Crate footswith, Fender Amp

[emoskacrewman]

I bought a fender princeton 112 plus (2 channels, reverb) at a yard sale but the seller could not find the footswitch. I bought a 2 button marshall switch a while back, plugged it in, and it didn't work properly, so i returned it. I recently bought a crate one off Ebay and some interesting things are happening.

with the amp's channel button off and using a cord that has tip/ring/sleve 1/4 plugs at both ends...

1. if both ends of the cord are fully in the amp and switch inputs, the first button works as an on/off switch for the channel and the reverb at the same time; therefore, I either have a completely clean sound or an overdriven and reverbified sound.

2. if the cord is plugged completely into the switch but is only partially in the amp, either button will work to switch the channel but the reverb stays on.

is there some rewiring I can do in the switch or the amp to fix this?

[ChrisK]

Well, one might need to get the schematic for the Fender Princeton 112 plus amp and the schematic for the footswitch.

Dang, the amp schematic gives all the info needed, since it has a schematic for the Fender footswitch.

Do you need more help, or can you "see" it.

[emoskacrewman]

thanks.
I can't find a downloadable schematic since it seems that Crate only does that with discontinued products, so i'll look in the switch as soon as possible to see if i can figure out a fix. the fender switch schematic makes sense to me for the most part, but how do i know which channel's going to the tip or the ring?
if anyone knows how to find a schematic for crate's csf2 footswith, a link would be much appreciated.

[sumgai]

emo,

Hi, and welcome to the NutzHouse! ;D

how do i know which channel's going to the tip or the ring?

I don't see a tip-and-ring connection on that footswitch. The very simple explanation of what's happening is that the channel is chosen by grounding a certain part of the circuitry, ditto for the reverb. The jack merely provides a remote way to ground those circuit parts. The beauty here is, ground is ground, so there's no need for separate connections, thus, it's tip and ground only, no ring needed.

The footswitch unit itself is a horse of a slightly more complicated story. In order to achieve the simplicity of the mono cable connection, the two diodes in that footswitch serve to direct the grounded signal to the correct circuit components. Let's not get into a lot of electrical theory here, you just need to know that your amp expects those two diodes. (The LED's help to keep you informed, but they can't do the job by themselves, the diodes are the necessary components here.) If you can't buy a unit already wired thus, you'll have to make changes to your current pedal. (Knowing how the Crate pedal is wired is essentially moot - if you keep it to use with this amp, you'll need to re-wire it anyways......) Feel free to ask for more details, should you elect to go this route.

And at this point, your stereo cable (TRS) will be overkill. Use a standard mono cable (which was Fender's intent all along), and all should be well. (That is, if the amp is working OK. )

HTH


sumgai


p.s. The reason Fender went through all these shenanigans is subject to debate, but one of the nice outcomes is, the cable type doesn't matter! You can use a guitar cord, a speaker cord, a microphone cord (with the right adapters), it won't matter. This is all digital, so there won't be any issued of hum, or loading, or balance, or anything like that. The amp's internal circuitry is way over-complicated for this singular benefit, but there you have it - a roadie's dream.... it don't matter, just grab any cable and it'll work! ;D

[ChrisK]

I can't find a downloadable schematic since it seems that Crate only does that with discontinued products

One isn't needed. The Fender schematic sez it all.

The footswitch unit itself is a horse of a slightly more complicated story. In order to achieve the simplicity of the mono cable connection, the two diodes in that footswitch serve to direct the grounded signal to the correct circuit components.

Polarity is. The footswitch just prevents the detection of both a positive voltage by comparator U6A (channel), and a negative voltage by comparator U6B (reverb), injected from 31 VAC thru R73, when the respective switch is on.

When the channel switch is on (S1A), channel selection is forced thru diode CR16 and the footswitch will have no channel selection effect.

When the footswitch cable isn't plugged into the amp, the shorting contact on the footswitch jack (J5 pin 4) via diode CR15 will force the reverb to be continuously ON.

Let's not get into a lot of electrical theory here, you just need to know that your amp expects those two diodes. (The LED's help to keep you informed, but they can't do the job by themselves, the diodes are the necessary components here.)

FWIW, LEDs are crappy diodes (meaningless reverse voltage ratings) and the additional two "real" diodes are needed to insulate/isolate the LEDs from the injected 31 VAC. Otherwise, they quickly become DEDs (darkness emitting diodes).

If you can't buy a unit already wired thus, you'll have to make changes to your current pedal. (Knowing how the Crate pedal is wired is essentially moot - if you keep it to use with this amp, you'll need to re-wire it anyways......) Feel free to ask for more details, should you elect to go this route.

Yep, you get to rewire the footswitch to work like the Fender one.

While the amp may have questionable "vintage value", I'll bet that the footswitch has less than none.