Why two inputs on each channel?

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Why two inputs on each channel?

Postby vez on Fri May 12, 2017 10:28 pm

Sorry for the dumb question.
But why does Fender put high and low impedance inputs on each channel? Is it for microphones or accordions or something?
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Re: Why two inputs on each channel?

Postby slider313 on Fri May 12, 2017 11:08 pm

It's not high and low impedance, it's a 6 db difference and for guitars with hotter pickups. Some humbucker guitars may push the front end too much in input one and sound just right in input two.
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Re: Why two inputs on each channel?

Postby Gasstationman on Fri May 12, 2017 11:26 pm

It's both Hi/Low impedance and 6db drop. Hi is 1 Megaohms and Low is 136 Kohms input impedance. Hi is insignificant drop and Low is 6db drop. But the drop on Low will increase with higher ohms on pickupwinding.
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Re: Why two inputs on each channel?

Postby vez on Sat May 13, 2017 2:24 am

Really, for hot pups? Fender have been making the inputs like that for a long time.
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Re: Why two inputs on each channel?

Postby Gasstationman on Sat May 13, 2017 6:54 am

The pups together with the strings is the signalgenerator for guitars with passive electronics. More turns = higher output and higher internal resistance.
Fender amps was used for vocals back in the days so everything is not about guitar.
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Re: Why two inputs on each channel?

Postby pdf64 on Sat May 13, 2017 1:27 pm

I think it most likely that by far the primary reason amps traditionally have more than input per channel is to facilitate the use of more than one instrument / signal source per channel.
Amps were expensive, and plenty of inputs may have allowed the whole band to use just one amp.
The impedance and padding characteristics that occur when just one or other of the inputs are used being secondary effects, artifacts of the chosen input mixing arrangement; potentially useful, but I doubt they were key features.

Note that the lower input impedance of the padded input will tend to dampen the resonant peak of passive pickups, thereby dulling their response a little; a similar effect to turning the instrument's tone control down a bit.
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Re: Why two inputs on each channel?

Postby JJman on Sat May 13, 2017 1:53 pm

Most of the "reasons" given are technically accurate. My uncle and I were both using my '71 DR once and his guitar is an LP with very hot dimarzio HBs in it. In #1 of the channel he was using, the preamp was getting overdriven so he moved it to #2 and it was clean.
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Re: Why two inputs on each channel?

Postby Unit_1 on Sat May 13, 2017 10:06 pm

If you use a mic and guitar on the same amp, you can use the low gain channel for the mic (no squeal) and the high for the guitar. I use this setup on my self built dr504 and the vocals come out spectacular.... Mic on normal low gain, guitar on bright high.
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Re: Why two inputs on each channel?

Postby Factory Guy on Tue May 23, 2017 8:23 pm

Why JUST two?

Fender amps have had more than 2 inputs "per channel" on some amps. They also used to label each input different as well, not Just using numbers "1" and "2".

Fender Tweed Champ amp had 2 inputs, 1 vol.
Fender Tweed Princeton amp had 2 inputs, Vol & Tone
Fender Tweed Harvard amp had 3 inputs, Vol & Tone.
Fender Tweed Deluxe amp had 3 inputs, 3 knobs.
Fender Tweed Vibrolux had 3 inputs all marked instrument, Vol, Tone, Speed, Intensity.
Fender Tweed Tremolux Amps had 4 inputs, 2 for Mics, 2 for Instruments, Mic Vol, Inst Vol, Tone, Speed, Intensity. Technically a 1 channel amp because of the shared tone stack with 2 volume controls.
Fender Tweed Pro also had 4 inputs and 5 knobs.
Fender Tweed Twin had 4 Instrument inputs, 2 normal, 2 bright, with volumes for each, Bass, Treble, Presence. Technically a 1 channel amp with dual sets of inputs.
Fender Bandmaster also had Mic inputs and Inst inputs, Mic Vol, Inst Vol, Treble Bass, Presence.
Fender Super Amp ditto.

Basically all of the professional level amps had mic inputs. And the amps went to "12"!

There were a few crappy Fender amps (Solid State) in the late 60's that also had weird input and volume configurations.

In the books on old Fender amps with schematics the input impedance of one input was designed for a Crystal microphone like a harmonica player would use. Even though it says "Mic" on the input (or sometimes not depending on the amp) the Mic input was designed for the old Crystal microphones and sound amazing! They don't sound good with a modern SM-57 with an impedance matching transformer since the impedance is not the same as a Crystal mic. You can even use the old Crystal mics in a Blackface amp with really good results for Harp players.

Try every input and use all the controls, open a few new musical doors and rock on!
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