Replacing PCB input jacks with Switchcraft on 68 (or 65) Custom PRRI

[markeyd123]

An input jack on my 68 Custom Princeton Reverb reissue is shot, and needs to be replaced for a second time. I want to ditch the PCB mounted plastic jacks and put Switchcraft 12A shunted jacks to replace both of them.

Does anyone know how they would be wired together. I took a look at the PR wiring diagram from @robrob 's site,

---

.

Ultimately I'd like to wire up something along those lines then tie them into the circuit where the existing ones tie in.

Does anyone have a wiring diagram like that I could use, or suggest modifications to the attached one?

Thanks

 

[Esquire Jones]

I recently picked up a 65 PRRI.

What exactly is the design problem with the input jacks?

Is there anything preemptive that can be done?

 

[schmee]

I recently picked up a 65 PRRI.

What exactly is the design problem with the input jacks?

Is there anything preemptive that can be done?

They are plastic non Switchcraft types I think, famous for wearing out fast or breaking... at least compared with metal Switchcraft jacks. The original Cliff brand were pretty good, but too expensive for many makers who prefer to pay cents for them.

 

[schmee]

An input jack on my 68 Custom Princeton Reverb reissue is shot, and needs to be replaced for a second time. I want to ditch the PCB mounted plastic jacks and put Switchcraft 12A shunted jacks to replace both of them.

Does anyone know how they would be wired together. I took a look at the PR wiring diagram from Robrobs site, but the value of the resistors are different and there are 3 instead of 2. (attached).

Ultimately I'd like to wire up something along those lines then tie them into the circuit where the existing ones tie in.

Does anyone have a wiring diagram like that I could use, or suggest modifications to the attached one?

Thanks

I imagine it's out there on line. Look for "pinouts for a pcb jack" or something like that.
Worst case: plug a cable into your old plastic jack, discover which pin is "tip" by testing with your VOM. mark where that wire goes on the PCB.
Repeat this for the other tabs including ground. I'm not sure how your plastic jack is grounded or is made to NOT be grounded, so you will have to work through that. Look for a wire off of it to ground, you could test pins until your VOM tells you one is grounded.

I made this when I did it on a Champ 12, but not sure if yours is similar:

 

[markeyd123]

I recently picked up a 65 PRRI.

What exactly is the design problem with the input jacks?

Is there anything preemptive that can be done?

They fail pretty commonly. I'm not sure if it is the plastic jacks themselves, but possibly more often the problem that I had and others seem to report is the solder points where the jack meets the PCB fail due to pressure/movement when plugging in or out, etc. Also the jacks are grounded by screwing into the chassis and this can create pressure in a certain direction that pulls the jack off the board potentially

 

[Paul G.]

An input jack on my 68 Custom Princeton Reverb reissue is shot, and needs to be replaced for a second time. I want to ditch the PCB mounted plastic jacks and put Switchcraft 12A shunted jacks to replace both of them.

Does anyone know how they would be wired together. I took a look at the PR wiring diagram from Robrobs site, but the value of the resistors are different and there are 3 instead of 2. (attached).

Ultimately I'd like to wire up something along those lines then tie them into the circuit where the existing ones tie in.

Does anyone have a wiring diagram like that I could use, or suggest modifications to the attached one?

Thanks

The Resistors stay on the board, you can just do it like this: https://music-electronics-forum.com...-twin-deluxe-reverb-input-jacks-horrible-part

I recently picked up a 65 PRRI.

What exactly is the design problem with the input jacks?

Is there anything preemptive that can be done?

The design problem is that the jacks are cheesy plastic that will wear out and fail. Wait until they do then have them replaced with open frame Switchcraft 12A jacks. Or you can not wait until they fail and have them replaced with open frame Switchcraft 12A jacks. All modern (not custom shop) Fender amps, including "reissues" have the same junky setup. Argh!

 

[schmee]

Found this too: Can't vouch for it 100% though. Or even if this type are used in your amp.

 

[schmee]

delete

 

[markeyd123]

They are plastic non Switchcraft types I think, famous for wearing out fast or breaking... at least compared with metal Switchcraft jacks. The original Cliff brand were pretty good, but too expensive for many makers who prefer to pay cents for them.
View attachment 992349View attachment 992350

Yes.

Found this too: Can't vouch for it 100% though. Or even if this type are used in your amp.

View attachment 992354

Thanks for that. The setup is different on the 65 and 67 PRRIs. The plastic jack has 6 posts I think and the resistors are on this little board that I want to get rid of. Then tie the ground and signal wire I to the main board, so I think it will wind up looking more like robrobs with the resistors on the jacks. I will study your pics though. Thanks

 

[schmee]

Yes.

Thanks for that. The setup is different on the 65 and 67 PRRIs. The plastic jack has 6 posts I think and the resistors are on this little board that I want to get rid of. Then tie the ground and signal wire I to the main board, so I think it will wind up looking more like robrobs with the resistors on the jacks. I will study your pics though. Thanks

I think I see only 2 wires going to the big board right? IIRC, the resistors are on the little board? If so, that's easy peasy. Solder the resistors to the jack like the old Fenders have. (Your pic post 1)
Find out which of those two wires goes to ground by testing from one of them to the chassis or other obvious ground. (Power Transformer lug?) Now you know where to ground your Switchcraft jack!
(I'm guessing here from your pics.)
Be sure to get the Switchcraft shunt jack type ....I show in post #3

 

[schmee]

Is it this easy?

 

[markeyd123]

Is it this easy?
View attachment 992383

Yes that's exactly right: the resistors are on the little board. That was a photo I grabbed online, but I think it's just 2 resistors, not 3 . . . But yes it would be ground and signal right to the main board and then ditch the little board. I found the following photo in another thread. It's hard to see exactly how everything is connected, but I think between that and what you so kindly posted, I should be able to figure it out. I'm lazy and want things handed to me on a silver platter though, lol. In the photo below it's a little sloppy. I think I'd use the original connecter by splicing into the wires that came from the original little board.

 

[markeyd123]

Is it this easy?
View attachment 992383

So if I do this, just use the wiring diagram from post 1, and go with the 3 resistors and stated values instead of the two that were on the original board. Perhaps 2 of the 3 resistors attached to the jacks are the equivalent of one on the PCB, but the end result is the same? If so then I can totally do it as you describe just making sure I use the resistor values in the diagram vs. the values on the little board?

 

[schmee]

So if I do this, just use the wiring diagram from post 1, and go with the 3 resistors and stated values instead of the two that were on the original board. Perhaps 2 of the 3 resistors attached to the jacks are the equivalent of one on the PCB, but the end result is the same? If so then I can totally do it as you describe just making sure I use the resistor values in the diagram vs. the values on the little board?

check out this thread...

Trouble With Input Jacks On PRRI

Silly question, but have you tried spraying them with contact cleaner? Yes. Rubbing alcohol on a q-tip first, then deoxit. I think the problem is solved. Bad solder joints on the PCB. Re-flowed them. Played it a couple hours this morning with no issues.

www.tdpri.com

 

[markeyd123]

check out this thread...

Trouble With Input Jacks On PRRI

Silly question, but have you tried spraying them with contact cleaner? Yes. Rubbing alcohol on a q-tip first, then deoxit. I think the problem is solved. Bad solder joints on the PCB. Re-flowed them. Played it a couple hours this morning with no issues.

www.tdpri.com

Thanks. It's hard to see exactly how he wired those jacks but Ill fiddle . . . Thank you.

 

[NoTeleBob]

Those plastic Fender jacks are not grounded to the chassis. I don't know if that matters on a PRRI but check: figure out whether signal ground is also chassis ground. You may need isolated jacks.

 

[Lowerleftcoast]

So if I do this, just use the wiring diagram from post 1, and go with the 3 resistors and stated values instead of the two that were on the original board. Perhaps 2 of the 3 resistors attached to the jacks are the equivalent of one on the PCB, but the end result is the same? If so then I can totally do it as you describe just making sure I use the resistor values in the diagram vs. the values on the little board?

(When working on an amp, unplug it from the wall. Discharge the caps. Be safe.)

This is what I would do.
I would wire it like Rob shows. There are 3 resistors on the small board... or should be. You claim they are not the same values as Rob shows. The 68 Custom is a different animal. As of yet there is not a schematic readily available on the interwebs so the resistors may not be 68k but I will bet the 1M is the same on the 68 Custom as the original. You can use the values on your 68 Custom or you can use the original Princeton values (2 x 68k and 1M) your choice. (Don't make the mistake of getting the wrong multiple on the resistors 68 Ohm, 6800, and 680K are not 68k.) The PRRI shows 1/4 watt resistors. These particular resistors are in the most sensitive part of the circuit and 1 watt resistors are quieter than 1/4 watt resistors. Replace all three of these with 1W metal film resistors if you can find them. (Some shock brothers prefer 2W.) It doesn't matter if they are 1%, 5%, or 10% tolerance.

I you have a multimeter... you want to know how the jacks were grounded. Take out the original jacks and small board. Set your meter to ohms and measure from the places I show in green on the photo below to the chassis. (If you must you can set the meter to continuity for this test.) If there is no continuity from the green places on the board to the chassis you will need to connect a wire from the sleeve terminal of the new jacks to the most convenient place of one of the green places shown on the board.

Rob's diagram shows the two resistors connected to a lavender wire. The other end of that wire connects to pin 2 (green wire) of the first tube socket. In the picture below I show a lavender wire tucked into the fold of the chassis. Clip out the green wire connected to pin 2. Route your wire from the two resistors to pin 2 of the first socket and solder the wire to pin 2. You want to keep the wire tucked into the fold of the chassis and against the metal of the chassis as much as possible. The chassis will then act as a partial shield for the signal wire keeping noise from being picked up and amplified. (The two resistors Rob shows do not need to be flying in the air either.)



When the new jacks are installed all of the green places I show on the picture should have continuity with each other.

EDIT: When soldering on the tube socket pin install a tube so solder does not wick into the socket.

 

[markeyd123]

(When working on an amp, unplug it from the wall. Discharge the caps. Be safe.)

This is what I would do.
I would wire it like Rob shows. There are 3 resistors on the small board... or should be. You claim they are not the same values as Rob shows. The 68 Custom is a different animal. As of yet there is not a schematic readily available on the interwebs so the resistors may not be 68k but I will bet the 1M is the same on the 68 Custom as the original. You can use the values on your 68 Custom or you can use the original Princeton values (2 x 68k and 1M) your choice. (Don't make the mistake of getting the wrong multiple on the resistors 68 Ohm, 6800, and 680K are not 68k.) The PRRI shows 1/4 watt resistors. These particular resistors are in the most sensitive part of the circuit and 1 watt resistors are quieter than 1/4 watt resistors. Replace all three of these with 1W metal film resistors if you can find them. (Some shock brothers prefer 2W.) It doesn't matter if they are 1%, 5%, or 10% tolerance.

I you have a multimeter... you want to know how the jacks were grounded. Take out the original jacks and small board. Set your meter to ohms and measure from the places I show in green on the photo below to the chassis. (If you must you can set the meter to continuity for this test.) If there is no continuity from the green places on the board to the chassis you will need to connect a wire from the sleeve terminal of the new jacks to the most convenient place of one of the green places shown on the board.

Rob's diagram shows the two resistors connected to a lavender wire. The other end of that wire connects to pin 2 (green wire) of the first tube socket. In the picture below I show a lavender wire tucked into the fold of the chassis. Clip out the green wire connected to pin 2. Route your wire from the two resistors to pin 2 of the first socket and solder the wire to pin 2. You want to keep the wire tucked into the fold of the chassis and against the metal of the chassis as much as possible. The chassis will then act as a partial shield for the signal wire keeping noise from being picked up and amplified. (The two resistors Rob shows do not need to be flying in the air either.)

View attachment 992531

When the new jacks are installed all of the green places I show on the picture should have continuity with each other.

EDIT: When soldering on the tube socket pin install a tube so solder does not wick into the socket.

This is great, thanks. I built a 5f1 kit so have some knowledge but don't always know why I am doing something. So, to clarify you are saying:

1. Wire jacks like rob does in the diagram, upgrade from 1/4 watt to 1 or 2 watt. Great advice.
2. Attach ground from jacks to main board where it used to be connected before the little board was deleted.
3. Test all those ground points you circled. Wire to 1 of those points from sleeve terminal IF NECESSARY.
4. Do not connect the lavender to the main board where the "signal" wire used to be connected to main board (not next to ground connection on main board coming from jacks). Instead clip existing wire off v1 pin2 and connect new (lavender) wire to v1 pin2. Dress wire appropriately.

Question: And I am asking so I have a better understanding as to the how and why for my own edification. Would skipping step 4, and connecting the lavender wire to the place on the main board next to the ground wire coming from the jacks work also? Or, would it not work at all that way? Is there an advantage to going direct to v1, or is it a mandatory requirement?

Thanks so much for those instructions. It will help me greatly.

 

[Doctorx33]

Those kind of jacks suck. Plain and simple. I had the same problem with my AC30CC2. The jacks are soldered to a circuit board with leads connecting it to the chassis. One of the jacks went south on me and I had to fix it.
I wanted to use Switchcraft jacks too, and I figured out a way to do it without the board. I have all the parts to do it, but I also had replacement jacks for the board. I was in a hurry to get the amp running again, so I unsoldered the old and installed the new. I’m still going to build the assembly with the switchcraft jacks and installed them one day.

 

[Lowerleftcoast]

Wire jacks like rob does in the diagram, upgrade from 1/4 watt to 1 or 2 watt. Great advice.

Theoretically upgrading the components and the wiring layout will be quieter than the original design. Whether it will make a noticeable difference??? For me, doing a half-fast connection to the the board looks like some amateur tech messed with your 68 Custom.

Attach ground from jacks to main board where it used to be connected before the little board was deleted.
Test all those ground points you circled. Wire to 1 of those points from sleeve terminal IF NECESSARY.

If there are *two* points to the chassis. such as the new jacks connected to the front panel and the printed circuit board with a connection to the chassis, When you connect the sleeve (ground) of the jacks to the ground of the circuit board with a wire you have created a ground loop. There will be two paths to ground. Chances are you will get away with this ground loop but you might not. Let's not put in the wire if it is not needed. (By the way, use the locking washers on the jacks to make a better electrical ground connection.)

Do not connect the lavender to the main board where the "signal" wire used to be connected to main board (not next to ground connection on main board coming from jacks). Instead clip existing wire off v1 pin2 and connect new (lavender) wire to v1 pin2. Dress wire appropriately.

Right. We are deleting the old pathway for the input signal voltage and replacing it with the (lavender) wire. The old pathway had the signal wire *up in the air* from the jack PCB to the main PCB. The signal wire was again *up in the air* from the main PCB to V1 p2. We don't know if the trace (wire) through the PCB had a protective electrical shield along the length of the trace. This input signal wire can act like an antenna, so any of those sub-optimal pathways have the potential to pick up noise (RF, EMF). Using the chassis fold and laying the (lavender) input signal wire on the chassis will partially shield the wire and reduce the potential for the wire to act as an antenna. (If you wish you can take it one step further and use shielded wire to replace the (lavender) wire, then using the partial shield of the chassis would not be necessary because the wire would be fully shielded.)

Question: And I am asking so I have a better understanding as to the how and why for my own edification. Would skipping step 4, and connecting the lavender wire to the place on the main board next to the ground wire coming from the jacks work also? Or, would it not work at all that way? Is there an advantage to going direct to v1, or is it a mandatory requirement?

Yes, you can use the original path. Electrically all the connections are the same. I think I addressed why, (for aesthetic reasons and lead dress (noise) reasons), I would do what I suggested.

You do not have to take my advice. Your amp will probably be just as quiet if you make the (choose the descriptor... easy, ugly, simple, amateurish, quick, smart, questionable) repair shown in post #12.