MC2505 / MC2105 - mono?

damacman

Resident Psycho
Obviously, we all know that running MC2505s and MC2105s in mono is not part of the original feature set. However, I've got a beautiful MC2105 just chilling here and it's killing me. I'd like to use it in the multi-channel set up along with another metered McIntosh amp - center (mono) and surrounds (stereo) so I've got all Mc power.

MC2505s and MC2105s are pretty easy to find and can be had reasonably. Is there some kind of modification one can make to the amplifier so that it can be used in mono like the MC250 / MC2100?

If not, I may sell my MC2105 and look for a pair of MC2125s . . .
 
How about merging L&R channel from the sorce with a Y addaptor into one side of the amp?
 
Probably - but not without involving some butchery which will probably lay a big hurting on your amplifier(s) at the register come sale day.

Frankly, I like the (2) 2125 idea better and besides, the meters work better on those.* :yes:

*Then you'll need to change your sig to, "It's just easier to leave the meter range switch on the "WATTS" setting . . ." :D
 
Last edited:
Well, the center channel is already mono in nature . . . so the input thing isn't what I'm worried about. It's the tying the left and right channels together part . . .

62caddy . . . I like your sense of humor! I've actually had a bunch of MC2125s over the years and only one MC2105. The cosmetics of the MC2105 just kind of pulled me in and I'd really prefer to run a pair of them since I already have one . . .
 
Understood, my friend!

2505/2105 are a bit less "cluttered".

It's an interesting idea all the same.
 
I've located a REALLY nice MC7104 for super reasonable money . . . hmmm . . .

But, I'd still like to know the answer to this question. Terry? c_dk?
 
Thought I'd give the old avatar a refresh for a while.

Don't worry, the '62 will be back! :D
 
The 70 s and 80 s Mac amps do not "bridge" they parallel the two channels to deliver the same signal, mono, to two speakers. The owners manuals often show how to wire up the two , mono, signals to one speaker if so desired. I believe the Mc2255 was the first amp to bridge the two channels.

If you look at a mc250 or 2100 schematic you can see the mono switch is really just a switchable "y" plug circuit. Can replicate it with an external y plug.

I think it would be easier to mod if needed and sound better to do a passive biamp of the center speaker.
 
Is there some kind of modification one can make to the amplifier so that it can be used in mono like the MC250 / MC2100?

Yes of course it can be done, the first part will be in fact a "Y" lead......

The second part is the tie between the two 4Ω taps.....

Then you can follow the Parallel mono instructions for wiring the speakers....

Easy......:thmbsp:
 
Yes of course it can be done, the first part will be in fact a "Y" lead......

The second part is the tie between the two 4Ω taps.....

Then you can follow the Parallel mono instructions for wiring the speakers....

Easy......:thmbsp:

:banana:
 
The stereo mono switch on a 2100 does two things. First it switches the input to the Left driver card from the left output of the input card to the the right channel output of the driver card. Second, it ties the two 4 ohm out puts of the Left and right autoformers together. Not as simple as one would think. Then remember you can only parallel the outputs as the commons are tied to ground.
 
Keep in mind, mono parallel only doubles current, not the voltage output - so a McIntosh amplifier in mono mode would play no louder than it would in stereo mode.

The only benefit is that in mono, you could run double the load the amplifier's maximum for stereo mode; ie: If lowest taps were 2 ohm (stereo), it could run 1 ohm in mono; 1 ohm (stereo) becomes 0.5 in mono and so on...

True bridging doubles your voltage.
 
The 70 s and 80 s Mac amps do not "bridge" they parallel the two channels to deliver the same signal, mono, to two speakers. The owners manuals often show how to wire up the two , mono, signals to one speaker if so desired. I believe the Mc2255 was the first amp to bridge the two channels.

If you look at a mc250 or 2100 schematic you can see the mono switch is really just a switchable "y" plug circuit. Can replicate it with an external y plug.

I think it would be easier to mod if needed and sound better to do a passive biamp of the center speaker.

c_dk - understood on the parallel mono business (or "strapping"). I don't have an MC2100 or MC250 service manual at my disposal, but do have an MC2300 service manual (which is likely very similar - would you be so kind as to confirm?). There's also that issue about using the right gain control as the gain for the amp when used in mono and I can see clearly how Mc did that in the schematic.

What I think I may do is add a switch to the rear panel of the amplifier at the output of the input board, just as McIntosh did in the original design. That way, I can use only the Right channel input and that gain control will provide the exact gain to both channels of the amplifier. It looks like Mc used shielded wire for the connection between the output of the right channel input board and the stereo / mono switch and I actually have some of that exact stuff that I snagged out of a basket case MC2300 (and possibly also the stereo / mono switch).

Assuming I can make this mod, are you saying that I should have no problem paralleling the L and R outputs?
 
The stereo mono switch on a 2100 does two things. First it switches the input to the Left driver card from the left output of the input card to the the right channel output of the driver card. Second, it ties the two 4 ohm out puts of the Left and right autoformers together. Not as simple as one would think. Then remember you can only parallel the outputs as the commons are tied to ground.

twiiii - I do not see that in the MC2300 schematic. Is the MC2100 different in this regard?
 
Keep in mind, mono parallel only doubles current, not the voltage output - so a McIntosh amplifier in mono mode would play no louder than it would in stereo mode.

The only benefit is that in mono, you could run double the load the amplifier's maximum for stereo mode; ie: If lowest taps were 2 ohm (stereo), it could run 1 ohm in mono; 1 ohm (stereo) becomes 0.5 in mono and so on...

True bridging doubles your voltage.

P = I*E
2P = 2I*E or I*2E
 
The stereo mono switch on a 2100 does two things. First it switches the input to the Left driver card from the left output of the input card to the the right channel output of the driver card. Second, it ties the two 4 ohm out puts of the Left and right autoformers together. Not as simple as one would think. Then remember you can only parallel the outputs as the commons are tied to ground.

It actually is pretty simple.......Ah yes, sorry "Y" lead wont do it, you have to drive the two driver boards with one gain control because you cant have any difference between the signal going to the two driver boards.......
So the switch links the two 4Ω taps, and redirects the signal from the left input (post gain controls) to the two driver boards....
 
Last edited:
Yeah, this does look like a simple mod. Thanks guys. Now, I need to score another MC2105 and I can get busy. Interesting how the 4 Ohm taps are tied together via the Mono / Stereo switch with the MC2105, but not with the MC2300 - at least according to the respective service manuals.
 
Yeah, this does look like a simple mod. Thanks guys. Now, I need to score another MC2105 and I can get busy. Interesting how the 4 Ohm taps are tied together via the Mono / Stereo switch with the MC2105, but not with the MC2300 - at least according to the respective service manuals.

Yeah for sure, I reckon it will be an easy mod......

I wonder why they didn't have the parallel mono option on the 2105? Maybe they wanted to lure people into the more powerful amps.....
 
Last edited:
The Mc2300 schematic shows no connection between the autoformers and the stereo/mono switch.

I do not have a users manual here but would assume the taps would be hooked up with a jumper, in parallel, halving their value. The schematic so states the power output doubled and all the taps halved.
 
Back
Top Bottom