Balanced/Unbalanced switch action on MC302 amplifier (or similar)

[LazyBorzoi]

I got a question for owners of MC302 or similar Mc amplifiers that have a switch on the back that allows switching between balanced and unbalanced input connections.

(1) If I connect to the amp using unbalanced cables (RCA) and keep the switch in unbalanced position, I get one volume. If I then flip that switch to balanced position but keep the same cables, the music still plays but the volume slightly goes down. To be honest, I don't understand why I still hear the music - shouldn't it completely switch to the balanced inputs which in my case are not wired???

(2) Then I removed the RCA cables and replaced them with balanced cables (XLR). In this case, I still hear the music in both positions of the switch (balanced or unbalanced) but the volume doesn't change like it did in case (1).

If you have MC302 or another Mc amp that has balanced/unbalanced switch, could you please verify/confirm that what I see is a normal behavior?
Thanks in advance!

[Macuser]

I did the same thing when I first brought my mc1201's home. I was told by someone in the know not to have both types of cables plugged in simultaneously and use that switch for comparison as it could damage something. The same fellow said to forget about the rca and use the balanced input for a better connection. I followed his advice and it's been working well ever since.

[LazyBorzoi]

Originally Posted by Macuser

I did the same thing when I first brought my mc1201's home. I was told by someone in the know not to have both types of cables plugged in simultaneously and use that switch for comparison as it could damage something. The same fellow said to forget about the rca and use the balanced input for a better connection. I followed his advice and it's been working well ever since.

I only plugged one type of interconnects at a time. Could you please check if you still hear the sound if you were to flip the switch to the other state (regardless of what type connects you are using)? I'm just trying to figure out if my amp works properly...

[W9TR]

The McIntosh amps I have MC 602 and MC 2301 behave exactly like your MC 302. The unbalanced input and balanced input are not completely separate. The unbalanced input uses the + side of the balanced input.

Tom

[Masterlu]

Originally Posted by W9TR

The McIntosh amps I have MC 602 and MC 2301 behave exactly like your MC 302. The unbalanced input and balanced input are not completely separate. The unbalanced input uses the + side of the balanced input.

Tom

This is “not” the same with other brands.

[miketuason]

Like Lazy Borzoi, I use the Bal/Unbalance switch one at a time, I have the MC601 that I use for both stereo listening and home theater, for stereo, I use balance cable from preamp to amp then for home theater, I unplugged the balance cable from the amp and plug the RCA coming from the preamp processor to the amp and change the switch to Unbalance, works wonderful.

[destan705]

As W9TR mentioned, the unbalanced input and balanced input are not completely separate. The input mode switch on the MC302 (I have one) is not really a selector switch as it is in other amps. The + leg of the balanced input and the unbalanced input both feed the + input of a differential input amp. Whether they are actually tied together inside the MC302, I'm not sure, but I wouldn't risk feeding two active sources into the MC302 simultaneously (balanced and unbalanced at same time). The input mode switch on the MC302 when switched to "unbalanced" sends the input to a unity gain inverting amp and an inverted copy is made which feeds the - input of the differential input amp. This is why its 6 dB louder when the switch is set to unbalanced and you are feeding an unbalanced signal: the signal goes into the + input of the differential input amp, and the inverted copy of the input signal feeds the - input of the differential input amp. Switch back to balanced (on the switch), and an inverted copy of the input signal is no longer made, and the - input of the differential input amp is now connected to ground instead of of the inverted signal (6 dB quieter).

Hope that made sense.

[LazyBorzoi]

Originally Posted by destan705

As W9TR mentioned, the unbalanced input and balanced input are not completely separate. The input mode switch on the MC302 (I have one) is not really a selector switch as it is in other amps. The + leg of the balanced input and the unbalanced input both feed the + input of a differential input amp. Whether they are actually tied together inside the MC302, I'm not sure, but I wouldn't risk feeding two active sources into the MC302 simultaneously (balanced and unbalanced at same time). The input mode switch on the MC302 when switched to "unbalanced" sends the input to a unity gain inverting amp and an inverted copy is made which feeds the - input of the differential input amp. This is why its 6 dB louder when the switch is set to unbalanced and you are feeding an unbalanced signal: the signal goes into the + input of the differential input amp, and the inverted copy of the input signal feeds the - input of the differential input amp. Switch back to balanced (on the switch), and an inverted copy of the input signal is no longer made, and the - input of the differential input amp is now connected to ground instead of of the inverted signal (6 dB quieter).

Hope that made sense.

It does actually make sense. Thank you so much for this!
To be honest I still don't understand the choice behind combining the + of the differential input with the unbalanced signal. Sounds like a recipe for disaster...

[eziggy]

That's funny timing, started a new thread on this for the MC452 not seeing this thread (thanks Maks). Sorry for the new thread, I assumed the questions was going to random.

Spoke to Chuck at McIntosh about this since I heard it on the balanced side as well. I had the switch on unbalanced and was using balanced. Testing new cables, was getting super disappointed at the results. When sound was playing never bothered to check the toggle switch.

Everything mentioned above is spot on, only thing to add is that it does impact the balanced side as well (using balanced and switch on unbalanced). Having both connected at the same time isn't recommended, but more for the preamps than the amp itself.

[LazyBorzoi]

Originally Posted by eziggy

Testing new cables, was getting super disappointed at the results.

Just curious what you mean by "disappointed"?
Were you expecting a noticeable difference from switching from unbalanced to balanced?