ARC LS 25 Mk 11 Bypass


I'd like to get better "2 channel" performance out of my HT system (Bel Canto Evo 6 amp and PrePro processor, Theta CD transport). When I was at my local stereo store the salesperson recommended that I simply purchase the LS 25 Mk II. He told me that it has a "bypass" feature that will allow me to use the LS for 2 channel music and the PrePro for HT and multichannel applications...without having to move cords everytime I want to move between music and HT. I've tried to find literature on line that would explain how the wiring would work, but I've been unsuccessful. Has anyone out there done this with the LS 25 or some other preamp? If so, did you find the 2 channel sound to be substantially better than simply running it through the processor?
Thanks everyone.
riccap
I have and it does make quite a difference. Another issue to think of though is whether you actually want to mix HT and a music system. I have, and regret it every day. Screws up the imaging to a good extent, but worst it changes the dynamics of the room as the sound room becomes a media/play room for the whole family. I truly believe that the sound room should be a refuge. My 14 year old daughter is in there with her friends whenever my son is not. My 20 year old son has every known video game console in there and a satellite TV receiver with a hard drive. Add to all this the hard drive from the computer, also in the room, and you have to wonder why we all try for a great s/n ratio and quiet tubes with no rush and the like with all the whirring sounds around.

I started a second system, but that is another story and I have soon found out that whenever someone is in the basement sound room (despite all the sound abatement installed when building it)enough sound leaks out to make listening in the living room immediately above it a PITA.

So, word to the wise...
I did this exact application with a ARCLS25MK2 about 3 years ago. I used a Theta Casablanca home theater processor, and fed the left front channel and the right front channel outputs (via XLR cables) from the CB into the "By-Pass" inputs of the LS25MK2. I then, obviuosly, connected my CD player direct to the ARC preamp, and from the LS25 out to my monoblock amps, and finally to 2 front speakers. On the remote for the LS25, there is a button that i recall read "Pass Through", as in to pass an incomming signal (from your HT Processor) through and out the preamp. You hit that button and it switches inputs on the back of the pramap to the Home Theater By Pass Input and simply routes that input out the main outputs of the preamp with out touching its volume. You HT Processor still has complete control over volume.

If Music is your main concern, I am going to go out on a limb and make the statement that with out question, if you have a good cd player (high end DAC's), you will always get better sound running it through an analog 2ch preamp versus running it into ANY home theater processor, regardless of cost. I also really like the ARC LS25MK2, but there is 1 potentially big drawback if you really care about home theater. When running home theater through a 2 channel analog preamp, most preamps, including the ARC ls25mk2, will be processing to some minor degree the signal and thus degrade it. With the ARC LS25, home theater front right and left DID sound worse running throught the ARC. Not horrible, but just not as good as running from the processor directly to the amps. I easily lived with it because my only critical concern was 2 channel, but you can easily hear the difference between running the processor direct vs. running it throught the LS25MK2. On the other hand, my 2 channel setup sounded marvelous comming off the LS25.

FWIW, 12 months ago i replaced the ARC with a VTL7.5, and ran it in the same hometheater by pass mode. With the VTL, I could not distinguish a difference in home theater. I guess for 13K, it had better darn work well!!!!!
you would connect the pre-amp left and right outputs of your HT processor to the "Processor" input on LS-25(either single-ended or XLR). After that's done, there is a front panel toggle switch on the 25 to activate the processor loop. I wouldn't worry about degrading HT performance. Just use same good cables you were originally using with your HT processor and that'll do.
"When running home theater through a 2 channel analog preamp, most preamps, including the ARC ls25mk2, will be processing to some minor degree the signal and thus degrade it"

Absolute nonsense ...it is a pass through and no degradation of the signal.

I use my ARC Ref 3 "Processor" input (AKA through pass) for my HT function and there is no degradation of signal
Oneobgyn, I don't know how the processor loop works on REF3 but with the LS-25 I do beleive the signal still runs through some sort of a signal path of the preamp.
However, I'm with you that that it has no or minimal impact to the sound quality. The most improtant factor sonically here would be the quality of interconnects that is used between HT pre/pro to LS-25 and a pair from LS-25 to amp. Use good cables and you will sacrifice nothing.
thank you everyone for your information and input. It sounds like I would enjoy a significant improvement in my 2 channel performance if I went the 2ch preamp route. Other than the ARC LS 25 and the VTL mentioned...does anyone have any other recommendations in terms of a good 2 ch. preamp that offers the "bypass" capability.

Thanks again everyone!
"The most improtant factor sonically here would be the quality of interconnects that is used between HT pre/pro to LS-25 and a pair from LS-25 to amp. Use good cables and you will sacrifice nothing."

as much as I am a cable tweak, I again respectfully disagree
The Ref 3 and the LS25 MKII do the same function. They provide a "pass thru" for the signal from your HT processor. I've been running mine for over two years without a problem. That's the whole reason for having the bypass circuit is to allow the HT processor signal to run straight thru to the 2 channel preamp without being altered by the preamp?
"The Ref 3 and the LS25 MKII do the same function. They provide a "pass thru" for the signal from your HT processor. I've been running mine for over two years without a problem. That's the whole reason for having the bypass circuit is to allow the HT processor signal to run straight thru to the 2 channel preamp without being altered by the preamp?"

precisely my point and even though I am a cable zealot the previous comment of needing good cables so that nothing is sacrificed is also nonsense
Oneobgyn, I wasn't complete in my post above in regards to cables and it was easily taken out of context(which you successfully accomplished by the way).
I meant that HT pre/pro into the amp directly with a given pair of ICs should sound as good through LS-25 processor loop should the same ICs be used in and out of the LS-25. That is what I meant to say and is why I mentioned good cables. Not because I belevie good cables will fix a bad component. If it's nonsense to you, it's your right to take it for what it is.
Happy New Year!
Sorry to have been so judgemental but I understand your point once expounded upon.

Likewise to you...Happy New year
Hello
I do this same thing with my sound room. I take the output from my Meridian HT system, front left & right to the proc input on the Ref3 then from the Ref3 output to the amps, This lets me be very flexable. This allows the Ht or Stereo to control it's own volume. With it this way you can also send the digital output from your equipment to the HT system & all the analog outputs to your stereo preamp. Then you see which sounds best to you and use the system that way. When you have people over you can use the HT and send sound to all speakers also.
The only thing you should do then in my opinion is optimize the room for 2 channel and use the digital abilities of the HT processor to adjust the HT part of the system. You also might want to cover your screen even one that is flat, with something when listening to 2 channel cause that way you will get a better imaging & a better sound stage between the speakers.
I have always wondered how this process works too. Does this mean that when your listening to HT through the 2 channel preamp the sound level on the 2 channel preamp can be set at zero or 100 and it doesn't matter because the HT is controlling the volume as long as the switch is flipped? Is their any sonic improvement from using a superior preamp and running the front left and right channels of the HT processor throught the 2 channel preamp or is this a mood point.
Simply put, it is a theater throughpass and the volume is controlled by your pre-pro. There is no sonic improvement. What you are doing is using your processor's left and right front channel outs into the processor (bypass) left and right inputs on your stereo preamp. From there you are running your left and right main outs into your amp. I just don't get why all you guys are so confused
“Absolute nonsense ...it is a pass through and no degradation of the signal.”

Maybe you are the One who is confused. When you say it’s a pass through, are you implying it just passively switches wires because that is not the case. The preamp is accepting the analog signal just like it would from any other source and then setting its volume level at unity gain, so as not to change the output level of the incoming signal.

Does your home theater bypass work when your REF3 is turned off? I don’t think so, and I know it does not work with the LS25MK2 turned off (we are talking about the LS25MK2 here aren’t we). If the 2ch preamp has to be turned on, then it is NOT just passively switching wires, it is actively doing "something", and I am telling you for a fact, that with the LS25MK2 in home theater bypass mode, it does change the sound from your ht processor and not in a positive way. I would assume the REF3 would be on the same level as a VTL7.5, and the change in sound through those units would be (is) extremely minimal, but this is not the case with the LS25MK2. The lowering in sound quality (degrading) was easily noticeable.
I respectfully disagree.
"I am telling you for a fact, that with the LS25MK2 in home theater bypass mode, it does change the sound from your ht processor and not in a positive way."

What I don't understand is how you make that comment inasmuch as you need to use the throughpass mode to accept the L + R main channels from your pre-pro to be used for HT.

Now if you tell me that you are using the preamp part of your processor for 2 channel music I would suggest that any good 2 channel preamp will always sound better than a HT pre-pro.

For you to suggest that the sound is degraded by your ARC preamp suggests that you have to have used only your HT pre-pro for music listening without using the thoughpass input (IOW, your L +R main outs from your pr-pro go directly to your amps). I have done this with my system and I still disagree with you. There is just no degradation of signal when used through the "processor" input on my Ref 3
This whole discussion hints at a feature I have wanted from tube preamp manufacturers out there: implement HT pass-through WITHOUT the need for the tube unit to be powered on. Why is this so difficult? If all we want is to route a pair of inputs directly to the outputs, can't this be done through the use of one toggle switch? And in the other position, which perhaps is an open circuit, the preamp works in a normal way when powered on.

As for all the back-and-forth posts above, no matter how the Ref3 may differ from the LS25 sonically in "normal" mode, I gotta believe that they would NOT differ in HT pass-through if none of their active stages are in line for this mode. I suspect ARC's implementation (switches, wires and connectors) with HT pass-through is consistent from model to model. With that said however, it escapes me how insertion of any component (with its input and output connections and the additional IC) can result in NO kind of signal degradtion vs. the pre/pro's front channel outputs directly to the amp. In a high-resolution system, just that one extra pair of ICs can do far more damage than any inserted "pass-through" component. This may be a miniscule difference, and for the sake of HT usage, who cares, but I suspect there would certainly be a noticable change in dynamic contrasts even with the most linear ICs out there.
"If all we want is to route a pair of inputs directly to the outputs, can't this be done through the use of one toggle switch?"

you could do this yourself with a simple A/B switch and forget about a theater through pass input
you could do this yourself with a simple A/B switch and forget about a theater through pass input

True, but I still want the tube line stage there to make use of my 2-channel analog sources. And I do not want to fuss with disconnecting the IC-pair to the amp everytime I choose the line stage or the pre/pro as a purist might do. All I ask for is this simplistic "toggle function" wrapped in the line stage's implementation. And for days and days or weeks where only movies might be played, the line stage is powered off.
Billbench & Oneobgyn
Yes it does alter the sound, it has to because the signal passes through the tubes, but the Ref 3 is so good that I think it gives it a better sound stage. I have a Meridian G68 for HT.
I had a VAC Standard LE Tube Preamp by the way and it just passes the signal through wiring and not the tubes, it can be off while you are in HT mode.
AND tlg.
The stereo preamp that has HT mode either sets the output volume at a constant and repeatable level all the time or just pass the siganal straight though via wiring. Your HT is controlling the volume as if the stereo preamp was not there and it can also be calabrated correctly.
Also this stops you from having to set the volume on your stereo preamp. If you do not set the volume exactly same way everytime any calabration you have done will not be correct. A HT not calabrated is a waist off time and money.
As with most analog volome controls, because they work with resistance, being off a little can mean alot so you are much better off this HT passthrough.
I just ordered an LS 26 and spoke with Leonard at Audio Research. According to Leonard, the sound will be improved through the HT Pass through of the LS26. I will post a note when i try it myself next month. Happy listening!
Stevecsi, please do. Curious about LS-26 in general.
The quality of the signal path offered by any ARC preamp with a unity gain processor input is far superior to that of any digital surround processor, enough so that it will not be a source of sonic degradation. Many listeners may actually find that the sound improves when going through the ARC.

The type of listener who uses a dedicated 2-channel analog preamp with a processor input, does so precisely because of its superior sound quality and signal handling purity. If their digital surround unit was capable of sounding as good, there would be no reason for them to pursue a dedicated preamp in the first place.
I have a similar set up to most of you here. Using a Meridian 568.2 with L & R output going thru a Aesthetix Calypso. For pass thru the Calypso is set to unit gain. Which I think sounds better. As I have only a dvd transport, when I listen to 2 channel, I take the calypso out of unity gain. I generally set the meridian to maximum gain and adjust the volume with the calypso, which to me sounds much better.

The only tube preamp I have read that has a thru bypass is the Cary SLP 05 or Cary SLP 2002.