VAC Sig Ren MK2a Headscratcher


I am thinking about adding a solid-state amp (DNA-500) to my system to drive the bass cabinets of my VR-7se's. Currently I have 1 set of balanced outs going to 2 VAC 300.1s that are each driving a VR-7se speaker full range. The other set is driving my subwoofer.

If I disconnect the sub and hook up the 500 to these balanced outputs from the pre, with the 500 speaker outputs going to the bass cabinets of the VR-7se's, will this work? Only problem I can see is that both modules of each speaker will be receiving a full range signal, but only using a portion of it depending upon the drivers. Balancing will be a snap as the volume control will control the 500, with the attentuating knobs on the VACs available to balance the rest of the speaker to the bass.

Will I be doing any damage this way? Is there a better way to do this w/o complicating things with crossovers, etc? Does what I'm proposing make sense? The 7's love power and I had the DNA-500 sitting in a closet.... Seems like this way I can get the best of both worlds, with about 750w going to each bass unit and 300 VAC tube watts (50w+/- Class A) going to each mid/tweet/super-tweet module. On paper, seems like a great idea, BUT...Before I go very far down this path, I'd really like to get some feedback and answers to these questions above.

Thanks in advance for any light you can shine in the tunnel.. :-)

BTW- just replaced noisy Dragon 6dj8 pre driver tubes with Seimens NOS 7308's - quieter(obviously), better imaging, bigger soundstage, more air and a bit tighter bass - after 1 hour!! Will only get better - more expensive but worth it IMHO. YMMV.
fplanner2010

Showing 3 responses by almarg

What you are describing is a conventional passive bi-amp arrangement. It won't do any damage. The crossover circuits in each of the two sections of the speaker will filter out frequencies that should not be applied to the corresponding drivers, just as they do in your present configuration.

I believe that your preamp has a transformer coupled output, which results in a low output impedance across the entire audible frequency range. If so, there won't be any impedance compatibility issues driving the DNA-500's relatively low input impedance (10K iirc).

Given that, the major question as I see it is how coherently the sonics of the two different amplifiers will match. But since you already have the McCormack amp, there would be nothing lost in giving it a try.

Obviously, when you do this any connections that presently exist between the two sections of each speaker, either directly or through bi-wire cables, should be removed.

Regards,
-- Al
Steve McCormack as quoted in this review:
The DNA-500 is a Class A/B amplifier that's biased fairly rich. Because I don't have to use extremely high voltages, it runs only warm at idle and I don't need a huge amount of heat sink surface area. If it were pure Class A, I would have had to use a huge heatsink to dissipate all that continuous heat. The heat sink in the DNA-500 is actually quite generous and can handle extreme operating conditions, including very low-impedance speaker loads.
As Steve explains elsewhere in the review, the need for extremely high voltages is avoided by incorporating two amplifier circuits, bridged together, for each signal channel (left and right).

Enjoy!

-- Al
... the ability to finally drive the bass enclosures of my 7se's like they were made to be driven means I should no longer need my sub (except maybe for movies).
I suspect that if you connect the sub you would be connecting it to your Integra processor, and using the preamp's cinema (home theater bypass) mode. If, however, you ever find yourself wanting to connect the sub via its speaker-level inputs, an important point to keep in mind is that the sub's negative speaker-level input terminals must not be connected to the negative output terminals of any of the amplifiers.

Since the DNA-500 is fully balanced, and the 300.1's are being operated in bridged mono mode, all of their negative output terminals have full-range, full amplitude signals on them, rather than being grounded. Connecting the sub's negative input terminals, which presumably are grounded, to the negative output terminals of the amps risks shorting those output signals to ground (depending on the internal grounding configurations of the sub and the amp), and causing damage.

If you want to connect the sub to the outputs of the DNA-500, either of the negative input terminals of the sub should be connected to a circuit ground point on the amp. Chances are that a chassis screw is such a point. That could be verified by using a multimeter to check for continuity between the screw and the ground sleeve of one of its rca input connectors, or between the screw and pin 1 of an xlr connector (while nothing else is connected to the amp).

If you want to connect the sub to the outputs of the 300.1's, since there are two of them one of the negative input terminals of the sub should be connected to a circuit ground point on the preamp.

The two negative speaker-level input terminals of the sub are most probably connected together in the sub, so only one of them would need to be connected externally. The positive speaker-level input terminals of the sub would be connected to the positive output terminals of the amp.

Regards,
-- Al