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 #128647  by JustinJohn
 Tue Jun 04, 2013 6:29 pm
I'm trying to figure out how to run my MC250 in bridged mono (100w), and I'm finding some conflicting info on the net, particularly about mc250's in certain serial# groups having different bridged-mono requirements than mc250's in other sn# groups.

I saw the directions Mijknahs posted which say, For a cab rated at 4ohms (which mine is):

1. Use a jumper wire to jump the 8 ohm (R and L) terminals together. I use a short speaker wire.
2. Have the amp set on MONO
3. Plug in your preamp to the Right side only.
4. hook your speakers up to the 8 ohm and COM on the terminal strip (doesn't matter which side since they are bridged).

....can someone help clarify what I need to do?
My MC250 SN# is: 12L75

Also - in bridged mono, do I only use one volume knob?

 #128648  by waldo041
 Tue Jun 04, 2013 7:20 pm
Let's first be sure you understand what your amp is and what you are asking the amp to do. The mc250 is 2 amplifiers each with their own input (preamplifier), left and right channel which work separately when ran in stereo. Mono is to run the mc250 as 1 amplifier so what you are doing is combining the 2 amplifiers together, but since they both have their own inputs(preamps) only 1 is needed. So your mono/stereo switch switches the mc250 from using 2 inputs to only 1 input (mono)and sends its lone signal to both amplifier sections which also need to be jumpered together at the outputs to combine the amplifiers together. When you jumper the outputs you are paralleling the autoformers thus halving their output impedance. So when you jumper the 4 ohm taps you are creating a 2 ohm tap,when you jumper the 8 ohm taps you are creating a 4 ohm tap and when you jumper the 16ohm taps you are creating an 8 ohm tap.

as Mr. Shank stated, you need to jumper the output tap your speaker load requires and attach you speaker to it and a com(mon). Place the stereo/mono switch in mono and use whichever input the amp calls for for mono use.

 #128678  by Pete B.
 Wed Jun 05, 2013 7:13 am
Hey J,
If you want to A/B your MC250 with mine, we can do that.
fwiw, I know mine is benching ~85W per side (did your tech test yours for output power?).
I've never had it past 12 o'clock on a gig.
I run it in stereo with each speaker having it's own volume knob, though. I've never ran it in mono (yet).
Something doesn't sound right, It should be basically like running two Twin Reverbs, volume wise.
 #128687  by JustinJohn
 Wed Jun 05, 2013 9:28 am
I'm running it in mono using only one side, and my cab has 2 speakers - so I'm guessing I halved the power twice - once by only using one side of the Mc, and again by splitting it between 2 speakers...? Tho I'm not very knowledgable regarding how electronics and power all work. :oops:

Yea man! I'd love to A/B your Mc and mine sometime - would be interesting at the very least... I have a gig this Friday at the Rose Festival at 6, then at White Eagle at 9:30 - so I'll definitely have a feel for the thing by days end.

 #128690  by mijknahs
 Wed Jun 05, 2013 9:59 am
Make sure you are hooking up your speakers in parallel (red on one speaker to red on the other speaker and same for black). This would be a 4 ohm cabinet (assuming these are 8 ohm speakers). Hook the cab to one channel using the 4 ohm tap. Try the other channel too to see if its louder.
 #128693  by Pete B.
 Wed Jun 05, 2013 10:49 am
Hey, I'm on that gig with you Fri @ 6pm, on Steel!
I think I am hangin' with the backline amp, though.
I could easily bring the wiring harness if you want to experiment with stereo.
 #128695  by JustinJohn
 Wed Jun 05, 2013 11:29 am
Thanks for the input Jim! =)

Awesome Pete!! Ill see you friday!! :cool:

here's pics of how my speakers are wired - both are 8ohm JBLs - the top input only feeds 1 speaker, the bottom feeds both


Image I should be tapping 4ohms (mono), and 8ohms (bridged mono) out of the MC?
 #128701  by mijknahs
 Wed Jun 05, 2013 12:31 pm
It looks like that has to be wired in parallel. So if you are using only one channel separately (switch on "stereo") you would use the 4 ohm tap and the appropriate input. As Pete B. does, you could also run each speaker from separate channels (8 ohm tap - still on "stereo" setting) but you would need to run a signal into both inputs (split your single preamp signal into two cables).

If you bridge the channels, you would bridge the 8 ohm taps together (and com taps together) and flip the switch to "mono". Then the 8 ohm taps would "become" a 4 ohm tap. You could hook up to either side since they are bridged. I think its the right channel input and gain knob that would contol it.
 #128702  by JustinJohn
 Wed Jun 05, 2013 12:48 pm
Thanks for the input and expertise Jim, Pete, and everyone! I sincerely appreciate it! :hail:

Yea - I'm definitely gonna go the "bridged-mono" rout - jumping the 8ohms together, the coms together, connecting speakers to the right 8ohm and com, and using the right input and gain knob.

I'm pretty thrilled to finally be getting so close to the rig of my dreams!

:smile: :smile: :smile: :smile: :smile:
 #128723  by JustinJohn
 Wed Jun 05, 2013 7:39 pm
I figured out why my MC wasn't as loud as it should have been - bad cable! (from pre into MC)

I replaced that and BOOM! I can hardly turn it past 9 o'clock!!

I gotta say - what a big difference! The feel is so much snappier then the Twin's power section, the sound is tighter, more "taught" or "firm"... for lack of a better description.

Im a true believer in the magic of the McIntosh!

:smile: :smile: :smile: :smile: :smile: :smile: :smile: :smile:
 #128747  by Pete B.
 Thu Jun 06, 2013 10:35 am
JustinJohn wrote: I can hardly turn it past 9 o'clock!!
This is exactly my expieience.
 #128755  by mgbills
 Thu Jun 06, 2013 11:34 am
Also to be checked cincinnatiohio is the output of your preamp.

This is especially true of an SMS. When I first got mine I was running the trimpot at 11:00. I was in a small practice room with a very loud drummer with my Mc250 cranked, and I couldn't hear myself. If you have an SMS, crank the trimpot and it'll match the output of a Twin preamp. It also makes the output less nasal.

Also, an the stereo's only really necessary to hookup in stereo if you're using different speakers as Pete B. is, or your using speakers of different impedance ratings.

If you just wire the cab in parallel, you have backup in case of a speaker failure...and have the advantage of increased output.

If any of that makes sense...