Powering Infinity Prelude MTS

Wanted some input on how you's with the MTS are powering them and which way you prefer.

Do you power them with just speaker outputs from your amp?
Do you power them with the output from your preamp and then your amp?
There may be some with other type systems... chime in.
Which do you prefer? Why?

Have been trying both ways and can't really tell much of a difference except for the bass.

Seems like I get a little more bottom end with direct from my amp.

Short info on my 2-channel system...

Speakers: Infinity Prelude MTS
Preamp: Krell Audio Video Standard
Amp: Krell KSA-250
Cables: Monster Sigma
I connect the entire system direct to the amplifiers (Wyetech Labs Topaz SET mono-blocks or Bryston 14B-SST2 s/s amp). Nice speakers, but one of the mid-range drivers and a tower woofer has started buzzing with certain types of music... hope I'll be able to source new drivers...
Yea, I feel your pain.
Haven't had that problem since going with Krell amplification. And we play LOUD!
Had 2 midranges that had started buzzing when I was powering them with my Phase Linear gear. No problems now. Maybe just a coincidence?

You can still get the Woofer & Tweeter through Harman. Already got a backup of both just in case. Paid around $54 for each one, through Harman, about a month ago.

As far as the Midrange Driver. Good luck. Finding those are TUFF.
Have two I purchased last year for the same reason.

It definitely shouldn't be your amps. You have great amps there.
Some were over-driving them with lesser amps.

Have you ever tried the hook-up from your preamp?

Thanks for your 2 cents...
Hi Joysjane, thanks for the heads up re the woofer and tweeter. I don't think it's an amplification issue as I can hear a slight scraping sound when I push the particular mid-range and woofer manually with my thumb(with no music playing) to simulate an excursion. There is no scraping with the other drivers.

Where did you source the mid-range unit from last year?

No, I have never tried hooking the pre-amp direct to the woofer. I use these speakers as a secondary system and therefore haven't experimented with them much in the year and a half or so that I've owned them. One thing I haven't been able to nail perfectly with regards to speaker positioning is image stability and focus - my PMC speakers always seem to 'lock' vocals more tightly between the speakers than the Preludes - do you toe in your speakers, and if so, at what angle from the listening position? Also, how far away have you kept them from the back walls?
Yep, definitely the voice coil.
What I meant by amplification was that people were pushing the Preludes too hard with lesser amps and ending up damaging the voice coils. Mostly folks with receivers.
You wouldn't have that issue with your amps.
I didn't mean that it was your amp that was the problem.

I was lucky enough to catch Harman at the beginning of last year when they happened to have gotten some midrange drivers in.
I was on a list to have them contact me if they had gotten some in stock.

Harman said they (MTS' Midrange Drivers) won't be available through them anymore.
I still keep contacting them just in case.

Once in a while you can find someone selling them on ebay.

I do have mine toed in. They're focused about 3' behind my listening position.
I've had the best luck with them 4' from the rear wall and 3' from the side walls.
I'm 10' from the speakers and they're spaced about 10' apart.

How are your speakers set up from your listening position? Distance, width, toed?
Have you experimented much with different placement?

They're sweet speakers!!!
Agree these are very beautiful speakers. I drive mine with 12 watt Wavelength Cardinal 300B monoblocks, and haven't had voice-coil failure. I don't have them toed-in.

For owners that have had problems, it's a shame that Harman Kardon doesn't provide better parts support.
I have done very little experimentation thus far with these speakers as I haven't had the chance to use them much. I originally set them up almost face forward and about three feet from the back wall. I later tried toeing them in significantly and pushing them back closer to the wall, which resulted in a smaller but more precise and focused sound-stage. I have also only applied RABOS only once, before I adjusted their positioning, so I need to do that again at some point. The volume control of one of the woofers has come off, which I will have to get fixed - yes, the QC issues are a bit tiresome. I'll probably spend more time experimenting with them one of these weekends.

Agree that these are very good speakers in a number of ways, especially for use with lower power amps. They are a bargain used - a very neutral speaker with innovative design features for relatively little money on the used market.
Did you know that the Infinity RABOS website has a calculator that computes the settings when you input the meter readings?

The RABOS means that the distance from the back wall isn't critical. I recommend no toe-in. The listening position should make a close triangle with the distance between the towers, e.g., if towers are 7' feet apart, then your ears should be circa 8' back from the center point between the towers.

I doubt that the volume knob was a QC issue. Are you the first owner?
Hi Jburidan, I didn't know that, thanks for the heads up. Will try positioning them as advised. No, I'm not the first owner, I bought these last year (or was it the year before?) for a second set up used but in good condition. I was looking for a reasonably efficient speaker with an active sub and a small footprint, and these checked all the right boxes on paper. I have enjoyed their relatively uncoloured and lively presentation, and certainly feel I can as yet get more out of them with a bit of work.

The volume control was working fine until last month when I gently turned it to lower the sub's volume and it fell back into the sub enclosure. The sub spikes have also come off as they were glued to the base, and aren't the screw on variety. So I do feel that Infinity packed in the technology but scrimped on build quality relative to its high price tag when new... even though the couple of problems I've had (other than the mid range driver) are niggles, such an expensive speaker should function flawlessly for years. Glad that it sounds good though.

The original spikes screw in. Sp the first owner must have glued after-market spikes on them. If you're handy, recommend you try to fix the volume knob yourself. Also, when you do the RABOS measurements, make sure the tiny pots are all in the fully clockwise position. I love these speakers with 300B SET amps.
Thanks, I will check the bases and see if I can source the screw on spikes. Speaking of SET amp friendly speakers, have you compared these by any chance to Avantgarde or similar horn speakers? Any thoughts?
I own Tannoy 215 DMT II speakers rated sensitivity 101dB. Dual concentric 15" drivers with compression horn tweeters, i.e., one of the greatest speaker designs ever made. I love both the Tannoy and the Prelude MTS, but they sound totally different.
Those Tannoys are studio monitors, correct? They look huge. I also own a pair of studio monitors, the PMC MB2s, and no home speaker I've owned matches their lack of compression and clarity. Unfortunately they require a good few hundred watts of clean power and a medium sized room to come alive, hence my foray into efficient speakers for a tube based second system.
Yes, the 215 DMT II is a huge professional studio monitor, a.k.a. the poor man's Westminster. They look ugly unless soffet-mounted, but sound wonderful. and express every nuance even at very low volume. The Art Audio Jota HC amps with 300BXLS tube drives them nicely.
Hey again Viajero5000,

I did a little experimenting with hooking up the Preludes via the separate component guide in the owner's manual. The bass modules driven with the preamp using the internal 850w internal amplifier.

I found that the bass amp in the Infinity's didn't have the control over the woofers as well as the Krell amp does.
Was listening to an SACD of Boston and had the woofers reaching their limits and started to distort. Granted that's at quite loud listening levels. At that same level I had no such issues with the KSA-250.

You would think the 850w BASH Amp inside those subs would outperform the 250w of Krell amplification. Not so!

Will be going back to hooking up the Infinity's directly from the amp.
One hook-up sends line-level signal to the BASH. Second hook-up sends speaker-level signal to the BASH. Either way, BASH powers the MTS sub. I might be mistaken, but I'm pretty sure.
Hi Joysjane, my understanding is also the same as Jburidan's... feeding the signal from the amp does not cause the sub-woofer amps to be over-ridden by the external amp, the subs are always self powered. I'm guessing what you may be hearing is the difference between the amplified vs the unamplified signal. Perhaps it may be worth checking what the speakers' user manual recommends between the two?
An engineer from Harman who helped me with the initial system set-up, recommended using line-level to the sub. If you switched to speaker-level, I believe you'd have to re-run the RABOS CD tracks for making the final system adjustment.

Would that engineer know if you're running speaker level input to the Preludes whether or not you're by-passing the subs amp?
I've noticed when I run line level input that the front of the sub gets warm where the sub's amps are. When I hook it up with speaker level inputs that that area wasn't getting warm.
I too could be mistaken... I just assumed that the sub's amps were being bypassed.
I haven't read anything in any of my manuals indicating that's the case. I think some furhter searching may be in order for me to verify.

I think the plate amp is Class D, so it shouldn't radiate much heat in either case. I don't know much about Class D amps. But I think they were developed for automotive applications.
Hey guys,
Just a follow up after finding out about line vs speaker level input.

Got and email response from Harman...

They confirmed what ya'll said.
Makes no difference whether feeding the Preludes line or speaker level. They both go through the sub's amps.

Thought that was nice of Harman. I actually got a personal response from one of the designers of the Prelude MTS'!

Thanks again for ya'lls input.
Thanks for the update. These are extremely good speakers. It's a shame that Harman quit making them.
Is thre any way to power the subs with external amps?
I don't believe so, but I've never tried.

Im jumping on this thread because its hard to find other Prelude MTS owners. I've never likes the sound of the preludes and was hoping for your feedback...

My two primary complaints are:
1) high-end is very bright
2) difficult to optimally place towers when on subs as subs perform better in different locations.

I listen and measure frequency response with REW (mic and frequency sweeps that show frequency and time domain measurements, often used for room correction and/or digital x/o).

My related components are: "audiophile" pc Jriver MC playing redbook, 24/192 and DSD files -> firewire -> Mytek 8x192 m-ch Pro DAC -> Lexicon MC12 in analog bypass mode (to only use volume control) -> Theta Dreadnought m-ch amp

Do any of you share my feeling of overly bright and imperfect integration of sub with tower?

Thanks in advance!!

1) I agree that all signals to the sub use the sub amp

2) I've deciphered the switch positions one the sub (1, 2, 3) and what they do in various configs (basically pass speaker signal (vs line) or not; filter frequency response to sub or not (set high frequency limit, i.e x/o or none)

3) Im still testing line vs speaker connection to sub, but will likely use line, si I can bypass internal x/o in tower and sub and drive as 4 speakers using digital x/o to flatten frequency response (remove brightness and adjust for room nodes)

...Just trying to be helpful
I have never, never, ever have the problems you are speaking about. The Preludes have been stellar in every way since I got them in 2001 or 02. They are easy and unfussy to set up in my rooms. They sound great, never bright, they throw an awesome wall-to-wall soundstage that is deep and well layered. Lovely smooth treble, bass to 25hz. The Midrange is right on the money. Great height to the performers they sound life-like and as real as it gets. Piano, Wow, bass Drums, Wow. Great PRAT depending on amp. I have used with great success the following:

Cary v12
Cary 300B SEI
Golden Tube 300B
Leben CS600
Music Reference RM 10
Cary SLP 98
Audible Illusions M3A
Conrad Johnson PV10AL
Primaluna Dialogue 1
Rega 3 with various, Grado Platinum at present
Cary CDP
Sony as above, but with Modwright mods
Bel Canto DAC 1
Eastern Electric Mini Max DAC

Speakers are terrific and I always wondered why this line wasn't more successful? Especially for low-powered amps. Easy 6-8 ohm impedance, 96db sensitive with built-in bass to 25Hz.
Winslowst, I've just logged on to AG after a very long time, but FWIW I have never found the Preludes to be bright in any way - they work very well with my tube amps, neutral but not at the expense of musicality. The problems I've had are a buzzing mid-range driver and a broken sub volume control. Otherwise I don't think I could've done much better for what I paid for them.
Hey Winslowst

Been a while for me to have been on a-gon myself. Had to get over the new a-gon, me hates change!

As far as my MTS' ever sounding bright... I've never had that problem. And that's with me driving them with my Krell KSA-250.

Maybe our room has enough fabric furniture, drapes that cover a whole wall, carpet and a huge amount of space behind my speakers to tame any brightness that may be there. I don't know!
They've always sounded absolutely awesome! Not just with the Krell either, with my Sim Audio, Legacy-Audio, Musical Fidelity KW, Sunfire & even my old Phase Linear gear.

Also never had any problem with the subs to seamlessly integrate with the towers. No time coherence issues.

The only thing I was thinking of doing once was to separate the towers from the subs but, never was able to get the stands for the towers.
To be perfectly honest, I'm not sure that would be a good idea anyway seeings how the designer built them to be mated together.