ARC Ref 3 Main Output Impedance Question

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.

remember that buffer needs to break in a bit and yes Tom is a great guy...

Thanks again to all for the great advice. I am writing this follow up post because I noticed something today that was quite interesting. On 4/25 I said "[a]s to sound quality, I can say with 100% certainty, my rig does NOT sound worse [because I installed the impedance buffer]. 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 night. It's just subtle, kinda like a tweek, maybe two or three tweeks."

Well here's my last update. Since April 25th, I've been listing mostly to vinyl. I haven't used my CDP much at all. Today, I loaded up my new Norah Jones CD and just sat back and closed my eyes to listen and relax. I have a very good auditory memory of the Norah Jones CD because I've played it quite a bit since acquiring it. I think it's pretty well recorded and I just like the music.

After a couple of minutes of listening, I noticed something very different than what I remembered. I was amazed at the significant improvement in stereo imaging in 3D space. I could actually make out the separate voices of Norah Jones singing next to her co-vocalists belting out the tunes. Bass response was phenominal -- great slam, not boomy. And so forth and so on.

I attribute the significant sonic improvements to five possible tweaks. First, as I reported in another OP, I retubed my ARC amp with KT-120 tubes. I retubed the amp a couple of weeks before picking up the impedance buffer. Maybe the KT-120s continued to break in??? Second, perhaps, as Gary (aka Hifigeek) remarked above, the impedance buffer needed to break in some more. Three, I raised the combined output impedance of the loads presented to the Ref 3 from 16-18K Ohms to 157K Ohms. Four, the Ref 3 was presented with a symetrical load - all balanced from the amp (Main 1) and the impedance buffer (Main 2). Five, I removed a major artifact from the sub woofer circuit (i.e., the Paradigm X-30 controller/crossover) and replaced it with a less invasive artifact (Tom Tutay's impedance buffer).

In summary, it appears that one or more of the tweaks listed above effected a very noticeable improvement in my system sonics across the board. My advice to fellow A'goners is to be mindful of how you load your equipement. Also, if your power amp uses 6550 tubes, think about retubing your amp with KT-120 tubes, after first checking with the factory to ensure compatibility.

Cheers!