Grateful Dead Music Forum

A place to talk about the music of the Grateful Dead 

 #137480  by slatelacy
 Tue Mar 11, 2014 4:35 pm
Just got my SMS preamp. I have a couple questions on the set up. I'm running to a Mac Mc2120 to a 2x12 HT cab with E120s. The best I can figure by looking at the Mac manual is to run the main speaker cable to left com and left 8ohm with a jumper from left 8 to right 8. Sound right? Also, should I run the Mac gain wide open and make adjustments with the SMS? Thanks in advance!!
 #137481  by cripeowner
 Tue Mar 11, 2014 5:10 pm
There is no need to bridge the 2120 I believe it's 120 w per side plus I don't think the macs sound good bridged. Just use 1 side using the 4 ohm tap. Also try each side I found each side can sound different.
 #137482  by tcsned
 Tue Mar 11, 2014 5:35 pm
I have a MC2100 and I don't bridge and I have not needed the extra power even for big outdoor gigs. Some folks here crank the Mac up pretty high (but not all the way) and use the master volume on the guitar to control the volume. If you've got a guitar with the OBEL and buffer/master volume then that might work. I don't do that or I haven't yet. I may experiment with that method. I would think that using the preamp to control your volume would lead to a wimpy tone.
 #137485  by mgbills
 Tue Mar 11, 2014 7:37 pm
Bridging definitely not needed. I run the Mc at 50-75% on the volume knob. 2nd channel off. Crank the trimpot on the SMS. 11:00 o'clock for crispy clean (gain). 1:00-2:00 for some warmth. You can crank the Mc, but you'll be barely cracking your guitar volume with a buffered guitar. I like it that way. House volume all the way to "chase the neighbors dog out of the country"…all on your guitar. And I live on 5 acres in the woods.
 #137491  by TRG
 Wed Mar 12, 2014 5:28 am
I agree, bridging not needed.

I used to run my rig this way:
SMS Trim pot: Maxed
SMS Gain: 11:00
MC250 (each side going to a K120 in an SSP 2x12 cab): 25%

I now run it this way:
SMS Trim pot: Maxed
SMS Gain: 1:30
MC250 (each side going to a K120 in an SSP 2x12 cab): 40%

Of course the vol. on the guitar is now set lower, but by bumping up levels on the SMS and MC250, it provides more fullness to my sound, especially with the high notes. Atleast it sounds that way to me... :-)
 #137497  by RiseandFall
 Wed Mar 12, 2014 9:35 am
One thing to factor in....that SMS will sound worlds better in a few months. The more hours you put on it the better it will sound.
Brad had me leave mine on for a week when I first got it. It made a huge difference. Then I would leave it on for 8 hours a day for a couple more weeks. It just keeps getting better and better.

Per settings, I have the MC 50 all the way up and the trim pot on the back of the SMS almost all the way up.
My volume on the front of the SMS is about 10:00.
My guitar volume is maybe at 40%.
This works for me.
 #137498  by schmidtz
 Wed Mar 12, 2014 9:50 am
You guys must play loud. I run my Twin at ~3.5, and if I turn my 250 up to 50% (just one side, not bridged) my speaker (2 E120's) are jumping out of their baskets, like, visibly moving with every note.

Any higher than that, and the lights dim in my room with every note.
 #137503  by Bobbybriand
 Wed Mar 12, 2014 12:14 pm
I run my MC2300 bridged @ 1ohm into a 4x12 cab with E's . Com is COM left right dont matter cause its ground it where you hook up your positive that matters and the amount of speakers and how theyre wired together make the decision for you. My modded preamp tapped twin ab768 circuit all juiced up with waldo mods volume is at 5 and my MC2300 sound card modded volume is at about 2 to 3. I do run 2 K's for inside practise but I just use a rocktron300 velocity bridged at 4ohms with 2 K's in parrallel. I have one MC2300 still in the box and is left untouched more for a collector item but my main 2300 unit is amazing especially the range from output impedance from .5ohms to 16 is outstanding. You can always try swapping sound cards to the mono side may have an improvement or do some up grades on the mono channel. I don't see how bridging can make the MC sound worse it only uses the output transformer sector and joins it with your mono side so all the output power is redirected to one side.
 #137541  by zambiland
 Thu Mar 13, 2014 9:55 am
cripeowner wrote:There is no need to bridge the 2120 I believe it's 120 w per side plus I don't think the macs sound good bridged. Just use 1 side using the 4 ohm tap. Also try each side I found each side can sound different.
I think your amp needs attention. The two sides should not sound different. They should be identical. These are hifi amps and if they sounded different, it would mess with the stereo imaging something fierce. I use a MC2105 for my home studio and both sides sound exactly the same. These amps have also been used in mastering studios (I believe Joe Gastwirt used my setup for a number of the mastering of the CDs we love: Mac amp to ProAc Studio 100s). If there were any inherent differences between amp channels, they would never get used in this setting.

There's no reason a mac shouldn't sound good, bridged, as well. I can understand how yours might sound bad bridged, because if one channel is not operating properly (as evidenced by the apparent sonic difference between your channels), then the amplification will be asymmetrical, resulting in audible distortion.
 #138925  by Bobbybriand
 Sat May 10, 2014 7:01 am
There's nothing too fierce about it. Each side runs on its own asf slot soundcard. They are major factors in the cleanliness and headroom of each sides sound seperately. Now whether you ve been using the bridge switch or not. No two two parts are gonna age the same especially if theres jerry mods on the cards or just the bridged one. Take a look but I wouldn't call fierce.