There are two types of volume controller - Impedance matching and Non-impedance matching. If you connect your speaker parallel to the receiver or connect the speakers into an impedance protection speaker selector, use impedance matching volume controller. If you connect just one pair of speaker directly to the receiver or your speakers are connected directly into an impedance matching speaker selector, use regular volume controller.  
    
When OSD entered the volume control arena, they choose to make the best sounding volume control with the widest frequency response and the best all around value on the market. The VKR series transformerless volume controls are the net result. They offer the widest frequency response of any volume control on the market today with virtually no high or low end roll off resulting in audiophile sound quality. This is a statement that no other manufacture can claim with their autoformer volume controls.

This Audiophile quality volume control is best to use with speaker selector or multi-zone amp. It is not impedance matching volume control.  It features optimized sound quality with minimal low end roll off due to high permeability steel utilization. The VKR120 controls feature impedance matching capabilities and removable connectors.

All of the OSD volume controls feature two ounce double-sided G10 glass epoxy PCB’s, a non-shorting design utilizing a "make before break" switch which prevents the amplifier from ever seeing a dead short and 12-14 gauge solderless speaker terminals with easy top termination. Every volume control includes a color coded knob, Decora(r) metal/plastic insert and mounting screws. All Phoenix Gold volume controls will install as follows in single gang boxes from 18 to 14 cubic inch, except VKR120 with not fit a 14 box; double-gang in all 32 cubic inch or larger boxes; and triple-gang in all 42 cubic inch or larger boxes.