Mic Eliminator degrading my sound - SOLVED

[PhiloBeddoe]

I bought a mic eliminator through a Randall dealer and installed it into a Marshall 1960B cabinet loaded with V30s. I also have a 1960A without a mic eliminator. I began being suspicious that the mic eliminator was having a negative effect a long time ago since the 1960A always sounded much better than the 1960B.

So today I finally took the original Marshall jackplate and replaced the mic eliminator and the sound improved immensely. Put the mic eliminator back in and yuck again. Basically all the low end disappears and it sounds really ratty with the mic eliminator.

I can't imagine what I could be doing wrong but I suppose anything is possible. Am I missing something or do I have a bad part or what?

Ideas?

Many thanks!

 

[bbp]

Sounds like you've got one of the units with phase problems. Try switching the polarity of two of the speakers, ie put the red wire where the black one is now and the other way around. I can't tell you which ones you should rewire since I don't know how the cab is wired though.

 

[audioholic]

yup

wired wrong, this is a known issue i believe

 

[PhiloBeddoe]

OK, you guys rock.

I switched the polarity on the two left speakers and voila, the tone is 100% better.

Marshall 1960s have 16ohm speakers. The left two speakers are wired in parallel with each other totaling 8ohms and the right two speakers are wired in parallel with each other totaling 8ohms. In mono mode the two sides are put in parallel with each other totaling 4ohms. In stereo mode there are separate 8ohm loads, one on each side. So the jackplate just has a black and red going to the left side and another black and red going to the right side. From the mic eliminator jackplate I ran the black to the positive speaker terminal and red to the negative speaker terminal on the left side and all was fixed. Doing this on the right side instead should have had the same effect but I didn't try it.

I couldn't find any threads regarding this problem so I'd love to know which side should be switched. I don't think there's any way to tell by just looking at the board or something. Maybe I could test with a cord and a meter (hmmm, just thought of that now).

Thanks again!

 

[tlingen]

PhiloBeddoe, how does the mic eliminator sound now and is it a exact fit to replace the Marshall 1960 jack plate? I have a 1960 also and want to get a Mic Eliminator for mine?

 

[PhiloBeddoe]

PhiloBeddoe, how does the mic eliminator sound now and is it a exact fit to replace the Marshall 1960 jack plate? I have a 1960 also and want to get a Mic Eliminator for mine?

Sounds fine now. I didn't a/b with the old one after I made the wire swap because it's too much of a pain to switch the jack plates back and forth. I suppose someone could rig a wiring scheme to a/b if they cared to. For me, after I swapped the wires it was just "aaahhh, there it is" and all good.

No, it's not an exact fit. You have to make the hole a little larger so there is no going back to the old jack plate.

Another recommended upgrade is metal handles. If you record loudly you may find that your plastic handles rattle. This also required me to enlarge the handle holes just a little but I've given up caring about having a pristine cab. These things aren't worth that much anyway.

 

[jlbaxe]

we had the same issue on rig-talk.com and that was the fix.It was on a 2x12 cab and didnt matter which one was reversed as long as it was only one side.

 

[Katash]

can you buy the mic eleminator without buying a cab? ; )

 

[tlingen]

Yes you can purchase direct from Randall for $149.95. I was recently looking into one.

 

[PhiloBeddoe]

FWIW, I went ahead and found out which side was bad. I unplugged the mic eliminator jackplate from the speakers, plugged a TS cable into it and did continuity tests between the jack plate leads and the TS cable. The tip of the TS cable should correspond to the red leads from the mic eliminator and the sleeve to the black.

The side feeding the right speakers was reversed. I have no idea if this is uniform across all mic eliminators or not, but if you buy one to retrofit into a cabinet or to replace a broken one you'll definitely want to check this.