Grateful Dead Music Forum

A place to talk about the music of the Grateful Dead 

 #79158  by czyfingers
 Mon May 03, 2010 10:05 am
Sweet rig man! Did you make the silver face for the 2105? It looks great.
Regarding the switch in question, here's an answer I found on another forum to the same question. So I take no credit for how accurate it is, but it sounds reasonable.

The input coupling switch when in the direct position will bypass a .22mfd input coupling capacitor that is in the input circuit when the switch is in the normal position. Basically the capacitor is their to block any DC Voltage Offset from say a pre-amp that might get into the amplifier otherwise. The safe way to use the amplifier is with this switch in the normal position if your not sure if a pre-amp has any DC Offset on its Output!
 #79176  by 540EYE
 Mon May 03, 2010 12:22 pm
Thanks man, for the compliment. I did see that capacitor on the schematic, but could not figure out what it is there for. Thanks for clearing it up. Normal position it is !!

Yeah, the aluminum front is a homespun deal. I got the 2105 with busted glass and figured this would be a good fix. Trouble is, if I had one with good glass, I wouldda broke it so I had an excuse to do the metal front !! I can't leave NUTHIN alone. That Mc emblem has been in a "junk box of stuff" for the last 15 years or finally found a home.

Stay upwind

 #79196  by mijknahs
 Mon May 03, 2010 5:19 pm

Nice looking rig. How old are those speakers? Are they reconed? They look so new. My JBL cones are not even black any more. Kinda faded looking. Still work fine though.

 #79265  by 540EYE
 Tue May 04, 2010 1:47 pm

The (2) E's on the bottom cab are original cones. They are a bit "blacker" than the upper (2). The grain of the paper is just a tad smoother on them as well. If you look close, you can see that I had to fix the domes w/ some black silicone. They started to separate from the cone and would "buzz" every now and again. Haven't had any issues since the fix.

The top (2) are kinda "grayer" and a bit more grainy on the cone.......I would guess recones.....? I have (4) K's also and seem to have the same thing going on........(2) are blacker and have a bit less grain, while the other (2) are grayish with a bit more grain.
On both of the "blacker" cones (K's & E's) you can easily see they are original.
I've compared sound between the E's and the K's . Maybe the K's are slightly less "edgy" but kinda hard to tell. They all "sound like JBL's" !!

I'll probably change the E's for the K's just because they are lighter.

Thanks checking my rig.

 #79267  by mijknahs
 Tue May 04, 2010 2:07 pm
I think I have about 6 JBL E120s and I know 2 of them I bought new in May 2003 (I wrote it on the back of the speakers). They are all now more "grey" than dark black like they were originally. They still work fine but the dark black of the cones seems to have faded. Maybe the climate? I live about a mile from the beach. I have two that were recently reconed and the cones on those are very black. Yeah, to me E-120s and K-120's aren't that different except for weight and power rating.

 #152001  by zambiland
 Mon May 02, 2016 11:09 pm
540EYE wrote:Hi,
Just finished reworking a Mc2105 into a rack mounted unit. Glass was busted and got it pretty reasonable. I use a home made "Y" from mono pre out into the Mac's L+R channelsEach channel runs a 2 x 12" cab with (2) E-120's @ 8 ohms / cab. Also running an outboard Mac P-438 Power Guard that I scored from Brad. Depending on the mood, I run either an Intersound IVP or a GT Trio. Right now, I'm kinda diggin' the IVP. It does "Jer" extremely well, although it is more associated with Weir. Very tweakable, crisp and QUIET.
There is a switch on the back of the 2105 labeled "Direct" or "Normal".....haven't figured out what the difference is. Can anyone shed some light on this??

BTW, I love this place!!
Image Image

Where did you get the metal faceplate for the Mac? I want one!