Proper way to hook up a REL Sub

[Mac6]

Originally Posted by SCAudiophile

Not sure on a multi-tap amp; I would take the 'keep it simple' approach that the RELs should be connected on the exact same taps as your speakers are which in this case looks to be the 8-ohm tap(s), correct?

***Since hooking up the 2nd sub tripped the Sentry Monitor on your amp, I'd definitely call or write to REL and see if they've seen this config with your amp before and have a specific recommendation first.

I've left the connection on the 8 ohm taps and everything has been fine. Played the system pretty much all weekend and no Sentry Monitor trip. I will say that 2 RELs sounds fabulous with the MC275.

I will definitely be calling REL today just to make sure.

[Msegal]

I run my stereo REL G1 with a pair of MC275LEs. The black wire is unattached to anything.
It was set up this way by the REL distributor.
It sounds incredible.

[Mac6]

Originally Posted by Msegal

I run my stereo REL G1 with a pair of MC275LEs. The black wire is unattached to anything.
It was set up this way by the REL distributor.
It sounds incredible.

Interesting. I talked to REL product support yesterday and he said I was connecting to the MC275 VI the correct way (yellow/red together on each positive channel, black to chassis ground). He said I could also connect it with just the red or yellow (one, not both) to each positive channel but I would then need to increase the gain. This reduces something(too tech for me). I'm trying this now just to see how it is. But he said it really should not matter - that both ways should work and are safe. Obviously there are a few ways to hook up the RELs that are working for people.

The MC275 Sentry Monitor came on and shut the amp off just the first time I powered up with both REL T9i subs. Since then it has not happened again - around 20 hours of operation and on/off several times. I called REL just to make sure I wasn't off base with the connections.

[Stahle]

The difference between a balanced amplifier and an unbalanced amplifier has always been confusing to me. Is it simply a matter of how the amplifier is connected to the preamplifier or is it actually the design of the amplifier no matter the connection? For example, if I connect an MC275 to say a C2300 via a balanced connection with the input switch on the MC275 set to balanced, is the MC275 then fully balanced? And then assume I change the connection between the MC275 and the C2300 to a set of unbalanced RCA cables and set the input switch on the MC275 to unbalanced, is the MC275 then an unbalanced amplifier? I think this might be why there is some confusion about connecting a REL subwoofer to an MC275.

[W9TR]

It's actually pretty straightforward. In a truly balanced amplifier, the (-) output terminals are not connected to ground.

The 275 is not a balanced amplifier. Its (-) terminals are at ground potential.

It has two sets of inputs, single ended rca and differential XLR. Sometimes these differential inputs are called balanced inputs. But that description doesn't change the underlying topology of the amplifier.

The MC 452 is a truly balanced amplifier. The (-) terminals are not at ground potential, they go as far below ground as the (+) terminals go above ground. So you can't hook a REL sub to the (-) terminals of a 452.

Did this help?

[Stahle]

Originally Posted by W9TR

It's actually pretty straightforward. In a truly balanced amplifier, the (-) output terminals are not connected to ground.

The 275 is not a balanced amplifier. Its (-) terminals are at ground potential.

It has two sets of inputs, single ended rca and differential XLR. Sometimes these differential inputs are called balanced inputs. But that description doesn't change the underlying topology of the amplifier.

The MC 452 is a truly balanced amplifier. The (-) terminals are not at ground potential, they go as far below ground as the (+) terminals go above ground. So you can't hook a REL sub to the (-) terminals of a 452.

Did this help?

It helps, maybe it's a naming thing for me that's always been confusing. If an amplifier is hooked up via its balanced inputs, it makes me think it's a balanced amplifier.

[W9TR]

I agree it is very confusing.

[Mac6]

Originally Posted by W9TR

It's actually pretty straightforward. In a truly balanced amplifier, the (-) output terminals are not connected to ground.

The 275 is not a balanced amplifier. Its (-) terminals are at ground potential.

It has two sets of inputs, single ended rca and differential XLR. Sometimes these differential inputs are called balanced inputs. But that description doesn't change the underlying topology of the amplifier.

The MC 452 is a truly balanced amplifier. The (-) terminals are not at ground potential, they go as far below ground as the (+) terminals go above ground. So you can't hook a REL sub to the (-) terminals of a 452.

Did this help?

This is very interesting. Can you please point me to the evidence that the MC275 is not balanced? This surprises me. I am always learning new things about this hardware. Either way is fine as the MC275 sounds fantastic. I'm am curious about this though.

The MC275 has a "balanced/unbalanced" switch, and XLR inputs which I am using. Also, I was told by the REL service person not to hook up the black wire to the (-) terminal of the MC275 because it is balanced. I am using the chassis screws as grounds. Same as I did for my MC402, which is balanced.

[PHC1]

As far as I recall, the MC275 is not fully balanced. In fact the single ended/RCA engages an extra tube which balanced mode does not use leading me to believe it is handled by opamps to convert the signal. Also the gain was 6dB higher with single ended. Ear-wise, I always preferred the single ended on my MC275MKIV. Things may have changed, what is the current generation, an MKVI?

[Msegal]

Originally Posted by Mac6

This is very interesting. Can you please point me to the evidence that the MC275 is not balanced? This surprises me. I am always learning new things about this hardware. Either way is fine as the MC275 sounds fantastic. I'm am curious about this though.



The MC275 has a "balanced/unbalanced" switch, and XLR inputs which I am using. Also, I was told by the REL service person not to hook up the black wire to the (-) terminal of the MC275 because it is balanced. I am using the chassis screws as grounds. Same as I did for my MC402, which is balanced.

Definitions vary but a balanced circuit traditionally applies to a low level signal. It has a positive signal, an inverted signal (one half the amplitude of the positive signal) and a third common ground. This allows for transfer of low signal levels over long distances preventing the effects of RFI (its a mathematical equation which I won’t delve into).
When discussing whether an amplifier is balanced it’s important to differentiate between a balanced input stage and a balanced output stage. Only the latter is truly balanced.

The input on the MC275 accepts a balanced input, converts the signal to a non balanced state (only a positive lead and a ground). The amplifier only powers one lead of the speaker cable, let’s say positive,+. The amplified signal allows the waveform in the positive lead to move up and down relative to the negative lead. Therefore, the signal passes from the positive speaker cable to the speaker and than travels back to the amplifier via the negative cable. Of course a negative signal in the + lead will cause the opposite flow of electrons, to use an hydraulic analogy (not entirely accurate).

Think of it as a rope from the amp to the speaker (positive) and a second rope from the speaker to the amp (negative). The amp is a pulley system where the two ropes are attached. They must move in opposition. Pull the + rope, the speaker cone moves out and the negative rope moves in the opposite direction. Push the positive rope out and the speaker cone moves in, the negative rope moves out. In this model the amplifier only moves the positive rope, the negative rope is passive.


Now, let’s go to the input of a balanced amplifier. Instead of converting the signal back to a single ended circuit it takes the signal and leaves it with both a positive and an inverted signal. Two signals=two circuits. The + and the - signals are each amplified relative to the amplifiers ground. Not just the positive + going up and down relative to the ground - but also the negative - signal going down and up relative to the common ground. When the amplifier sends the signal out the speaker cable the positive limb and negative limb move in opposite directions. Not only does the signal return along the negative but is actively pulled along its course . The two out of phase signals are never combined until they reach the speaker cone.
Returning to our rope model, in a balanced amplifier the pulley system now does not need the two ropes to be connected. There are two pulley systems which are connected but not the ropes. Therefore, the amplifier can pull and/or push either the positive or negative ropes. The positive rope is controlled by the positive low level signal and the negative rope by the negative low level signal. As the positive is actively pulled the negative is actively pushed.

This has nothing to do with the purpose of the original low level “balanced “ signal but has been deemed “balanced” due to the symmetry of two circuits working in opposite phases.

The question is whether doubling your amplification circuits is beneficial, of no consequence of harmful. I believe that it all depends upon the application. It seems only the MC275 and MC75 are not balanced in their output stage. I am not sure about McIntosh’s direct coupled amps. All of their SS Autoformer amplifiers and the MC2301 have a balanced output stage.

We can also discuss the creation of a balanced signal at the source via a phono or DAC but that is a different story.

Best.
Mike S.