noise from transformer

[john-china]

i need help of someone who has ever used good transformer.

when you put ears close to transformer , can you hear any noise from transformer. specially in heavy current of class A amplifier.

I bought some transformers , but i never got any very quiet transformer while heavy working.


pls tell me whether your transformer is like mine?

[Brian Donaldson]

My first transformer for my Alephs was 60Vct 20A EI . It was pretty and very heavy, but it buzzed like an electric razor. I still haven't put power to my new Avellindbergs. I hope they are quiet.
If you can't hear them from 1 foot away, I wouldn't worry. You'll never hear it in a nice aluminum chasis.

[Nelson Pass]

I buy the best there is, and that means Plitron as far as I
can tell. We test them with stethoscopes while driving diode/lightbulb loads (ask CyclotronGuy, it's his job among
many, many others) and there will always be some finite
noise.

When I first met Joe Sammut (1975), he had amps mounted in
the basement just below the speakers, and ran the wire up thru
the floor. He was pretty happy at the time, driving stacked
Dayton Wrights.

Work on it or get used to it. When I really want to be critical
I run 240 VAC transformer primaries at 120V, and I still use
Plitron, but you'll never hear it....

[wijgers]

A friend of mine found 2 transformers with sec. 24 V - 10 A.

Are two of those transformers suitible for a Aleph 30, each channel 1 transformer.
Or are those transformers overated and is the voltage after brige and Caps to High? According to the formulas it would be around 28 V, I presume. Is this to high?

Nils

[Andypairo]

I have a 500 VA 22+22 trafo and it works fine (rails are 29+29V), however if possible I would raise the VA rating to 800 VA at least.

Cheers

Andrea

PS if the trafos don't have 2 secondaries each you must use both of them to get a suitable PS for a Aleph (mono or stereo..)

[wijgers]

Andrea,

Did you also change some values off the resistors, or did you keep them at the same values as the scheme.

I can think of some changings due to a higher rail. But don't know in wicht direction I have to think. Raise off the value to prevent a lower curent. or visa versa

Nils

[Klaus]

Hi,

I also had some transformer problems with my Alep4 mono blocks, had! Lucky to have solved it and I learned a lot about that stuff.

I started with 600VA full resin filled toroid core transformers. Those super duper special audio stuff from Schuro/Germany. They both buzzed like a shaver! Even at 20% of nominal load (created by a simple glow lamp) and small caps of 22000uF it did. Total misconstruction, it seamed, or just a quality problem. I think the core of the toroid was not resin glued, so the spiral rolled metal layers could have resonated caused by the load peak current created magnetostrictive forces. Strong peaks were pushed by the ultra "hard" electrical design of the transformer, just 2,5% of voltage loss from idle to nominal load, that´s extreme. Tons of copper in… I am lucky Schuro accepted my reclamation with full money back.

Next specialist for audio transformers, Thel in Germany. Almost equal design – from the outside. Inner values are different: "softer" electrical design (Mr. Hartwig from Thel explained: 5,5% for peak reduction) and totally NO noise to be complained at any load. The core is also resign baked, that seam to make THE difference – also in price of cause. Higher winding resistance reduces the nominal power rating to just 450VA. Funny effect: the sound of my Aleph is much better with Thel than with Schuro. Maybe the hard peaks disturbed the function.

Lesson learned: naked VA numbers tell nothing about transformers quality or potential. All components of the transformer have to be baked with resign. From the outside nothing can be examined about the inner quality of a black block transformer… Cheap transformers w/o resign are creating a danger of hum – weight your risk versus short term savings.

Regards

Klaus

[Andypairo]

Originally posted by wijgers
Andrea,

Did you also change some values off the resistors, or did you keep them at the same values as the scheme.

I can think of some changings due to a higher rail. But don't know in wicht direction I have to think. Raise off the value to prevent a lower curent. or visa versa

Nils

I did almost anything, just trimmed the offsets.
If you want to control the current you have to change R19; raising it increases the current, lowering it decreases the current.

Cheers

Andrea

[Brian Guralnick]

Originally posted by Nelson Pass
When I first met Joe Sammut (1975), he had amps mounted in
the basement just below the speakers, and ran the wire up thru
the floor. He was pretty happy at the time, driving stacked
Dayton Wrights.

How odd, I've ended up doing the same with my main power amp.

1 thing I've noticed about toroids is that they can start up in an extra loud humming mode. Dont know why, but, they will stay on like that. Turning on & off the power usually fixes it, this is 1 reason I just leave my amp on 24/7.

!!!> The other thing I'v noticed is if you have a light dimmer, or, 1 of those 2 level brightness halogen lights set to 50% bright on the same AC line, or fuse as the amp, they will make the transformer hum extra loud, and depending on you equiptment, add distortion to the sound.

[vdi_nenna]

Is the hum an indication of something dangerous, like it will explode or burn up eventually?