Hi guys!
maybe my question is silly, but wich are the difference between those configurations?
I tried to search on forums, website and application notes, but I didn't found anything about this topic.
Why all the gainclones use inverted input and not the non-inverted input that has higher impedance and so on?
Thank you all.
Bye, Fabrizio
maybe my question is silly, but wich are the difference between those configurations?
I tried to search on forums, website and application notes, but I didn't found anything about this topic.
Why all the gainclones use inverted input and not the non-inverted input that has higher impedance and so on?
Thank you all.
Bye, Fabrizio
Faber said:
if it makes you feel better, pretty much all solid state amps are non-inverted. NSC's application note on those chips are non-inverted, as BB's for the opa54x family.
I have asked the same question here before and other than "inverted is better", I have yet to receive a convincing answer.
I have tried inverting and non-inverting (on the lm3875) and for the life of me I couldn't tell them apart.
so I would be also interested in what you can find this time.
I've never built a gain clone...
...But, the gainclone is based on an op-amp, and op-amps usually have lower distortion when operated in an inverting configuration. That is due to the fact that the voltage on the input stage stays at a constant value, when operated inverted. This means that the differential pair (the input section of the op-amp) operates at constant voltage levels, causing less distortion. (Remember, Op-Amps in theory, have 0 volts between the + and - inputs when operating)
Do some research on input stages to op-amps (Or ask for further info here), if you're interested in more theory on this.
Hope this helps!
-Dan
...But, the gainclone is based on an op-amp, and op-amps usually have lower distortion when operated in an inverting configuration. That is due to the fact that the voltage on the input stage stays at a constant value, when operated inverted. This means that the differential pair (the input section of the op-amp) operates at constant voltage levels, causing less distortion. (Remember, Op-Amps in theory, have 0 volts between the + and - inputs when operating)
Do some research on input stages to op-amps (Or ask for further info here), if you're interested in more theory on this.
Hope this helps!
-Dan
peranders said:
here is a link with some data, and you can see the magntitude on the 2134.
http://www.dself.dsl.pipex.com/ampins/webbop/2134.htm
The main reason why op-amps perform better in inverting mode is that the input and feedback signal are summed at the input of a single device (one half of the differential input stage).
In non-inverting mode the input and feedback signal are fed into different inputs and different devices, the effectiveness of distortion cancellation is entirely dependent on how closely matched the two halves of the differential input stage are matched which although usually very good it can never be perfect, hence higher distortion.
In non-inverting mode the input and feedback signal are fed into different inputs and different devices, the effectiveness of distortion cancellation is entirely dependent on how closely matched the two halves of the differential input stage are matched which although usually very good it can never be perfect, hence higher distortion.
peranders said:
WOW!
That's great, but why this distinction is not mentioned in the datasheet nor application note?
I'm using an LM3886 and I didn't find any distinction about inverting and non-inverting THD+N graphs.
In addition, normally I see that opamps (also discrete designs) are used in a non-inverting config.
Can you tell me were to find some doc about this lower distortion theory?
TIA
Ciao, Fabrizio
For discrete differential input stages I prefer inverting (shunt feedback) since precise matching of input devices is not easy (or even possible).
Common-Mode-Rejection-Ratio is the measure of how closely matched the inputs are and for op-amps (where the devices are fabricated on the same piece of silicon) CMRR is very high and so distortion is very low whichever configuration is used.
Distortion in op-amps may be 10 times worse in non-inverting mode but ten times worse than what? does 0.01% distortion sound worse than 0.001%? maybe not but given the choice...
Common-Mode-Rejection-Ratio is the measure of how closely matched the inputs are and for op-amps (where the devices are fabricated on the same piece of silicon) CMRR is very high and so distortion is very low whichever configuration is used.
Distortion in op-amps may be 10 times worse in non-inverting mode but ten times worse than what? does 0.01% distortion sound worse than 0.001%? maybe not but given the choice...
For discrete differential input stages I prefer inverting (shunt feedback) since precise matching of input devices is not easy (or even possible).
Common-Mode-Rejection-Ratio is the measure of how closely matched the inputs are and for op-amps (where the devices are fabricated on the same piece of silicon) CMRR is very high and so distortion is very low whichever configuration is used.
Distortion in op-amps may be 10 times worse in non-inverting mode but ten times worse than what? does 0.01% distortion sound worse than 0.001%? maybe not but given the choice...
Common-Mode-Rejection-Ratio is the measure of how closely matched the inputs are and for op-amps (where the devices are fabricated on the same piece of silicon) CMRR is very high and so distortion is very low whichever configuration is used.
Distortion in op-amps may be 10 times worse in non-inverting mode but ten times worse than what? does 0.01% distortion sound worse than 0.001%? maybe not but given the choice...
peranders said:
this confirms Self's numbers in that the two are about 2x apart in thd+noise figures, both are below audible range (around 0.01% if I recall correctly).
in other words, if those figures are repsentative, few can hear the difference between those two configurations.
One cannot argue that the inverting configuration is better between of lower thd, and then turn around saying that listening is the ultimate test. Because if that were true, one would be indifferent between the two configurations.
Something my experience confirmed.
Richard C said:
if one can lower distortion 10x by going to an inverting design and that reduction is material, you would have imagined that all power amps and opamps would have gone to inverting designs long ago, especially for discrete amps where cmrr is that much worse than opamps.
The fact that almost all power amps are non-inverting and a lot of opamps are used in non-inverting designs should have told us how material this "10x" figure is.
A bunch of "science" for exactly nothing.
Yes it's strange that very few discrete amplifiers are inverting when it appears to be a superior arrangement (technically at least), I think I've only ever seen it used on one power-amp design.
Since both arrangements are comparable in terms of complexity and component count and as far as I know there is no sonic advantage to using non-inverting I favour inverting for no other reason than it appears to be technically better. I very much doubt that I could hear a difference between the two but it might be worth investigating.
Since both arrangements are comparable in terms of complexity and component count and as far as I know there is no sonic advantage to using non-inverting I favour inverting for no other reason than it appears to be technically better. I very much doubt that I could hear a difference between the two but it might be worth investigating.
I've been reading up on circuit and IC noise in TI's guide "Opamps For Everyone."
I haven't tried out the calculations yet, but it seems that the extra noise with two inverting circuits is going to be more than the overall noise in a single non-inverting circuit. Since equipment mfg need to maintain proper polarity of output signals relative to inputs, then running opamps non-inverting provides the benefits of less noise and fewer parts.
ensen.
I haven't tried out the calculations yet, but it seems that the extra noise with two inverting circuits is going to be more than the overall noise in a single non-inverting circuit. Since equipment mfg need to maintain proper polarity of output signals relative to inputs, then running opamps non-inverting provides the benefits of less noise and fewer parts.
ensen.
Most are noninverting amps.
Could be that as the gain block gets better and better , the distortion is already so low that we don't really hear it. In addition the non-inverting mode might improve the S/N ratio ( as compared to non-inv). Even that might be lower than what is audible .
Looks like power amps with higher distortion figures may benefit most from shunt feedback at the expense of higher noise. Tube amps ?
Cheers.
Could be that as the gain block gets better and better , the distortion is already so low that we don't really hear it. In addition the non-inverting mode might improve the S/N ratio ( as compared to non-inv). Even that might be lower than what is audible .
Looks like power amps with higher distortion figures may benefit most from shunt feedback at the expense of higher noise. Tube amps ?
Cheers.
Yep. Using an inverting mode setup, the signal fed to the (-) input is simply the difference between the normal input signal and an *exact* representation of the output signal (via the feedback resistor of course).Richard C said:
With non-inverting mode, the feedback signal has to suffer the indignity of passing through at least the base-emitter of the (-) input differential transistor, and by the time it leaves the emitter to be subtracted from the input signal from the (+) input, it cannot be truly regarded as representing what is happening at the output.
Short version -> The junction of 2 passive resistors gives a more accurate signal to feed the amp. Probably more stable too, seeing there is less transport delay.
Circlotron said:
that's only true if the opamp in question is ideal. For anything less than that, you will have current on the + or - input (otherwise, how can the opamp amplify?).
I think we should all settle on the notion that there are pros and cons to both configurations and the differences aren't material enough to make a generic statement.
purplepeople said:
In a domestic hi-fi set-up, odd numbers of inverting gain-stages don't necessarily require evening-up with an extra inverting stage, simply make the correction at the loudspeaker end.
Aternatively: inverting pre-amp followed by inverting power amp = no unecessary gain stages and no change at the speaker end.
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