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Old 30th March 2008, 12:31 AM   #21
TheMG is offline TheMG  Canada
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Quote:
Originally posted by dfdye
What would the benefit of this approach be over a thermal circuit breaker?

The ability to adjust the temperature set-point, temperature sensors can be had in everything from SMT packages to TO-220, so mounting them to the transformer becomes easier than finding room for a mechanical breaker. There is also the ability to do whatever you want with it. For example you could have it simply attenuate the volume instead of shutting the amplifier off.

Couple this idea with a PIC microcontroller for example, and you have yourself a very flexible and versatile form of thermal monitoring. One PIC could monitor temperatures for the transformer, rectifier diodes, and output stage heat sinks all at once. The possibilities are endless!
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Old 30th March 2008, 10:13 AM   #22
AndrewT is online now AndrewT  Scotland
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I just witnessed a miracle.
Daniel said much of what I've been promoting for years, but in his typical colourful language.
Quote:
However, the output quality was useless.............on a 24va for an experiment
Quote:
extra capacitors can run smaller transformers
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Old 30th March 2008, 10:16 AM   #23
AndrewT is online now AndrewT  Scotland
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fitting a thermal sensor to the outside of a power transformer is almost useless.
The sensor must monitor the worst case temperature and that must be internally, not at the surface.

How would an amateur measure the worst case internal temperature and decide what surface temperature could be a suitable indicator of what was going wrong with the transformer or the duty it was being subjected to?
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Old 30th March 2008, 05:57 PM   #24
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Quote:
Originally posted by AndrewT
I just witnessed a miracle.
Daniel said much of what I've been promoting for years, but in his typical colourful language.
Oh I'm glad you're here!

How small is too small?
At what point, or where, does one need to consider a larger transformer rather than additional capacitors?

How big is too big?
Oh, and here's a really wild guess on how big is too big, and I'm wondering if there's any validity, so fasten your seat belt
I try a very large transformer running such a small amplifier that the load is insignificant to the transformer. This wipes out the midrange. To compensate, I reduce the amount of capacitance. The midrange is still missing. So, I reduce the amount of capacitance again.
Soon, the smoothing is insufficient (buzz), yet the amplifier is otherwise playing within acceptable standards--although closer to a Fletcher-Munson LC than level, and dynamics are still small.
Is this a too-big transformer, or is it imagination?

P.S. Accurate location of max-rated temperature, according to Allied, is inside the transformer core, which isn't expected to work on spec if modified to fit a temp probe. Andrew is right. Allied also suggests to temp probe some other hot part of the device, such as an amplifier heatsink, because its output will be in proportion to the transformer that powers it.
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Old 30th March 2008, 06:39 PM   #25
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Quote:
Originally posted by danielwritesbac


This wipes out the midrange.

and dynamics are still small.
Is this a too-big transformer, or is it imagination?


This matches exactly my experience. Both with solid state and tube amps. Have several huge transformers (>1kVa) which are completely unusable for audio. Weird.
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Old 30th March 2008, 08:20 PM   #26
tinitus is offline tinitus  Europe
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My 50watt monos use 500watt trafos(UI-core), works perfect...they drive 2ohm load easily

My next 150watt monos will use 2kwatt trafos(UI-core), but only because I have them standing on my floor but I will use only 40watt trafos fore input/diver stage
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Old 2nd April 2008, 08:45 PM   #27
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This makes me wonder if a battery powered amp could have such consequences.
Too large capacity bank of battery's...
Too small...

Honestly, I don't believe it can be too big, if it's a stable voltage source which can deliver the power that's asked...

Maybe the caps are too big and would benefit if they would be paralleled with caps at 10 % and 1% the capacity of the largest ones. (might clear up the mids┐)

I'm confused

I need a hug

B.
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Old 12th April 2008, 10:26 PM   #28
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But... there have to be a limit when big is to big.

How about magnetising of the cores and raisetime to get the expected voltage, when working against a big capacitorbank ?
And how are we expecting the rectifyerbridge to behave ?

What happens if you put your PSB to a big industrial 100000VA transformer ?
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Old 25th April 2008, 06:43 AM   #29
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question

since a AB amp is about 65% efficient.

Is it correct to say 45% of your powersupply is turned into heat.

When you calculate your powersupply needs , don't you then at least
need to add that power loss into heat to your powersupply needs?

or is it just not as simple as that.

other problems are voltage drop at higher loads.

so with all of that a 150VA transformer is kind of borderline small for a 100W amplifier
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Old 25th April 2008, 08:16 AM   #30
AndrewT is online now AndrewT  Scotland
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most recommendations for a 100W amplifier fall in the range 100VA to 200VA.
You will find that a middle ground value of 1.5times the maximum output power works well.
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