Guys,
I may have missed the arguments, but why not run the input on a 10k pot to the +input and scale the feedback network back to 1 K and 22K?
All those large values only generate unnecessary noise as well.
Every standard text will tell you that this setup gives unnecessary offset, which may not damage the speaker but puts the voice coil eccentric.
Why this peculiar ranges of values?
Jan Didden
I may have missed the arguments, but why not run the input on a 10k pot to the +input and scale the feedback network back to 1 K and 22K?
All those large values only generate unnecessary noise as well.
Every standard text will tell you that this setup gives unnecessary offset, which may not damage the speaker but puts the voice coil eccentric.
Why this peculiar ranges of values?
Jan Didden
millwood said:
You are right re 60mV, but...
When I designed the JLTi I actually measured it @ 0.1uA...
So this circuit with 300K is the circuit I understand Thorsten now recommends, it should give 30mV DC. This tallies well with what Peter is getting, he got 28mV using 250K.
An externally hosted image should be here but it was not working when we last tested it.
The 0.2uA is mentioned in the application note as typical, but several dozen samples I've used it is nearer to 0.1uA - maybe that is because I got them of the same batch? If so, then so has Peter?
But then we could expect that the new 'approved' circuit, which I gather looks like above (with 300K) will give DC Offsets in the range of 30-60mV.
So I think we are in heated agreement.
Joe R.
PS: Can KYW confirm the 'approved' part of my statement?
PPS: Eliminating input cap will amplify DC, so maybe not a good idea.
Konnichiwa,
Well, if you actually measure inverting vs. noninverting opertion (or listen) you will find that inverting operation sounds and measures notably better (see under Early Effect - common mode distortion).
Do they now? How much Ein is generated under "worst case" conditions for the Inverting Amp? The 100k Pot is at middle travel and thus the effective impedance to ground becomes 25k from the Wiper, in series with 10k. The feedback resistor is 330k and thus we have 31k impedance to ground from the inverting input.
This equals around 25nV |/ Hz Resistor Johnson noise. The circuits noisegain at this worst case condition is a little above 10, so for a 20KHz bandwidth the output becomes 250nV * 141 = 35uV or 0.000035V, which is -98db below 2.83V / 1 Watt or -112db below nominal output of 25W/8R.
Okay, it is possible to have less noise, but not really with the LM3875 wich is pecified as having an Ein of > 2uV A WEIGHTED, which once linearised no lower if not higher than the resistor noise.
!!!??? This setup gives several quite neccesary effects (lowered distortion, better transient perfomance) compared to the conventional circuit, the rest (primarily offset) is minimal. Typhical offset reported with this circuit is < 40mV, the same is often found on many a commercial "High End" or "HiFi" Amplifier (examples - measured in stereophile Perraux R200 Amp at 9/13mV and Musical Fidelity A3.2 21/26mV). Using a law-faked linear pot as volume control also has many advantages, most of them sonically.
What you illustrate to me is what I feel is wrong with both the AES/JAES and the "objectivist" side of audio. You see something unusual and instead of actually trying to understand you simply bash as "bad design" and suggest that same self (inherently BAD) design that is being avoided for perfectly good reasons.
The fact is that those who choose unusual design approaches usually do so for VERY GOOD reasons. Another fact is that those choosing unusual approaches CAN very well design using the usual ones, but have for any number of reasons choosen to not do so. What would behoove those seeing such a design well is to try to understand the why (which may take some research) instead to simply say "you should have just done the same as everyone else"....
Sayonara
janneman said:
Well, if you actually measure inverting vs. noninverting opertion (or listen) you will find that inverting operation sounds and measures notably better (see under Early Effect - common mode distortion).
janneman said:
Do they now? How much Ein is generated under "worst case" conditions for the Inverting Amp? The 100k Pot is at middle travel and thus the effective impedance to ground becomes 25k from the Wiper, in series with 10k. The feedback resistor is 330k and thus we have 31k impedance to ground from the inverting input.
This equals around 25nV |/ Hz Resistor Johnson noise. The circuits noisegain at this worst case condition is a little above 10, so for a 20KHz bandwidth the output becomes 250nV * 141 = 35uV or 0.000035V, which is -98db below 2.83V / 1 Watt or -112db below nominal output of 25W/8R.
Okay, it is possible to have less noise, but not really with the LM3875 wich is pecified as having an Ein of > 2uV A WEIGHTED, which once linearised no lower if not higher than the resistor noise.
janneman said:
!!!??? This setup gives several quite neccesary effects (lowered distortion, better transient perfomance) compared to the conventional circuit, the rest (primarily offset) is minimal. Typhical offset reported with this circuit is < 40mV, the same is often found on many a commercial "High End" or "HiFi" Amplifier (examples - measured in stereophile Perraux R200 Amp at 9/13mV and Musical Fidelity A3.2 21/26mV). Using a law-faked linear pot as volume control also has many advantages, most of them sonically.
What you illustrate to me is what I feel is wrong with both the AES/JAES and the "objectivist" side of audio. You see something unusual and instead of actually trying to understand you simply bash as "bad design" and suggest that same self (inherently BAD) design that is being avoided for perfectly good reasons.
The fact is that those who choose unusual design approaches usually do so for VERY GOOD reasons. Another fact is that those choosing unusual approaches CAN very well design using the usual ones, but have for any number of reasons choosen to not do so. What would behoove those seeing such a design well is to try to understand the why (which may take some research) instead to simply say "you should have just done the same as everyone else"....
Sayonara
Konnichiwa,
I do not understand the part "approved"?
The IGC is a public domain circuit which has seen a few variations, all concerend with keeping the circuit stable, offset low and so on. There is not, nor can there be an "approved" circuit.
The 330k simply come from comments that people who added the 22k from the negative input to ground felt it sounded "worse". So, increasing the feedback resistor from 220k to 330k will make sure that the circuit is stable without added resistors.
Yes, in theory a 330k resistor in parallel with a 10k/4u7 series circuit should be added on the positive input to ensure identical offset and similar AC impedances, yet again people have found that doing so makes the sound worse, so if you leave this out and simply put a wire bridge in you will have 60mV worst case and probably < 30mV normal DC offset, which is normally considered unproblematic.
What has "approved" to with anything?
Sayonara
Joe Rasmussen said:
I do not understand the part "approved"?
The IGC is a public domain circuit which has seen a few variations, all concerend with keeping the circuit stable, offset low and so on. There is not, nor can there be an "approved" circuit.
The 330k simply come from comments that people who added the 22k from the negative input to ground felt it sounded "worse". So, increasing the feedback resistor from 220k to 330k will make sure that the circuit is stable without added resistors.
Yes, in theory a 330k resistor in parallel with a 10k/4u7 series circuit should be added on the positive input to ensure identical offset and similar AC impedances, yet again people have found that doing so makes the sound worse, so if you leave this out and simply put a wire bridge in you will have 60mV worst case and probably < 30mV normal DC offset, which is normally considered unproblematic.
What has "approved" to with anything?
Sayonara
Kuei Yang Wang said:
Well, yes, I understand all that, but I also see pages and pages of posts on that offset. I didn't say "you should do like everyone else", I just pointed out a way to get rid of the offset.
And your shot at the engineering world is totally misplaced. Do you really think that those engineers that designed your beloved GC chip did this by listening? Its the guys and girls from the AES and JASA that gave you those wonderfull chips and drivers and DACs that makes this forum possible at the first place. You wouldn't take such cheap shots if you had only a minimum of historical perspective.
And I DID say: "I may have missed the arguments", so you COULD have answered: "yes Jan, indeed this is because you didn't read all those previous posts, we've been there" or to that effect.
It seems you have an uncanny ability to read about 120dB more from my post than I put into. It really scares me. I say one thing and presto: out comes a complete analysis of the way I think, work, what have you.
Why is it that so many people on this forum, in particular you and a few others, are so focussed on scoring? You don't strike me as very insecure, so I am really at a loss here.
Maybe I am too naive, maybe this is all about scoring and not about audio at all?
Jan Didden
millwood said:
I thought about it a little on the way to work and I think I was wrong. in an inverting design where the non-inverting input is grounded, the inverting input then acts like ground so the input impedance should be the input resistor in parallel with the feedback resistor. Since the feedback resistor is much bigger, the input impedance is mostly that of the input resistor.
janneman said:
you are right, having the input cap essentially makes the amp look like a follower (1x gain) for DC offset thus reducing DC offset. However, the source of the DC offset I was talking about here is input biasing. and it is only dependent on the resistance from the inverting input to ground. so it stands to reason that lower resistance there (for example, lower feedback resistor, or elimination of the input cap) would help lower (that kind of) DC offset.
I would agree with you 100% if the DC offset were caused by something else.
while I agree that eliminating the input cap helps from the perspective of reducing input bias induced DC offset - got to highlight it, it has many down sides as had been pointed out by many, including the one below.
janneman said:
one more thing. If you lower the voltage on the non-inverting end, you may be able to offset the DC offset caused on the inverting end. Take the 60mv DC offset for example. The closed loop gain of the amp is 30x, right? so a 60mv/30x=2mv negative voltage on the non-inverting end will do it. since the input bias on the non-inverting end is also 0.2ua, you can ground a resistor of 2mv/0.2ua=10K (?) to eliminate DC offset caused by input-bias.
And if you work through the math, I am sure that that resistor takes always the value of the input resistor, an assertion that had been made a few times before.
Konnichiwa,
Is it?
Well, there is a telling little note at the end of the BP200 Application note for the Overture chips....
Also, certain measurements have shown behavious that suggest that the results of a number of studies on hearing physiology/psychology where taken into account with the LM Overture series, but NOT it virtually ANY other series of chips.... I find that interesting. I guess someone should talk to the Head Dude at NS when they developed the "Overture" core.... I do have sneaky suspicions.
I am not complaining so much about history (other than fairly recent one), but present.
Okay Jan, I THOUGHT the argument for inverting mode use of Op-Amp's for removal or reduction of several distortion mechanisms was one that is well published all across the board, including the writings of Hawkesford, Duncan, Self and others, so that it was "obvious" to those skilled in the art (of electronics).
Actually, perhaps I am wrong and mistaken as to my assumptions what constitues "general knowledge" among other EE's? Given that I no longer actively, professionally work in the field and in fact note Solid State only in passing I make the assumption that if I have heard about it and am aware of it, that is (should) constitue(es) general knowledge.
So if it is generally known (and it really should be) that inverting operation leads to more inherent linearity in Op-Amp's having differential input structures (discrete or monolithic makes ZIP difference) then a criticism that says "you shouldd really use non-inverting mode" says to me:
"Look buster, just toe the party line or we run out of the club!" (incidentally, I'm no longer in the club for exactly those reasons)
Now I have mistaken this myself and what you where saying to me was "I don't understand". In which case I will still ask you why did not cary out some research of your own on the topic?
I am not focused on scoring. I do however as vigerously attack complacency and mediocracy as well as mindless ratteling of the orthodox position as your average "objectivist" takes any opportunity to attack subjects from Resistor/Capacitor/Cable "sound" to Jah know what. I do this partially as "excercise" and secondly because I feel that too rarely a well founded active defense is mounted in public groups against this extreme orthodox objectivist position.
In addition I do have an extremely low tolerance to what I percieve as Trolls and also people who I percieve to behave deliberatly Idiotic. My perception may be very flawed, true.
But let me ask you honestly, when you see an unorthodox circuit, is your first reaction "I wonder why they did this and what improvement they gain?" or is it "They really should have done A/B/C/X like everyone else does!". The feeling I get from your postings is the latter, a simple defense and re-guritation of orthodoxy.
It is something that I have problems with in ANY subject area. By definition the orthodox position is ultimatly 99% wrong, though often only slightly wrong, but enough to make it rather unusable.
If I mistake you, I am sincerely sorry. However in this case I would perhaps suggest to avoid to suggest as "fix" to any unorthodox circuit you see a reversion to orthodoxy. Maybe just ask "why" or look it up?
Sayonara
janneman said:
Is it?
janneman said:
Well, there is a telling little note at the end of the BP200 Application note for the Overture chips....
Also, certain measurements have shown behavious that suggest that the results of a number of studies on hearing physiology/psychology where taken into account with the LM Overture series, but NOT it virtually ANY other series of chips.... I find that interesting. I guess someone should talk to the Head Dude at NS when they developed the "Overture" core.... I do have sneaky suspicions.
janneman said:
I am not complaining so much about history (other than fairly recent one), but present.
janneman said:
Okay Jan, I THOUGHT the argument for inverting mode use of Op-Amp's for removal or reduction of several distortion mechanisms was one that is well published all across the board, including the writings of Hawkesford, Duncan, Self and others, so that it was "obvious" to those skilled in the art (of electronics).
janneman said:
Actually, perhaps I am wrong and mistaken as to my assumptions what constitues "general knowledge" among other EE's? Given that I no longer actively, professionally work in the field and in fact note Solid State only in passing I make the assumption that if I have heard about it and am aware of it, that is (should) constitue(es) general knowledge.
So if it is generally known (and it really should be) that inverting operation leads to more inherent linearity in Op-Amp's having differential input structures (discrete or monolithic makes ZIP difference) then a criticism that says "you shouldd really use non-inverting mode" says to me:
"Look buster, just toe the party line or we run out of the club!" (incidentally, I'm no longer in the club for exactly those reasons)
Now I have mistaken this myself and what you where saying to me was "I don't understand". In which case I will still ask you why did not cary out some research of your own on the topic?
janneman said:
I am not focused on scoring. I do however as vigerously attack complacency and mediocracy as well as mindless ratteling of the orthodox position as your average "objectivist" takes any opportunity to attack subjects from Resistor/Capacitor/Cable "sound" to Jah know what. I do this partially as "excercise" and secondly because I feel that too rarely a well founded active defense is mounted in public groups against this extreme orthodox objectivist position.
In addition I do have an extremely low tolerance to what I percieve as Trolls and also people who I percieve to behave deliberatly Idiotic. My perception may be very flawed, true.
But let me ask you honestly, when you see an unorthodox circuit, is your first reaction "I wonder why they did this and what improvement they gain?" or is it "They really should have done A/B/C/X like everyone else does!". The feeling I get from your postings is the latter, a simple defense and re-guritation of orthodoxy.
It is something that I have problems with in ANY subject area. By definition the orthodox position is ultimatly 99% wrong, though often only slightly wrong, but enough to make it rather unusable.
If I mistake you, I am sincerely sorry. However in this case I would perhaps suggest to avoid to suggest as "fix" to any unorthodox circuit you see a reversion to orthodoxy. Maybe just ask "why" or look it up?
Sayonara
Konnichiwa,
Yes.
Isn't it obvious? Long tailed pair inputs have a very limited Common Mode rejection (regardless of device, be it Valve, BJT or FET) and a non-inverting Amplifier has a common mode signal equal to the signal, an inverting amplifier equal to ZERO.
The CMRR generally falls off according to 2nd order function and is pretty low to start with, causing added distortion (usually around 4 - 6db over inverting mode), which rises above a designdependent point with a 2nd order slope. If you actually make a resonably linear amplifier (in other stages) you may find this nonlinearity at higher frequencies to determine the behaviour of the (looped feedback) Amplifier!!!!
The implications for non-harmonic distortion components (especially all sorts of noise modulation and PIM) should also be obvious.
Again for starters check Self on the subject. He very well describes the mechanisms and some possible partial remedies (apart from my own - "Invert Da Suckah!!!!" or "Death to the Long Tail Pair - CFB RULEZ").
If you are asking - is there an audible difference?
My experience is "Yes", but I also hear differences between different Capacitors, Resistors and Cables, so WTFDIK?
Sayonara
millwood said:
Yes.
millwood said:
Isn't it obvious? Long tailed pair inputs have a very limited Common Mode rejection (regardless of device, be it Valve, BJT or FET) and a non-inverting Amplifier has a common mode signal equal to the signal, an inverting amplifier equal to ZERO.
The CMRR generally falls off according to 2nd order function and is pretty low to start with, causing added distortion (usually around 4 - 6db over inverting mode), which rises above a designdependent point with a 2nd order slope. If you actually make a resonably linear amplifier (in other stages) you may find this nonlinearity at higher frequencies to determine the behaviour of the (looped feedback) Amplifier!!!!
The implications for non-harmonic distortion components (especially all sorts of noise modulation and PIM) should also be obvious.
Again for starters check Self on the subject. He very well describes the mechanisms and some possible partial remedies (apart from my own - "Invert Da Suckah!!!!" or "Death to the Long Tail Pair - CFB RULEZ").
If you are asking - is there an audible difference?
My experience is "Yes", but I also hear differences between different Capacitors, Resistors and Cables, so WTFDIK?
Sayonara
Kuei Yang Wang said:
so do I get you right that having a common mode signal on both inputs is better than not having a common mode signal on both inputs?
If so, why don't we all inject identical random noise on our amplifier's input and feedback ends and our $10 boombox will sound as nice as our Krell / or whatever of your favorite brands,
Seriously, I don't understand your reasoning. CMRR is what it is, no matter what signal you have on either end.
Kuei Yang Wang said:
I know what you mean, but I think you misunderstood me.
I suppose I felt apologetic for modifying/amending/appending a circuit diagram/schematic that I attributed to you as the source (is it?). Like violating 'copyright' but hopefully for the right motive.
In a sense if someone posts a schematic or anything graphic, that doesn't entirely make it PD, does it?
Also, I wanted to elicit from you a nod (in that sense 'approval') that the circuit shown is now what you had in mind. Nothing more than that. I think we got it, the nod I mean. And I agree with the change, for whatever that is worth.
At least we are not discussing 'moving goalposts' as we were earlier on, the schematic is now there for us to reference to.
Joe R.
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