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Chip Amps Amplifiers based on integrated circuits

LM3886 & LME49720 composite amp
LM3886 & LME49720 composite amp
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Old 2nd February 2015, 09:49 PM   #21
jcx is offline jcx  United States
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snowy day, hadn't fired up LTSpice in a while...

can't see how its going to be stable

the dotted box is a crude linear "macro model" for LM3886 with enough excess poles that it is unstable at below ~ Av 5
happy with gains of 10+ like expectation from the data sheet min gain spec

if you have a stable prototype it aint wired like the pdf, from my sim
Attached Images
File Type: png badcompos.png (63.6 KB, 927 views)
File Type: png badcir.png (27.4 KB, 930 views)
Attached Files
File Type: asc badcomposit3886.asc (3.9 KB, 49 views)

Last edited by jcx; 2nd February 2015 at 09:54 PM.
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Old 2nd February 2015, 09:56 PM   #22
IO390 is offline IO390  United Kingdom
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I have built 4 of these boards so far and I'm listening to them right now.

It's stable...
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Old 2nd February 2015, 09:58 PM   #23
jcx is offline jcx  United States
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so show me the sim or circuit error
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Old 2nd February 2015, 10:00 PM   #24
IO390 is offline IO390  United Kingdom
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Quote:
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so show me the sim or circuit error
Huh? I never simmed this circuit, it's not complex enough to need it.
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Old 2nd February 2015, 10:05 PM   #25
jcx is offline jcx  United States
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my sim .asc file is right there for any to download, dissect show me the error

until then I maintain you didn't build that

whatever you did build, are listening to ain't the circuit shown
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Old 2nd February 2015, 10:07 PM   #26
IO390 is offline IO390  United Kingdom
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Jesus... Am I getting accused of not building the circuit I said I did?

I don't even see the point in that.
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Old 2nd February 2015, 10:15 PM   #27
jcx is offline jcx  United States
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its possible there are wiring and/or component value differences from the circuit shown and what you have

but it seems rather unlikely you have a non-oscillating build to the shown circuit diagram


so until anyone can show me my sim error I have to give the warning
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Old 2nd February 2015, 10:24 PM   #28
IO390 is offline IO390  United Kingdom
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So you're saying that I built AND published a circuit that doesn't work.

As I say, I've built 4 boards thus far (a friend is building another two), AND a point-point prototype so I'd know if I had made an error in component values.

I am well aware of how good LTSpice is, but you're testing a circuit with a different opamp model and an approximate LM3886 and yet you say that your simulation emulates my real life circuit?

Your LTspice model does not take into account the internal compensation of the LM3886 for example.
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Old 2nd February 2015, 10:34 PM   #29
jcx is offline jcx  United States
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the integrator feedback around the LT1469 renders the exact op amp pretty irrelevant

my LM3886 model isn't what I would call pessimistic but there is the possibility that all parts built today on modern processes are better than the typical specs in the decades old datasheet

but as an engineer I expect to actually design to worst case datasheet info with a margin

I wouldn't recommend building that circuit, with those values to any manufacturer as a safe practice

can't see giving a pass to anyone recommending such to hobby builders with even less electronic design sophistication, or even a decent oscilloscope
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Old 2nd February 2015, 10:38 PM   #30
IO390 is offline IO390  United Kingdom
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Quote:
Originally Posted by jcx View Post
the integrator feedback around the LT1469 renders the exact op amp pretty irrelevant
True

Quote:
Originally Posted by jcx View Post
my LM3886 model isn't what I would call pessimistic but there is the possibility that all parts built today on modern processes are better than the typical specs in the decades old datasheet
Probably not the case IMO.

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Originally Posted by jcx View Post
but as an engineer I expect to actually design to worst case datasheet info with a margin

I wouldn't recommend building that circuit, with those values to any manufacturer as a safe practice
Fair enough if you wouldn't recommend it. I'm not saying anyone should build it and I'm not here to sell it. I posted it here in case it interests anyone, and if they build it and like it then great.

But there's no point in saying it won't work and must be unstable because of some approximations you've made. If you build it and then find problems then great, I will accept that. It's things like this that deter me from posting on this forum (and most other forums).
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Last edited by IO390; 2nd February 2015 at 10:40 PM.
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