A few suggestions
Pat,
Did you look at the output of the 4562 with a scope? I'll bet it is oscillating. Since these LME parts have wider bandwidth they can have problems in some circuits and with bad power supplies. Just putting bypass caps right on the power supply pins usually won't help with the osc problem. Look at the output of your power supplies and see what is going on there. Sometimes a very low resistance series resistor before the bypass cap on the opamp power supply pins can help. Layout can also be an issue so cutting the power supply traces to the opamap and routing a pair of power supply wires directly to the opamp can also help.
What does the input to the LME49720/4562 look like? Sometimes a better opamp will pass through problem signals that the older, lower bandwidth, device filtered out. Also don't put caps across the opamp, except maybe a couple of pf silver mica, I never like slowing the opamp down to solve an osc problem, i.e. bandaid!
Just a few things to look at. Troubleshooting is difficult sometimes but I always enjoy it...especially when I finally find the problem!
Mark / audioman54
PS-Has anyone tried the LME49713 yet?
Pat,
Did you look at the output of the 4562 with a scope? I'll bet it is oscillating. Since these LME parts have wider bandwidth they can have problems in some circuits and with bad power supplies. Just putting bypass caps right on the power supply pins usually won't help with the osc problem. Look at the output of your power supplies and see what is going on there. Sometimes a very low resistance series resistor before the bypass cap on the opamp power supply pins can help. Layout can also be an issue so cutting the power supply traces to the opamap and routing a pair of power supply wires directly to the opamp can also help.
What does the input to the LME49720/4562 look like? Sometimes a better opamp will pass through problem signals that the older, lower bandwidth, device filtered out. Also don't put caps across the opamp, except maybe a couple of pf silver mica, I never like slowing the opamp down to solve an osc problem, i.e. bandaid!
Just a few things to look at. Troubleshooting is difficult sometimes but I always enjoy it...especially when I finally find the problem!
Mark / audioman54
PS-Has anyone tried the LME49713 yet?
Thanks for the reply audioman!
I have not tried the LME49713 yet. Is it interchangeable with the 4562? Is there something to recommend it over the 4562?
It sounds like I need to buy a scope... I have never had an issue until now using the 4562. The fact that LT1361, AD8032, LM4562 don't work seems to point to a problematic board layout.
I have not tried the LME49713 yet. Is it interchangeable with the 4562? Is there something to recommend it over the 4562?
It sounds like I need to buy a scope... I have never had an issue until now using the 4562. The fact that LT1361, AD8032, LM4562 don't work seems to point to a problematic board layout.
Pat,
The LME49713 is a current feedback opamp that was designed at National per my specifications for audio. CFB opamps are usually used in video circuits but they have some unique properties that make them a great choice for audio. In my listening tests in the sound room at National the LME49713 was my favorite part but in my latest D/A design (I have designed several D/A preamps at a bunch of audio companies over the last 20 years) I use both CFB and VFB opamps in the signal path depending upon the circuit requirements. For example a VFB part works much better in a Diff to single ended circuit because the input structures of the plus and minus inputs are identical where as in a CFB opamp the two input structures are quite different. Also CFB opamps are a bit harder to use as they require a fixed feedback resistance value for optimal performance. In the case of the LME49713 that value is around 1.2k. The following is an excerpt from the 49713 data sheet that talks about the fixed value for Rf...
"The value of the Rf, is also a dominant factor in compensating
the LME49713. For general applications, the LME49713 will
maintain specified performance with an 1.2kÙ feedback resistor.
Although this value will provide good results for most
applications, it may be advantageous to adjust this value
slightly for best pulse response optimized for the desired
bandwidth. In addition to reducing bandwidth, increasing the
feedback resistor value also reduces overshoot in the time
domain response."
I should also mention that in my audio designs I prefer to use inverting circuit topologies wherever possible.
Mark / Audioman54
The LME49713 is a current feedback opamp that was designed at National per my specifications for audio. CFB opamps are usually used in video circuits but they have some unique properties that make them a great choice for audio. In my listening tests in the sound room at National the LME49713 was my favorite part but in my latest D/A design (I have designed several D/A preamps at a bunch of audio companies over the last 20 years) I use both CFB and VFB opamps in the signal path depending upon the circuit requirements. For example a VFB part works much better in a Diff to single ended circuit because the input structures of the plus and minus inputs are identical where as in a CFB opamp the two input structures are quite different. Also CFB opamps are a bit harder to use as they require a fixed feedback resistance value for optimal performance. In the case of the LME49713 that value is around 1.2k. The following is an excerpt from the 49713 data sheet that talks about the fixed value for Rf...
"The value of the Rf, is also a dominant factor in compensating
the LME49713. For general applications, the LME49713 will
maintain specified performance with an 1.2kÙ feedback resistor.
Although this value will provide good results for most
applications, it may be advantageous to adjust this value
slightly for best pulse response optimized for the desired
bandwidth. In addition to reducing bandwidth, increasing the
feedback resistor value also reduces overshoot in the time
domain response."
I should also mention that in my audio designs I prefer to use inverting circuit topologies wherever possible.
Mark / Audioman54
Mark, sorry to hear about your layoff and the issues at NatSemi. There's a small irony here, in that the LM497xx/8xx series opamps are not available at retail in places like India, where I'd grab a few dozen to play with, if I could. However, that's not NatSemi's fault, but their distributors'. For now, I have to remain content with simulations.
Anyways, here's my first try at an ultra-low distortion low-power headphone amp with an LME49860. Nothing terribly clever, just a slightly tricked-up Class-AB Diamond-Buffer to increase the power capability, and a current-dumping reactive bridge to add a bit of feed-forward error correction. It can put out about 2W into 32 ohms, which is waaaay more than anybody needs for a headphone amp. At 0.5W into 32 ohms, it runs in Class-A. It will also give comfortable levels of power into higher-Z headphones, at even lower THD.
Edit: On a related note, is there a publicly-available Spice model for the LME49600 high-current buffer? I could greatly simplify this circuit with the LME49600.
Anyways, here's my first try at an ultra-low distortion low-power headphone amp with an LME49860. Nothing terribly clever, just a slightly tricked-up Class-AB Diamond-Buffer to increase the power capability, and a current-dumping reactive bridge to add a bit of feed-forward error correction. It can put out about 2W into 32 ohms, which is waaaay more than anybody needs for a headphone amp. At 0.5W into 32 ohms, it runs in Class-A. It will also give comfortable levels of power into higher-Z headphones, at even lower THD.
Edit: On a related note, is there a publicly-available Spice model for the LME49600 high-current buffer? I could greatly simplify this circuit with the LME49600.
Attachments
Hi, Linuxguru,
Do you have your version of patent #4,716,378? It reduce distortion because the main amp see a much higher impedance of the load.
Do you have your version of patent #4,716,378? It reduce distortion because the main amp see a much higher impedance of the load.
Is this the new "correct" comp circuit for the LME49810?
An externally hosted image should be here but it was not working when we last tested it.
Hi, Mark,
“Noise Gain Comp” circuit from Bob Pease, if I'm not mistaken, it should be placed in (-)input to ground or to (+)input. Is the "comp" pin equal to (-)input pin ?
“Noise Gain Comp” circuit from Bob Pease, if I'm not mistaken, it should be placed in (-)input to ground or to (+)input. Is the "comp" pin equal to (-)input pin ?
No, not that particular LB -- something was to have come out in 2008, but never got published/off the ground (to the best of my knowledge)
I think that the issue for National is that they have fallen behind TI and others in Class-D for consumer aps...I have no idea who the winners will be in Class-D.
I think that the issue for National is that they have fallen behind TI and others in Class-D for consumer aps...I have no idea who the winners will be in Class-D.
Good Morning Everyone,
Firstly, Jackinnj that is the correct circuit, however the LME49810 does not require that circuit although it probably won't hurt. That exact circuit is required on the LM4702 and the LME49811. For higher quality amplifiers under 300w use the 4702 or the 49811 with both have 5ma or so of output current. For higher power amplifiers that need the 50ma of output current to drive them up to 3kW the LME49810 is the way to go. (The 49810 has an extra A/B stage to get that extra output current.)
Secondly Linuxguru, yes the LME49600 would be a great choice for your headphone buffer as that is what the 49600 was designed for. It is built on the same process as the other LME parts and has the same sonic qualities. I might also suggest the LME49713 as a second possibility as it has 100ma of output current which means you don't need to use a buffer at all to drive your headphones. The metal can 49713 with a clip on heatsink would give you even a little more!
Mark / audioman54
Firstly, Jackinnj that is the correct circuit, however the LME49810 does not require that circuit although it probably won't hurt. That exact circuit is required on the LM4702 and the LME49811. For higher quality amplifiers under 300w use the 4702 or the 49811 with both have 5ma or so of output current. For higher power amplifiers that need the 50ma of output current to drive them up to 3kW the LME49810 is the way to go. (The 49810 has an extra A/B stage to get that extra output current.)
Secondly Linuxguru, yes the LME49600 would be a great choice for your headphone buffer as that is what the 49600 was designed for. It is built on the same process as the other LME parts and has the same sonic qualities. I might also suggest the LME49713 as a second possibility as it has 100ma of output current which means you don't need to use a buffer at all to drive your headphones. The metal can 49713 with a clip on heatsink would give you even a little more!
Mark / audioman54
Those additional application notes are mentioned in AN-1645. The engineer at National just doesn't have time to complete and publish the notes (a time consuming process). As Mark said (Hi Mark from Utah!), National doesn't want to play the long game, like pretty much every other company. National is about quick turn on ROI even though they know parts like the Overture series chip amps can have a lifetime of 20 or more years. The LM3886 was released in 1993 and is still selling. I am sure the 2 year ROI was not great but many parts with great 2 year ROI have non-existent ROI after 5 years. National has some great products, some excellent people but the management is killing them. I expect them to be bought by someone at some point after the high level management milks it.
-TH
-TH
The 2 year ROI is probably so important, because the managers themselves often don't last longer than two or three years at each place. So they need quick results to present them, when they apply for their next job, but couldn't care less about a 20 years perspective for products, companies or other people.
Of course the apllication engineer does not have time to complete and publish the missing application notes, if he gets laid off first.
Of course the apllication engineer does not have time to complete and publish the missing application notes, if he gets laid off first.
Quote
The 2 year ROI is probably so important, because the managers themselves often don't last longer than two or three years at each place. So they need quick results to present them, when they apply for their next job, but couldn't care less about a 20 years perspective for products, companies or other people. Unquote
Driven by the stock market investors. Sure, the management get fat salaries and bonus's, but they dance to the investors tune. The investors are advised by the analysts. The analysts are usually maths PhD grads in their late 20's or early thirties, lured away from a the career they were trained for on the promise of a quick buck . . . .
It's no wonder the world is in a mess, and our industry is screwed.
The 2 year ROI is probably so important, because the managers themselves often don't last longer than two or three years at each place. So they need quick results to present them, when they apply for their next job, but couldn't care less about a 20 years perspective for products, companies or other people. Unquote
Driven by the stock market investors. Sure, the management get fat salaries and bonus's, but they dance to the investors tune. The investors are advised by the analysts. The analysts are usually maths PhD grads in their late 20's or early thirties, lured away from a the career they were trained for on the promise of a quick buck . . . .
It's no wonder the world is in a mess, and our industry is screwed.
The engineer working on those notes is still at National. It is just now that high performance is not being pushed but some other flavor of the month, or quarter.
-TH
-TH
audioman54,
is there any advantage to substituting an lme49860 for an existing 4562? my sondcard (asus xonar essence stx, with diy external linear psu) uses 2 duals for i/v conversion, and a duall for balanced to single-ended for the output. the card ships with the 4562, and some jrc2114s. i have subbed lf353s for i/v, and am hunting for the optimal dual for the output.
any thoughts????
best regards,
Mark
PS- if you are who i think you are, have you ever found the soundtrack to that roddy piper sf movie you were looking for????
is there any advantage to substituting an lme49860 for an existing 4562? my sondcard (asus xonar essence stx, with diy external linear psu) uses 2 duals for i/v conversion, and a duall for balanced to single-ended for the output. the card ships with the 4562, and some jrc2114s. i have subbed lf353s for i/v, and am hunting for the optimal dual for the output.
any thoughts????
best regards,
Mark
PS- if you are who i think you are, have you ever found the soundtrack to that roddy piper sf movie you were looking for????
Thanks FZMAN for making me smile this morning, which is hard to do while I have been continuing my online job search. The name of the movie was They Live and I have the soundtrack for it now. Not audiophile quality but a very fun recording. Email me and let me know where we talked about that.
With regards to the opamps stay with what you have unless you need devices tested for +/-22VDC operation. Do get the metal can LME49720's though if you want the best sound quality. (the 49720 and 4562 are identical parts).
If you can use singles the LME49713 CFB opamp makes a better I/V part.
Best Regards,
Mark
With regards to the opamps stay with what you have unless you need devices tested for +/-22VDC operation. Do get the metal can LME49720's though if you want the best sound quality. (the 49720 and 4562 are identical parts).
If you can use singles the LME49713 CFB opamp makes a better I/V part.
Best Regards,
Mark
mark,
the 3 opamps on the soundcard are all socketed 8-dips.
i am decent with a soldering iron, but i am not sure if i am up to the task of doing two to-99 to 8-dip adaptor boards, or 3, if i were to replace all three opamps with the metal can versions-- although it sounds like it woould be worthwhile.
is the 49860 really any different than the 4562, except for the higher rail voltage?
the card has an emi shield, and i am not sure how much space it affords, or wether it really does much of anything. the outboard psu via the molexconnector did make a big improvement. the psu is choke regulated, and the 12 v and 5 psus are totally sperate, sharing only the iec connector.
here's a link to the soundcard and a bunmch of pix, which loads quickly. http://www.hardwarecanucks.com/foru...lusive-asus-xonar-essence-stx-sneak-peak.html
i have only jsut begun posting on this site, and so far cannot email you, but i am working on it. perhaps you can email me???
best,
Mark
the 3 opamps on the soundcard are all socketed 8-dips.
i am decent with a soldering iron, but i am not sure if i am up to the task of doing two to-99 to 8-dip adaptor boards, or 3, if i were to replace all three opamps with the metal can versions-- although it sounds like it woould be worthwhile.
is the 49860 really any different than the 4562, except for the higher rail voltage?
the card has an emi shield, and i am not sure how much space it affords, or wether it really does much of anything. the outboard psu via the molexconnector did make a big improvement. the psu is choke regulated, and the 12 v and 5 psus are totally sperate, sharing only the iec connector.
here's a link to the soundcard and a bunmch of pix, which loads quickly. http://www.hardwarecanucks.com/foru...lusive-asus-xonar-essence-stx-sneak-peak.html
i have only jsut begun posting on this site, and so far cannot email you, but i am working on it. perhaps you can email me???
best,
Mark
Mark,
Yes the opamps are the same part with the 860 being tested to assure a higher voltage rating. Don't change if you dont need the higher voltage rating.
The metal can devices can easily have their leads bent to fit into a dip socket. I do it all the time! Putting a dip into a round metal can socket...now that is difficult!
Mark
Yes the opamps are the same part with the 860 being tested to assure a higher voltage rating. Don't change if you dont need the higher voltage rating.
The metal can devices can easily have their leads bent to fit into a dip socket. I do it all the time! Putting a dip into a round metal can socket...now that is difficult!
Mark
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