Why four jacks?

[Robert Delahunt]

I hate to ask, but I'm a newbie with my amp, and I'm not sure of something. If there's only one output section, as I was told, why have four input jacks? It's a 1972 silverface Fender Twin Reverb, and has two Normal channel inputs and two Vibrato channel inputs. Also, which one is what, in terms of left versus right inputs on the channels? How does the "Hi" and "Lo" input thing work? (I don't see those words written on the amp, though).

Just wondering.

 

[Low_fidelity2100]

Re: Why four jacks?

2 jacks per channel. The one located on the left (when faceing the amp) is the HI/1 input. The one on the right is the LO/2 input. The high input attenuates less signal to ground before it reaches the first gainstage. Obviously the second input attenuates more signal to ground. The original purpose behind this was lower output pickups (single coils, for instance) would get plugged into the HI input, so they would have a stronger signal. Higher output pickups (Humbuckers) would plug into the low input so they'de have a lower output signal, Thus making them less likely to Over load the preamp tubes, and help you avoid distortion. In reality everyone tends to just use the HI input.

The First two jacks are attached to the Normal channel, The second two to the Vibrato channel. The Normal channel Has no reverb or Vibrato. The Vibrato Channel is where you'de plug in if you wanted access to the Reverb and Vibrato.

 

[Rich_S]

Re: Why four jacks?

The inputs on each channel, used separately, function as Hi and Lo - 1 should give you a bit more gain than 2. If you plug in two instruments simultaneously, 1 and 2 have pretty much the same gain. Or, they can be used to daisy-chain amps using a cable in/cable out arrangement.

The two channels are just what they say - Normal and Vibrato. Back in the old days, people would share amps, so the two channels give independent volume and tone controls for two players. These days, no one shares amps anymore.

You might find the Vibrato channel has a bit more gain - there is an extra gain stage in there for the vibrato circuit that the Normal channels doesn't have.

On this amp paralleling the channels won't work (like it does on a Marshall or a Bassman). Because each preamp stage reverses the phase of the signal, and the vibrato channel has one extra stage, using both channels simulataneously (for the same guitar)causes out-of-phase signals, which will sound weak, thin, or not at all.

Experiment, and find which input you like best.

 

[Fresh_Start]

Re: Why four jacks?

Originally Fender put two jacks in their amps so that two instruments could play through a single amp at the same time. Part of the "standard" two-input-jack circuit includes resistors to isolate two separate signals.

On a Tweed Deluxe, you can jumper between the two input channels (hi-1 to lo-2, plug guitar into hi-2) and get major mojo. At least that's what I've been told. This does NOT work on all two channel amps with separate inputs, so check with an expert before you try jumpering channels.

Rich: I think I see what you mean about the Normal and Vibrato channels being out of phase, but the Silver Face Twin Reverb those sure look like Hi/Lo jacks to me.

Chip

 

[LesStrat]

Re: Why four jacks?

The inputs on each channel, used separately, function as Hi and Lo - 1 should give you a bit more gain than 2. If you plug in two instruments simultaneously, 1 and 2 have pretty much the same gain. Or, they can be used to daisy-chain amps using a cable in/cable out arrangement.

The two channels are just what they say - Normal and Vibrato. Back in the old days, people would share amps, so the two channels give independent volume and tone controls for two players. These days, no one shares amps anymore.

You might find the Vibrato channel has a bit more gain - there is an extra gain stage in there for the vibrato circuit that the Normal channels doesn't have.

On this amp paralleling the channels won't work (like it does on a Marshall or a Bassman). Because each preamp stage reverses the phase of the signal, and the vibrato channel has one extra stage, using both channels simulataneously (for the same guitar)causes out-of-phase signals, which will sound weak, thin, or not at all.

Experiment, and find which input you like best.

I wondered if anyone else remembered the amp sharing days. My Dad had a SuperReverb, and sometimes they plugged in a bass and a guitar.

Often, he would plug in a guitar and a microphone.

 

[Rich_S]

Re: Why four jacks?

My first tube amp was a 35 watt Bogen PA head with a homemade 2x12 cabinet. I sang and played guitar through it all the time. I'm sure the vocals sounded like crap.

 

[The Golden Boy]

Re: Why four jacks?

My bass amps are considered "stereo" amps- although "bi-amp" and "dual mono" describe them more accurately than "stereo."

You have one input going into the preamp(s), at which point it goes to the power section, which can be bridged for mono- or run at two controlled volumes either as "stereo" (dual mono) or bi-amped.

The reason it's not "stereo" is that it's not running seperate signals either into the amp or from individual preamp to individual power section. While someone may consider bi-amping to be "stereo" it's still the same signal, just split into lows and highs.

 

[jeremy]

Re: Why four jacks?

On a Tweed Deluxe, you can jumper between the two input channels (hi-1 to lo-2, plug guitar into hi-2) and get major mojo. At least that's what I've been told. This does NOT work on all two channel amps with separate inputs, so check with an expert before you try jumpering channels.

it will sorta work on a tweed deluxe but is more effective on larger tweed amps like the bassman, super, pro and bandmaster. on the deluxe i find it sounds better just plugged into one channel