2 REL Strata Subs and Mono amps

Thanks for all of your input.
My issue deals with the specific nature of my Audio Research VM220 Mono Bloc
amplifiers. They accept BOTH balanced and single ended inputs with a toggle switch selecting the appropriate configuration. So....I'm not clear if this specific amplifier uses a differential circuit when running balanced. Also am I safe using the black speaker binding post if running single ended? Overall, a confusing mess. It's not clear if the chasis screws can provide a safe ground connection.
Of course I called Audio Research a number of times and have not gotten a call back. This is a similar experience other Audio Research owners have had since their sale.

Can any one help?

Thanks

Jdolgin, I do not have a circuit diagram with me and won't have it till I'm back at work on Tuesday. The problem is...I believe, both the 0 and 4 ohm taps are both chassis and speaker ground. Some ARC amps come off of chassis ground by 10 ohms. That may or may not solve your problem. I don't remember if the balanced input ground is wired the same way. I can contact the factory for you on Tuesday and ask them. Happy New Year!

Hifigeek,
Many thanks.
It's just so frustrating to get no tech support from AR after so many years as an owner of MANY of their products, and, having had such good customer service over the years.

I guess nothing stays the same.
Other than audiophiles supporting one another.

Happy New Year to you as well.
All the best.

J Dolgin

Very nice, guys, I learned a lot from you last 24h...

Al, I think I was told everything I needed in this particular situation that I simply did not know. Tnx once again. I am gonna write to Krell these days...

Vladimir, my main speakers right now is a pair of B&W 805S, but this is a temporary solution rather than long-term choice. When budget allows, I will probably go with higher class speaker - Focal Utopia Diablo, for instance (use to own Utopia Micro Be - fabulous speaker), maybe Dynaudio Confidence C1, but - addressing to your question - whatever I choose, it will be a standmount, almost for sure (room size issue). Certain possibilities to try Magnepan 3.7 pannels, which deeply impressed me, but I am sceptical due to room size (15x15).

Thanks, Hifigeek. Jdolgin, descriptions I found of the VM220 indicate pretty clearly that it is fully balanced. However, as Hifigeek's comments make clear, the fact that it is a tube amplifier having an output transformer introduces still more variables and unknowns into the already "confusing mess" which you aptly described.

I've seen some older ARC schematics, such as this one for the fully balanced VT130, showing circuit ground as being connected to the 4 ohm output tap of the amp, rather than the common (black) terminal, and with circuit ground and chassis ground being connected to each other through a 10 ohm resistor.

*If* Hifigeek determines that the design of the VM220 is similar in those respects, I think that you could connect the black wire to the 4 ohm output terminal of the amp, and the red and yellow wires to the 8 ohm terminal.

Alternatively, assuming that is how the design is implemented, you could connect the black wire to the 4 ohm output terminal, and the red and yellow wires to the common (negative) terminal. Doing that would introduce a 180 degree phase reversal between the sound produced by the sub and by the main speakers, which you would correct for with the sub's phase reversal switch, assuming it provides one. Doing it that way would result in the sub receiving a somewhat (about 8 db) greater signal level than if you were to connect between the 4 and 8 ohm terminals.

But we'll see what Hifigeek determines.

Regards,
-- Al