I've read through some threads online about jumpering with 4 input amps to get more gain, and mentioned here and there was using an aby pedal to do it with a 2 input amp. I was interested in the idea of doing it to get a little bit more gain. Is it worth trying/buying an aby pedal, and if it is, how do I go about setting it up? This is on an Ampeg Jet. If it is something that works, could someone explain to me in simple terms how it works?
Jumpering a 2 input amp
- Thread starter Zaxxon
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eclecticsynergy
Well-known member
Re: Jumpering a 2 input amp
Depends on the circuit. It worked with vintage style Marshall circuits and many of the 1950s amps. Didn't work with vintage Fenders because the channels wound up out of phase. You might ask on some of the electronics forums to see if it'd work for your Jet.
And if your amp can't jumper channels, there are a thousand gain pedals out there nowadays.
Depends on the circuit. It worked with vintage style Marshall circuits and many of the 1950s amps. Didn't work with vintage Fenders because the channels wound up out of phase. You might ask on some of the electronics forums to see if it'd work for your Jet.
And if your amp can't jumper channels, there are a thousand gain pedals out there nowadays.
Re: Jumpering a 2 input amp
I do it on a 4 hole Marshall but it's not really about more gain. It's not akin to adding a stage of gain. The treble and normal inputs have a different tone. It's about getting a blend of the two, the warmer normal input and the brighter treble input.
The ABY allows switching between one or the other, or both. That said, it may work differently with your Ampeg Jet. There are passive ABY switcher/pedals and active units. An active unit like the Radial or Fulltone has phase reversal switch which would allow you to compensate if phase is inverted on one of the inputs. They also have an advantage over the passive units in that they don't lose any signal when the signal is split. The also have a ground lift switch and are buffered (switchable). They do cost a good deal more. I cant speak to the Radial, I don't own one. But they are highly recommended. The Fulltone, which I do own, has been a great unit.
Of course, you may do just fine with a $30 passive ABY.
I do it on a 4 hole Marshall but it's not really about more gain. It's not akin to adding a stage of gain. The treble and normal inputs have a different tone. It's about getting a blend of the two, the warmer normal input and the brighter treble input.
The ABY allows switching between one or the other, or both. That said, it may work differently with your Ampeg Jet. There are passive ABY switcher/pedals and active units. An active unit like the Radial or Fulltone has phase reversal switch which would allow you to compensate if phase is inverted on one of the inputs. They also have an advantage over the passive units in that they don't lose any signal when the signal is split. The also have a ground lift switch and are buffered (switchable). They do cost a good deal more. I cant speak to the Radial, I don't own one. But they are highly recommended. The Fulltone, which I do own, has been a great unit.
Of course, you may do just fine with a $30 passive ABY.
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Re: Jumpering a 2 input amp
Thank you both.
eclecticsynergy, I see, lots of different amp designs out there. Thanks for the electronics forum tip. I may end up going for a used pedal on CL, but I'd read about the jumping and liked the idea of using the amp on itself. I wanted to see if it was possible to get a small amount of bluesy grit, uncolored by an outside source, with the jumping.
darg1911, thanks for the info. I hadn't known about the passive/active distinction. I'd wondered if the the signal was split or doubled with an aby pedal. Is the only difference between a passive aby and a y cable, the switching ability?
If I can't get any gain by jumping, it may not be worth it for me, as I can't hear a huge amount of difference between the normal and bright channels on the Jet. I haven't really tried much to distinguish the two since I got the amp though; I've mostly just used the bright channel.
Sorry if this is a really basic question, but In an amp like this Jet, that has two preamp tubes and two power tubes, what all is in use when it is functioning on one channel? Is it one preamp and one power for each channel? Or are all four tubes going? Or one preamp and two power tubes?
Thank you both.
eclecticsynergy, I see, lots of different amp designs out there. Thanks for the electronics forum tip. I may end up going for a used pedal on CL, but I'd read about the jumping and liked the idea of using the amp on itself. I wanted to see if it was possible to get a small amount of bluesy grit, uncolored by an outside source, with the jumping.
darg1911, thanks for the info. I hadn't known about the passive/active distinction. I'd wondered if the the signal was split or doubled with an aby pedal. Is the only difference between a passive aby and a y cable, the switching ability?
If I can't get any gain by jumping, it may not be worth it for me, as I can't hear a huge amount of difference between the normal and bright channels on the Jet. I haven't really tried much to distinguish the two since I got the amp though; I've mostly just used the bright channel.
Sorry if this is a really basic question, but In an amp like this Jet, that has two preamp tubes and two power tubes, what all is in use when it is functioning on one channel? Is it one preamp and one power for each channel? Or are all four tubes going? Or one preamp and two power tubes?
PFDarkside
of the Forum
Re: Jumpering a 2 input amp
Power tubes are always active for each input. Depending on the design, one half of a preamp tube could be used for one channel and one half for the other (standard preamp tubes actually have 2 gain stages each) or the individual channels could each feed the first gain stage.
EDIT - just looked at one of the Jet schematics, it's just two inputs with different input resistors and a capacitor on the bright channel to cut a little input bass. The preamp one half of one preamp tube (the other half is for tremolo) and the second preamp tube is setup as a driver/phase inverter.
Definitely need a pedal for more gain.
Power tubes are always active for each input. Depending on the design, one half of a preamp tube could be used for one channel and one half for the other (standard preamp tubes actually have 2 gain stages each) or the individual channels could each feed the first gain stage.
EDIT - just looked at one of the Jet schematics, it's just two inputs with different input resistors and a capacitor on the bright channel to cut a little input bass. The preamp one half of one preamp tube (the other half is for tremolo) and the second preamp tube is setup as a driver/phase inverter.
Definitely need a pedal for more gain.
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Re: Jumpering a 2 input amp
To answer the question in your earlier post ... yes, a passive ABY is basically just a foot switchable Y cable. With a passive, or most of them anyway, you can also use them in reverse ... they can be used to switch between two instruments into a single amp. Cant do that with an active.
To answer the question in your earlier post ... yes, a passive ABY is basically just a foot switchable Y cable. With a passive, or most of them anyway, you can also use them in reverse ... they can be used to switch between two instruments into a single amp. Cant do that with an active.
eclecticsynergy
Well-known member
Re: Jumpering a 2 input amp
Darg is correct, but there's another consideration- using both channels won't give you more gain in the sense of preamp distortion. But it will be feeding more signal to the power amp, and driving the power tubes harder can result in a more gainy final sound. That depends on how loud you like to run your amp- if you're getting a bit of overdrive from the power stage already, you'll get more. Many find power tube drive a bit different from preamp tube drive. I do. Partly in terms if tone but more importantly in terms of feel.
Darg is correct, but there's another consideration- using both channels won't give you more gain in the sense of preamp distortion. But it will be feeding more signal to the power amp, and driving the power tubes harder can result in a more gainy final sound. That depends on how loud you like to run your amp- if you're getting a bit of overdrive from the power stage already, you'll get more. Many find power tube drive a bit different from preamp tube drive. I do. Partly in terms if tone but more importantly in terms of feel.
eclecticsynergy
Well-known member
Re: Jumpering a 2 input amp
I'm not an expert but I think it isn't as simple as that. I've jumpered the channels on my '50s Magnatone and my '60s Silvertones, which aren't like Marshalls. And I never tried it on my '65 Bandmaster, but I've been told the channels would be out of phase even though it doesn't have reverb.
I'm not an expert but I think it isn't as simple as that. I've jumpered the channels on my '50s Magnatone and my '60s Silvertones, which aren't like Marshalls. And I never tried it on my '65 Bandmaster, but I've been told the channels would be out of phase even though it doesn't have reverb.
Re: Jumpering a 2 input amp
I don't know if that's necessarily true. If you split the signal passively, or jump the inputs of a 4 holer with a cable you are going to lose about 3db of signal from the passive split. I don't know how to apply the math such that it figures in the preamp tube (1/2 the signal into each triode of the tube versus full signal into one triode) but I have a feeling it's going to be close to a wash. But with an active switcher, the signal going to each triode should be the same as the original signal from the guitar. In other words, there is no loss of signal due to the split because of an amp inside the ABY. At least the Fulltone ABY works that way (I think). As I mentioned, I don't really hear an increase in gain but in theory, that additional signal should ultimately make it to the power tubes. I would think anyway.
I don't know if that's necessarily true. If you split the signal passively, or jump the inputs of a 4 holer with a cable you are going to lose about 3db of signal from the passive split. I don't know how to apply the math such that it figures in the preamp tube (1/2 the signal into each triode of the tube versus full signal into one triode) but I have a feeling it's going to be close to a wash. But with an active switcher, the signal going to each triode should be the same as the original signal from the guitar. In other words, there is no loss of signal due to the split because of an amp inside the ABY. At least the Fulltone ABY works that way (I think). As I mentioned, I don't really hear an increase in gain but in theory, that additional signal should ultimately make it to the power tubes. I would think anyway.
eclecticsynergy
Well-known member
Re: Jumpering a 2 input amp
A jumper has always seemed to get me a little extra when I've tried it. Certainly not twice as much, still, enough to notice. Don't now the math either but especially with tubes, I doubt the ratio of input to output is strictly linear.
A jumper has always seemed to get me a little extra when I've tried it. Certainly not twice as much, still, enough to notice. Don't now the math either but especially with tubes, I doubt the ratio of input to output is strictly linear.
Re: Jumpering a 2 input amp
I've never thought about it in the past to test it, let alone even pay enough attention to notice. I cant really crank the 4 holer I have now to test the theory either. But, I'll certainly take your word for it. That said, if it works for jumpering or a passive switcher, you ought to have even a little more gain with an active switcher, assuming it has a unity gain buffer/amp.
I've never thought about it in the past to test it, let alone even pay enough attention to notice. I cant really crank the 4 holer I have now to test the theory either. But, I'll certainly take your word for it. That said, if it works for jumpering or a passive switcher, you ought to have even a little more gain with an active switcher, assuming it has a unity gain buffer/amp.
Re: Jumpering a 2 input amp
only on reverb amps as a general rule. the vibrato channel has one extra stage of gain and phase gets flipped at each stage
theres no reason for your channels to be out of phase unless something was modded
only on reverb amps as a general rule. the vibrato channel has one extra stage of gain and phase gets flipped at each stage
theres no reason for your channels to be out of phase unless something was modded
eclecticsynergy
Well-known member
Re: Jumpering a 2 input amp
So my vibrato channel won't be put of phase with the regular one despite having an extra gain stage? Good to know, thanks jeremy. Don't use my Fenders much & hardly ever run the Bandmaster since I got a blackface Bassman, but I'll keep it in mind for future reference.
So my vibrato channel won't be put of phase with the regular one despite having an extra gain stage? Good to know, thanks jeremy. Don't use my Fenders much & hardly ever run the Bandmaster since I got a blackface Bassman, but I'll keep it in mind for future reference.
eclecticsynergy
Well-known member
Re: Jumpering a 2 input amp
Thanks; I'll have to try it with the Bandmaster one of these days. And maybe the Bassman too. Really just curiosity on my part; generally I look to other amps when I want gainier tones. But I still like knowing what each of my amps is capable of.
Thanks; I'll have to try it with the Bandmaster one of these days. And maybe the Bassman too. Really just curiosity on my part; generally I look to other amps when I want gainier tones. But I still like knowing what each of my amps is capable of.
