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ARC Ref 3 Main Output Impedance Question

I need some advice on how to hook my ARC Ref 3 pre up to my self-powered Paradigm Signature Servo subwoofer. As further explained below, ARC recommends that I use a crossover/connector tdevice hat has a higher input impedance than the one I currently use and is set up for balanced operation.

The Servo's input impedance is 25KOhms in SE mode and 20KOhms in balanced mode. I use the Servo for low frequencies (10hz to 35hz) in mono mode. To do this, I sum the L/R outputs of the Ref 3 by using a Paradigm X-30 crossover unit. The X-30 has an input impedance of 20KOhms in SE mode. There is no provision for balanced interconnect.

My Ref 3 is connected to the rest of the system as follows. Main 1 outputs are connected directly to my ARC VS-115 in balanced mode. The VS-115 has an input impedance of 300KOhms in balanced mode. Main 2 L/R channels are connected to the X-30 unit in SE mode. The X-30 sums the channels into mono and connects to the Servo is SE mode.

Based on a call with ARC, I was advised that my current subwoofer set-up is compromising the sound quality of the Ref 3 because (a) the X-30 input impedance of 20KOhm is the bare bones minimum that is recommended and (b) I am running one Main output in balanced mode and the other Main output in SE mode. Further, I was told that the current set up is making the Ref 3 work harder than it should.

ARC recommend that I use a crossover/connector device that operates in balanced mode and has a higher impedance than 20KOhm. If I recall correctly, something north of 40-50KOhm would be much better.

Any suggestions would be appreciated. Thanks
bifwynne
bifwynne OP
2,206 posts
 
Hifigeek, that makes perfect sense. As stated above, I expect that there will be two benefits to the device. One, longer tube life (b) because the pre will be loaded at a higher impedance level AND (b) because the load will NOT be asymetrical, i.e., balanced on Main 1 and SE on Main 2. Two, hopefully, some sonic improvement.

I'll report back after I set the device up and run it for a while. Thanks to all for the great advice.
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bifwynne OP
2,206 posts
 
Bob, why poo-poo'ed? If pure resistive, why not just stick a resister in series with the load?
hifigeek1
770 posts
 
Bob, as there is no such thing as a straight wire with gain, an active device added to the signal path will have some effect on the sound. However the effects should be minimal as the buffer used is being set to unity. I don't know which buffer Tom is using but he's very good at what he does. I'm sure the benefit of impedance matching is worth the minimal effects. Has anyone thought of doing a tube buffer stage?? Interesting. It would certainly be more expensive because buffering is needed for the inverting as well as the non-inverting input, but might be worth it. Maybe I need to make one if enough people would be interested
atmasphere's avatar
atmasphere
11,837 posts
 
Hifigeek1, we've built tube buffer versions of our preamp. They have a direct-coupled output. IME what you run into with tube buffers is voltage loss that is more noticeable than with semiconductors. As long as your sources have enough voltage that is not a problem.

I'm not buying the idea that the asymmetrical loading of the ARC would have any effect on tube life. Most tube preamps can be connected to a dead short without the tube life being affected...

Now the asymmetrical loading issue is another matter, but the way I have seen ARC preamps designed, that should not be a big problem if one half is loaded differently from the other.
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