input jumpers?

[stonabus]

i read this on the fender forum:
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I just stumbled across this today, its reall kind of stupid. But I was playing with my RI Bassman today and changed the input jumper and got a huge pumping tone.

Normally I run into normal input 1 and jump from normal 2 to bright 1 and adjust the volumes to taste. but usually I have to play pretty loud to get a good thumpin tone and the low end is a bit mushy.

But today I switched the jumper to go guitar to normal 1 jump from normal 2 to bright 2 the low gain input, and WOW!!! huge thumping tone at a lower level and a tighter low end.
Its plenty loud for gigging but man what a difference and its not as harsh.

I know it dumb and simple and the amp is stock except for 2 ceramic speakers mixed with the Jensen RI's but what a huge sound and major thump much more Marshall like I was gettin some pretty wicked AC/DC ZZ Top tone's.

I got a real JTM45 vibe happening, I dont know why I never tried this before I alway just jumped the inputs like everyone else and wailed. It even had a nice squeeze to it very tube rectifire even though I'm running the SS rectifire.

I dialed up the amp like this
Normal Vol 4
Bright Vol 3ish to taste
Treble all the way up to 12
Bass on 5
Mid on 8
Presence on 8

I just ran my Paul through a FD2 and straight in.
Very cool I'll have to keep playing around.

GIve it a try, let me know what you get

Just wondering
Thanks
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is this safe to do? what does it do?

 

[OlinMusic]

Re: input jumpers?

Is this the same on Marshalls?

 

[stonabus]

Re: input jumpers?

i dont know, i guess its something to be done on amps with clean 1/2 and bright 1/2 er sumpin like that. this is all i could find using the search.

 

[stonabus]

Re: input jumpers?

im guessing that this is similar to bridging an amp in your car?
i think i found an answer,
There are 4 inputs - each channel has two identical inputs and one channel is slightly brighter than the other. So you can plug into one of the inputs of channel 1 first and run a jumper to channel 2 or you can do it vise versa. Either way, you are running the two channels in parallel.

The difference is going to be the series resistance that the signal sees prior to hitting the grids on the first gain stages. There's a 68K resistor on each input so if you plug into channel 1, there's 68K of resistance going into the first triode. If you jumper into channel 2, there's an additional 68K on the second jack of channel one and 68k on the jack of channel 2 for a total 204K of resistance into the grid of channel 2's first gain stage.

Since the channels are voiced a little differently, the amount of input resistance for one channel via the other will make it sound even more different. How the values of the resistors have drifted over time will further accentuate the differences for each signal path.

On my 4-input tweed super, I find that if I plug into the "mic" channel and jumper over to the "inst." channel, it sounds a little brighter than if I do it the other way around.

This was a little long-winded. Does it make sense?

 

[PUCKBOY99]

Re: input jumpers?

You normally see guys jumping Normal 1 to High 2 & plugging into High 1....For single coils, I like jumping High 1 to Normal 2 & plugging into Normal 1...............

I've never tried this though; I guess I'll hafta' give it a shot :bigthumb:

 

[stonabus]

Re: input jumpers?

it is pretty sweet. fat, round, loud & chunky!
.....but is it safe?

 

[Stratman]

Re: input jumpers?

This trick does not work on a lot of fender amps because the phase gets inverted within the circuit and you'll get on weak out of phase tone.

But it does work on certain older amps and RI's with similar circuits..