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Author Topic: MP-1 Front Input Jack  (Read 325 times)

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CrunchQuest

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MP-1 Front Input Jack
« on: Time Format »

Hello, ADA users!  I've got an original MP-1 that I purchased back in the late 80's that has an input jack that needs fixing and I'm, hoping someone on here can offer some advice.  Looking at the rear input conversion mod instructions (http://adadepot.com/mods/ADA_MP-1_v1.xx_Rear_Input_Jack_Conversion_Mod.pdf), it looks like the front input jack is a 6 prong jack, but only 5 of them are actually used (http://adadepot.eu/_shop/parts_stock/partspics/mp-1-jack-large.jpg). I can't find an identical part in stock anywhere, but I did find a Fender 9-pin input jack (https://www.amazon.com/Fender-chrome-Amp-Jack-Stereo/dp/B002HF84HM/ref=pd_bxgy_img_3/141-1375355-9267516?_encoding=UTF8&pd_rd_i=B002HF84HM&pd_rd_r=cd221a3f-d4cc-460d-8078-65236cf3b5a9&pd_rd_w=bwzrB&pd_rd_wg=GU632&pf_rd_p=f325d01c-4658-4593-be83-3e12ca663f0e&pf_rd_r=DMRF1ZEVSQ7ERD0Y98ND&psc=1&refRID=DMRF1ZEVSQ7ERD0Y98ND&tag=thegearpage05-20) that looks like it could work since there appears to be 9 holes available on the MP-1 circuit board (http://adadepot.com/mods/ADA_MP-1_v1.xx_Rear_Input_Jack_Conversion_Mod.pdf). The extra 3 holes on the MP-1 circuit board do not appear to connect to anything on the board so I'm assuming they are dead ends if I solder anything to them. I'm clueless about circuit boards and electronics in general, but I'm assuming that functionality of the 6 matching Fender pins would be the same as the 6 ADA pins and the extra 3 pins on the Fender just add some additional signal paths that some Fender amps use and the MP-1 does not.

Assuming that the 6 matching pins are functionally the same, does anyone know what will happen if I solder this Fender 9-pin input jack into my MP-1 circuit board? Will it work without any further modification? Will there be any grounding/noise issues when I'm plugged in?

ADA MP-1 input jack from http://adadepot.eu/_shop/parts_stock/partsmp1.htm:


Fender stereo input jack 099-0913-000:


There's also a Fender 4-pin jack out there and the prong numbers seem to coincide with the numbers shown in the input mod instructions:
« Last Edit: Time Format by CrunchQuest »
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Harley Hexxe

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Re: MP-1 Front Input Jack
« Reply #1 on: Time Format »

Hey CrunchQuest,

      Welcome to the Depot :wave:

      I think the best person to answer that question will be MJMP.

      The jacks used in the original MP-1's have been out of production in China for a long time and they won't make any special orders! (We tried, they don't answer us).

      I do know there have been a few mods to use Switchcraft jacks, which seem to last longer than plastic cased replacements, but maybe there are others available that I'm not aware of. In any case, MJMP will steer you in the right direction.

Harley 8)
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rnolan

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Re: MP-1 Front Input Jack
« Reply #2 on: Time Format »

Hey CrunchQuest, welcome to the depot  :thumb-up: .  Probably best approach is to buy the rear jack mod kit from MJMP (http://www.marshalljmpmodshop.net/miscellaneous_parts_and_replacement_tubes.htm), the front jack becomes a standard (long sheathed) "normal" jack and the back jack comes in the kit (see picture on his site).  This is a relatively easy mod to install, the rear jack is a little fiddly as you have to squeeze it in to the back panel (or take the back panel off (which means undoing all the rear jacks)).
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Studio Rig: MP2/MB1 > Eurorack UB2442FX-Pro > TC M-One XL > Behringer Truths (with Truth Sub) / QUAD ESL 63s
Live Rig: MP2/MB1 > Alesis Quadverb > Alesis Midiverb 4 > Yamaha AM802 > B200s/Carvin TS100/DCM200L > ADA Split Stacks/Mesa P112s

MarshallJMP

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Re: MP-1 Front Input Jack
« Reply #3 on: Time Format »

Problem with this jack is that the screw thread is not long enough, so you can't put the screw and washer on it. So the jack can't be secured to the front panel, which can lead to mechanical stress on the pcb. It's better to do the rear jack mod anyway, this way the rear input can be used for guitar and is no longer a line in which won't work with guitars.
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CrunchQuest

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Re: MP-1 Front Input Jack
« Reply #4 on: Time Format »

Problem with this jack is that the screw thread is not long enough, so you can't put the screw and washer on it. So the jack can't be secured to the front panel, which can lead to mechanical stress on the pcb. It's better to do the rear jack mod anyway, this way the rear input can be used for guitar and is no longer a line in which won't work with guitars.

Ah, I knew the Fender jack was too good to be true! 

I'm not too keen on doing the full rear input mod because I don't think I would use the rear input ever and I'd rather not increase the odds of my sloppy soldering ruining the board.  I did recently have success installing a Freeway switch in my strat, but that is the entire extent of my PCB soldering experience so I am definitely still a novice.  If I am reading the schematics correctly, it looks like I can install a Pure Tone guitar jack with the ground going to Pad 1, the tip going to Pad 2, and a jumper going from Pad 6 to Pad 5, and that will restore my front input while only eliminating the functionality of the rear input and the respect of the braver individuals on this message board who are willing to hot rod their MP-1.  Can anyone tell me if that is correct?




« Last Edit: Time Format by CrunchQuest »
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MarshallJMP

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Re: MP-1 Front Input Jack
« Reply #5 on: Time Format »

That jack won't work. You need a jack with a long nose, and it also has to have a switch that will short the input to ground when nothing is plugged in. Also you will need the fiber washers since the hole in the mp-1 is too big.
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CrunchQuest

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Re: MP-1 Front Input Jack
« Reply #6 on: Time Format »

That jack won't work. You need a jack with a long nose, and it also has to have a switch that will short the input to ground when nothing is plugged in. Also you will need the fiber washers since the hole in the mp-1 is too big.

Thanks, MarshallJMP.  I didn't realize I need to isolate the jack from the chassis with the fiber washers.  Like I said before, I'm clueless.  I saw in another thread you listed the best jack as the Switchcraft L12A.  I think the Pure Tone jack does have the same 0.375" long nose, but it definitely doesn't have any switch like the L12A.  Is the shunting switch still needed if I'm going to skip the rear input mod and just permanently disable the rear input?  If so, can you tell me how to wire the L12A?  I'm assuming that the ground still goes to Pad 1 on the board and the tip still goes to Pad 2, but what pad does the shunted switch connect to and do I still need to do the Pad 6 to 5 jumper?  Thanks, again.
« Last Edit: Time Format by CrunchQuest »
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MarshallJMP

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Re: MP-1 Front Input Jack
« Reply #7 on: Time Format »

Yes sleeve to 1 (ground), tip to 2 and the switch also to ground, just use a wire from the switch contact to the ground connection on the jack. Also best to use a piece of small shielded wire, 3.5" long should do it.
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CrunchQuest

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Re: MP-1 Front Input Jack
« Reply #8 on: Time Format »

Awesome!  Thanks for the help.  Much appreciated.  I'll post back when I'm up and running.
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CrunchQuest

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Re: MP-1 Front Input Jack
« Reply #9 on: Time Format »

I'm going with the simplest route to fix the front input, but I did see a couple of jacks that looked like they could restore the original functionality of both the front guitar input and the rear line input, but I wasn't sure if there would be enough room to wire all 5 connections or if they would actually work.  Here's what I found:

https://www.stewmac.com/electronics/components-and-parts/jacks/9-lug-stereo-jack.html




https://leeselectronic.com/en/product/16190.html


Both of them would also require a rubber grommet to isolate the jack but the schematics seem to be correct if you ignore the second SPDT switch lines. 
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MarshallJMP

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Re: MP-1 Front Input Jack
« Reply #10 on: Time Format »

I think the nose is to short?
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Harley Hexxe

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Re: MP-1 Front Input Jack
« Reply #11 on: Time Format »

What about running short leads from the solder lugs to the PCB?

Harley 8)
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I used to be ambivalent. Now, I'm just not sure...
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