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Old 9th August 2008, 12:57 AM   #1
F1 FAN is offline F1 FAN  Canada
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Default DIY Opamp article

I have a couple of questions regarding the circuit in fig. 16 in Nelson's DIY Opamp article.

1)I want to operate it at a gain of 10db, is it likely to be stable?If not will adding a cap (like say a 100pf poly) across feedback resistor Rd likely to help it be so?

2)Will adding a 150 ohm pot in series with the 1.5k (R2)resistor give me some offset adjustment if I want to direct couple the output.

Any input would be apreciated.Thanks in advance.
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Old 9th August 2008, 05:04 PM   #2
F1 FAN is offline F1 FAN  Canada
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Sorry I should have posted a link to the article.Fig 16 is on page 8. http://www.passdiy.com/pdf/diyopamp.pdf
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Old 9th August 2008, 06:05 PM   #3
BDP is offline BDP  United States
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Old 10th August 2008, 12:09 AM   #4
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Quote:
Originally posted by F1 FAN
Sorry I should have posted a link to the article.Fig 16 is on page 8. http://www.passdiy.com/pdf/diyopamp.pdf
I would expect that to be stable at 10 dB. I suggest a Gate resistor
in series on the P channel Mosfet.
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Old 10th August 2008, 04:57 PM   #5
F1 FAN is offline F1 FAN  Canada
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Thanks Nelson for the reply,I shall place a 221R on the gate of the Mosfet.

Thanks BDP for the link to that thread.I will give it a good read.
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Old 10th August 2008, 06:30 PM   #6
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The ZVP3310 probably favors higher values, but the way to tell
is if it oscillates, and that requires a scope.

You can alternatively uses a PNP transistor with an adjusted value
off the Drain of the input transistor to give about .7V across it.
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Old 10th August 2008, 08:09 PM   #7
F1 FAN is offline F1 FAN  Canada
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Thanks I already have the the 3310's so will use them, but I will certainly scope it to be sure its not oscillating.
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