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Old 18th March 2012, 06:59 PM   #3701
a.wayne is offline a.wayne  United States
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Quote:
Originally Posted by ThorstenL View Post
Hi,


Well, that depends on your definition of "better".
Better sonics...!

Quote:
Originally Posted by ThorstenL View Post
My Amp will already have 4pcs 18,000uF per channel (72,000uF per channel in magazine Spec's) so how much bigger can we realistically get?
Well that's OK if for 200 watt max amplifier, some may like the sound of their lower filtered supplies ..

Quote:
Originally Posted by ThorstenL View Post
Chokes store energy, resistors do not.
Chokes give a 2nd order filter, resistors a 1st.

The so-called "really big cap's" have their own problems.
OK, what exactly, what are the negativities of going with big psu (250,000uf/ch for eg.) storage, of course with bypass caps and smaller caps right at outputs.


Quote:
Originally Posted by ThorstenL View Post
As I am not trying to drive speakers with 75dB/2.83V/1m efficiency and sub 1 ohm bass impedance I do not see the need for stupidly big PSU Cap's.
Hey now... It's ....79db.....

Quote:
Originally Posted by ThorstenL View Post

As a rule, bigger values are better, but for me (existing chassis/PCB's that must accept modification) size was the main constraint, so I asked the factory that made the samples to give me something for 10A DC, 50mOhm DCR per choke and the given size core and the maximum "L" that would go for this. They came out at 1mH appx...

Ciao T
Bigger as in say a 10 mh choke, laminate or aircore odds are the impedance will be low , if not using specific transformer as you ...
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Old 18th March 2012, 07:07 PM   #3702
bcarso is offline bcarso  United States
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Default 3685 followup --- comparison of two very similar sources

So what we see here are two bipolar/JFET ~5mA I sources (or sinks). Both have an output resistance of 394Mohm. The output capacitance out to about 1-2 MHz of the one with gate to emitter feedback is about 58fF, of the other 1.7pF out to >100MHz.

When we contrive to examine the distortion associated potentially with the voltage-variable output capacitance of each, loaded with a "perfect" current source and a 1Mohm resistor, and drive with a +/- 1uA current signal, thus getting a +/-1V signal at the drains, we see THD out to the tenth harmonic of 2544ppm for the left hand one, 44.6ppm for the right. Second harmonic dominates for both, at -52.5dBr and -86.9dBr respectively. Third is -81dBr for the left circuit and -121dBr for the right. Of course these are sweet Spice lies, but maybe not too ridiculously so.

In many practical applications this performance may be irrelevant --- what can we load such a circuit with that doesn't itself contribute a boatload more of variable C etc.? Well, good question

BTW the "2SC1815A1" is roughly comparable to a 2SC1815BL (the highest-beta sort).

Last edited by bcarso; 18th March 2012 at 07:15 PM. Reason: upper/lower case blunder
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Old 18th March 2012, 07:36 PM   #3703
dvv is offline dvv  Serbia
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Quote:
Originally Posted by ThorstenL View Post
Hi,

...

Second is that I'm a tube guy and if I see two identical capacitors on the same rail I feel someone has forgotten the filter choke that goes inbetween.
...
Unless you do it right from the start - filter out the mains hash BEFORE it even reaches your device. And not just the power amp, but your entire system.

Wihtout any false modesty, my power line filters have got by far the greatest raves from tube audio owners, and among them, in particular Research Audio gear owners.

I don't want to plug them, I'm merely saying that filtering after the power transformers is acting after the fact, so to speak - I hope there is no-one here who believes that powwer transformers are not stressed by line hash. When they start humming is only the last stage, by that time, you have a catastrophe on your hands.

You can actually measure this as simple off load power consumption without or with - with is 7...10% less. And your power supplies have to deal with this c**p whether you like it or not.

With all respect, T., filtering is far more efficient and thorough BEFORE all that junk even gets to the transformer and starts to stress it. You discover that with efficient external filtering bofre the device your transformers become noticeably more efficient, so for the same effect, feel free to use one size down (say, a 400 VA unit instead of a 500 VA unit) as you lose nothing.

Lastly, a quality filter battery will filter the power of the entire system, in addition from preventing anything happening among devices attached, as would happen with a single filter; it would protect from the grid, but not from each other AFTER the filter. My way, where each output has its own filter, is about as good as it gets, albeit for a price - this is ESPECIALLY true of tube audio, as demonstrated over the last 11 years.

Just giving you thought food.
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Old 18th March 2012, 07:49 PM   #3704
Previously: Kuei Yang Wang
 
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Hi,

Quote:
Originally Posted by Wavebourn View Post
Ok, it is good that you got high dynamic resistance, and it is good that it is equally high on wide frequency band!
Now, what happens when you vary temperature?
In my particular schematic above, if you vary the temperature, nothing much happens, hence the LM329 (essentially zero tempco) AND the BC550... A monolithic dual would be better, for most uses the thermally coupled individual ones work well...

Ciao T
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Old 18th March 2012, 08:00 PM   #3705
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Dejan,

Quote:
Originally Posted by dvv View Post
Unless you do it right from the start - filter out the mains hash BEFORE it even reaches your device. And not just the power amp, but your entire system.
There are many ways here. Filters are limited. I generally my stuff so it does not need them.

The chokes in the PSU are used to kill rectifier noise/ripple. Your filters cannot do that.

Quote:
Originally Posted by dvv View Post
Wihtout any false modesty, my power line filters have got by far the greatest raves from tube audio owners, and among them, in particular Research Audio gear owners.
I am not surprised. I really do not want to say more...

Quote:
Originally Posted by dvv View Post
Just giving you thought food.
No food there. I have from day one considered the "needs external filter" approach flawed, maybe a result of exposure to german pro-gear, which has it all build in.

Ciao T
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Old 18th March 2012, 08:16 PM   #3706
dvv is offline dvv  Serbia
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Quote:
Originally Posted by ThorstenL View Post
Dejan,

There are many ways here. Filters are limited. I generally my stuff so it does not need them.
...
The chokes in the PSU are used to kill rectifier noise/ripple. Your filters cannot do that.
...
I am not surprised. I really do not want to say more...
...
No food there. I have from day one considered the "needs external filter" approach flawed, maybe a result of exposure to german pro-gear, which has it all build in.

Ciao T
If you ever want to give it a try, just let me know, we'll work something out. Ultimately, I'll send you DIY kit.
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Old 18th March 2012, 08:17 PM   #3707
tvrgeek is offline tvrgeek  United States
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If I am reading the following correctly, the single FET CCS is the best linearity, but not great impedance. The cascode fet-fet has by far the best LF performance.
So with this set of options, one must choose for low frequency performance or linearity. Better transistors may change everything, as will when I put them in the complete model. Of course, then there is reality.
Attached Images
File Type: png ccs-ac.png (55.3 KB, 85 views)
File Type: png ccs-model.png (40.7 KB, 84 views)
File Type: png ccs-2.png (51.9 KB, 84 views)
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Old 18th March 2012, 08:24 PM   #3708
bcarso is offline bcarso  United States
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Quote:
Originally Posted by tvrgeek View Post
If I am reading the following correctly, the single FET CCS is the best linearity, but not great impedance. The cascode fet-fet has by far the best LF performance.
So with this set of options, one must choose for low frequency performance or linearity. Better transistors may change everything, as will when I put them in the complete model. Of course, then there is reality.
If the impedance is high enough, who cares how it varies with voltage?

Variation IS a potential distortion mechanism, important to different degrees depending upon the circuit in which the variable thing is embedded. The distortion will be different if the variation is linear as opposed to nonlinear. But it will still be distortion.
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Old 18th March 2012, 08:26 PM   #3709
bcarso is offline bcarso  United States
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And yes, the bipolar-JFET combo will work best, especially if the gate is returned to the emitter (see my posted comparison circuits above), AND if you have enough voltage in the circuit to pinch off the JFET. Which, for your application as a tail current generator in an amplifier with substantial closed-loop gain, you do.
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Old 18th March 2012, 10:28 PM   #3710
tvrgeek is offline tvrgeek  United States
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Made up a copy of the 120 IPS. Grounded the negative input. Just 50K loads. It was more revealing about steps in load. Set to 2 mA tail current. Again the twin FET outperformed the other configurations. Looking at the FFT, there were no appreciable differences looking at the first stage output.

I admit to pretty much guessing at a lot of the part values, considering I was guessing with what was in Spice.
Attached Images
File Type: png IPS-CCS.png (35.7 KB, 82 views)
File Type: png IPS-step.png (35.1 KB, 80 views)
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