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Old 4th March 2014, 02:14 AM   #101
gootee is offline gootee  United States
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Quote:
Originally Posted by ginetto61 View Post
Hello and thanks for the advice
I am sure that your procedure is much more telling that the simple test i was thinking of, but i do not know even how to switch on a scope.
I still think that basic tests can be tellling as well to show deviations from an ideal behaviour.
What i was meaning is that in the end the instruments if well used do not lie.
And i always like the instrumental approach that gives evidence of phenomena going on.
I can calculate the right amount of uF and then run in a bad batch, for instance, and fail to get the predicted performance (and the instrument will tell this).
I would even place one of these voltmeters on the front plate.
A failure/lack of performance in the ps caps would be immediately evident.
And i would add uF to get the needle stable, at least at normal listening levels.
When the basic requirements are fulfilled than we can pass to others ...
What is the reason, so to speak, to improve topologies to get the last drop of detail when then the PS voltage sags under pressure ?
And to the people that do not believe in instruments i would just tell that this attitude is unrespectful to famous audio Brands that invest million of dollars in lab instruments.
Thanks againg for your valuable advice
Kind regards,
gino
Again, the VOLTAGE is NOT very important. In fact, it MUST sag, otherwise NO signal could come out of the amplifier.

The output music signal is CURRENT. And the capacitor voltage must sag, or else no current would be discharged, to make the signal.

More voltage sag at the caps might make a very slight increase in non-linearity. But PSRR of amplifier usually makes it negligible. Clipping at very high output level is usually the only significant problem related to voltage sag.

Voltage sag being able to be larger (i.e. lower capacitance) MIGHT tend to make current signal from caps more agile, which might give more-accurate transient response, which might be perceived as sounding better. OR, that could be hogwash because more capacitance might more than compensate for that effect and still be better sounding. [Needs research.]
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Old 4th March 2014, 03:29 AM   #102
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gootee I think you're doing circles.

If you want the benefit of what allows sag, use several smaller capacitors... but overall capacitance doesn't have to be particularly low.

Look at basically every amplifier ever made, it would appear they already know this stuff... Typically there are stages, large reseviors, and smaller ones near the actual amplification (transistor, switcher, whatever).

I suspect there's one more factor at play here, which I'll refrain from mentioning
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Old 4th March 2014, 03:51 AM   #103
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Quote:
Originally Posted by gootee View Post
Voltage sag being able to be larger (i.e. lower capacitance) MIGHT tend to make current signal from caps more agile, which might give more-accurate transient response, which might be perceived as sounding better. OR, that could be hogwash because more capacitance might more than compensate for that effect and still be better sounding. [Needs research.]
I agree this area needs a lot more research giving some datapoints. In my experience more capacitance always sounds better provided the layout isn't comrpomised. Having more caps provides a lower impedance for PSU currents - the flip side of this is it makes the circuit even more sensitive still to slight errors in the layout.

Just last week I was playing with adding crazy amounts of capacitance to my DAC's power supply. Just tacking on a big capacitor array to an existing circuit provided improvements in some areas (dynamics) but made others worse (imaging). Re-working the grounding layout (only a change of 1 or 2 mm of soldered connection) fixed up the imaging problems without losing the dynamics.
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Old 4th March 2014, 08:08 AM   #104
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Quote:
Originally Posted by gootee View Post
Again, the VOLTAGE is NOT very important. In fact, it MUST sag, otherwise NO signal could come out of the amplifier.

The output music signal is CURRENT. And the capacitor voltage must sag, or else no current would be discharged, to make the signal.
But the level of sag depends on the size of the caps. Or use regs. So you can lower sag very much.
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Old 4th March 2014, 08:41 AM   #105
AndrewT is offline AndrewT  Scotland
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Originally Posted by mrWagner View Post
But the level of sag depends on the size of the caps. Or use regs. So you can lower sag very much.
the regulator lowers the peaks much more than it lowers the sags.
The regulator may not lower the sags at all when the mains supply voltage falls, it will still lower the peaks.
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Old 4th March 2014, 12:35 PM   #106
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Stab will lower the max voltage, but until the cap voltage doesn't drop near the reg voltage, it is kept more or less linear. And not fall even if the cap voltage drops. So the amp will see a steady voltage and not the caps saggy voltage.
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Old 4th March 2014, 05:29 PM   #107
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I'm actually very surprised it is not possible to prove the effect of different components used in an amplifier.

The only thing I see is theoretical assumptions, sims and subjective listening experiences (including mine).

My profession is Injection molding process development specialized in molding of CD, DVD, CDR etc.

I have learned in the 20 years plus working in this field that its impossible to design a injection molding process only on theoretical calculations.

Well, for maybe 95% its is possible but the last 5% that is missing in the theory determines if the process will work or not.

Many times I have tried to improve the process based on theoretical ideas being sure it would work positively and had to found out it did not work at all.

One time someone that studied for 6 years on the university specialized in injection molding thought he could easily improve the process resulting in a train wreck, the machine produced completely NOT.

In my case it was luckily easy to measure the result of the experiments done (theoretical or not) because the quality of the end product was easy to measure.

In this case of experiments with different components in an audio amplifier the results stay very subjective, therefor I think its hard to prove what is best and I think the discussion will probably continue for ever
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Old 5th March 2014, 12:46 AM   #108
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Joerytech,

It's funny you say that. I was realising that an OpAmp is no more than a SERVO SYSTEM. When fine tuning a process, I never have to analyse the servo in the system, just tell it what to do and hope it doesn't reach its limits of operation.

You change a process and you get a result. It might not be what you expected and you try to explain what just happened, but proving your explanation is a lot more difficult. These amps are the same.

A simulation is far more than a theoretical calculation. Its a copy of your process that you can run offline. With a simulation your only concern is if the model is correct, in a real process it's if you can measure it correctly and don't blow it up.
Back when I was programming robots it would have been great to have been able to do simulations. I could have tested the programmes sitting behind my PC and not expose the machines to the risk of a stupid programming mistake.
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Old 5th March 2014, 10:26 AM   #109
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Originally Posted by Joerytech View Post
Okay, again I understand a bit more how things work and I'm very grateful for the very extended explanations done here.

For me this thread is a search for the reason why (many) think a GC reproduces sound signal better with a low capacitance than a higher one.

It might be a hype that is based on a rumor spread one day but to be honest, its too much accepted by so many that I think there must be a reason for it.

From both sides (for and against low capacitance) I see a lots of theories but no actual proof like scope readings from comparisons of input and output signals with block-wave, sawtooth wave, etc. what might be able to shed a light on the statements from both sides.

I want to ask both sides what they think could be a good test to prove who is telling the truth and then I mean a test without theoretical explanations but as clear as listening.
In my humble opinion it should be something like a advanced scope reading from input and output signal.
Ideally those 2 should be identical
I understand you, been there done that. From what I recall, the vast majority of proponents of using small capacitance rely on their ears and subjective feelings, while those who advocate big capacitance tend to base their opinions in EE theories and formulae. Who is right? I tend to agree with the second ones, but who am I to judge what are you (or you 'believe' you are) hearing?

As a side note, could it just be that due to LM3886's high PSRR it just become unnoticeable having an small amount of capacitance?

Now that regulators have been metioned, hacing in mind all pros and cons exposed on this thread, isn't a regulator placed really close to the IC pins more appropiated than big capacitors? I mean, you could theorically get away with an small capacitance.
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Old 6th March 2014, 03:37 PM   #110
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Quote:
Originally Posted by Joerytech View Post
I'm actually very surprised it is not possible to prove the effect of different components used in an amplifier....
Hello, i have one question.
When you say to prove you mean to measure ?
Thanks a lot and kind regards,
gino
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