Swapping Op-Amps... you have checked to see it's stable haven't you ? - Page 2 - diyAudio
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Old 23rd June 2011, 02:32 PM   #11
coluke is offline coluke  Italy
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Originally Posted by Mooly View Post
Well perhaps you could link another forum post to this...
Well, for sure, but you can't see the pictures unless you are registered to diyaudio

L.
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Old 23rd June 2011, 02:34 PM   #12
AndrewT is offline AndrewT  Scotland
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A very well put together summary of what this Forum has been preaching almost since it started.
Thanks Mooly.
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Old 23rd June 2011, 02:38 PM   #13
Mooly is online now Mooly  United Kingdom
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Originally Posted by coluke View Post
Well, for sure, but you can't see the pictures unless you are registered to diyaudio

L.
Thats a good reason to join diyAudio then

'cos between us all, I think we are the best
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Old 23rd June 2011, 02:40 PM   #14
Mooly is online now Mooly  United Kingdom
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Thanks Bonsai and AndrewT.

I never thought of a Wiki tbh
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Old 23rd June 2011, 03:36 PM   #15
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OP amps should always be in band limited ciruits.
Best way is to have a capacitor in the feedback loop.
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Old 23rd June 2011, 04:18 PM   #16
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Originally Posted by nigelwright7557 View Post
OP amps should always be in band limited ciruits.
Best way is to have a capacitor in the feedback loop.
Only if its unity gain stable!
Don't forget the series output resistor if there is a capacitive load.

I also do not like the swappers habit of using IC sockets and stacked DIL-SMD converters. Video op-amps, which a lot of the > 10 MHz parts are, do not like the extra power supply inductance
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Old 23rd June 2011, 04:33 PM   #17
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Originally Posted by nigelwright7557 View Post
[snip]Best way is to have a capacitor in the feedback loop.
Be careful! If you have an opamp or circuit that is not unity-gain stable, that cap will surely make it sing!
Such a feedback loop cap should only be used if you really know your circuit, like if you want to correct some phase shift elsewhere and not cause oscillations by decreasing the closed loop gain.

jan didden
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Old 24th June 2011, 07:44 AM   #18
Bonsai is offline Bonsai  Taiwan
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Here are some guidelines from another post. Do just ONE of these things and you are likely to have problems. As noted above, the faster the op-amp, the more careful you need to be.

Happy 'op-amping'!

1. run a non-unity gain stable opamp at unity gain
2. run a decompensated opamp without a comp cap, or too small a comp cap for the gain setting
3. fail to fit an isolation resistor (usually about 50 Ohms) in series with the output when driving a real world load - like a cable for example, or a capacitive load.
4. fail to ensure that the junction of the feedback network is located physically very close to the op-amp feedback input pin (usually the inverting input)
5. fail to locate the input filter as physically close as possible to the op-amp input (usually the non-inverting input)
6. fail to decouple the supply rails adequately and close to the opamp supply pins
7. you use an opamp not characterized for wide band audio usage that has an inadequate slew rate
8. Fitting the comp cap across the wrong pins in an uncomensated op-amp (i.e 1-5 instead of 1-8 and vice-a-versa)
9. Failing to scope your physical design out . . . always follow Mooly's example
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Old 4th September 2011, 09:38 PM   #19
RCruz is offline RCruz  Switzerland
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Thank you for pointing me this thread Mooly.

Suddenly I started to understand and correlate all the points I have read about (separatedly).

I also want to thank all involved for the clear and consise sharing
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Old 4th September 2011, 10:51 PM   #20
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Originally Posted by SY View Post
Get a scope. Seriously. Why in the world would someone try to do electronics without the basic tools? May as well try to get by without a soldering iron.
I don't like being brow-beaten (esp. by a moderator!) into spending $150-200 minimum on a tool that might get used once a year. Seriously. Is that unreasonable?

(One of NP's early articles, A40, even has a suggestion on how to check DC at the outputs for the DIYer who HAS NO volt meter....!)
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