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This chip is supposed to have very good noise rejection ratios, so is decoupling that critical with this chip? Should I decouple directly between the V+ and V- pins (as I have in more sensitive chips) and should I also individually decouple each rail terminal to earth?
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As with most "slow" op amps....they don't require any bypassing except an electrolytic........I usually use a Blackgate N. Yes, I have tried these 4562 op amps and I find the midrange slightly threadbare.....I prefer the new slow Burr Browns (opa 211 and opa 827....both singles...no duals yet). I have played with opamps for years and the only ones that were squirrely were your super high speed jobbies. Slow op amps are pretty easy to use. Now, if you are using it as a buffer and no cap across the feedback then you are talking some bandwidth and might need some playing with to make stable...but for most other uses....just plug and play.
Thanks for the reply. I've already put one in with no extra decoupling and it sounds very good with no signs of oscillation. It changed/improved much more in the first 60 hours than any other op amp I've experienced and it's still seems to be improving slightly at 75 hours. I find it very dynamic with lots of detail and very transparent: independent threads stay independent. For some reason voices are pushed back, but still have lots of detail and emotionality. I'm going to add a couple of 47 uF caps on the rails to earth and see if that improves things even further.
How about doing what it says on the datasheet? Perhaps the manufacturer has some experience with the chip.
Best,
CAC
And that would be what?
Obviously I've read the data sheet. Just wanted some real life experience of this fairly well known chip. Don't know what has happened to this once great site. Won't bother to ask in future.
Usually it's power supply pins to ground
The consensus on here to stop oscillation is a cap directly between the v+ and v- pins as close to the point they leave the chip, rather than bypassing to ground! That's what I've done with other chips like the 6172 over the last 6 or 7 years. I'm just asking for anyone's particular experience with the 4562.
The consensus on here to stop oscillation is a cap directly between the v+ and v- pins as close to the point...
....My experience, and my instinct, is that that would make oscillation worse. But I can't prove anything.
Thanks for the reply. I suppose it might do that in some situations. I wonder what the theory would be to explain it.
Well, my take is that if the capacitor connects the rails at ac, when one rail goes up it will want to pull the other one up. When it goes down it will want to pull the other one down. So ground is staying where it is and the whole amplifier is jumping up and down relative to it. If the positive input is referenced to ground, well, it's seeing [what we think is ground] jumping down and up, and it wants to amplify the jumps. Because it's an amplifier and it wants to amplify things that are applied to its input.
This can't be good. You want the amplifier to be on a secure platform, if for no other reason than decorum.
M
I suppose in theory both rails will be shorted to ground by decoupling caps earlier on, but any inductance from the tracks to the point where the rail connects to the IC will mean that the decoupling will become less effective as frequency increases. I think the stability of the opamp circuit is also affected by capacitive negative feedback (through actual capacitors and stray capacitance). So I think some circuits and opamps will be much more affected than others.
What cap and value do you use for v+ to v- for 6172? I recently added Rubycon ZLH 2200uf from pin 4, 8 to ground and it has good result. Never tried 4562 but it should be the same, I guess.
I use 2 x 0.47uF BG Nx-HiQ caps connected in an L cancelling pair. The 6172 is much faster and has a wider bandwidth so is more likely to oscillate than the 4562. The newer chip also has better noise rejection, so in theory it should not be quite as touchy as the 6172. Whether practice is the same as theory is another matter though, hence my request for people's experience. I suppose I'll just have to suck it and see.
...can't believe nobody's got any experience to share.
If current is taken from ground you should of course have caps between supply voltage and ground. A good start is to have 100 nF /63 V polyester, ceramics etc, physically small caps, between V+ and gnd and V- to gnd. Avoid big caps since their resonance frequency become lower => works as inductance over the resonance.An another good idea is like someone else point out is to read the datasheet for the opamp in mind.
Edits: 05/09/09 05/09/09 05/09/09
Thanks for the reply. Yeah, reading the datasheet was the first thing I did. Just wanted some real world experience.
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