Do any of these measurements suggest an op amp I / V Stage? - diyAudio
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Old 23rd January 2016, 11:03 AM   #1
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Default Do any of these measurements suggest an op amp I / V Stage?


I am trialing a discrete op amp in my pre/dac, and have been advised they may become unstable in I/V conversion.

I don't really know much about op amps or their different applications.... yet!

I have measured dc voltage and wondered if any of the results suggest any of the three positions are I/V ?

Much appreciate any feedback,
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File Type: pdf Op Amp Voltage.pdf (67.3 KB, 53 views)
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Old 23rd January 2016, 02:02 PM   #2
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I am afraid I cannot understand ANYTHING for your .pdf!

More information. please. What does it represent?
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Old 23rd January 2016, 02:53 PM   #3
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What has DC voltage got to do with stability, for I/V or anything else?

I too have no idea what the pdf is trying to convey.
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Old 23rd January 2016, 03:58 PM   #4
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If you are not aware of the particular application, let alone circuit schematic, in which you are 'trialing' op-amps you are risking trouble. For example, your diagram shows pin 4 (-V) as very wrongly connected to pin 8 (+V).
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Old 23rd January 2016, 06:50 PM   #5
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Oh dear sorry, forgive me I am learning and as you may well guess don't have much of an idea as of yet.

Each of the boxes on the .pdf is an op amp, I have 3 locations with dip sockets that I can change over easily to the new discrete op amp. These locations are where I have measured the voltages marked on the .pdf.

The line between 4 and 8 is where I connected the multi meter across set to Vdc, and then connected it across 3 and 5 once again Vdc.

The pre/dac was on with the cdp connected and on, but no music was playing,
Power amps were not connected .

I hope this may help explain what I have done...
Even if we are none the wiser as to why I have measured those values....??

I am only just starting to realize that an op amp can have many applications, and when a new upgrade replacement is stated to be a direct replacement for a particular model of op amp - I assume that means I can replace it, swap it over - I am learning this may not be the case as the specific application may require a different design of op amp, and so it is therefore not a direct replacement..

If I am understanding things correctly, I/V conversion has a zero gain.. at which these particular replacements may well have trouble, and I don't really want to keep them in a place where they may have trouble..

Thanks for your replies!

Last edited by Deaf Cat; 23rd January 2016 at 07:05 PM.
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Old 24th January 2016, 06:56 AM   #6
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Unfortunately, these measurements don't give any useful information. Stability is related to dynamic behavior of the circuit. So, in order to analyze that, you need a good function generator and an oscilloscope, as a minimum. Then you need to know what to measure, where and how. And then, how to interpret the results. Some people here can help, but not from the point of giving a short course of electronics engineering
Also, schematic would be helpful.
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Old 24th January 2016, 04:12 PM   #7
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Ah yes, I was thinking about that, these measurements may not be enough...

I was thinking if the gain is zero, for I/V, I have only measured the input voltages and supply voltages, so not exactly related to gain at all :-(

I am unsure how I would measure the gain, or even the output voltage, I only have a standard multi meter...

So for actual stability measurements I fall well short on equipment and know how, is there away to measure the gain, just to see if this may indicate zero gain, which may in turn indicate I/V stage?

Much appreciate your replies so far :-)

Afraid I have no schematic, I may well have a little look around for one as I would guess someone may even be able to tell from a schematic what is what...
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Old 24th January 2016, 06:41 PM   #8
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Are you of the opinion that an I/V stage has zero gain? Why would that be? What use is anything with zero gain?

Anyway, even with a multimeter you can measure gain. Take a small mains transformer, take the secondary and pad it down with two resistors to say 0.1V. That is your input signal. Now measure the output signal. Gain = Vout / Vin. Done

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Last edited by jan.didden; 24th January 2016 at 06:43 PM.
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Old 24th January 2016, 07:52 PM   #9
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Ah well I read that somewhere about zero gain as it is just converting I to V ... ??
Not being used to amplify anything but convert.. ??

Okay, sorry getting a little out of my comfort zone with extra transformers.. and I don't have one.. (Beginner in electronics)

If I measured voltage across pins 7 & 5 and then 3 & 1, would that not give how much gain there was in Volts, and turning the volume knob would make a difference in that reading... or not, if I/V

Have been reading a little on op amps but they seem to be able to do so many different things!

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