2 REL Strata Subs and Mono amps

I contacted Audio Research only to be told that someone had already called to get the info. The bottom line is, use the 4 ohm tap as signal and chassis ground are isolated by 10ohms. That should be sufficient. That's the info I received from ARC.

Very insightful thread, for me at least.. Grateful to all of you.

Happy New Year to all, lots of music!

Zormi, I forgot to add that you should copy the grounding scheme of the pag. 12 (top) example for the (bottom) example, of course. I think the chassis screw grounding will work for Krells, but ask them first just to make sure.

Good that you say that, I thought about it but at the end didn't write anything. I used my REL Storms with mono and stereo amps at different times. The example on pag. 12 (top) of the REL manual is of course for a stereo amplifier; for mono amplifiers, use the pag. 12 (bottom) example and just imagine the gray amplifier divided by a vertical line through the center, so that you have two separate mono amplifiers, a left one and a right one. The potential grounding problem still stands, so it's better to ask Krell or get your dealer to do it.

@ Vladimir

Yes, I've just checked the Gibraltar G1 manual, and they indeed give on the p. 12 the same advice Al gave to me above (if power amp is balanced ie differential).

What they don't say is what to do in case of having two subs (stereo sub system) and balanced amplifier, as I have... Following strictly their user guide (bottom half of the p. 12), an average audiophile in my position will normally connect even fully balanced amp with two subs, the way REL suggests, and probably damage the amp.

The C1 IIs sound better than the Mk Is, but I would take that Diablo bargain from your dealer in two seconds flat!

By the way, I used a Storm III for many years with several speakers, including B&W Matrix 805s, 805s and 804s. One thing most people don't know about RELs is that they can improve the bass of almost any speaker, but that's not their main advantage; it is the way they improve the soundstage and the general sound of the main speakers because of the ambient clues hidden in the low frequencies and the way they 'come from underneath' the main speakers.

Enjoy the music!

Wow Vladimir..

Nice idea with C1 MkII, already under consideration. I know them well, since I use to own original edition Confidence C1... In fact, I owned both Utopia Micro Be and Confidence C1 until the end of 2008, simultaneously. Two different worlds, each one impressive on his own way... I now prefer a bit the Utopia Diablo because a slight edge over Dyn C1 in mid/high clarity and detail rendition. Bass aside, this is where C1 excells, but RELs defeat that area as a serious issue. Price wise, I have a great dealer from Belgrade, Serbia, which is able to bring me a pair of Diablos including dedicated stands for the same money as pair of C1 MkII without stands at another dealer. But, price doesn't matter too much... differences between the two simply not prominent enough to have any serious impact on decision.

12-30-12: Vladimir
I checked the Gibraltar manual online and on page 12 it explains the way to connect to differential amplifiers such as your Krells, basically to connect the black Speakon wire to a chassis screw as was explained by others here.

Thanks, Vladimir. However, as I indicated in my first post dated today, based on my research it appears that these particular Krell amps are not differential or balanced or bridged. I suggested confirming that with Krell, though.

Regards,
-- Al

Zormi, I normally don't suggest components unless the poster asks or presents alternatives himself. In your case, I would suggest giving a good listening to the Confidence C1 IIs at about half the Diablo's price. In my humble opinion they are among the best standmounts ever, for several reasons: deep and controlled bass enough even for medium-sized rooms, a soundstage that includes height reproduction, something rare among non-tower speakers (even Vandersteen 5s and 7s, as well as highly rated standmounts such as Raidhos don't do it), and all around sound as good as anything at two or three times the price. The C1 IIs definitely don't need a crossover, just augment their already impressive bass with your RELs at about 30Hz or a bit below.

By the way, I checked the Gibraltar manual online and on page 12 it explains the way to connect to differential amplifiers such as your Krells, basically to connect the black Speakon wire to a chassis screw as was explained by others here. That's also how Nelson Pass suggest doing it with his balanced amplifiers, and he provides another set of ground posts just for that.

Amazing....how complex the solution can be for a seemingly simple question.
Oh well, I guess in the hiigh end game NOTHING is ever simple.
Thanks everyone.
jdolgin

Thanks, Hifigeek. Jdolgin, descriptions I found of the VM220 indicate pretty clearly that it is fully balanced. However, as Hifigeek's comments make clear, the fact that it is a tube amplifier having an output transformer introduces still more variables and unknowns into the already "confusing mess" which you aptly described.

I've seen some older ARC schematics, such as this one for the fully balanced VT130, showing circuit ground as being connected to the 4 ohm output tap of the amp, rather than the common (black) terminal, and with circuit ground and chassis ground being connected to each other through a 10 ohm resistor.

*If* Hifigeek determines that the design of the VM220 is similar in those respects, I think that you could connect the black wire to the 4 ohm output terminal of the amp, and the red and yellow wires to the 8 ohm terminal.

Alternatively, assuming that is how the design is implemented, you could connect the black wire to the 4 ohm output terminal, and the red and yellow wires to the common (negative) terminal. Doing that would introduce a 180 degree phase reversal between the sound produced by the sub and by the main speakers, which you would correct for with the sub's phase reversal switch, assuming it provides one. Doing it that way would result in the sub receiving a somewhat (about 8 db) greater signal level than if you were to connect between the 4 and 8 ohm terminals.

But we'll see what Hifigeek determines.

Regards,
-- Al

Very nice, guys, I learned a lot from you last 24h...

Al, I think I was told everything I needed in this particular situation that I simply did not know. Tnx once again. I am gonna write to Krell these days...

Vladimir, my main speakers right now is a pair of B&W 805S, but this is a temporary solution rather than long-term choice. When budget allows, I will probably go with higher class speaker - Focal Utopia Diablo, for instance (use to own Utopia Micro Be - fabulous speaker), maybe Dynaudio Confidence C1, but - addressing to your question - whatever I choose, it will be a standmount, almost for sure (room size issue). Certain possibilities to try Magnepan 3.7 pannels, which deeply impressed me, but I am sceptical due to room size (15x15).

Hifigeek,
Many thanks.
It's just so frustrating to get no tech support from AR after so many years as an owner of MANY of their products, and, having had such good customer service over the years.

I guess nothing stays the same.
Other than audiophiles supporting one another.

Happy New Year to you as well.
All the best.

J Dolgin

Jdolgin, I do not have a circuit diagram with me and won't have it till I'm back at work on Tuesday. The problem is...I believe, both the 0 and 4 ohm taps are both chassis and speaker ground. Some ARC amps come off of chassis ground by 10 ohms. That may or may not solve your problem. I don't remember if the balanced input ground is wired the same way. I can contact the factory for you on Tuesday and ask them. Happy New Year!

Thanks for all of your input.
My issue deals with the specific nature of my Audio Research VM220 Mono Bloc
amplifiers. They accept BOTH balanced and single ended inputs with a toggle switch selecting the appropriate configuration. So....I'm not clear if this specific amplifier uses a differential circuit when running balanced. Also am I safe using the black speaker binding post if running single ended? Overall, a confusing mess. It's not clear if the chasis screws can provide a safe ground connection.
Of course I called Audio Research a number of times and have not gotten a call back. This is a similar experience other Audio Research owners have had since their sale.

Can any one help?

Thanks

Zormi, I would like to know what your main speakers are, because I believe you have a totally different problem to Jdolgin, and it hasn't been addressed: you have an active crossover in your system (Krell Phantom's crossover board option) and RELs aren't designed for this; they are supposed to 'augment' the main speakers from below their natural roll-off frequency, without the use of a crossover like the Phantom's. If this is the case (unless you already purchased the subwoofers), you don't need REL Gibraltars as there are many good and less expensive alternatives, some of them with room correction built-in. On top of that, if your main speakers are full-range floorstanders, you don't need the Phantom crossover to use the RELs; if they aren't full-range and depending on their bass response, you can go either way.

Zormi, thanks very much for the nice words.

I would go with no. 1, connecting the subs to the outputs of the Krell amplifiers. I looked through the description and the manual for the 400e at the Krell site, and did some other searching via Google, and I found no references anywhere to the outputs of that amp being balanced or bridged, and I found no statements anywhere cautioning against grounding the black (actually blue?) output terminal.

Yes, the amp provides an XLR input, but that in itself says nothing about whether its internal signal path and its outputs are balanced.

I would suggest contacting Krell to confirm that the outputs are not balanced, and that it is safe to connect the black output terminal to the ground of a subwoofer. And if the outputs are actually balanced, if a chassis screw would be suitable for use as a subwoofer ground.

If it turns out that neither approach is suitable, then I would suggest using the RCA input connector to provide a ground connection, as I described earlier. To do that, you would obtain an RCA plug, such as this one, and solder the black wire to the connection point for the ground sleeve, which is the thing that projects out toward the right side of the photo. Do not connect the center pin to anything. Inserting that plug into the RCA connector on the rear of the amp will provide a proper ground connection.

I would expect that with a little care it should be possible to connect the red and yellow wires to the output terminals of the amps, together with the main speaker cables, without degrading contact integrity. That is probably what most people using REL subs do.

2) connect the REL G1 via low level input, RCA type.... I am a bit confused (since have two REL G1s) whether to put the RCA cable from preamp into the right or into the left RCA low level input of the woofer? Al, which one is the accurate, please..?

Since the two inputs get summed together in the sub, it shouldn't matter which input you connect to. If you use that approach, it might be a good idea to connect a shorting plug, such as this one, to the unused input, to eliminate the possibility of noise being picked up at that input and being summed together with the signal. Although chances are that wouldn't be an issue anyway.

Regarding that approach, also, if the connection between the Krell preamp and amps is via XLR, rather than CAST, connecting the preamp to the subs via RCA could conceivably have a slight adverse impact on the sonics produced by the main speakers. That might occur if the design of the preamp is such that the RCA and XLR outputs are not driven from separate output stages, and the signal that is output via RCA is the same as one of the two signals in the balanced signal pair that is provided to the XLR connector. That is another possible reason why having the preamp provide the inputs to the sub may not be the best approach.

Regards,
-- Al

Primare A32 is (was?) planned solely for feeding the REL woofers.

Removing the Primare from the chain basically imply several possible solutions, as far as I can see (I am far from any qualified tech know-how in electronics):

1) simply connect the REL G1 (via Neutric high level input wires) to the Krell Evo-400e blocks, simultaneously with the main speakers, as Al suggested above. Possibly uncomfortable a bit, since Krell has only one par of output terminals. Plus, above discussed possibility of some damage to monoblock amps..? However, this solution ensures reflecting the sonic nature of the main amp(s).

2) connect the REL G1 via low level input, RCA type, which was my natural, initial idea, until I saw the "REL connectivity" section on their website and their strong advice to use the Neutric high level input for best sonics. I can still use REL's RCA low level input to connect the woofer directly to the Phantom preamp low-end RCA output. In this case, any complications with the power amps should be eliminated, but benefits from "reflecting the nature of the main amp", as REL recommends, will be lost. BTW, in this case, I am a bit confused (since have two REL G1s) whether to put the RCA cable from preamp into the right or into the left RCA low level input of the woofer? Al, which one is the accurate, please..?

3) keeping the option with Primare, but connecting the black wire to the amp chassis, instead of black output terminal. Unconfortable a bit, but safe for amp. Krell power amps' sonics "lost" for the woofers.

4) employing another big stereo Krell (btw fully balanced as well) instead of Primare, which will keep the Krell sonics for woofers. Too pricey solution, out of my reach.

5) employing another stereo power amp, which is not balanced design. Krell's sonic nature definitely lost for woofers, but all other problems eliminated. Good that this one may be relatively modest in power and price - as Al elaborated above, relative lack of power may be compensated by putting the woofer's yellow wire to the red amp's terminal, plus additionally reinforced utilising woofer's own amplifiers.

Great inputs Al, anyway, thank you very very much. You truly deserve all positive reputation from us fellows overhere.

12-29-12: Zormi
Personally, I have a piece of Primare A32 250Wpc stereo amplifier planned for that task. The main part of my system is consisted of Krell Phantom preamp (with active crossover onboard) and a pair of Krell Evo-400e monoblocks. This combo is supposed to drive the main speakers, while Primere A32 is planned to feed two REL Gibraltar G1, via high level inputs, as REL strongly recommends in user manual.

If the only function the Primare would be serving is to drive the subs, it would be better to simply remove it from the system and connect the subs to the Krells.

The reason REL recommends driving the subs from high level power amp outputs is to enable the subs to see the same signals as the main speakers, with the signals that are seen by the main speakers and the subs both reflecting the sonic effects of the main power amp. That purpose would be defeated by driving the subs from a different power amp than the one driving the main speakers. It would also mean that your investment in the Primare would be pointless.

Or does your reference to an active crossover function mean that the Primare is to be driving the low frequency sections of the main speakers, in addition to driving the subs, with the Krells just driving the higher frequency sections of the main speakers?

Regards,
-- Al

12-29-12: Wolf_garcia
I imagine you only need one positive lead per mono amp, as otherwise a single REL sub combines those signals anyway to utilize both channels.

If the amps are not balanced or bridged, I suspect that results in most cases would be similar or identical regardless of which output terminal the yellow wire is connected to. If it is connected to the black terminal, the internal circuitry of the sub will see a signal level that is 6 db less than if it were connected to the red terminal. The level control on the sub would be increased to compensate for that.

If the amp is particularly low powered, it would suggest the likelihood that it would be preferable to connect both wires to the red terminal, resulting in a higher level after the two inputs are summed together. If the amp is particularly high powered, it would perhaps suggest the possibility that connecting the yellow wire to the black terminal would be preferable. Although it is possible that it would make no difference in both of those cases.

HOWEVER, if the amps are bridged or balanced, connecting the red and yellow wires to opposite colored terminals would result in essentially no sound from the sub, because since the two signals are inverted relative to each other, they would cancel when summed together in the sub.

12-29-12: Sunnyboy1956
For a balanced /bridged amp check with REL. If I remember the G1 manual covers all scenarios. The input impedance of the G1 is in excess of a 1k ohms and amp damage is not likely.

Input impedance has no relevance to the damage possibility I described earlier. Input impedance refers to the impedance seen "looking into" the inputs of the sub from the red and yellow wires (i.e., the signal inputs), and has nothing to do with the impedance between the black (ground) wire and the sub's internal ground, which can be presumed to be a direct (zero ohm) connection. In the scenario I described in my previous post that might result in damage (depending on how the grounds are handled in the specific designs), the signal on the black output terminal of the bridged or balanced amp would be shorted to ground through essentially zero ohms.

12-29-12: Zormi
Huh..

Primare A32 is fully balanced design, as emphasized on their website, so it seems that I will have to look elsewhere. Safety is of course the most important issue, at least for me..

Not sure what you mean by "look elsewhere." My previous post described three possible approaches that are applicable to your situation, starting with trying a connection of the black wire to a chassis screw or other ground point on the amp.

Regards,
-- Al

Huh..

Primare A32 is fully balanced design, as emphasized on their website, so it seems that I will have to look elsewhere. Safety is of course the most important issue, at least for me..

Thank you all for very insightful set of opinions.

Zormi
My amp is a CJ LP 70S.
Almarg is absolutely correct that the wiring scheme of red+ yellow in the neutrik speaker wires tied to the +(red) terminal of the amp's speaker binding posts and the black to the -(black) speaker post is the way to go in respect of an unbalanced amp. For a balanced /bridged amp check with REL. If I remember the G1 manual covers all scenarios. The input impedance of the G1 is in excess of a 1k ohms and amp damage is not likely.
The G1 is an amazing sub.
Njoy

Rel has the correct wiring for Neutrik plugs on their website I think (or in the manuals) as I found 'em for making my own REL cables...in any case, once you figure out which wire is going to the negative speaker post, I imagine you only need one positive lead per mono amp, as otherwise a single REL sub combines those signals anyway to utilize both channels. I also suggest the "angled" Neutrik plugs as they allow easier placement close to walls...I love those damn Neutriks.

Connection of the red and yellow wires to the red output terminal of the amp is fine. Connection of the black wire to the black output terminal of the amp is fine if the amp does not have balanced outputs, and is not bridged.

If the amp has balanced outputs or is bridged, the black output terminal will have a full-amplitude audio signal on it, equal but inverted with respect to the signal that is on the red terminal. If a path exists between the circuit ground of the sub and the circuit ground of the amp, the result of connecting to the black terminal in that situation would be that the signal on that terminal will be shorted to ground, possibly damaging the amp. Whether or not such a path will exist depends on the internal grounding configuration of the two components. If both components have their circuit ground and chassis ground connected together, for instance, that path would exist via the AC safety ground wiring in their power cords, and the house wiring (or internal wiring in a power strip or conditioner, if one is being used) that interconnects the respective outlets.

If the amps are balanced or bridged, connecting the black wire to a chassis screw should be safe to try, and may or may not work acceptably depending on the grounding scheme of the amp. If hum or other issues result, and the amp has an unused RCA input connector, an approach that would definitely work is to solder the black wire to the ground sleeve connection point of an RCA plug, leaving the center pin connected to nothing, and inserting that plug into the unused connector. Similarly, if there is an unused XLR input connector, connecting the black wire to XLR pin 1, using a mating XLR connector instead of an RCA plug, would also be a good approach.

Regards,
-- Al

Brownsfan,

My appologise, I obviously missed your advice to ask the amp manufacturer themselves, as also missed to say thank you.

Truly appreciate your input.

Sunnyboy1956, thanx a lot.

May we know what an amp(s) do you use? I am familiar with certain rumours that, reportedly, some fully differential balanced amplifiers could have serious problems with above-mentioned setting of configuration (ie. red plus yellow wires from the woofer connected to the red output terminal of the amp, while woofer's black wire to the amp's black output terminal).

Personally, I have a piece of Primare A32 250Wpc stereo amplifier planned for that task. The main part of my system is consisted of Krell Phantom preamp (with active crossover onboard) and a pair of Krell Evo-400e monoblocks. This combo is supposed to drive the main speakers, while Primere A32 is planned to feed two REL Gibraltar G1, via high level inputs, as REL strongly recommends in user manual.

Is good idea to ask Primare factory, perhaps? They should know well whether REL's high level input connection method is environment safe enough for power amplifier design employed in their A32..

Thanx once more guys, tips like these may apear as a true paramount for me.

Zormi
I have a pair of REL G 1s connected in the manner suggested by the OP ie red and yellow to the red terminal and the black to the black terminal. This is what the manual says. Alternately, the yellow ground lead can be connected to a exposed screw(metallic face showing) on the amp on the rear etc
I have 5 REL subs connected in this way
Cheers

My advice is to contact the manufacturer of your amplifier to ensure that it is compatible with the intended use.

Brownsfan,

Could you publish your advice overhere, anyway? I face a very similar dilema with a pair of REL Gibraltar G1.

Thanx.

Be careful. I sent you a message with more detail.