replacing input jacks

[bsco]

Thought I'd post this...I had somebody drop off a Randall combo amp a few days ago, and he wanted me to replace the input jack...which he supplied...in a Fender package...yes it was a new one....So I tested it first to make sure of the problem, then went ahead and took the amp apart and removed the input board...had to remove the output board and slide it back in order to get the input board out so it could be worked on. Somebody was already in there and re-soldered the input jack...huge blobs of solder on the pins...pads not fully covered with solder, etc....so I replaced it and tested the amp........went to install the input board, the screw hole in the rear corner of the circuit board on the input jack side, would not line up with the metal stand off that was there.....I thought first that the board was not fully seated but after sizing this up, it turns out that the input jack was slightly larger than the original ........just enough so that the hole on the board and the hole in the stand off was off by half of the hole diameter and that was enough so that the screw could not be installed...so I had to enlarge the hole in the circuit board and then I had to place an insulating washer between the trace side of the board and the top of the metal stand-off so that there was no way that something could short out...I was going to install a plastic stand off but didn't have the right height...and he wanted it done fast...but I had this issue and at first it threw me off as both jacks looked identical....there was about a millimeter in the difference in the size....go figure.....
Cheers,
Bernie

[soundguruman]

Yup, there are small differences in jacks...
And manufacturer will often use odd ball jack to save money,
or to cause customer to come back, and buy special sized parts.

[Leo_Gnardo]

Somebody was already in there and re-soldered the input jack...huge blobs of solder on the pins...pads not fully covered with solder, etc.

Yeh, he went to the skool of "the bigger the solder blob the better the connection." Seen lots of that. Even more now that "safe" non-lead solder is the standard available from Radio Shaft.

Whenever possible I put in good ol' fashioned Switchcraft 12A or 11. If they last 60+ years in Fenders, they'll outlast any rinkydink plastic crapola jacks the manufacturers can think up. Sometimes have to open up a hole with a reamer or drill, or washers to 'shrink' it. On occasion I've even sawed off the corner of the PC board if it's in the way.

[soundguruman]

Yeh, he went to the skool of "the bigger the solder blob the better the connection." Seen lots of that. Even more now that "safe" non-lead solder is the standard available from Radio Shaft.

Whenever possible I put in good ol' fashioned Switchcraft 12A or 11. If they last 60+ years in Fenders, they'll outlast any rinkydink plastic crapola jacks the manufacturers can think up. Sometimes have to open up a hole with a reamer or drill, or washers to 'shrink' it. On occasion I've even sawed off the corner of the PC board if it's in the way.

Big blob of solder to make better connection
That's called:

"Agricultural Soldering."

HEY! Get familiar with the terminology here.

[bsco]

Here is one thing I really don't understand and I find it a lot with the newer Marshall gear and others as well........The input jack is only for a guitar connector...maybe with a shorting type to prevent the pick up of hum if the volume is cranked up with no input connected...but a jack with 7,8,9, or more pins.....for a guitar input??? I mean really.....is there any need of this crap??

[Mick Bailey]

When replacing an insulated socket with a Switchcraft (or similar) it's as well to check that the amp isn't going to hum when put back together. Before replacing the socket I plug in a guitar and short the barrel of the plug to the chassis. If it hums, chances are the insulated socket is important to the grounding scheme. Then you need an insulating bush for the replacement Switchcraft.

[bsco]

Ok...I get that part...but a multi-pin guitar input jack......even it the body is plastic so it is insulated....is there a need for all these pins......

[soundguruman]

Here is one thing I really don't understand and I find it a lot with the newer Marshall gear and others as well........The input jack is only for a guitar connector...maybe with a shorting type to prevent the pick up of hum if the volume is cranked up with no input connected...but a jack with 7,8,9, or more pins.....for a guitar input??? I mean really.....is there any need of this crap??

The jack has internal switches.
The switches MUST operate.
Otherwise, change the design of the amp.

Yes the pins are necessary, many times, depends on the design.

The plastic was needed to insulate the jack from the chassis.
Preventing a ground loop or hum.

The plastic CLIFF jacks, used by Marshall, are really hard to kill.
Just as long lasting a metal switchcraft jacks.

If you are seeing plastic jack, made in China,
Change it to CLIFF UK jack. Usually, you CAN.

[bsco]

*******change the design of the amp********
I already stated that I can see why the jack is made from plastic...so that it is insulated from the metal chassis...and most of the pins are connected to ground..the guitar cable only has two connections....signal and ground....so an input jack with 9 pins...to me sounds like a way to screw people over and force them to purchase a special part...the Marshall input jacks like this one costs $9.99 plus shipping, a handling fee and appliable taxes...By the time you get it in...it's about $35..for a jack that is worth less than $1....total junk....I have not repaired as many amps as you have but the ones that I have seen with these types of input jacks are all junk...not one of these jacks were fit to use.....for an experiment, I have a couple of old crap fender amps downstairs that use the same garbage...One of them has a bad jack...go figure?? so I am going to see if I can install a metal one and insulate it from the chassis just to see what happens...

[soundguruman]

You can buy the 9 pin jack from a different source. Cheaper for sure.
Antique Electronic Supply
try that.
or look up the part in the CLIFF cataloger.

Or redesign the amp.

You are absolutely right.
Manufacturer uses oddball jack, to have parts replacement monopoly.

But it's less time to buy the exact replacement...
than to modify and redesign.

[bsco]

I'll check out Antique Electronic Supply and also the CLIFF catalog....but I am still going to experiment with those junk Fender amps I have here...just to see what happens.....and how long it takes....at least that way I will learn some something...good or bad......thanks for those supply resources...
Cheers,
Bernie

[Leo_Gnardo]

bsco, "I feel your pain..." In some amps for instance the Fender current HotRod Deluxe & similar, the multipin (9) jacks are necessary to conform to their FX send/return switching scheme. But the input jacks (4-pin) on these can easily be replaced with Swcr 12A - one of the 4 pins isn't even connected to anything on the PCB - and they are so close to the board's grounding lead, no need for insulting oops insulating bushings. For these I ordinarily add a star washer to "grab" the chassis metal, just like the classic Fenders did in the 'good old days," and 3-inch fly leads from jack to board. These newer Fenders occupy a large segment of my shop time & attention, they are so popular.

Other amps might need insulating bushings to use Swcr 12A's as Mick Bailey mentioned. You'll know, when a hum results upon swapping jacks. I find the Cliff jacks recommended by SGM to work OK, also ReAn, if you must use a plastic jack. And there are some "special cases" where it's unavoidable to use some fancy-dan jack.

[Leo_Gnardo]

I'll check out Antique Electronic Supply and also the CLIFF catalog....but I am still going to experiment with those junk Fender amps I have here...just to see what happens.....and how long it takes....at least that way I will learn some something...good or bad......thanks for those supply resources...Cheers, Bernie

Antique has Cliff & ReAn switches, at least the simple ones. Also the Fender 4-pin & 9-pin in Fender "Gear-Head" packaging (x-pensive) or without Fender packaging (cheap.) Amazing the way a plastic bag and cardboard tag can run up the price $5 each. Lots 'o good stuff at Antique. Now guitar parts too.

[bsco]

Thanks Leo.....I can see those jacks being used with sends and returns due to the switching designs....but like you said for an input jack....it is stupid in my opinion...I have noticed that one pin is not connected in the Hot Rod series amps by Fender...this Randall amp and a lot of the Marshall gear uses these stupid 9 pin jacks for guitar inputs..... and some of the Fenders do as well......I don't have the experience that other people here have...that is why I am here...and *most* people are pretty forgiving when you ask something...there is the odd person however that kind of forget that once upon a time they didn't know a whole lot either.......thanks for the re-assurance....It is much appreciated...I am going to experiment with those junk Fender amps I have here to see what happens...I'll let you know how I make out with it....might be a week or two before I get to that as I have a ton of stuff here to do.....and people are generally impatient when wanting something repaired...most of them wanted it done by yesterday....funny thing...they take forever to pick the stuff up...

[Leo_Gnardo]

One thing Marshall started doing @ 1980 with their JCM800 series amps, and other manuf's started following suit, was using a normally closed switch contact on the ground side of the input jack to short the output of the preamp stage so the amp wouldn't hiss until a jack is plugged into the input. I call it the original "Blame Shifter" circuit. Prior to this sneaky move, whatever noise the pre was making, was evident to the ear. Logic told us "if the amp is quiet, and noise appears after plugging in, then whatever you plug into the input is responsible for the noise." With the new input jack wiring, that's no longer the case, but for those trained in the usual logic of troubleshooting, it drove us batty. Something the boffins of Marshall didn't take into account was bringing the output of the - high gain - preamp physically close to the input often resulted in hi-pitched or ultrasonic feedback squeeks and squeals. Now you don't need 9 pins, just 4 to accomplish this nefarious task. In some amps I have cut away the PC trace that brings the preamp output to the input jack. Though some whoosh noise is evident, it does away with the hi-pitch feedback racket. Some manuf's may use "offset switches" on those complex jacks to do much the same thing, using a relay or LDR to do the preamp muting at a distance from the input jack.