John Curl's Blowtorch preamplifier part II - Page 2524 - diyAudio
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Old 30th July 2012, 03:39 AM   #25231
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Thank you, SY, for your input. Now what does Scott think?
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Old 30th July 2012, 04:43 AM   #25232
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I would connect output to inverting input, and ground non-inverting input. Or may be connected both inputs to the rail, depending on topology.
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Old 30th July 2012, 05:08 AM   #25233
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Thank you, Wavebourn.
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Old 30th July 2012, 05:11 AM   #25234
bcarso is offline bcarso  United States
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What Wavebourn said.
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Old 30th July 2012, 06:21 AM   #25235
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Quote:
Originally Posted by Wavebourn View Post
I would connect output to inverting input, and ground non-inverting input.
What Wave said except I'd use a 10k resistor between non-inverting in and gnd.
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Old 30th July 2012, 07:50 AM   #25236
RNMarsh is offline RNMarsh  United States
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If you are having latching problems -- maybe exceeding common-mode range - do this:

Place output to (-) input, and ->
Place (+) input at zero via center tap of a pair of equal value (10K?) resistors - one 10K from the + supply and one 10K from the - supply. R values not critical. -RNM

Last edited by RNMarsh; 30th July 2012 at 07:54 AM. Reason: what to do with unused opamps
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Old 30th July 2012, 07:54 AM   #25237
PMA is offline PMA  Europe
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Originally Posted by john curl View Post
Now what does Scott think?
Free lunch?
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Old 30th July 2012, 08:03 AM   #25238
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by john curl View Post
How would you suggest we tie the pins of the unused op amp, to keep it from effecting the others, especially on turn-on?
Parallel them with the used section and keep this opamp away from high impedance sources if possible.
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Old 30th July 2012, 11:27 AM   #25239
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Thanks everybody. It appears that what we did, initially, is OK.
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Old 30th July 2012, 02:03 PM   #25240
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Quote:
Originally Posted by john curl View Post
NO, I made a mistake, it is probably 50 uH. Sorry about that. You could have HAD me, Scott. Keep sharp! '-)
Darn, I missed a shot also...

Quote:
Originally Posted by Wavebourn View Post
About 150 micro Henry for 2 wires, 20 meters. How long wires does Billy Gates have?
Sigh..

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Originally Posted by fas42 View Post
You sure, Wave? Rule of thumb, 7nH per cm of conductor in free space, I make it 15uH for that scenario ...

Frank
Sigh..

Quote:
Originally Posted by Wavebourn View Post
Let's check.

Click the image to open in full size.

For 20M of 2mm thick copper wire it is 39386.7389298843 nH
2 wires in a cable will give approximately 4 times more. 140 micro Henry.

My rule of dumb gives closer result.

Did I miss anything?

Here is online calculator: Inductance of a Straight Wire: A Calculator
Sigh..

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Originally Posted by RNMarsh View Post
Boy! This is great. We have 15uH, 50uH, 140uH and 150uH. Good thing you all dont do design work for a living.
Yah, but we have plenty of choices...

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Originally Posted by Wavebourn View Post
Join the company. What will be the number if to design for living?
Here ya go..this is the result of applying the Terman equation to a 12 guage wire.

A single wire inductance can only be calculated as the internal inductance of the conductor, which is 15 nH per foot. The external inductance of any wire has to include the return path of the current. Without knowing the return path, one cannot calculate total inductance.

John

BTW, the vertical scale is in NANOHENRIES PER FOOT of conductor pair.. #12 romex is probably about .4 inch spacing.
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File Type: jpg 12 guage inductance vs spacing.jpg (44.9 KB, 116 views)

Last edited by jneutron; 30th July 2012 at 02:06 PM.
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