[YoungDave]

Some of these issues have been discussed in other threads, but not from a tech/wiring POV.

I'm going to biamp my VMPS RM40's with an outboard active crossover.  I have the version without the toggle switch, and the schematic I have is for a toggled setup.  So, I have a few questions & am looking for a sanity check to see if I am thinking straight.

It looks as though there is a 2.8 mH inductor in series with the woofers, which I would think should be removed in a biamp scheme - Yes or no?

Also, it appears to me that the 55.03 mfd series capacitor, the 1.1 mH series inductor, and the 2 ohm series resistor should be removed from the mid circuit - yes or no?

My thinking is that the proper configuration would have the woofs fed directly from their terminals, with no other components in the circuit.  

The mids would be fed directly from their terminals, with no other components in the mid circuit except for the paralleled hi circuit.

The high would parallel to the mid circuit, fed by the same mid terminals, and would include the same 1.37 mfd  cap and .25 mH shunt inductor as in the original configuration - the only components remaing after removing all the passives from the woof & mid circuits.

How say you all?

I'm not sure the schematic I attached below will work, but it is in my album on page 38 of the gallery.

Thanks!

[Occam]

Dave,

I think you'd be better off if you asked your question over on the VMPS Circle where you could get some feed back from those with specific experience.

The 1.1 mh coil and 2 ohm resistor in series with the midranges for a lowpass that filters the hf output which is provided by the tweeter and its crossover. Although you're bi-amping with a line level crossover which would ideally divide the signal between the woofer and combined mids/tweet, you still need that R and L to lowpass your mids.

You also need to take a clue from that description 'Quasi Second Order' which I think refers to the use of both the 55uf cap and the 2.8 mh coil. Note the wire connecting the top of the 55uf cap to top of the 2.8mh coil. I believe this provides a second order lowpass to the woofer and a second order higpass to the mids, but both filters have staggered poles, hence the 'Quasi'. This is not an intractible problem, but will not be emulated with 'standard' line level crossover slopes. It would require, fiddling/calculating appropriate component values to emulate those slopes. I would also think that Brian was quite aware that the impedance seen by the woofer is not a constant, and varies with frequency which effected his choice of components. I don't know if you plan to have your active crossover emulate that 'Quasi Second Order' characteristic or if you'll choose different orders/Qs.

VMPS has a board here, or you could communicate directly with Brian Cheny, which is far prefferable than listening to me.....

Regards,
OldOccam

[woodsyi]

YoungDave,

I have a pair that I am actively biamping.  I am still using the passive x-over between the ribbons.  There maybe a way to reproduce the quasi 2nd order slope by combining active and passive element, but I am just using 24 dB slope active X-over with 200Hz highpass and 300Hz lowpass.  You can audition them if you want.  I am near the Vienna metro.

[JoshK]

I have a question about the toggle switch part of the circuit.  If I understand this correctly, with the toggle switch up, points 1&2 are connected and points 4&5 are connected while 2&3 and 5&6 are open.  Toggle switch down would be 2&3 and 5&6 are closed, while 1&2 and 4&5 are open.  

If this is the case, wouldn't the tweeter be amped while the mids+woofers amped with the second amp?  I have always understood (but never verified) that the mids and tweets would be disconnected from the woofer circuit in biamp mode and the mids and tweets would be driven from the upper amp. The drawing seems to suggest that this is not the case unless I misunderstood the switch.

[YoungDave]

Joshk,that's part of the problem I have - I can't make this schematic representation of the switch work.  However, that may be moot in my case as on my speakers, there is no switch, just 2 sets of inputs.  I guess I'm going to have to open my box up & map out the connections there, and also do a little study of quasi second order filters to see which components I can delete for the lp between the woofs & mids, while leaving the HP between the mids & highs.

Or maybe I'll just take them all out & triamp!

Cheers

[woodsyi]

YoungDave,

After you take the bass woofer out and bunch of fiber glass fill, you can see the the wire connected to the coil that goes to the woofers.  You just unsolder one one wire to bypass the coil and connect it directly to the binding post.  I did not physically removed the coil.  TRT caps are in a huge cluster -- you can't mistake it for the woofer coil.