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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
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bifwynne OP
2,206 posts
 
Bob, by active or passive, I assume you mean powered or not. FWIW, it plugs into a 120 AC socket. Tom mentioned that it has a 1:1 op amp in it -- whatever that means. I don't know if it uses a transformer.

Hifigeek, 2 other A'gon posters have recently asked similar questions about impedance and asymetrical loading. At least in the case of ARC gear, being a retail owner of an ARC pre, phono pre, CDP and amp, I believe it's a fair question to raise with Calvin. Even more so if the inquiry is from a technical novice, especially since not correcting the problem can prematurely wear out the tubes in the pre. BTW and FWIW, Calvin asked for Tom's contact information. I can only assume this question may come up from time to time.

hifigeek1
770 posts
 
When you set up an op amp you can choose the amount of gain you want. Since it's acting as a buffer, no gain is required and therefore, the op amp is set to 'unity' or 1:1 gain. Meaning the signal you put in is the same as you get coming out.
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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