Proper way to hook up a REL Sub

[Mac6]

Originally Posted by Msegal

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.

Thank you for the detailed explanation. I have a couple of questions:

1. I believe you are saying that the MC275 design causes the speaker cones move in as opposed to out - is this correct? If so, should phase on the REL be set to 180 or 0?

2.Based on the MC275 not having a balanced output, should I be connecting the black wire of each REL to the negative speaker post instead of grounding it to the chassis or does it matter either way?

Thanks again.

[Msegal]

Originally Posted by Mac6

Thank you for the detailed explanation. I have a couple of questions:

1. I believe you are saying that the MC275 design causes the speaker cones move in as opposed to out - is this correct? If so, should phase on the REL be set to 180 or 0?

2.Based on the MC275 not having a balanced output, should I be connecting the black wire of each REL to the negative speaker post instead of grounding it to the chassis or does it matter either way?

Thanks again.

1. The speaker cone moves both in and out as the amplifier signal can move both forwards and backwards.

2. I do not know. Sorry.

[W9TR]

This is very interesting. Can you please point me to the evidence that the MC275 is not balanced? This surprises me.

Sure - here is the schematic. This is a push-pull amplifier, not a balanced amplifier. However note on the right side that the output transformers (-) terminals are floating and not connected to ground. This is an older MC 275 but the new ones are pretty much the same.
Given that the outputs are floating, I'll need to re-think what I said in an earlier post and also look for more recent schematics of a 275 to see if McIntosh changed anything in the output circuit.
Bottom line, REL has not adequately planned for connecting to the speaker outputs of different types of amplifiers, so people are having trouble.
Ron Cornelius of McIntosh has stated in other forums that McIntosh owners should use the high level inputs when connecting REL subs.

[trponhunter]

I cannot understand why and how the speaker level connection is supposed to work. It is simply a much higher distortion way to go versus line level- makes no sense. The only possible part of it that makes any sense is that the timing could potentially be better, as the signal has already run through the amp for both the main speakers and the sub. The part about matching the tonal character of the main speakers is just simply adding the same distortion and coloration that the main speakers get - a better way to me would be to eliminate as much distortion as possible going to the sub - and this would be line level. Either way - running a sub and main speakers "full range" and trying to "blend " them is usually very tricky at best. Generally better to use a proper crossover between the sub and mains.

[Mac6]

Originally Posted by W9TR

Sure - here is the schematic. This is a push-pull amplifier, not a balanced amplifier. However note on the right side that the output transformers (-) terminals are floating and not connected to ground. This is an older MC 275 but the new ones are pretty much the same.
Given that the outputs are floating, I'll need to re-think what I said in an earlier post and also look for more recent schematics of a 275 to see if McIntosh changed anything in the output circuit.
Bottom line, REL has not adequately planned for connecting to the speaker outputs of different types of amplifiers, so people are having trouble.
Ron Cornelius of McIntosh has stated in other forums that McIntosh owners should use the high level inputs when connecting REL subs.

Thank you. I believe I have it worked out now. I talked to REL twice and emailed McIntosh. The new MC275 has balanced inout but not output as you previously stated.
I am using the Hi Level input into the RELs with the Neutrik connector and connecting just the red wire from each REL to each of the (+) speaker terminals on the amp. The yellow wires are floating and taped. An alternate would be to combine the red and yellow on the (+) terminals. Either way will work with the combined having more gain. I find the one wire method to sound really good so I am leaving it that way (for now!). Since the output of the amp is not balanced, the black can either be hooked up to the (-) of each speaker terminal or float according to REL. I am going with the float for now. The REL support people were very generous with their time - really good service.
I am enjoying the sound of two RELs with this amp. Great sound all around.

[Cohibaman]

Did REL or McIntosh dissuade you from using either of the 2 additional C2300 outputs to feed the sub Low Level RCA inputs? I can’t for the life of me understand why this wouldn’t be the best connection method, while allowing on/off control to the sub.

[Msegal]

Originally Posted by Cohibaman

Did REL or McIntosh dissuade you from using either of the 2 additional C2300 outputs to feed the sub Low Level RCA inputs? I can’t for the life of me understand why this wouldn’t be the best connection method, while allowing on/off control to the sub.

My understanding from REL is that the use of the powered output from the amplifier allows for better tonal matching between the subs and speakers. The ultra high impedance of the input on the sub presents virtually no load to the amplifier, it will not alter the sound of the main speakers, does not require a high pass filter and is simpler in implementation.

[Mac6]

Originally Posted by Cohibaman

Did REL or McIntosh dissuade you from using either of the 2 additional C2300 outputs to feed the sub Low Level RCA inputs? I can’t for the life of me understand why this wouldn’t be the best connection method, while allowing on/off control to the sub.

I use the Hi level based on very good experience with my prior REl subwoofer. It sounds really good this way - blends in perfectly after dialed in. Give it a try if you can - see what you think.

[McGuyDLF]

If anyone is still following this...i'm about to get an REL T9 to connect to my MC402 - which I believe is fully balanced. Anyone else have this setup? Can you confirm that the red and yellow wires connect to the right and left positive speaker outputs and the black wire just floats, connected to nothing? thanks

[audioguy3107]

Originally Posted by McGuyDLF

If anyone is still following this...i'm about to get an REL T9 to connect to my MC402 - which I believe is fully balanced. Anyone else have this setup? Can you confirm that the red and yellow wires connect to the right and left positive speaker outputs and the black wire just floats, connected to nothing? thanks

McGuy - Check out all of the information in this thread that I was a part of regarding REL subs and the McIntosh 402...

https://www.audioaficionado.org/showthread.php?t=42358

Yes, the way you stated above is the way it's recommended from REL, verified with their tech support folks.....the rub here was that there was some incompatibility between the 402 and this hookup method....read through this. I always had to use the RCA connection when I had my RELs and the 402 due to lack of output. Read through it and report back when you get your REL.

- Buck