to anybody else's preamp, and they won't warranty them with the Infinity crossover in between a preamp and their amp.  Although these amps have a fine reputation, the company is rather difficult to deal with.  Just not worth it.

Have rejected Classe, because of their recent corporate issues--are they out of business or not?

Bryston 7B's on the list.  Cleeds mentions the 4B's, but these are getting a bit old now.  Would the 7B's be a more modern equivalent?

Ayre MX-R 20's on the list.  From all I've learned, they make a fine product.  Going to Colorado soon to audition them.

PS Audio M700's on the list.  dlcockrum mentions that the better Class D amps would work fine.  Is there a particular reason Class D would work well on these woofer towers?  The PS Audio M700 offers a lot for the money.

Texas25 mentions the Crown, which is a good candidate.  Do you need the damping factor on the servo-controlled bass?  How have these worked out? 

Thanks for the help and suggestions.
An Electron Kinetics Eagle 2 (A, B, C, or D version) can be had for around $500. A great amp for woofers. Yeah, it's an old design, but so are the Quad ESL and Magneplanar.