DIY Opamp article

F1 FAN · 9th August 2008, 12:57 AM

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.

F1 FAN · 9th August 2008, 05:04 PM

Sorry I should have posted a link to the article.Fig 16 is on page 8. http://www.passdiy.com/pdf/diyopamp.pdf

BDP · 9th August 2008, 06:05 PM

Thread for more information

Nelson Pass · 10th August 2008, 12:09 AM

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.

F1 FAN · 10th August 2008, 04:57 PM

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.

Nelson Pass · 10th August 2008, 06:30 PM

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.

F1 FAN · 10th August 2008, 08:09 PM

Thanks I already have the the 3310's so will use them, but I will certainly scope it to be sure its not oscillating.

9th August 2008, 12:57 AM	#1
F1 FAN diyAudio Member Join Date: Jun 2006	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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9th August 2008, 05:04 PM	#2
F1 FAN diyAudio Member Join Date: Jun 2006	Sorry I should have posted a link to the article.Fig 16 is on page 8. http://www.passdiy.com/pdf/diyopamp.pdf

9th August 2008, 06:05 PM	#3
BDP diyAudio Member Join Date: Apr 2002 Location: Washington State	Thread for more information

10th August 2008, 04:57 PM	#5
F1 FAN diyAudio Member Join Date: Jun 2006	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.

10th August 2008, 06:30 PM	#6
Nelson Pass The one and only Join Date: Mar 2001	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.

10th August 2008, 08:09 PM	#7
F1 FAN diyAudio Member Join Date: Jun 2006	Thanks I already have the the 3310's so will use them, but I will certainly scope it to be sure its not oscillating.