ARC Ref 3 Main Output Impedance Question

Bifwynne, what this means is that the preamp will drive a solid state amp the same way it would as if the tube amp was not even there.

ARC is pretty careful to make sure their preamps will drive the 10K input impedance of a solid state amp. So if its OK playing bass into that right now, then adding the tube amp will be of no consequence as its input impedance is about 10 times higher. If you work out the math, in engineering terms the higher impedance can be ignored.

Here's the math: 10K times 100K divided by 10K + 100K.

That works out to 9.09K ohms as opposed to 10K. I think you'll be OK :)

Thanks Ralph, as stated in the OP, "[b]ased 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. . . . ARC recommend that I use a crossover/connector device that operates in balanced mode and has a higher impedance than 20KOhm."

Using your formula, the combined impedance is 20K x 300K, divided by 20K + 300K, or 18.75K, which is below the minimum recomended threshold. Further, ARC commented that running the pre with "one Main output in balanced mode and the other Main output in SE mode" is not an optimal way to load load the outputs.

Thanks again for your comments.

Bifwynne, sorry, seems I have been shooting my mount off; upon looking at the specs of the preamp, I have to agree. It did not occur to me that the preamp was not designed to drive 10K as a minimum.

No problem Ralph. In fact, the combined impedance may even be a little lower. I read a review on the VS-115 the other day which reported that when the VS-115 was bench tested, its input impedance was only 266K Ohms -- not the 300K Ohms reported in the ARC literature. By itself, no big deal. But matched with a 20K OHM load on the pre's other output presents a combined load that's slightly lower still than the amount calc'd above.

Personally, I am dubious that I'll hear much difference in sound when I hook up Tom Tutay's impedance buffer device. But if nothing else, maybe the Ref 3 won't have to work as hard with the load currently presented and I'll realize extended tube life. Either way, I'll report back to the group.

P.S. And just as I was ready to hit the submit button, Tom's buffer just. Kinda curious how it works. I'll report back in a couple of days.

BTW, Tom sends his regards and spoke very highly of you.

To All --reporting back on results of using impedance buffer. Ok, I hooked up Tom Tutay's buffer. As a threshold matter, let me say a couple of things about Tom. He is very professional and knowledgeable -- a real gentleman. He turned around my order in lightening time. The shell of the buffer device is made wholly of metal, and is about 9" x 5" x 2". By all appearances from the outside, the device seems to be very sturdy and well made.

Now . . . as to how it works. As you can see from the posts above, the device was designed to: (a) load my Ref 3 symetrically (i.e., Main 1 and Main 2 in balanced mode), (b) sum the left and right channels without shorting the Mains since I am using only one sub, and (c) raise the impedance level of the two Mains to a level that better matches ARC's design specs.

As to tube life, I take it on faith based on conversations with ARC that by reducing the load on my Ref 3's outputs, tube life will be extended. I will have to wait and see.

As to sound quality, I can say with 100% certainty, my rig does NOT sound worse. Does it sound better?? Yeah, I think so. I think the imaging, detail and sound stage are a little bit improved. The highs seem a little smoother and better refined. But quite honestly, I don't think the change, if any, is day and nighgt. It's just subtle, kinda like a tweek, maybe two or three tweeks.

Now the impact on bass is more noticeable. Although I removed one active artifact from the system and added another, I think the X-30 crossover/controller did more than the buffer because the X-30 could adjust loudness, phase, cut-off and summed the channels. By contrast, the buffer has an active unitary op amp that raises the input impedance and just sums the channels. That's it.

When I first inserted the buffer, I initially thought something happened to the bass output from the sub. On Tom's suggestion, I tried using the old hook-up again by running an SE I/C from one of the SE Mains off the Ref 3 directly to the sub (sans X-30). I then ran the Ref 3 in mono mode to sum the channels. Interestingly, the bass seemed equally lame this way too.

Then I realized what was going on. I had set the cutoff frequency on the sub at 35 Hz to blend into my fronts. What I realized is that there simply wasn't very much going on below 35Hz in my source material. By contrast, when I raised the cutoff frequency -- bass galore.

So realizing what was going on, I then critically listened to some bass heavy source material, e.g., Norah Jones CD and Solti conducting Chicago Symph Orchest., Beethoven 9th 1st and 4th movements LP. Tons of bass in these source materials. But when I raised my sub's cutoff to about 50 Hz I had more than enough tight and smooth bass -- NOT boomy.

In summary, Tom Tutay of Transition Audio Design is a great resource for audiophiles. He is not limited to just buffer devices, but can custom design many different types of devices. Keep him in mind. Tom's phone number is: (850) 244-3041.

Thanks guys for the terrific advice.