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Topic: Fender inputs 1 and 2 |
Tommy Boswell
From:
Virginia, USA
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Posted 6 Oct 2012 8:15 am |
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| My Fender Bassman 70 head has 2 inputs for each channel, like many of the old Fender tube amps. Can anyone tell me what's the difference between input 1 and 2? |
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Cartwright Thompson
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Posted 6 Oct 2012 8:29 am
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| The second input is lower gain than the first, if it's like a blackface era amp. |
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Tim Marcus
From:
San Francisco, CA
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Posted 6 Oct 2012 8:33 am
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input 2 usually has a second resistor in series, which pads the input a little.
If you use a guitar with a hot signal, you may get more clean headroom using input 2
Marshall labeled theirs "Hi - Lo" but Fender only labeled them as 1-2. They are the exact same circuit
_________________
Milkmansound.com |
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J Fletcher
From:
London,Ont,Canada
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Posted 6 Oct 2012 10:39 am
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| #2 input on old Fenders also has a lower impedance than the #1 input. 136k versus 1 meg. You might notice that your instrument doesn't sound as bright in the #2 input...Jerry |
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Ken Fox
From:
Nashville GA USA
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Posted 6 Oct 2012 11:30 am
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Looks to me like the input Z is always around 1 meg. Input 1 see 34K between it and the grid and 1 meg to ground
Input two see 68K to the grid
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Tommy Boswell
From:
Virginia, USA
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Posted 6 Oct 2012 11:34 am
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I will try guitar both ways and compare.
What about running a line-level patch out of my Roland Cube? Should I use input 2?
Thanks for all the help! |
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Dave Mudgett
From:
Central Pennsylvania and Gallatin, Tennessee
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Posted 6 Oct 2012 5:46 pm
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Looking at the input circuit in Ken's post, Input 1 is clearly 1 Meg to ground. Input 2 is 136K to ground - the path to ground is through the two 68K resistors, and then directly to ground because Input 1's jack is shorted to ground, which shunts the 1 Meg resistor to ground.
Of course, if one was to just put an open plug into the Input 1 jack, opening up the shorted jack, that would make Input 2's impedance 1Meg + 2*68K = 1.136 Meg, but would change the voltage divider relationship and raise the input signal level to grid.
I would run a line-level signal into Input 2 - it might even need some padding, depending on how hot it is. But that's a reasonable place to start. |
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Ken Fox
From:
Nashville GA USA
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Posted 7 Oct 2012 4:34 am
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Let me go find the "dunce cap" again! I failed to see that contack shorting around the 1 meg! Thanks, I needed that  |
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Tommy Boswell
From:
Virginia, USA
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Posted 7 Oct 2012 3:50 pm
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Sorry Ken, but you don't get to wear the dunce cap. That's for me. I get lost real fast when you electronics guys start talking about megs & Ks & ohms & such.
But I did get what I needed from this post: 1 and 2 are different, and I need to try number 2. |
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Tony Prior
From:
Charlotte NC
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Posted 7 Oct 2012 4:08 pm
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Well, they are clearly different..( edited words)
Historically Fender claimed Input #2 was a supposed 8 or 10DB pad difference from input #1, for use with hi level output instruments such as keyboards. This prevented over driving the preamp. This circuit is common on a majority of 2 input Fender amps up thru the 80's if not all of them... A simple test of plugging in a 6 string to both inputs , comparing, will reveal the secret. I believe this is common for many brands of amps...
_________________
Emmons L-II , Fender Telecasters, B-Benders , Eastman Mandolin ,
Pro Tools 12 on WIN 7 !
jobless- but not homeless- now retired 9 years
CURRENT MUSIC TRACKS AT > https://tprior2241.wixsite.com/website
Last edited by Tony Prior on 8 Oct 2012 2:57 am; edited 1 time in total |
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Tommy Boswell
From:
Virginia, USA
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Posted 7 Oct 2012 4:13 pm
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| Who said they were the same? Did I miss something here? |
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Tony Prior
From:
Charlotte NC
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Posted 8 Oct 2012 2:56 am
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| Tommy Boswell wrote: |
| Who said they were the same? Did I miss something here? |
no..you didn't miss anything...
Poor choice of words on my part to get to the difference..
#2 is a supposed 10DB pad from #1 It's not about bright or headroom, it's about signal to the first stage preamp.
If you are running a very HOT line level out from another amp it still may be too hot for the #2 input...generally line level outs are sent to a BOARD or a power amp...
t
_________________
Emmons L-II , Fender Telecasters, B-Benders , Eastman Mandolin ,
Pro Tools 12 on WIN 7 !
jobless- but not homeless- now retired 9 years
CURRENT MUSIC TRACKS AT > https://tprior2241.wixsite.com/website |
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