Amp outlets

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Amp outlets

Postby hashtaff » Mon Dec 11, 2006 3:33 am

Now, this is going to make me look real stupid, but if it helps someone else I can live with that.
When you have two seperate inputs to an amp ( like a Fender Champ or Champ copy) You can plug harp mic /guitar into one of them (usually input 1) and if you take another lead FROM the other imput it acts like a line out and you can put that into anothe amp or the PA.
I wish I'd known that !!!
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Postby NEONMOONY » Mon Dec 11, 2006 3:41 am

You mean of they are parallel inputs and not separate channels?
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Postby ricochet » Mon Dec 11, 2006 4:58 am

Right.

It's also a handy trick to use where there's a "phono input" on equipment, like an amp, radio, Hammond organ... You can plug into that input and use it as a line out from the preceding amp stages.
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Postby jaybee » Sat Dec 16, 2006 3:36 pm

go from that "input" to your tuner and you have one less tone-sucking pedal in your signal chain
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Postby slickcat » Sun Dec 17, 2006 8:24 pm

Cool...I didnt know that. Thanks! :D
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Resistors in series

Postby Splash » Wed Dec 20, 2006 9:15 pm

My Super has a 68K to the grid of the 12ax7 in the first input and a 68K to the tip of the second input.

If I plug a line cord from the second channel to another amp it will add another 68K series resistance. A lower gain output?

I like the tuner idea. I'll give that a try.

PEACE
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Postby ricochet » Thu Dec 21, 2006 2:40 am

A series resistor in front of a grid affects gain negligibly. DC current isn't flowing through it, and at low frequencies where the input capacitance of the tube is small, there's almost no AC current flowing, either, so the resistor has almost no effect. What that resistor does is act in series with the tube's input capacitance to make a low-pass filter. Or looked at another way, a high-pass filter to ground. It rolls off frequencies above the "cutoff," which if I recall correctly is something like 13 kHz for a 68K resistor in front of a 12AX7's grid. As the resistance goes up, the cutoff frequency falls fast. Here's a great article on grid resistors:
http://www.aikenamps.com/InputRes.htm
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Grid blocking resistors explained

Postby Splash » Thu Dec 21, 2006 3:57 am

Thank you.

That was a very understandable explanation.
Ask and ye shall recieve.

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Postby ricochet » Thu Dec 21, 2006 3:59 am

You're welcome.

Randall Aiken's site has a lot of cool technical information about tube amps.
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Re: Grid blocking resistors explained

Postby jaybee » Thu Dec 21, 2006 6:33 pm

Splash wrote:Thank you.

That was a very understandable explanation.
Ask and ye shall recieve.

PEACE
Scott
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to me it was Chinese, but I guess it meant it's ok to do it theoretically. Me being me, I just try things and keep doing them if they sound ok, stop doing them if they sound like I shouldn't be doing them... 8)
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Postby rustyslide » Thu Dec 21, 2006 10:05 pm

This would explain how the jumper cable on those 4 input amps works (bassman, plexi, etc).
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Re: Grid blocking resistors explained

Postby ricochet » Thu Dec 21, 2006 10:42 pm

jaybee wrote:Me being me, I just try things and keep doing them if they sound ok, stop doing them if they sound like I shouldn't be doing them... 8)
If you try something and it smokes, stop and back up a step.
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Postby hashtaff » Thu Dec 21, 2006 11:11 pm

Well, it's all double Dutch to me. I just read it somewhere(using the 2nd input as a line out) and it worked. No idea how. Ric any chance of explaining to a 'lectronic moron like myself how that works.
How can you get a signal from an input, it just don't seem right.

and a happy christmas
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Postby ricochet » Thu Dec 21, 2006 11:41 pm

It only works when that input is connected either to another input that's being used, or to the output of a preceding stage that's got signal. Just another way to tap into the signal path.

You can walk out the "IN" door at the supermarket when it's open. Gets done all the time.

I've been known to pull out of a driveway with "Entrance" signs or "IN" arrows now and then, too.
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Postby rustyslide » Fri Dec 22, 2006 7:28 am

You mean the electrons don't get confused!?! :shock:
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