Channel Jumping

[Jason deBroux]

Recently played a 100 SLP PLEXI with the tremolo circuit. The tube for the tremolo was pulled so that circuit wasn’t availble. Plugged into channel 1 high and good to go. Jumped the channel 1 low to 2 high and noticed that the amp was immediately louder, which I expected but it also responded much stiffer, which was not expected. I had not encountered this before.

What’s the reason for this ?

 

[Matthews Guitars]

Maybe modded? Or you just had volume 2 set higher than volume 1.

 

[Jason deBroux]

Nope they were set equally, in that particular amp, is one channel spongier than the other ?

 

[neikeel]

That is an interesting observation. Is it an early or late one (spilt or shared cathode on V2 - ie first gain stage, assuming we call V1 the trem tube?)
A 100w trem has the stock channel 1 (lead ) and channel 2 has the trem channel. The trem is switched in and out and has unity gain so removing the tube and not selecting the trem (with the footswitch) should not affect the volume. Having jumpered the channels you normally get an added thickness/tonal shaping capability but only a small volume boost.
I agree wit Chris, maybe modded, but just be a first stage preamp tube with differential output levels.

 

[Jason deBroux]

Couldn’t tell you the history behind it, but the guys in the shop were telling me Michael Landau was in the shop earlier in the week playing to at amp and he was going directly in to the first input with no jumping. I would think that jumping the channel would in some cases could make the feel more spongy, but probably only once the amp was around 6, I didn’t go above 4, so that may have had a hand in it too….

 

[playloud]

Couldn’t tell you the history behind it, but the guys in the shop were telling me Michael Landau was in the shop earlier in the week playing to at amp and he was going directly in to the first input with no jumping. I would think that jumping the channel would in some cases could make the feel more spongy, but probably only once the amp was around 6, I didn’t go above 4, so that may have had a hand in it too….

Do you mean you were moving both volume controls in tandem? If vol II was higher than vol I, that could explain the phenomenon you described in the first post.

I believe (others could confirm?) that the tremolo circuits didn't move over to split cathode until '69ish. Channel jumping would have less impact if it's an earlier shared cathode design.

 

[Jason deBroux]

Volume 2 might have been higher now that I think about it….funny thing was I played a 67 JTM45/100 a couple weeks ago and didn’t notice that happened, but I realize while the 67 JTM45/100 is the predecessor to the #1959 there still are differences with component values that’s can alter the feel and tone of the amp

 

[playloud]

Volume 2 might have been higher now that I think about it….funny thing was I played a 67 JTM45/100 a couple weeks ago and didn’t notice that happened, but I realize while the 67 JTM45/100 is the predecessor to the #1959 there still are differences with component values that’s can alter the feel and tone of the amp

Absolutely. There are several variables that could affect this comparison (pot taper, bright cap value or lack thereof, "unmatched" triodes - as mentioned above).

 

[Matthews Guitars]

I usually run jumpered. Actually always. I should run an internal jumper wire from 1 low to 2 high and be done with it.

I set volume 1 to taste and add enough volume 2 to get the thump in the bottom end I want. Not too much, I don't want it getting flabby, but the right amount of added V2 makes you FEEL what you're playing. That's where the big chunky feel comes from.

 

[Jason deBroux]

I usually run jumpered. Actually always. I should run an internal jumper wire from 1 low to 2 high and be done with it.

I set volume 1 to taste and add enough volume 2 to get the thump in the bottom end I want. Not too much, I don't want it getting flabby, but the right amount of added V2 makes you FEEL what you're playing. That's where the big chunky feel comes from.

I like putting my start into the 2 high input and jump 2 lo to 1 hi, gets a nice little balance with a strat with a maple neck and board

 

[junk notes]

what?

I should run an internal jumper wire from 1 low to 2 high and be done with it.

nope, not on a Plexi., but your call.

 

[BigIronLittleJimmy]

I believe (others could confirm?) that the tremolo circuits didn't move over to split cathode until '69ish. Channel jumping would have less impact if it's an earlier shared cathode design.

Split cathode arrived sometime in early-mid 68 on 100w Tremolo amps

 

[Gene Ballzz]

While "Channel Jumping" can work quite well in many situations, it is not always a panacea for greatness. It's effectiveness can be impacted by many small factors (some of them mentioned above), as well as what the player is wanting to achieve. It is also helpful to understand what is actually going on with those four jacks, as they are not strictly wired in parallel. While Rob Robinette's dissertation is about Fender 4-hole amps, the wiring, component values and function are identical for Marshall and the Fenders that Rob details. The only difference is Fender used chassis grounded Switchcraft style jacks, whereas Marshall used isolated, Cliff Style jacks:

Input Jacks

How Fender Input Jacks Work

robrobinette.com

Notice that the jack you plug into, as well as the jumping configuration can produce a fairly wide (yet often subtle) variety of results! And then there are the differences between split and shared cathode treatments, as well as the values of components applied to those cathodes.

Just Jumpin'
Gene

 

[racerxrated2]

One thing you might try, to change the feel is tube roll in the preamp. Some preamp tubes like Tungsram can add body/clarity but my 72 Trem becomes a tad bit stiffer in feel. By contrast the Ei pre loses a smidge of clarity but the feel gets better. Small differences but noticeable.
I recently traded for a 67 50T… this one is perfect straight in to the top L input. Vs my 72, that I jump left low to R high and plug in to L high. Treb vol 1, bass vol 5 with a boost.
They all vary.

 

[Dean Swindell]

Old thread, I know - but too bad. I just got a Granger M50 and I have a question. I've used four input Marshalls before, jam nights, provided back line, wanking in a store etc. but this is the first I've owned. I've found my favorite sound to be in the Hi normal channel, no jumper, but the brilliant volume all the way up - it bleeds in highs kind of like a presence control much in the way of maybe a tweed Deluxe. Is this normal? I REALLY like it. I'll probably always use it this way.

 

[Dogs of Doom]

Old thread, I know - but too bad. I just got a Granger M50 and I have a question. I've used four input Marshalls before, jam nights, provided back line, wanking in a store etc. but this is the first I've owned. I've found my favorite sound to be in the Hi normal channel, no jumper, but the brilliant volume all the way up - it bleeds in highs kind of like a presence control much in the way of maybe a tweed Deluxe. Is this normal? I REALLY like it. I'll probably always use it this way.

there is no wrong/right. Many people like it like that. Some find the jumpering gets muddy, which it can, if you make it that way. It also depends on what your bass player is doing.

But, in the long run, if you like it, & it inspires you, & people notice that you're getting something more out of your guitar lately, then, by all means, do you...

 

[Dean Swindell]

there is no wrong/right. Many people like it like that. Some find the jumpering gets muddy, which it can, if you make it that way. It also depends on what your bass player is doing.

But, in the long run, if you like it, & it inspires you, & people notice that you're getting something more out of your guitar lately, then, by all means, do you...

Yes I agree, I just wondered if the channel bleed was a normal thing.

 

[Pete Farrington]

It depends on the details of the design, but unless a decoupling cap is bad or the valve has a lot of crosstalk, it shouldn’t be a bleed per se. More that the setting of the treble channel affects the frequency response of the normal channel. Mainly due to the bypass cap on the bright channel mixer resistor.

 

[junk notes]

It depends on the details of the design, but unless a decoupling cap is bad or the valve has a lot of crosstalk, it shouldn’t be a bleed per se. More that the setting of the treble channel affects the frequency response of the normal channel. Mainly due to the bypass cap on the bright channel mixer resistor.

Yes I agree, I just wondered if the channel bleed was a normal thing.

I had been informed that this (signal bleed/crosstalk) also happens at the 470k channel mix resistors before the grid of V2a.
Although not a 1959T, I too am hoping to address a signal bleed issue in my 1992, and that would be great!

 

[Pete Farrington]

I had been informed that this (signal bleed/crosstalk) also happens at the 470k channel mix resistors before the grid of V2a

That’s kinda their job really, as part of mixing the channels together
The behaviour I described above happens because with passive mixers, signal from one channel will appear at the output of the other channel, and so gets affected to some degree by its circuit (in regard of level / frequency response).
If you’re getting weird crosstalk, it’s always worth trying a different valve in V1; dunno how, and it’s pretty rare, but some do that.