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Amp outlets

PostPosted: Mon Dec 11, 2006 3:33 am
by hashtaff
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 !!!

PostPosted: Mon Dec 11, 2006 3:41 am
by NEONMOONY
You mean of they are parallel inputs and not separate channels?

PostPosted: Mon Dec 11, 2006 4:58 am
by ricochet
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.

PostPosted: Sat Dec 16, 2006 3:36 pm
by jaybee
go from that "input" to your tuner and you have one less tone-sucking pedal in your signal chain

PostPosted: Sun Dec 17, 2006 8:24 pm
by slickcat
Cool...I didnt know that. Thanks! :D

Resistors in series

PostPosted: Wed Dec 20, 2006 9:15 pm
by Splash
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
Scott
Believe in Magic!

PostPosted: Thu Dec 21, 2006 2:40 am
by ricochet
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

Grid blocking resistors explained

PostPosted: Thu Dec 21, 2006 3:57 am
by Splash
Thank you.

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

PEACE
Scott
Believe in Magic!

PostPosted: Thu Dec 21, 2006 3:59 am
by ricochet
You're welcome.

Randall Aiken's site has a lot of cool technical information about tube amps.

Re: Grid blocking resistors explained

PostPosted: Thu Dec 21, 2006 6:33 pm
by jaybee
Splash wrote:Thank you.

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

PEACE
Scott
Believe in Magic!


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)

PostPosted: Thu Dec 21, 2006 10:05 pm
by rustyslide
This would explain how the jumper cable on those 4 input amps works (bassman, plexi, etc).

Re: Grid blocking resistors explained

PostPosted: Thu Dec 21, 2006 10:42 pm
by ricochet
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.

PostPosted: Thu Dec 21, 2006 11:11 pm
by hashtaff
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

PostPosted: Thu Dec 21, 2006 11:41 pm
by ricochet
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.

PostPosted: Fri Dec 22, 2006 7:28 am
by rustyslide
You mean the electrons don't get confused!?! :shock: