G.Kleinschmidt said:
Hi Glen,
First, I suppose you have bypassed the input filter.
Second, strictly speaking, this approach isn't foolproof.
It depends on configuration of the input stage. If the phase and gain properties of the inverting and non-inverting input are identical, no problem. But this isn't always the case. For example, think of the classic JLH amplifier, a CFB op-amp or the Alexander amplifier. In these cases, the feedback signal is injected into the emitter of the input stage, not into a base, and the phase and gain properties of the inverting and non-inverting input are different.
So to be sure of reliable results, I always inject the test signal somewhere into the feedback path (and of course, ground the input).
Cheers, Edmond.
estuart said:
Hi Glen,
First, I suppose you have bypassed the input filter.
Second, strictly speaking, this approach isn't foolproof.
It depends on configuration of the input stage. If the phase and gain properties of the inverting and non-inverting input are identical, no problem. But this isn't always the case. For example, think of the classic JLH amplifier, a CFB op-amp or the Alexander amplifier. In these cases, the feedback signal is injected into the emitter of the input stage, not into a base, and the phase and gain properties of the inverting and non-inverting input are different.
So to be sure of reliable results, I always inject the test signal somewhere into the feedback path (and of course, ground the input).
Cheers, Edmond.
G'day Edmond.
I agree that the test would not be foolproof for all amplifier topology’s, but as a open loop test as I described it, for amplifiers unlike the JHL and the others you mention, with a differential input stage, the technique is pretty much rock solid.
Any phase and gain differences between the inverting and non-inverting inputs are very small and practically negligible.
Cheers,
Glen
edit:
Oh, and no I don't bother bypassing the input filter, I just connect the cro probe directly to the non-inverting input.
G.Kleinschmidt said:
Hi Glen,
I agree on that. Phase differences of input stages we normally use, are very small, less than +/- 1 deg.
But please, explain what 'rock solid' exactly means, as English isn't my native language. I thought something like 'foolproof under all circumstances', thus applicable to all amplifiers.
Cheers,
Pity that this thread has got so emotive - from both sides.
I guess one of the problems with this hobby/vocation is designers tend to settle on a toplogy or technique that they get familiar with and it becomes part of their toolbox and when someone else disagrees with it, they defend it.
I think this is the situation we have here. The coil camp and the coil-less camp.
Who is right? My guess is both but for different reasons. JC gets away with it because of how he compensates his amp and some other (old) tricks while the guys that use an output inductor are looking to satisfy some different design aims. Like I said before, how an amp sounds to your ear is a very personal thing and the best example is tube amps versus solid state.
I'm outta here.
Peace
I guess one of the problems with this hobby/vocation is designers tend to settle on a toplogy or technique that they get familiar with and it becomes part of their toolbox and when someone else disagrees with it, they defend it.
I think this is the situation we have here. The coil camp and the coil-less camp.
Who is right? My guess is both but for different reasons. JC gets away with it because of how he compensates his amp and some other (old) tricks while the guys that use an output inductor are looking to satisfy some different design aims. Like I said before, how an amp sounds to your ear is a very personal thing and the best example is tube amps versus solid state.
I'm outta here.
Peace
It's true, many people seem to prefer the sound of an amp with less detail & definition.
I can see how many would prefer such a "soft" sound if their source is not up to being fully exposed and It seems others still prefer a soft sound even if their source is excellent.
Whenever I hear these kind of arguments - "this makes a difference, oh no it doesn't, oh yes it does" etc, I identify different types of posters.
1) those who have not tried the idea that is being discussed and never-the-less decide that they cannot believe it.
2) those who are prepared to believe what is being discussed but would like to satisfy intellectual curiosity
3) those who have done tests ( subjective or objective ) and thus have some direct experience of what they are discussing and say they cannot hear / measure any difference.
4) those who have done tests ( subjective or objective ) and thus have some direct experience of what they are discussing and say they can hear / measure any difference
in this topic I am in group 2.
being in this position I am much more swayed with the comments of of group 4 & 3. However the people in group 3 may have less acute hearing than those in group 4 - so generally I pay most attention to those in group 4.
group 2 posters may make good theoretical & interesting auguments or ask good questions
I always imagine group 1 posters as being in a fairly small box and not realising they can break out of it ( into a bigger one ! )
My current system has no caps or inductors or crossovers in the signal path, fairly short interconnect & speaker leads and is pretty transparent - so I guess it's time for an experiment
mike
I can see how many would prefer such a "soft" sound if their source is not up to being fully exposed and It seems others still prefer a soft sound even if their source is excellent.
Whenever I hear these kind of arguments - "this makes a difference, oh no it doesn't, oh yes it does" etc, I identify different types of posters.
1) those who have not tried the idea that is being discussed and never-the-less decide that they cannot believe it.
2) those who are prepared to believe what is being discussed but would like to satisfy intellectual curiosity
3) those who have done tests ( subjective or objective ) and thus have some direct experience of what they are discussing and say they cannot hear / measure any difference.
4) those who have done tests ( subjective or objective ) and thus have some direct experience of what they are discussing and say they can hear / measure any difference
in this topic I am in group 2.
being in this position I am much more swayed with the comments of of group 4 & 3. However the people in group 3 may have less acute hearing than those in group 4 - so generally I pay most attention to those in group 4.
group 2 posters may make good theoretical & interesting auguments or ask good questions
I always imagine group 1 posters as being in a fairly small box and not realising they can break out of it ( into a bigger one ! )
My current system has no caps or inductors or crossovers in the signal path, fairly short interconnect & speaker leads and is pretty transparent - so I guess it's time for an experiment
mike
definition of 'rock solid'
Hi Bonsai, Glen and Mike,
Of course, I do know the meaning of 'rock solid'. The aim of my question was to let Glen explain how it can be that a rock solid measurement method is not appropriate for all kinds of amplifiers. Maybe we should call it a 'rock solid approximation'.
BTW Glen, how do you know that your method is reliable?
Probably, the only way to check this, is doing it my way.
Cheers.
Hi Bonsai, Glen and Mike,
Of course, I do know the meaning of 'rock solid'. The aim of my question was to let Glen explain how it can be that a rock solid measurement method is not appropriate for all kinds of amplifiers. Maybe we should call it a 'rock solid approximation'.
BTW Glen, how do you know that your method is reliable?
Probably, the only way to check this, is doing it my way.
Cheers.
pinkmouse said:
Al el Magnifico,
my main tool is language, i can spot 2 socks of the same color in a basket containing a million, be it ptfe or puppets.
Mr Courage will certainly not get the answers he so desperately desires from Mr Curl, but Mr Stuart might.
However, Mr Stuart still has the distinctive odor of good old Courage and both love to use quite a few different IP addressess. Courage is back on track after 7 months of radio silence, started posting a couple of weeks after the arrival of Sir Edmond Stuart.
Intelligent and amusing fellow, a shame he lacks every bit of integrity.
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