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Old 21st May 2019, 09:00 AM   #4481
ClaudeG is offline ClaudeG
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Thanks for going that effort: a picture makes things easier at first glance, much appreciated :-)

The PS bits look quite Ok to my novice eyes, but, err, doesn't your transformer need more than 15V outputs in order to have real 15V after the regulators ;-)

I understand you wanted to mix aswell some signal paths into that schematic. Why not... can't judge on this, but then wouldn't you need signal connection between the AK4137 and the ESS DAC ;-)

Thanks again, makes things clear and hence easy to spot possible misses...

Claude
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Old 21st May 2019, 09:28 AM   #4482
kaytata is offline kaytata  India
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Hi Claude,


Thanks for your comments.



You're right my mistake, again. The i2s connections between the ak4137 and dac should be on the other side. Modified diagram is attached below, thanks for pointing that out.


Regarding the PS, transformer is r-core 50va(aliexpress). Two 15v secondary can power the lm317/337 even up to 16-17v(measured by multimeter) as it is adjustable, don't ask me how as I have no idea. Plus, the transformer stays cool, not even warm when run. So does the voltage regulators.


Regards,
Kay
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Old 21st May 2019, 11:46 AM   #4483
ClaudeG is offline ClaudeG
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Al good then :-)

Guess the loas is low on the transformer hence a higher 'nearly no load' voltage... it is rated 50W and probably needs a few percents of it...
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Old 21st May 2019, 03:14 PM   #4484
Markw4 is offline Markw4  United States
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Quote:
Originally Posted by kaytata View Post
Like this is ok?
Yes, something like that should be good to try. See what you think.
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Old 21st May 2019, 03:28 PM   #4485
Markw4 is offline Markw4  United States
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Guys,

The story on transformers is that they are rated for RMS volts at full rated current. First, the peak voltage is 1.414 times the RMS voltage (for a sine wave). The peak voltage is reduced by the voltage drop across the bridge rectifier which is about a 1.4v loss if using regular silicon diodes. Second, the voltage from the transformer will be reduced by its internal resistance depending on how much current is drawn, with the drop being equal to I times R. Given the above factors, if the transformer is running at low current and if there is a big filter cap after the bridge rectifier then the cap might be able to charge up to the peak voltage (that remains after subtracting the rectifier drop) and not droop in voltage very much before the next charging pulse. If the the circuit only discharges the cap slowly, then the input voltage before the regulator may remain higher than you might expect.

My audio designer friend says he usually runs maybe a bit less than 10v across non-LDO regulators, as he thinks conventional regulators tend to sound best for analog audio circuits in that case. He also uses transformers rated for more current than he expects to draw so that the transformer source impedance is lower than otherwise, and its core operates at lower flux densities. That's for torroidal transformers, which it happens are often wound so as to be not too far from saturation (which is not a good thing). E-core transformers tend to be better in that respect because the standard rectangular winding window area vs core size makes it hard to over-wind the coils.

Last edited by Markw4; 21st May 2019 at 03:37 PM.
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Old Yesterday, 04:09 PM   #4486
Terry Demol is offline Terry Demol  Australia
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Quote:
Originally Posted by Markw4 View Post
Guys,

My audio designer friend says he usually runs maybe a bit less than 10v across non-LDO regulators, as he thinks conventional regulators tend to sound best for analog audio circuits in that case. He also uses transformers rated for more current than he expects to draw so that the transformer source impedance is lower than otherwise, and its core operates at lower flux densities. That's for torroidal transformers, which it happens are often wound so as to be not too far from saturation (which is not a good thing). E-core transformers tend to be better in that respect because the standard rectangular winding window area vs core size makes it hard to over-wind the coils.
That's not quite how transformers work - but don't worry, most people don't understand transformers very well, even EE's.

Running the transformer with a lower secondary current will not significantly affect the core flux density. The primary voltage, it's frequency, the number of turns, the core material and cross section will. If you want your transformer to run at a lower flux density, further away from saturation, you have to have it custom wound to do such. It will be running at that flux density with no load.

WRT E-core transformers being better for not saturating due to smaller winding window and being harder to 'over wind' - this doesn't make sense.
To run the core at lower flux, you need to have MORE primary windings, not less.

The trade off running core at lower flux is everything else suffers such as regulation (OP impedance) and size gets larger for a given VA.

This is just touching on the subject. All transformer designs have advantages and disadvantages.

T
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Old Yesterday, 04:38 PM   #4487
Markw4 is offline Markw4  United States
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Quote:
Originally Posted by Terry Demol View Post
.
To run the core at lower flux, you need to have MORE primary windings, not less.
Let's see if IIRC...

Flux depends on amp-turns (magnetizing induction) vs magnetic path length. With a bigger winding window area more amp-turns can be wound, and for a circular flux path (torroid) the ratio of window area to path length is maximized. On the other hand, the rectangular winding windows of E-cores and their longer magnetic path give a ratio that that is less easy to drive into saturation. One can only get so much copper into the window, even if using square cross-section wire. Amp-turns is then limited by resistive heating of copper.

Flux density, too much of which is what can cause saturation, depends on total flux vs the cross-sectional area of the core normal to the direction of the magnetic field lines. Frequency matters too, really volt-seconds integrated over one-half cycle. Increasing core cross-section reduces flux density, and makes the winding window smaller (for a particular effective magnetic path length). However, E-core and torroids come in standard form factors, so changing cross section or window shape is not usually an option. Basically, one must choose from standard core sizes.

In the case of a transformer with an open secondary, leakage and mutual inductances limit primary winding current.. There will be more inductance with more primary turns. Secondary current creates a counter flux so the total flux stays close to the same.

My friend has his torroids custom wound so as to keep them low resistance, far from saturation, and with extra electric and magnetic field shielding.

Also, its been awhile since I thought much about this subject. Slowly, some of it is coming back. Need to look up my old notes.

Last edited by Markw4; Yesterday at 05:04 PM.
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Old Yesterday, 09:35 PM   #4488
eslei is offline eslei  New Zealand
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i agree that secondary current will not significantly affect the core flux density. a power transformer running near to saturation will be very hot, so we don't have to worry about that if a device operating at a normal temperature.

one most obvious downside of the toroidal transformer is it's wider bandwidth. the perfect function of a power transformer is passing by only 50/60 Hz, any other frequencies will potentially bring sonic disadvantages.
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Old Today, 02:54 AM   #4489
Terry Demol is offline Terry Demol  Australia
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Quote:
Originally Posted by eslei View Post
i agree that secondary current will not significantly affect the core flux density. a power transformer running near to saturation will be very hot, so we don't have to worry about that if a device operating at a normal temperature.

one most obvious downside of the toroidal transformer is it's wider bandwidth. the perfect function of a power transformer is passing by only 50/60 Hz, any other frequencies will potentially bring sonic disadvantages.
Exactly on both counts.

When a transformer is running hot with no or low load you can almost be assured that
it's core is running too 'hard' (high a flux density). Often this is purely because the core material is cheap rubbish and not capable of running at a high fux density.

You can easily measure it too with a simple variac and current meter. As you ramp the primary volts up, with no load, there will be a point where the current starts rising rapidly.

Yes, the Toroid has very good coupling between the primary and secondary. as such makes a great wide band transformer.

T
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Old Today, 03:40 AM   #4490
abraxalito is online now abraxalito  United Kingdom
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Quote:
Originally Posted by Markw4 View Post
My friend has his torroids custom wound so as to keep them low resistance, far from saturation, and with extra electric and magnetic field shielding.
Custom winding isn't going to help with both low resistance (i.e. low copper losses) and keeping far from saturation. They're mutually opposed - the further you run from saturation for a given core material, the more copper losses you have to accept. Silver wire would help to lower resistance I guess.
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