biamping VMPS RM40 with 770 and tube amp

Hello,
I need help from all you experts. I recently acquired these speakers along with an Acoustic Research VT 100 (the original) amp at a very reasonable price. These are probably "higher end" then Outlaw 950, but the price was too good to pass up. I want to see if I can make this work. VPMS comes with a switch that allows biamping without external crossover. One set of terminals goes to 2 woofers and the other set goes to the midrange and the super tweeter. Can I use 2 channels of 770 to drive the woofers and ARC VT100 to drive the mids and up using 950 as preamp? If so, how do I set up the two amps? Do I need some sort of input gain control device between the amps and 950? In addition, how do you connect ICBM when you biamp the front speakers?

As you can see, I am new at the "audiophile" stuff. Any advice is welcome and please don't assume that I know anything.

Thank you,

You would really need to know what the crossover network requirements of your speakers are (what crossover frequency etc) and what the nature of the crossover is that is included in the amplifier. You will need level controls on at least one of the amplifiers (the one with the highest gain), and you will need some way to determine what the response is that you are achieiving (like an RTA program and a calibrated microphone). It is not a straight forward exercise to actively bi-amp any speaker, and there is some technical expertise required. If you decide to proceed, just be careful about what you are doing, as you can easily blow the drivers in the speaker system if you hook things up wrong.

Soundhound, thanks for the reply.
Here are some informations from a review.

Each speaker has two 9" woofers (actual measurement), four 3" x 6" foil planar drivers and two 1" spiral ribbon tweeters. Impedance is a "steady" 4 Ohms (3.6 minimum), and due to the ribbons, primarily resistive above the 166 Hz crossover point. Crossover slopes are 6 dB/octave, and efficiency is 90 dB.

For biamping VMPS suggests the following.

By switching the toggle to the UP position it is possible to biwire or biamp the system with no additional outboard crossover. The woofer is placed on one circuit accessible through the UPPER input terminals only. The ribbon mids and tweeters are accessible through the LOWER set of input terminals,
Biamping with non-identical amps, particularly solid state bass amps plus low-power mid/treble tube amplification, requires level matching by the mid/treble amp. Most tube amps have higher input sensitivity than solid state amps. It is advisable to use a mid/treble tube amp with input level controls. If your amp lacks such controls a passive input level control (also called a passive preamp) can be used in front of the amp inputs to match levels by turning down the mid/treble amp relative to the bass.

I am planning on using 2 channels from 770 for the woofers and ARC VT100 for the mids and tweeter. The specs on VT100 is as follows:

POWER OUTPUT: 100 watts per channel continuous from 20Hz to 20kHz. 1kHz total harmonic distortion typically 1% at 100 watts, below .05% at 1 watt. Approximate actual power available at "clipping" 110 watts (1kHz).

POWER BANDWIDTH: (-3dB points) 15Hz to 80kHz.

FREQUENCY RESPONSE: (-3dB points at 1 watt) 1Hz to 100 kHz.

INPUT SENSITIVITY: 1.9V RMS (Bal or SE) for rated output. (23.5 dB gain into 8 ohms.)
What is the input sensitivity for 770?

INPUT IMPEDANCE: 200K ohms Balanced, 100K ohms Single-ended.
OUTPUT TAPS: 8 ohms, 4 ohms.

OUTPUT REGULATION: Approximately 0.8dB 8 ohm load to open circuit (Damping factor approximately 11).

OVERALL NEGATIVE FEEDBACK: 10dB.

SLEW RATE: 15 volts/microsecond.

RISE TIME: 3 microseconds.

It looks like I need a passive preamp for the tube amp. What would you suggest? Since 770 is not balanced, I would use the single ended outputs on the ARC amp, right?
I don't recall 770 having output taps for 4 or 8 ohms but it shoudn't have any trouble driving 4 ohms load, right?

I don't want to blow any drivers. So, any advice you can think of would be very much appreciated. It may be that the whole thing would sound terrible and all the components are mismatched. The "audiophiles" don't use 770 in reviwing these speakers and probably poo poo on my trying, but I am banking on it being good enough to drive the woofers. Out of my ignorance, I am willing to give it a try. Afterall, isn't there some Sissypussian (sp?) joy in endless tweaking.

It appears that your speakers still retain the internal passive crossover network when the switch is thrown. If this is indeed the case (and this is very important since running a tweeter without a high pass network will destroy them), you should be able to just hook up the amps, adjust the relative levels, and your'e good to go.

I would hook up the amps even if they don't have level controls to see which one of them is too loud. The louder one is the one you will have to use a volume control with. A simple potentiomenter that you can buy at RadioShack will suffice. A 10K ohm audio taper or thereabouts will work fine. If you don't feel comfortable with soldering and drilling, a passive preamp will also work - just keep the interconnects coming from it's output very short - under 6 feet.

I don't have any specific preamp to recommend since I generally build my own stuff, and only buy "store bought" when necessary, like a DVD player or something like that.

Threers-

I am going for the exact similar setup, except not bi-amping. (RM 40's w/770 amp). How does it all sound? Is th 770 a good match? Should I bi-wire, or just run simple jumpers for now?

Thanks!

sbcgroup1,

I would just use the jumper or biamp if you have another pair of cables, but while you get good sound out of RM40, you don't fully tap their midrange potential with 770. I went with biamping because a quality high current amp (that would drive the woofers and be "musical") would cost thousands even used, whereas a good class a or ab tube amp will do justice to the highs and mids at a much reasonable cost. You will have to get a passive preamp or an DIY attenuator to balance the two amps. Much depend upon your room accoustics and cleaness of your power. I ended up putting in a dedicated 20amp outlet, rearranging a few things and putting up tastefull wall hangings. Just beware, there is no end to tweaking for that extra "euphonia". You have to find the best sound you and your room can get for the money you are willing to spend and be happy with it, because there will always be someone posting obout a system that sounds better, usually at a price that excede the GNP of Tanzania.

Good luck and you can check in on audiocircle.com and read up on all things done to RM40.

Threers-

I just spoke to John Casler over at Summit A/V in Los Angeles last night and I'm going to go with 2 Earthquake Cinenova 3 amps (600W x 3 at 4 ohms). He says he uses them to demo the VMPS systems and that they are on par with Krells, etc. He said the power on tap is awesome and an ideal match for the RM40's, etc. The price he can give them to me is very favorable and much cheaper than the 770 is. If you want his number, I'll give it to you, and tell him I recommended him to you. And I guess I'll probably just say goodbye to bi-amping for now and just use the trusty 'ol jumpers.

Later-

-Ed

Threers-

If I make it so that two of my 15A wall outlets are running on 20A circuit, will I have to change to a 20A recepticle? How would this work? Use an adapter? How would I do that if I wanted to use a good power supply/surge suppressor w/the Cinenovas?

I'd change those outlets to 20 amp receptacles. It's not that hard to do actually. I forget exactly what the price would be, but I think you're only looking at a buck or two for each outlet.

sbcgroup1,

Can't you get a shorter moniker? (tic)

I had a 2 20 amp lines put in using proper wires and circuit breakers but kept the normal 15 amp recepticles for the reason that I did not want to use adapters. I just wanted a robust circuit for the amps. All protections are done at the line conditioners and surge protectors, most of which are rated up to 15 amps anyway. So, if not having 20 amp recepticles limit my current supply, I am ok with 15 amps. The main thing for me was to get separate lines without branching outlets to insure that I get the cleanest power I can get from Virginia Power.

You may know this, but I thought I'd better mention changing your 15 Amp outlets to 20 Amp outlets does not give you a 20 amp circuit- not without a 20 amp breaker and, I believe, minimum 12 gauge wiring in the circuit. Besides, you will probably want your 20 amp circuits to be dedicated to your amps. Good luck!
By the way, Ed, are you saying the 2 Earthquake Cinevova amplifiers (6 total channels) are less money than the 770 (7 channels)? These are new?

Ed?

Cinenova grand 3 is 3.5k new. So I am assuming you mean 2 channels of this is what you will use with Rm40. If I am wrong and you are getting 2 amps each with 3 mono-aural channels, each weighing 120lb (ouch!)for less than the cost of one 770, give me john's number.

I think you are going to have to run this with a tube pre and not an ss pre.

I can not in good conscious say it's a good idea to put (or leave) 15 amp receptacles on 20 amp lines. You can get receptacles that don't need adapters. They're very easy to find at a major store, such as Home Depot. In all likelyhood he won't ever draw more than 15 amps at all, let alone long enough to fry the receptacle, but as long as the possibility is there he should fix it. Like I said before, it only costs a couple bucks and can save your house. That seems like a worthy investment to me.

Also, we don't know exactly what will be on the line in the next few months when he makes his purchases because he doesn't know yet. We also don't know what will happen years down the road. Don't say just upgrade then, he may not remember. Just do it right now and there are no worries.