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S2M outputs in stereo to mono conversion

Posted: 3 years ago Quote #940
Hello Edcor,

I need to convert a stereo line output signal from a digital audio broadcast tuner to mono. So I can pass it to the unbalanced line input of a mono amplifier.

The the right and left channel line signal levels from the tuner are max 1Vrms and the line output impedance is less than 100 Ohm.

Could the EDCOR S2M boxed stereo to mono coupler could be a good way to do this?

The S2M specifications don't tell about the exact amplification factor of the boxed matching transformer for each of the outputs.

Assuming the stereo right and left line signal levels from my DAB tuner are 1Vrms each. When I connect these to the S2M stereo unbalanced line input, will the
a) mono unbalanced line output from the S2M then be 1Vrms?
b) mono balanced line output from the S2M then be plus and minus 0.5Vrms?

Is it correct, that the S2M input and output RCA grounds are not internally connected?
Posted: 3 years ago Quote #941
The S2M can handle up to 5Vrms. and the ground are fully isolated. The S2M will not increase any signal level as it is more of a 1:1 ratio. It should not have any issue with the 100 ohms impedance.
Brian Weston
Tech Support
EDCOR Electronics Corporation
Posted: 3 years ago Quote #942
Thanks for your answer.

You write the S2M shouldn’t have any issue with the 100 ohms impedance.

Let’s now assume the case, I didn’t use any stereo to mono coupler, but just tied the (less than 100 Ohm) right and left channel line outputs from the tuner directly together, and connected them directly to the high impedance line input of my amplifier. Then I would overload each line output of my tuner. Because each output tries to drive the very low impedance of the other, forcing both outputs into current-limit and possible damage. As a minimum, severe signal loss would result.
    
It seems to me, if I use the S2M boxed matching transformer, I will get a similar problem:

Assuming the S2M boxed matching transformer looks like an Edcor PC6400 stereo to mono coupling transformer inside: http://www.edcorusa.com/content/images/thumbs/0001957_pc6400.png
Then it looks to me, that the two primary windings (pin1-p3 and pin2-pin3) of the S2M matching transformer will couple magnetically (by mutual inductance) through the common transformer core, working in effect like a 1:1 transformer. The result will be, that each (right and left) line output from the tuner tries to drive the very low impedance of the other line output through this 1:1 transformer. Again the consequence will be overload of each line output from my tuner.

Will my proposed use of the S2M boxed matching transformer in any way protect my tuner line outputs against the described overload problem?
Posted: 3 years ago Quote #943
If the secondary has an impedance of around 100 Ohms then that is what the primary will see. The only difference is if you are using the balanced line output. Most unbalanced line level outputs are 10K Ohms, but listed as the minimum impedance they can handle. I would double check with the manufacture with what the tuner can handle. The S2M can handle 100 Ohms impedance just fine. It really depends on what the equipment wants to see. The S2M will reflect the unbalanced secondary impedance into the primary with a 1:1 ratio.
Brian Weston
Tech Support
EDCOR Electronics Corporation