What type of jack is this?

[TomCarlos]

Forum members...

I wanted to call attention to just ONE thing, so I will open a separate thread.

Please take a look at a small piece of a Marshall schematic. You will see input jacks for Channels A and B. These are mono cliff jacks. Now take a very close look at the MIX input jack. That is a stereo jack. There are six pin holes in the PC Board. But when you look at the schematic, what do you see?

A) Three normally closed connectors?

B) That the Sleeve and Ring are normally closed but the tip is normally open?

C) Something else?

I am trying to determine if a schematic was drawn in error or if JCM really did use a jack like option B in some of their amps.

Thanks, Tom

 

[dtier]

Clearly B)

 

[TomCarlos]

Clearly B)

Thanks Dtier ... that is what the schematic indicated for the JCM 800 Series 2000. I noticed the 2001 also has the same design for the inputs. It is just that I have never seen a jack configured with NC, NC, NO (NO on the tip).

 

[TomCarlos]

Confirmed... the schematic shows a stereo Tip=NO, Ring=NC, Sleeve=NC. This jack was used for the Marshall Series 2000 guitar head and 2001 bass head. The jack must have been a special order. To the best of my knowledge, Marshall never used them again. I believe they abandoned the Mix A&B circuitry and moved towards traditional channel switching. So now you know.

 

[vogonpoet]

Weren't those built in collaboration with Angus Young from AC/DC?

I seem to recall he wanted that feature. Which is cool, as you don't need a cable to mix the channels.

 

[TomCarlos]

Weren't those built in collaboration with Angus Young from AC/DC?

I seem to recall he wanted that feature. Which is cool, as you don't need a cable to mix the channels.

After much research, I have learned there was a limited run of the 2000 (the guitar head) and the 2001 (the bass head). Both amps have the "Mix Input" and use a VERY RARE jack for the time. The Tip is Normally Open, the Ring and Sleeve are Normally Closed. I confirmed this with testing. I can also tell you a typical two button footswitch WILL NOT WORK. If you have a SPST, that does nothing more than short a connection or leave it open. When you are Adding and Mixing channels, and do that through a mechanical Input Jack, the footswitch needs to be wired properly to work with the circuit. I have this documented on the Music Electronics Forum site.

I did exchange emails with Marshall Amplification and they in fact confirmed that some of their amps use funky do stereo jacks, where one of the connections is open. The jack I am using looks just like the image I am posting here. With no cable plugged in, the Tip connections do not touch. When you insert the cable, the last tips connect. ALSO.... there is a difference between a Right vs Left sided jack!!!! Most if not all Marshalls use a Right side jack - look it up so you can become familiar with how they work.

Thanks for chiming in!!

 

[TassieViking]

I have seen those jacks on other Marshall amps in different places, I think some SS amps from the 80's used them on the headphone or headphone/line out jack on the front panel.