LM4562, LME49710, LME49720 Start-up Behavior

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carlalex
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Re: LM4562, LME49710, LME49720 Start-up Behavior

Post by carlalex »

Thanks for the tip on the unused stage; I'll do that.

Maybe I should have been clearer. That stage will almost never be shut down. The stages that will see more on and off cycles are the ones behind the "to low noise input and crossover" outputs. This is the stage that I see that wacky 90 Mhz on. Radio station makes sense; I was kinda wondering about that given the frequency after I started seeing that with the power off. I must have built an antenna on my breadboard accidentally.

Perhaps not too usefully, I didn't include the stages I plan in turning on and off, partly because I haven't built them yet and I'm asking out of precaution rather than solving a problem I currently have. And partly because those stages are more cumbersome to attach. But, all of those stages have even lower resistors, or are simple voltage follower buffers. The It sounds like I you think I should be safe.

Thanks for the tips!

--- Carl
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mediatechnology
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Re: LM4562, LME49710, LME49720 Start-up Behavior

Post by mediatechnology »

I think as a matter of precaution your voltage followers might benefit from having a 1K or so feedback resistor.

Also beware of using the TL0XX series as followers.
ricardo has more experience with them latching up but I recall the polarity reversal when they go out of common mode range contributing to the problem.

For some reason I had a mental picture of a low-power input stage in parallel with the balanced input for signal present detection.

You might find a clever way to use forward current in the input protection diodes to detect signal present.
Or use a low power always-on comparator to compare In+ and In- to op amp Vcc.
If the input terminals exceed the input supply rail, then signal present = power on.

IIRC Motorola used to make an op amp that powered on when it received input.
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carlalex
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Re: LM4562, LME49710, LME49720 Start-up Behavior

Post by carlalex »

My followers are also lm4562s. I'm using those for everything in the signal path. Unit cost is less of an issue when it's a hobby. The one place I was considering using something else was the input stage I posted. Since it's not in the audio path and on all the time I was going to look for something lower current and I don't care so much about noise or distortion.

I think I've heard of the tl0xx latch up and reversal, which might have been why I started looking around in the first place. But, I don't currently have any of those around.

I think your mental picture was close. The stage I posted will be the very first thing it inside the chassis and will always have power. The "to signal detector" goes to my logic, which also always has power. The other outputs I have at the top of my schematic are what goes to the mess of circuitry making up a low noise input balanced input, the cross overs, any eq or bandwidth definition I decide to put in, and the output stages to feed the power amplifiers - That will be the stage that gets the rails cut to save power.

Thanks.
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JR.
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Re: LM4562, LME49710, LME49720 Start-up Behavior

Post by JR. »

carlalex wrote:Hi,

New to this forum, and I came across this thread when looking around to understand the behavior of the lm4562 during start-up. Maybe my post should be a new thread "Designing with the LM4562" since I have some other questions unrelated to start-up, but I found this thread while googling.... (And by way of introduction, I'm an audio design amateur. My background is aerospace engineering at school and software engineering by trade. My circuit design experience is simple to moderate.)

My current project: designing some loud speakers with integrated amplifiers for home use.
Making saw dust is always fun but hard to improve upon decent commercial designs, while many consumer speakers are less than optimal.
I am using off-the-shelf hypeX amps and power supplies, and an entrodev power supply for the auxiliary circuit, which is what I a designing from scratch.
The Hypex amps designed by Bruno Putzey are very well respected.
The auxiliary circuit I am currently designing does a number of things:
- It's an active cross-over and balanced input stage built around lm4562 opamps. The design is heavily influenced by "the design of active crossovers" by Douglas Self.
Self is pretty well respected circuit designer, I didn't know that he designed speakers too? (someday I may read his book...nah).

Crossover design is much too complex for a brief post.but includes multiple moving parts related to; box tuning, driver transfer function, and physical alignment. I used standard filter alignments in professional crossovers back in the '80s but real speaker engineers these days use more custom approaches tuned to specific box and drivers.
- It controls power on signal detect, and power down after delay. The signal detection is based on the njm2072, with a 555 governing my timer.
I've heard of the 555 decades ago but had to look up the 2072. Kind of surprising that they made a dedicated IC for something that simple. If I understand your application, this needs to powered up all the time to detect input signal, then connected in front of your balanced input, unless you leave that powered up too. Not feeling very good about the input impedance of that 2072 I would drive it from a low Z (like input receiver output). Oddball parts like that have a bad habit of turning obsolete if major users stop using it, so if designed in maybe buy some spares.

I might be tempted to design something discrete to perform the signal turn on, but unless you leave it powered on, it gets tricky to not affect input balance, etc. If powered on continuously it gets a lot easier to design.
- The power management is currently designed to control the HypeX amps, but I would like to extend it to power down the cross over and all of those opamps that would be doing nothing but sucking power when everything else is in stand-by. (An idle lm4562 on +/- 15V rails runs warm and draws about 10mA.) That way during stand-by I could get by with only powering the logic circuits on the +5V rail, and a single op-amp on the +/-15V rails that is buffering for the signal detector. It is pursuing this goal that I started considering op-amp start-up behavior and came across this thread.

So, my immediate questions:
1) regarding the start-up behavior described in this thread, should I expect this behavior if I am using low impedance stages? All of my op-amp stages have been designed with impedance between 600 and 2k ohm to keep noise down.
For line level signals resistor noise is probably not a huge concern. but quiet is good. I will defer to the experience of others regarding start-up. I haven't used many of the latest generation parts.
Ultimately, the question I am trying to answer for myself is whether I can get away with letting signal hit my opamps before they are powered up, or do I really need to build in timers and relays into my signal path to manage this? As these are likely to be plugged in an left to the sensor to control power on/off 99% of the time, I don't want to burn my house down with something that latches, burns out an IC, and lets chaos ensue one out of every 50 start-ups. The simple thing for me to do is just cut the rails to the part of the circuit I want to disable. If I leave these portions connected to signal, it would be expected that signal would hit the audio path before and during power-up while my logic circuits are deciding to turn on the power on for a few milliseconds, and it would be expected in this case that input would be present while the audio path op-amps are suffering through whatever transients occur when the rails are reconnected. If I need to withhold signal for a few seconds, I have more work to do.
my understanding of op amp latch up is not likely to burn your house down. Just no audio passed with op amp pegged to a rail. That said if putting an amp and PS inside a wood box there may be concerns about flammability. Hopefully the PS and amp are well fused.

Regarding injury to un-powered op amps most will tolerate low level audio. For active circuits to be damaged you need input voltages more than +/- a couple diode drops, with enough current to damage silicon. Using very low impedances works against you here, providing more current, while the source impedance of most consumer gear is not very low.

Getting back to the op amp, for damage to occur from an input voltage significant current must flow and actually go somewhere. many ICs will have input clamps built-in. So stray input voltages may harmlessly charge up PS caps. Wayne referred to clamp issues with mic preamps that are made difficult by phantom power DC blocking caps that can dump amps of current if shorted.
2) are there other wacky start-up (or shut down) behaviors I need to consider? (I'm an amateur, nothing is too obvious to state.)
turn on clicks and pops are generally not fun to listen to.
3) I have other questions, but don't want to overload this post :). I'm still wrapping my head around oscillation. (what does it look like on a scope? will it be a small amplitude at a high freq? Obvious and rail to rail? at what freq?)
comes in different flavors. Serious oscillation will be rail to rail, low level HF signals may be borderline instability, or just RF noise pickup.
4) Also un-related, but something I saw that I really don't understand.... I've got my control circuit, RF and DC blocking stage, and a simple balanced buffer to feed the control circuit all bread-boarded up. I was looking at this circuit on a scope and I noticed that when the input was 0v (signal generator set to 0v), I would get a small (about 4mVpp) and very fast (90 MHz) signal. Schematic and picture of my oscilloscope attached. I have no explanation for this. Is this a glimpse into the op-amp internals? Noise from my scope bouncing around? Is it something I need worry about? I think I ruled out the control circuit; I see this even when I remove that signal path. Stranger still, I see this when I completely power down both my signal generator, and the circuit under test! (This buffer stage is not in the final audio path, so it's just thrown together with some higher resistor values I had on hand, and I'm currently experimenting with various gains to tweak the njm2072's sensitivity.)

Thanks in advanced for any help!

--- Carl
90Mhz sounds like FM band radio. The hypex is a switching amp so could have some small HF leakage but it won't switch up that fast, so more likely radio pickup or low level instability.

JR

PS: Any reason you can't use a on/off power switch?
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mediatechnology
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Re: LM4562, LME49710, LME49720 Start-up Behavior

Post by mediatechnology »

I see the NJM2072 has 20K input resistors: http://www.njr.com/semicon/PDF/NJM2072_E.pdf

Do you suppose that the NJM2072 could be bridged across the +In directly allowing the balanced input stage to be powered down?
I realize in this application the 10 mA of the first LM4562 doesn't represent a lot of standby current.
My only reservation is that with higher source impedances the loading of the 20K and 2072 ESD diode might raise THD when Vin is greater than the 2072 supply.

I had some Sony battery-powered mini-speakers years ago with auto-turn on.
It saved a lot of batteries.
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Re: LM4562, LME49710, LME49720 Start-up Behavior

Post by JR. »

mediatechnology wrote:I see the NJM2072 has 20K input resistors: http://www.njr.com/semicon/PDF/NJM2072_E.pdf
Unless I read that wrong it's "input resistor" as in just one resistor. I guess you could use two 2072s and hang one off both inputs, but that raises a second issue. The 2072 looks like inverting with gain of 5x and 7V rail voltage so when that 5x gain stage saturates, the input impedance jumps from 20k to 120k (?) at a little over 1V then may get even weirder at over 7v peak.

I repeat my suggestion to drive it from the low Z buffered input or maybe don't use it at all.

There may be better ways to skin that cat...

JR
Do you suppose that the NJM2072 could be bridged across the +In directly allowing the balanced input stage to be powered down?
I realize in this application the 10 mA of the first LM4562 doesn't represent a lot of standby current.
My only reservation is that with higher source impedances the loading of the 20K and 2072 ESD diode might raise THD when Vin is greater than the 2072 supply.

I had some Sony battery-powered mini-speakers years ago with auto-turn on.
It saved a lot of batteries.
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mediatechnology
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Re: LM4562, LME49710, LME49720 Start-up Behavior

Post by mediatechnology »

I was wondering if a low-power 5V standby voltage-powered op amp could be used as a comparator to detect signal presence and then bootstrap itself and the higher-current balanced input to +15V (and -15V) supply levels.

An input that powers itself down and provides a power on, mute output and/or signal fail indication is kind of neat and an interesting challenge.
Particularly the signal fail/silence sensor part.
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carlalex
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Re: LM4562, LME49710, LME49720 Start-up Behavior

Post by carlalex »

JR. wrote:
carlalex wrote: My current project: designing some loud speakers with integrated amplifiers for home use.
Making saw dust is always fun but hard to improve upon decent commercial designs, while many consumer speakers are less than optimal.
Crossover design is much too complex for a brief post.but includes multiple moving parts related to; box tuning, driver transfer function, and physical alignment. I used standard filter alignments in professional crossovers back in the '80s but real speaker engineers these days use more custom approaches tuned to specific box and drivers.
Point taken. The making of the thing is interesting in and of itself, as are the things I learn along the way. For what it's worth, the baseline speakers that this project will replace are Infinity Overture 3s. Will I exceed these? Don't know yet. Will I save money? Certainly not. Will I learn? Already have.
I've heard of the 555 decades ago but had to look up the 2072. Kind of surprising that they made a dedicated IC for something that simple. If I understand your application, this needs to powered up all the time to detect input signal, then connected in front of your balanced input, unless you leave that powered up too. Not feeling very good about the input impedance of that 2072 I would drive it from a low Z (like input receiver output). Oddball parts like that have a bad habit of turning obsolete if major users stop using it, so if designed in maybe buy some spares.

I might be tempted to design something discrete to perform the signal turn on, but unless you leave it powered on, it gets tricky to not affect input balance, etc. If powered on continuously it gets a lot easier to design.
The NJM2072 crossed my radar reading the ESP articles on soundwest. It's simple enough to use and wasn't hard to source from Mouser. Works like a champ on the bread board, but the input series cap is definitely required even though the spec sheet doesn't really say much about it. (Size that cap with the 20k input in mind - since it seems to form a high pass filter). I'm using it control various SSRs, indicator LEDs, and the 555 to manage the active/standby control pins of various external components.
Ultimately, the question I am trying to answer for myself is whether I can get away with letting signal hit my opamps before they are powered up, or do I really need to build in timers and relays into my signal path to manage this?
...
my understanding of op amp latch up is not likely to burn your house down. Just no audio passed with op amp pegged to a rail. That said if putting an amp and PS inside a wood box there may be concerns about flammability. Hopefully the PS and amp are well fused.
All the PSUs are fused. I'm buiding the assembly as a plate unit on an aluminum plate, but the issue of what the cavity is made from is on my mind. (My last electronics project was an electric brewing system - 25 amps at 240VAC surrounded by liquid - safety was foremost in that project.)
2) are there other wacky start-up (or shut down) behaviors I need to consider? (I'm an amateur, nothing is too obvious to state.)
turn on clicks and pops are generally not fun to listen to.
Yup. Current speakers have quite the vocabulary - pops on start-up, a lovely whine if you unplug them. I was mostly asking about serious problems over annoyances.
PS: Any reason you can't use a on/off power switch
What fun is that? Also, it would be a hard sell to the family to manually turn on each speaker one at a time.

Regards,

--- Carl
Last edited by carlalex on Tue Sep 22, 2015 12:16 am, edited 1 time in total.
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Re: LM4562, LME49710, LME49720 Start-up Behavior

Post by carlalex »

mediatechnology wrote:I see the NJM2072 has 20K input resistors: http://www.njr.com/semicon/PDF/NJM2072_E.pdf

Do you suppose that the NJM2072 could be bridged across the +In directly allowing the balanced input stage to be powered down?
I realize in this application the 10 mA of the first LM4562 doesn't represent a lot of standby current.
My only reservation is that with higher source impedances the loading of the 20K and 2072 ESD diode might raise THD when Vin is greater than the 2072 supply.

I had some Sony battery-powered mini-speakers years ago with auto-turn on.
It saved a lot of batteries.
Yes, feeding the hot input into the NJM2072 seems to work just fine from what I've tried, at least as far as its functionality is concerned. I can't speak to how this would impact other stages in parallel yet. I started toying around with a buffer in front of the NJM2072 since it has a fixed sensitivity of -36dBV, and it's not uncommon for me to have my receiver around that level late at night, so I was considering a gain stage in front of it for margin. If I decide I don't need the gain, I may ditch that stage. Impact on stages in parallel is a good point, so it might be another good reason to consider that arrangement. In practice, I do not expect Vin to exceed the +5v rail I'm supplying the NJM2072 with very often

As I said, I might have posted the wrong schematic for my initial question, since that wasn't the stage I wanted to power down, but it also wasn't too dissimilar from the sorts of values I have in my other stages, and I did have many questions (for which you guys have already been immensely helpful.)

--- Carl
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Re: LM4562, LME49710, LME49720 Start-up Behavior

Post by carlalex »

JR. wrote:
mediatechnology wrote:I see the NJM2072 has 20K input resistors: http://www.njr.com/semicon/PDF/NJM2072_E.pdf
Unless I read that wrong it's "input resistor" as in just one resistor. I guess you could use two 2072s and hang one off both inputs, but that raises a second issue. The 2072 looks like inverting with gain of 5x and 7V rail voltage so when that 5x gain stage saturates, the input impedance jumps from 20k to 120k (?) at a little over 1V then may get even weirder at over 7v peak.

I repeat my suggestion to drive it from the low Z buffered input or maybe don't use it at all.

JR
I didn't see anything particularly strange when I hit the 2072 with very high signals when I was playing with prefixing gain stages. I was interested in the low-end sensitivity, but hit it with over 20v out of thoroughness since that would be the other effect of a high gain stage in front of it. But, I wasn't looking at it's impedance, only it's behavior. Still, that's well outside it's spec sheet which indicates a limit of Vcc - 1 for Vin, so probably not advised.

--- Carl
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