Transformer VA rating.

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pre65
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#1 Transformer VA rating.

Post by pre65 »

I ask this question spurred on by a topic on another forum.

We all "know" that increasing the VA rating of a transformer in an amplifier power supply can make an improvement, but is it possible to model that in (for example) Spice ?

I use Power Supply Designer, but I don't think there is a way to input the transformer "power", unless the winding resistance indicates that ?

I tend to think that whatever VA is required (by calculation) that double, or even triple is more beneficial, but I'm not really sure why.
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Nick
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#2 Re: Transformer VA rating.

Post by Nick »

We all "know" that increasing the VA rating of a transformer in an amplifier power supply can make an improvement
Interesting mix of absolute 'We all "know"', and conditional "can make"

Below saturation, the difference is wire size and core size. Results are normally better regulation (in the transformer sense) and lower winding resistance (which is part of the same thing).
I tend to think that whatever VA is required (by calculation) that double, or even triple is more beneficial, but I'm not really sure why.
Neither am I, given you will try and save every penny. Using a transformer that is larger than required will result in the output voltage being higher than intended as the transformer is running at less than its rated load. That may be a good or bad thing.

Power Supply Designer, will show you some things, but its not perfect, it won't show you how the transformer may ring and so what HF spuria may be generated (for example).
Little known fact, coherent thought can destructively interfere with itself leaving no thought at all, that’s why I prefer incoherent thought.
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#3 Re: Transformer VA rating.

Post by JamesD »

This is a similar thing that we all 'know' - that adding capacitance to a psu filter chain makes it 'sound better'...

It's very situation specific as it can make it worse - the law of unintended consequences applies and psu component and system resonances will change maybe for the better - maybe for worse and that is before the effects on the stages the psu feeds...

Its like adding inertia to a cartridge headshell - a good thing without adding mass - maybe good, maybe bad but try splitting the two effects :D
oh and don't mentioned warped records either i.e the real world will have its say too....

OK so thats not helpful, maybe this will help - I find a well designed psu in PSU Designer is a damn good starting point for experimentation providing you investigate the psu performance after a current step function and minimise ringing and overshoot also make sure your on the latest version of the software
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pre65
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#4 Re: Transformer VA rating.

Post by pre65 »

JamesD wrote: Mon Jul 06, 2020 11:43 am I find a well designed psu in PSU Designer is a damn good starting point for experimentation providing you investigate the psu performance after a current step function and minimise ringing and overshoot also make sure your on the latest version of the software
Latest build info.
2.20.0
23/02/2020
Build 74 released. Rectifiers are now stored as XML files for easier sharing and updates. macOS version now available. Fixed multiple issues with Windows 10 permissions.
Life is what happens to you while you're busy making other plans. John Lennon

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Cressy Snr
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#5 Re: Transformer VA rating.

Post by Cressy Snr »

pre65 wrote: Mon Jul 06, 2020 11:51 am ......macOS version now available.
Now there’s interesting...

Just need to unplug Mac Mini from the TV, buy a monitor for it and redeploy it to the hobby room I spent all last week clearing the rubbish out of. I’ve been banned from the kitchen table for future projects after I scratched the top of it to buggery with the lockdown amp project :lol: ....no, not funny really.

Still, it’s great to have a Mac version at last.....Then of course it’s going to stop working when Apple move to ARM processors with OS11. :roll: FFS!
One more reason to keep the Mac Mini for as long as possible.
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ed
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#6 Re: Transformer VA rating.

Post by ed »

Cressy Snr wrote: Mon Jul 06, 2020 12:21 pm
One more reason to keep the Mac Mini for as long as possible.
you sure?
snigger
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#7 Re: Transformer VA rating.

Post by Cressy Snr »

ed wrote: Mon Jul 06, 2020 1:28 pm
Cressy Snr wrote: Mon Jul 06, 2020 12:21 pm
One more reason to keep the Mac Mini for as long as possible.
you sure?
snigger
I’m so far into the walled garden after 30 years, there’s no escaping. Even writing this on my iPad carries risks. :lol: ....Big Siri is watching you.
“The sound you love today may not be the sound you love tomorrow, and with tube circuits you can continually retune your gear to what reflects your current vibe...so you can get even down deeper into your truth.” (Harvey Rosenburg.)
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