ARC Ref 3 Main Output Impedance Question

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!

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, I don't know. Call Cal at ARC. He'll want to know how you hooked up the Ref 2 to your amp and sub, i.e., balanced and/or SE, and what the impedance loads of each application are.

In my case, I had a double problem: (1) the imput impedance of my pre was too low; and (2) the Ref 3 was asymetrically loaded, i.e., Main 1 to the amp was balanced and Main 2 to the sub was SE. Not a good set up. Cal explained that as a result, I was prematurely aging the tubes AND potentially denigrating sonic performance.

If Cal thinks you need a buffer device to increase the impedance loading of your Ref 2 and sum the channels into mono for the sub, call Tom Tutay at Transition Audio Design. His number is listed above. The other posters above say he is solid. He's currently building an impedance/channel summing custom buffer for me.

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.

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.

Bob, why poo-poo'ed? If pure resistive, why not just stick a resister in series with the load?

Atmasphere, do you think asymetrical loading would affect sonic quality? Not being an electronics techie, I of course have no view. All I can say is that ARC did not think it was a good way to load the Ref3.

Certainly an interesting discussion. However, in my case, now that I have been alerted to the issue, the problem is moot because Tom is making a custom buffer device with high impedance balanced inputs that will sum the channels for my sub. I am a little curious if I will detect any sonic improvements, albeit lower and tighter bass response, lower noise or cleaner output (i.e., less distortion products).

FWIW, just wondering out loud for a second, I wonder if the issue of asymetrical/low impedance loading is just an ARC issue or cuts across the board for all pre/line stages, regardless of type (i.e., SS or tube). If this is more of a ubiquitous issue, then Hifigeek's suggestion about an objective test might benefit other A'gon members, IMHO.

Well Al, . . . if one of you techies think this could potentially affect a significant swath of owners of tube pre/ equipment, other than the Atmasphere OTL type of course, perhaps someone with the equipment and know-how will run some tests as Hifigeek mentions above to see whether this issue is just hype or real.

As I already stated, the point is moot for me now, but it might be useful for other A'gon members. However, as soon as I hook up my impedance buffer with the balanced inputs, I'll A/B my set up to see if there are any noticeable sound improvements and report back. Right now, I'm still getting used to the exchange of my old SED 6550 tubes for new Tung Sol KT-120s, which as I said in another post are quite impressive. In any case, it may be that the only improvement I realize will be longer tube life rather than significant sound improvement. We'll see.

Cheers.

Thanks Ralph: I believe the amp, as you suspect, is balanced a AND differential, whatever that means. I clipped an excerpt from the ARCDB website, which describes the amp:

"Drawing upon the successful REF110 input stage design, the VS115 uses a FET input with two 6H30 triodes in each channel for gain and as a cathode follower-driver for the 6550C-equipped output stage. This allows both balanced and single-ended connections in a true differential topology yielding a much wider power bandwidth (110kHz in contrast to 40kHz for the VS110)."

So does that mean that the asymetrical loading of the Ref3's main outputs with a combined load that may have lower impedance than recommended will NOT affect the sonic quality of the power amp's output? I think both Tom Tutay and ARC thought there could be some rolloff on the low frequency side of the spectrum in such cases. I don't know at what frequency that would occur, but here again, this could be a big whoop too because I can adjust bass loudness.

Bottom line here: does all of this mean the issue which is the subject of the OP does NOT impact sonics, but perhpas just tube life??

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.

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.

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!