Author Topic: MXR 6 Band EQ  (Read 4907 times)

ncdb07

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MXR 6 Band EQ
« on: March 23, 2014, 11:53:25 AM »
I ran across an old blue box MXR 6 band eq at a nice price. It was in poor not working condition. I bought it and figured I would fix it later. Between the time I purchased and the time it arrived I ran across a guy on ebay selling several NOS MXR boards complete with schematics and parts layouts with original MXR part #'s for the build kits.

So when the eq arrived I opened it up. It was in horrible shape. The jacks were rusted the wires were brittle the traces on the pcb were corroded and the sliders were filled with 30 years of nasty gunk.

I decided to roll the dice and buy the nos pcb from the guy on ebay. I then decided if I was going to completely rebuild it I would use 1% Xicon resistors and 5% Panasonic ECQ-V series capacitors. I think the tantalums are TDK. I also socketed the opamps and installed TLO72's to make it quieter than it was originally. I found a video on You Tube that showed how to disassemble, rebuild, and re-lube the original sliders to like new condition. I bought new Switchcraft enclosed jacks like the original and even used the red, yellow, blue, and black wiring configuration the original had. The only thing I did different was drill and install a dc jack for modern use. I thought about adding a foot switch but wanted to retain as much of it's originality as possible.

I had done all this with the intention of flipping it. I knew I would lose some money potentially but wanted to make something old new again and put it back into service. Hopefully it would have made someone very happy, and they could have swapped the opamps to OPA2134's or something. I was going to include all the original parts, build docs I used and pictures on a disc to give it some history.  Anyway when I plugged it in I fell in love with it and have no intention of selling it.

Here are a few pics as it currently exists:





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jubal81

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Re: MXR 6 Band EQ
« Reply #1 on: March 23, 2014, 12:10:54 PM »
Now that's looking really spiffy. Great job - and great story.
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GrindCustoms

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Re: MXR 6 Band EQ
« Reply #2 on: March 23, 2014, 05:12:06 PM »
Nice restoration, digging this :)
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culturejam

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Re: MXR 6 Band EQ
« Reply #3 on: March 23, 2014, 05:13:02 PM »
Man, that is excellent work!

I really love a resurrection story.

jkokura

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Re: MXR 6 Band EQ
« Reply #4 on: March 23, 2014, 05:26:07 PM »
Ya, no doubt that's a spiffy build.

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slimtriggers

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Re: MXR 6 Band EQ
« Reply #5 on: March 23, 2014, 05:29:18 PM »
Really nice!  I love how old PCBs have those curvy, organic looking traces.

I kinda like to see the restoration process pics, too, if you have 'em  8)

ncdb07

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Re: MXR 6 Band EQ
« Reply #6 on: March 23, 2014, 05:44:42 PM »
Thanks for all the nice comments guys!

I don't have any pics from the process unfortunately. I wish I had been more diligent about that. I can take pics of the old components for a comparison, and I could dig up the You Tube video that showed the restoration process on the sliders. I could also take pics of the build docs and share them.

On a side note, during my plan of attack phase I compared the OEM parts list with the Six Shooter EQ from Josh @ 1776 effects and his parts are right on! The only difference is the sliders are 15k and He lists the pots as 20k. I doubt there would be a lot of difference.

I am also amazed that the tiniest bump in direction yields a lot of difference in sound. It is no wonder this was a huge part in creating so many guitarists sounds through the years.
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lincolnic

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Re: MXR 6 Band EQ
« Reply #7 on: March 23, 2014, 10:49:41 PM »
Really great looking restoration there.

stevewire

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Re: MXR 6 Band EQ
« Reply #8 on: March 25, 2014, 10:28:17 AM »
Hey ncdb07,
This is pretty awesome.

Jean-Rock

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Re: MXR 6 Band EQ
« Reply #9 on: March 25, 2014, 11:07:35 AM »
Wow that's really neat ! Bravo!
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Govmnt_Lacky

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Re: MXR 6 Band EQ
« Reply #10 on: March 25, 2014, 11:55:45 AM »
Awesome restoration!!!

Any chance of sharing your PCB connection? I wouldn't mind tackling a build like this but... making my own enclosure  ;)

ncdb07

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Re: MXR 6 Band EQ
« Reply #11 on: March 25, 2014, 02:02:50 PM »


Any chance of sharing your PCB connection? I wouldn't mind tackling a build like this but... making my own enclosure  ;)

I am sure it came from this guy on Ebay. http://www.ebay.com/itm/Vintage-MXR-Block-Phase-90-Printed-Circuit-Board-New-Old-Stock-/111294172323?pt=LH_DefaultDomain_0&hash=item19e9a64ca3

He doesn't seem to have any of the eq at the moment or he does not have them listed. Keep in mind  you can't find the exact slide pots any more. Also the traces on these are a lot thinner than we are used to which is why I used a new board instead of reusing the old one. It is real easy to burn right through the trace.
« Last Edit: March 25, 2014, 02:05:20 PM by ncdb07 »
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ncdb07

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Re: MXR 6 Band EQ
« Reply #12 on: March 25, 2014, 02:10:32 PM »
Here is the video I used to learn how to refurbish the CTS slide pots. The ones in the Eq are a little different but the process is the same.

http://www.youtube.com/watch?v=b_OObpWlWMo
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