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Please technically explain this audible mod
Please technically explain this audible mod
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Old 1st November 2017, 11:17 AM   #61
abraxalito is offline abraxalito  United Kingdom
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Poor bass dynamics due to greatly raised supply impedance at low frequencies.
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Old 1st November 2017, 12:02 PM   #62
infinia is offline infinia  United States
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Quote:
Originally Posted by elmura View Post
PS - I know the free version of RMAA limits what you can see and the software doesn't get much development but I'm very familiar with it and have made myself a library of test results. If you know of a better app, I'm all ears.
Id rather see the RMAA plots you are reporting 1 dB and less changes from and photos of the pulled caps plus re-wiring job. Your source probably also has a DC block and short circuit protection resistor, My pre-amp also has "lab outputs" which are the normal one w/o the DC block.

Id retake the RMAA plots with the source PC in loopback mode rather than using the 2nd one.. Id expect changes for the better. e.g. less common mode noise.
Id say your eyes maybe just as good as your hearing. e.g picking out 1dB resolution on RMAA plots. If (from your posts) you are relying on the software to give a number then I'd question any reported changes due to repeatability of the experiment as null -n-void.
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Last edited by infinia; 1st November 2017 at 12:13 PM.
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Old 1st November 2017, 01:01 PM   #63
Idiosyncrasy is offline Idiosyncrasy  Netherlands
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Please technically explain this audible mod
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Originally Posted by abraxalito View Post
Poor bass dynamics due to greatly raised supply impedance at low frequencies.
What about when the op amp is operating in class A?
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Old 1st November 2017, 01:27 PM   #64
infinia is offline infinia  United States
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Originally Posted by Idiosyncrasy View Post
What about when the op amp is operating in class A?
What makes you think that. I see the base currents cancelling and the left over is supplied through a small output resistor biased at 0V.
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Old 1st November 2017, 01:33 PM   #65
abraxalito is offline abraxalito  United Kingdom
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ClassA by itself doesn't tell us whether the opamp's power supply current is invariant. As opamps have push-pull output stages I believe its not possible to have a single opamp's output loading arranged to make its supply current invariant.
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Old 1st November 2017, 06:57 PM   #66
Idiosyncrasy is offline Idiosyncrasy  Netherlands
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Please technically explain this audible mod
Quote:
Originally Posted by infinia View Post
What makes you think that. I see the base currents cancelling and the left over is supplied through a small output resistor biased at 0V.
Meant it more in general.
Quote:
Originally Posted by abraxalito View Post
ClassA by itself doesn't tell us whether the opamp's power supply current is invariant. As opamps have push-pull output stages I believe its not possible to have a single opamp's output loading arranged to make its supply current invariant.
Thanks, I'll make sure to test how low frequency dynamics are affected next time I use such rails filtering. I suppose it would be relatively easy to visualize this on a scope with a realistic load? Or would you advise some other method?

Last edited by Idiosyncrasy; 1st November 2017 at 07:06 PM.
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Old 1st November 2017, 08:22 PM   #67
Chris888 is offline Chris888  United Kingdom
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If the OP is not imagining the differences, then it seems to me there is something going on with real music which is not revealed by measuring with sine waves?
It's tempting to suggest putting it back to standard and building from scratch.

See the LM317 thread and ask yourself about the effects of 2 470uF on each reg output.
It makes me wonder what the rails look like in actual use.

Maybe it needs to be tested in different ways to see the effects of the mods.Maybe think in the time domain. Throw some arbitrary wave forms at each channel and see what it does?
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Old 2nd November 2017, 01:28 AM   #68
abraxalito is offline abraxalito  United Kingdom
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Quote:
Originally Posted by Idiosyncrasy View Post
Thanks, I'll make sure to test how low frequency dynamics are affected next time I use such rails filtering. I suppose it would be relatively easy to visualize this on a scope with a realistic load? Or would you advise some other method?
I would prefer to do it in simulation (I use LTspice) as then you're not limited by your scope's capabilities and you can quickly explore various options. I'd recommend LC filtering, rather than RC but watch out for getting the damping right.

I don't know how to correlate yet what I see in sim with what I hear but I do my best to minimize supply ripple, most especially signal-correlated ripple.
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