Macintosh Balanced outputs - How was it confirmed?

[cpitts]

Hey guys,

There's lots of mentions of the output to the power amp being balanced. Just wanting to understand HOW this was confirmed to be balanced v's unbalanced.

Having done some reading up on both formats, there seems to be ways and means to convert between the two formats (even at the connector level) so just wondering where this common statement of 'its balanced' came from? Has it been confirmed by Clarion?

Very interested as this whole 'upgraded amp' thing could be very quickly sorted.

Also, has anyone tried re-earthing the HU with decent fuses and cables to the battery (incl clean 12v power) to see if it gets rid of the hiss?

[Ric]

All the audio passes down a multiwire cable coming out the back of the McIntosh.
It's labelled "DIN CORD" in this diagram:



and is the thick black cord you can see someone holding in this pic:



and this is the pinout of the DIN plug that I've worked out by experiment:


You can see there is a "+" and a "-" signal for each audio channel.
Neither of these is connected to ground, and you would probably damage the HU if you did connect one side to ground.


Also, has anyone tried re-earthing the HU with decent fuses and cables to the battery (incl clean 12v power) to see if it gets rid of the hiss?
When can you hear hiss? Mine is very quiet. The noisiest bit is the cooling fan on the power-amp.

[Mo_GT]

Hey guys,

There's lots of mentions of the output to the power amp being balanced. Just wanting to understand HOW this was confirmed to be balanced v's unbalanced.

Having done some reading up on both formats, there seems to be ways and means to convert between the two formats (even at the connector level) so just wondering where this common statement of 'its balanced' came from? Has it been confirmed by Clarion?

Very interested as this whole 'upgraded amp' thing could be very quickly sorted.

You can convert any unbalanced signal to a balanced signal with a LOC or line driver with this function and using the proper rca that supports this.

From Ric's diagram it doesn't look like the output to the amp is balanced +ve to -ve .

But since the term "balanced" can be used creatively, if i were marketing this product and i wanted to throw a fancy term in to make it sound impressive I could say that it has balannced signals and mean that the outputs from the Hu were balanced to the input of the amp.

[Ric]

...
From Ric's diagram it doesn't look like the output to the amp is balanced +ve to -ve .
...

What makes you say that?
For the five channels (FR, FL, RR, RL, and SUB) there is certainly a "+" and a "-" signal. Both of them are swinging, presumably in antiphase. That is certainly "balanced" in my book.

[cpitts]

Ah, ok, so the theory is based on the +/- aspect of the diagram. In which case the balanced aspect is assumed.

Have you measured voltages to test your theory?

[Mo_GT]

...
From Ric's diagram it doesn't look like the output to the amp is balanced +ve to -ve .
...

What makes you say that?
For the five channels (FR, FL, RR, RL, and SUB) there is certainly a "+" and a "-" signal. Both of them are swinging, presumably in antiphase. That is certainly "balanced" in my book.

Usually, on a balanced pair there is a third wire for each pair(ground).

A pic i found online:

[Mo_GT]

I should add that some twisted pair rca's might use a metal foil sheid that acts as ground and is able to carry a balanced signal thru.

Balanced:


Unbalanced:


With these RCA's there's no third wire but the number of twists per length becomes the main factor in keeping the signal balanced.

[cpitts]

Mo_GT, you're reasonings are exactly why I'm questioning whether the signals from the plug ARE actually balanced.

From what I can see, I see a high density connector to replace a large wad of standard RCA cables (all which have 2 cores).

This may be not quite as hard as people are making out. (At least, in my mind.)

Not meaning anyone harm, just seeking appropriate ratification of this commonly held belief.

[Ric]

Usually, on a balanced pair there is a third wire for each pair(ground).

In an "unbalanced" connection, the signal is between the signal wire and ground.
In a balanced connection, the signal is between "+" and "-". Ground is just there for protection. You can regard the power supply ground as forming this connection in the McIntosh lead.

Yes, I've measured the voltages. After studying Electronic Engineering for four years, and being a practicing electronic engineer for 25 years, in my considered opinion this IS a "balanced" connection.
(But I also think you could easily connect is to an unbalanced system with just a small coupling transformer for each channel.)

[cpitts]

Something worth noting is that the current McIntosh car head unit line-up consists of all HU's having line level RCA Line Outs for connection to amps.

eg: http://www.roger-russell.com/caraud.htm

and

http://www.mcintoshlabs.com
- look under the owners reference area at Car Audio. There's a manual for their current HU offering.

EDIT: My point here being that companies don't just change tact for one head unit in their line-up. Esp if it's built to a price point for OEM delivery.

[Mo_GT]

Yes, I've measured the voltages. After studying Electronic Engineering for four years, and being a practicing electronic engineer for 25 years, in my considered opinion this IS a "balanced" connection.

Your qualification and experience trumps mine in this area so your opinion trumps mine

Just out of interes, what were the voltages of the outputs from the HU?

[Ric]

I unplugged the cable from the power amp, placed a 1k resistor between "+" and "-" on each channel, and watched the RMS AC voltagerise and fall as I adjusted volume and balance to identify each channel (and bass to confirm which was the sub).
As I recall, it was just over 1V at full volume.
What I didn't do was connect both "+" and "-" to an oscilloscope, to confirm what each wire was doing in relation to ground.

[overl0ad]

ric, do you do stuff like this just cos you're bored?

[cpitts]

Any chance you can do the CRO check? I know it's a massive ask but if you still have the unit out on the bench . . .. .


Edit. Oops, I accidentally edited your post instead of quoting it as I intended. Sorry, I lost a coiple of lines. Ric

[Mo_GT]

Cool, when i have some time i might try and wire up a rca to one of the speaker outputs and send it to an amp and see if the voltage is high enough for the amp to receive.

cpitts, you can get a line driver and solve your problem?