Doubling up the amps!

[4-2-7]

The MONO-BRIDGE operation of the MC 7270 amplifier always requires the speaker load to be connected between two opposite channel impedance terminals. The common terminals are not used. Do not connect leads independently between left and right channel impedance taps as this will cause high circulating currents and overheating. Connect the speaker leads to the output terminals as listed in this chart:
Load Impedance Connect the Connect the In Ohms -Speaker Cables to: +Speaker

Cables to:
Terminal 2 Left 1 Ohm Terminal Right 1 Ohm
Terminal 4 Left 2 Ohm Terminal Right 2 Ohm
Terminal 8 Left 4 Ohm Terminal Right 4 Ohm

AMP
Terminal 16
Left 8ohm speaker
Left 8 Ohm Terminal
Right 8 ohm speaker
Right 8 Ohm Terminal

Neither output terminal is at ground potential. To use the MC 7270 to feed a line whose constant voltage is 25 volts, connect the speaker cables for 2 ohm MONO-BRIDGE output.

 

[leftside]

What is the impedance of your speakers?

8 ohms. But, the B&W's quite often drop down to 3 ohms. A few people (including you ) recommended I used the 4 ohm tap. The McIntosh manual states that if using the 4 ohm tap in stereo mode that you should use the 2 ohm tap in mono block mode.

 

[4-2-7]

View attachment 648090

Your reading it wrong

Colum on the left is the amp 16 ohms >> to drive left or right terminal (ie Speakers) @ 8ohms middel and right colum.

 

[4-2-7]

8 ohms. But, the B&W's quite often drop down to 3 ohms. A few people (including you ) recommended I used the 4 ohm tap. The McIntosh manual states that if using the 4 ohm tap in stereo mode that you should use the 2 ohm tap in mono block mode.

I went and looked at the manual for you amp and speakers.
Again in mono bridge mode if you want to drive a speaker @ 4ohms you use the 8 ohm tap on the amp.
if you want to drive a speaker @ 8ohms you use the 16 ohm tap on the amp

 

[leftside]

I'll sleep and on it, and read the manual again tomorrow. This is the first time I've configured mono block speakers, so I admit I could be wrong

 

[4-2-7]

I'll sleep and on it, and read the manual again tomorrow. This is the first time I've configured mono block speakers, so I admit I could be wrong

I'll sleep and on it, and read the manual again tomorrow. This is the first time I've configured mono block speakers, so I admit I could be wrong

Yeah it's just you always step up (higher number) when bridging
Stereo 8 ohm speaker you use the 8 ohm taps.
Mono bridged 8 ohm speakers you use the 16 ohm tap.

Yes you can as you where doing diving them at 4 ohm in stereo, so then you would use the 8 ohm tap.

 

[damacman]

4-2-7 ... Your mind is wrapped around strapping, not bridging. He has the amps wired correctly for 4 Ohm speakers.

 

[leftside]

Yes, I think I have it correct damacman:
https://en.wikipedia.org/wiki/Bridged_and_paralleled_amplifiers

Bridged amplifier
Example. Two amplifiers, each rated 100 watts maximum into 4 ohms, in bridge mode they will appear as a mono amp rated 200 watts into 8 ohms.

 

[leftside]

Certainly sounds good configured like this anyway. Currently listening to some John Lee Hooker and the imaging is superb.

 

[4-2-7]

4-2-7 ... Your mind is wrapped around strapping, not bridging. He has the amps wired correctly for 4 Ohm speakers.

Ok so then what's the difference between bridge and straped.
He has 8ohm speakers.
My two mc275 at 90 wpc are straped. here I have the two 8 ohm taps joined with the provied gold bar as are the two comons. Do I still have 180 wpc? BTW this is when I had it hooked to 6ohm speakers.

 

[leftside]

Create another thread, don't hijack mine lol. Seriously, this is a good question and could warrant a separate thread... I'd certainly follow along.

 

[twiiii]

Let's see. 25 volts squared= 625 divide by 540 watts= 1.15 ohms. 70.7 squared = 5000 divided by 540 watts= 9.2 ohms. , So yes the 2 ohm hook for 25 volt seems reasonable and the 8 ohm almost for 70.7 volts. We all know a 7270 will put out 300 watts a channel so the 8 ohm is correct. Remember most of the time 25 and 70 volt lines the transformers feeding the speakers can be compromised below 70 HZ, so always be prepared to install Hi pass filters to the inputs of the amps to prevent excessive current from over heating the amps, causing pre-mature failure and engaging the Power Guard prematurely.

 

[Velocityboat]

Your reading it wrong

Colum on the left is the amp 16 ohms >> to drive left or right terminal (ie Speakers) @ 8ohms middel and right colum.

He is reading right. Here is schematic of an 8 ohm speaker tapped to MC2500 in bridge and parallel mono. The chart for MC2500 is written like his amp. Same column format.

 

[62caddy]

Ok so then what's the difference between bridge and straped.

I believe bridging doubles output voltage while mono parallel (a/k/a "strapped") doubles current.

 

[4-2-7]

He is reading right. Here is schematic of an 8 ohm speaker tapped to MC2500 in bridge and parallel mono. The chart for MC2500 is written like his amp. Same column format.

It looks like Briged does not use the (-Comon on the amp) and after switching the Mono switch on, they run off the 8ohm taps left to (-) of the 8 ohm speaker, and right to (+) of the 8 ohm speaker.

Parallel Mono like all my amps say to do it is Turn the Mono switch on, Strap the comons together and they go to the (-) of the speaker. If you have 8 ohm speakers you strap 16 to 16 ohm taps together and the goes to (+) speaker, This doubles the power of the amp.

In fact with the MC 402 you can't double the power in parallel mono to a 8 ohm speaker. Thats because the 402 does not have a 16 ohm tap. If you want to mono the 402 and get the 800 wpc you need 6 & 4 ohm speakers.

 

[leftside]

Took in both my amps for testing and to upgrade the LED's. I was pretty sure one was quieter than the other. I also thought they were both the same model 7270, but it turns out one is slightly newer than the other - and McIntosh changed the potentiator's. One uses 50k and the other uses 100k. Well I'm glad it wasn't my hearing that was going and it's also meant to be a simple upgrade for the one unit. Just watch out if you are trying to mono-block these older amps - there might be differences...

 

[damacman]

Interesting. That shouldn't be an issue with the gains maxed though as they're effectively out of circuit.

 

[leftside]

I did have both amps on max gain, so I'm not sure. Maybe there is also another issue. I'll mention it to the tech.

 

[leftside]

Oh dear - slight disaster. The slightly older unit can't be modified to the specs of the slightly newer unit. McIntosh no longer carries the parts. This is a real shame. My tech says these are the two best 7270's he's ever seen. So.... I'm keeping both units for now and simply adjusting the gain. But, I'm on the look out for another minty 7270. Chances are this one will match one of the two that I already have. Once you've tasted mono-blocking you can't go back

 

[Velocityboat]

Get a MEN220 or Lyndorf unit with Room Perfect. It will adjust gain as needed and you will have no amp to sell. Plus it will sound even better if you have room acoustic issues.