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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
atmasphere's avatar
atmasphere
11,834 posts
 
Normally if you have a balanced circuit, 20K should be no problem. Balanced circuits **should** be able to drive 600 ohms- so 20K should be like a walk in the park. But many high end audio products don't support the balanced standard, and ARC is one of them.

So here is something you can do. Jensen makes a transformer that can perform the operation of going balanced to single-ended, and the transformer I have in mind is optimized for subwoofer operation, so it won't compromise the bass.Their part number is JT-112P-2HPC. you need two for stereo. If you set it up right, it would load the preamp at about 47K (or 39K, which ever you want). This would allow you to run balanced or single-ended. It would be a very simple matter to add a summing network at their outputs, bypassing the need for your summing crossover.

Tom Tutay is also an excellent resource.

FWIW, (disclaimer: manufacturer) we make a preamp that does support 600 ohm balanced operation so you could bypass the need for the summing amplifier- it can drive both the 20K and 300K input impedances in parallel in the balanced mode.
bifwynne OP
2,206 posts
 
Vmk & Atmasphere:

Thank you very much for the suggestions. I called Tom Tutay and discussed the problem with him. Tom will build a custom connector box having stereo SE and balanced inputs and a mono SE and balanced output. The inputs will have a 300KOhm impedance, which should match well with the ARC Ref 3 Main 2 output. As stated in the OP, the Main 1 balanced output is also loaded at 300KOhms into the VS-115 balanced input, so the Ref 3 Main 1 and Main 2 balanced outputs will see the same load.

The price was very reasonable, especially since the device will be custom built to my spec. Tom was very knowledgeable and seems like a real gentleman. I'll report back when I get the unit and try it out. Tom said that it will take a couple of weeks to build.

Thanks again for the help!
hifigeek1
770 posts
 
Bifwynne, Tom is a great guy. I have had quite a few nice conversations with him...
bifwynne OP
2,206 posts
 
Hifigeek, agreed 100%. I should get the connector device in about 7 to 10 days. Tom is loading the balanced input at 330KOhms, which is close to the input load of my ARC VS-115, which is 300KOhms balanced. Does that seem good to you?

BTW, as crazy as this may sound, Tom does not use a PC, does not advertise on the net, nor does he subscribe to A'gon or other similar forums. So, he relies entirely on hand out ads and word of mouth.

I look forward to receiving the connector so I can objectively review it. Tom comes with such high recommendations, I can only assume I will be 120% satisfied. So . . . after I get the device and review it, I would like to help Tom out by posting something a little more conspicuous than a forum thread. I'll figure something out.

BTW btw, another A'goner just raised a very similar question to the one on this OP. It goes to show you that this issue does arise from time to time.

Be well and regards.
no_money
638 posts
 
hmmm.... never looked at this. I have a REF2 connected SE to a Velodyne. Am I working the pre to hard?
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