What is the story with MP1 front input jack?

[rockman627]

I have 2 MP1's where the front jack goes in and out. On other amps I have retouched the solder joints or installed a regular switchcraft  jack and wired to the appropriate spots with good success. From what I can tell from Google searches these will not do it. I've seen posts about the rear jack conversion but can't find instructions on how to do this.
I found replacement jacks on amprepairparts.com, but I don't know if they are direct replacements for the front or the back.
Can somebody tell me what the issues are for front jack replacement and or point me to instructions for rear jack conversion?

[Dante]

Welcome to the Depot!

I did a quick search of the forum for "rear jack" and found this:
https://adadepot.com/index.php?topic=2036.msg23163#msg23163

Hope it helps

[Kazinator]

A switchcraft jack can absolutely be used for the front. There are even some ancient instructions on how to do this which I think came from ADA themselves.

I suspect that in an old MP-1 that has the line level rear jack, it's possible to preserve that one while installing a switchcraft one in the front, such that when the front is unplugged, the rear jack is enabled.

I have recently proved that that A and B output can be replaced by switchcraft units. However I had to file away a small chunk of circuit board to get them to fit.  I posted about this on this site back in September or so.

On the topic of the front jack being intermittent, I've been able to greatly improve the reliability by inserting a miniature flathead screwdriver, and very gently prying the contacts to make them a little tighter against the plug. You kind of have to get behind and give a little bend.

Warning: the front jack is a lot more robust against this than the rear ones. You can shatter the plastic casing of the rear ones if you try this, even if you're gentle.

[rnolan]

Hey rockman627, welcome to the depot .  Check this post gain issue

I attached the rear jack mod instructions in one of my replies (and here also for you), also MJMP chimed in to help.

The rear jack mod (designed for the original top switch units which have a line level rear input) replaces the front jack with a switchcraft L12A (which has a longer thread to fit the MP-1 front plate) and also replaces the rear jack and makes it inst level (more useful).  But as you can see in the post, MJMP can help give you instructions to just do the front jack.  PM him on here or email him MJMP Mod Shop

The rear jack mod instructions are also available in the The Vault along with a bunch of other useful stuff.  The mod and instructions was put together by MJMP, he also sells the parts mostly pre wired (check his site)

The post Dante included includes/refers to the output jack mod, which I hadn't seen before, put together and posted by Kim back in 2018 (but he wrote it in 2004).

@Kaz this may have helped you and alleviated the filing you had to do

@Dante, can you add this to the Vault please

@Kim, the rtf Output Jack Mod file refers to pics (e.g. Pic A etc) which aren't in the file.  Any chance you still have them so they can be included and maybe make a pdf? (complete with pics)

[Kazinator]

@Kaz this may have helped you and alleviated the filing you had to do

I'm skeptical because I found  a picture of the exact part from Radio Shack that the document calls for: see this image link to eBay. It look exactly like a Switchcraft. It doesn't look like it would fit into my MP-1. Maybe there are some differences between MP-1 revisions and how much clearance there is?

Also: you do not need a switched jack for the output jacks. Only two wires need to be hooked up, not three. The schematics are confusing because they are shared between the MQ-1 and MP-1, and I believe the reason for that is that the circuit board itself, the layout, it shared. What is Out A on the MP-1 is actually an input on the MQ-1, and in that unit it does some input-related switching. The MP-1 output jacks don't switch anything.

Also: here's no need to solder anything from both sides of the board. The through holes are plated through holes. If the original jack had required at soldering from both sides it would not have been possible to install since it sits flush on the board. Some of the soldering in the MP-1 looks like it is from both sides. That's just because the solder wicked through to the component side of the hole.

[Kim]

@Kim, the rtf Output Jack Mod file refers to pics (e.g. Pic A etc) which aren't in the file.  Any chance you still have them so they can be included and maybe make a pdf? (complete with pics)

Wow sorry I haven't seen this!   
I do indeed have the original pics from that, but I have absolutely no idea how to make a pdf. Hairston did all that for me after I sent him whatever info I had.  I'll attach them here...

[Kim]

The rest of those pics: