Silent Transformers in Europe

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wuffwaff

wuffwaff

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Joined 2001
#1
Hi,

after having tried a lot of things (DC-Filters, other Filters, PS-Audio Power Plants, less current , mechanical isolation etc. ) without success I think it is time to buy a new set of transformers for my pair of Aleph-x Amps because they are just too noisy (mechanical hum). I can hear them from 3 meters away (no music playing), the level changing depending on what comes in through the mains.

I´ve tried quite a few transformers in different (class-A) amps. They were from Amplimo, Tauscher, Schuro. Most of them were potted and vacuum filled with some sort of resin. All were around 500-600VA.
All of them made more or less noise induced by the not so perfect mains here in Ingolstadt.

Since it seems to be possible to put silent transformers in class A amps (see the Pass Labs products) maybe someone knows where to buy transformers like that in Europe or even Germany.

So if somebody knows please tell....

thanks,

William
 
#2
wuffwaff said:
Since it seems to be possible to put silent transformers in class A amps (see the Pass Labs products)
Click to expand...

When I took a tour of Pass Labs last year, I was surprised at the pile of rejected transformers. Those were the humming ones, and not placed in a customer's product.

It's not just you having problems with humming transformers, I would say that 1/3 - 1/2 of the one's I've used hum.
 
#3
there is a lot of humming transformers. i've been Lucky. i have never had any hum problems in my builds. wel. not at the transformers foult at least 🙂
i guess the mains are to thank for that. i have always used ordinary open transformers. wiring have a lot to say ofcourse.
 
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#6
Bensen said:
Hi William,

I'm using 2 500VA R-cores from in my last setup. An other amp next to it with a 650VA Amplimo toroidal is clearly more noisy. Have no idea whether a R-core is inherent more silent?

R-CORE pour châssis - Transformateurs - Composants électriques - Sommaire

Cheers
Click to expand...

Hi,

looks interesting. The 300VA 2x18V could even fit. At the moment the Aleph-X uses around 150Watts as I already reduced the bias to keep the noise down (still enough to power ca. 100dB/watt speakers.

Would a 300VA be enough for a constant 150Watt load?

william
 
#13
Yes, I also tried many (Schuro, Tauscher, Multi-PCB, ......) and now I only order from Tomaz of Toroidy.
My Aleph-X 100W has no audible hum unless you open the case and put your ears next to it.

A few things on top :

1) Use a core at least 3x your actual load. The F5X consumes 180W and use 600VA core.
2) Draw a schematics including rectifiers, size of caps, current draw after the caps , and voltage you expect.
3) DON'T use potted ones, even though they look pretty (I leant this from a UK manufacturer for the audio industry).
4) Use one bridge rectifier for each secondary.

If there is still a problem, then you need to clean up the mains.
Maybe a big EI isolation transformer in a separate room ?
Or use a 2000W Ncore with SMPS and a Cordell Func Gen as input to generate a 50Hz low distortion sine wave (as mains).

🙂


Patrick
 
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#16
wuffwaff said:
Never saw a class-A amp with an SMPS, is there a reason for this?

William
Click to expand...

good question.... I use some of the high output smps for valve heater supplies(9-20v up to 12A) where they work well for triodes like sv572 and gm70. The ebay offerings are very cheap in the £6-£10 region per unit.

The outputs seem to vary in how much high frequency hash they put out though and it's necessary to confirm that they have floating outputs as some I've seen have neg tied to chassis ground....which is a no no if you want to serial connect or produce a split rail.

I would give it a try only all my F amps are reasonably quiet with airlink transformers.

Ed

example: http://www.ebay.co.uk/itm/UK-Stock-...t=LH_DefaultDomain_3&var=&hash=item232fa76535
 
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#19
EUVL said:
.........................
A few things on top :

1) Use a core at least 3x your actual load. The F5X consumes 180W and use 600VA core.
...................
Click to expand...
The F5x is a 50W ClassA amplifier.
The normal range of transformer VA to use is 6times to 10times the maximum power.
i.e. for a 50W ClassA amp use a transformer rated for 300VA to 500VA of output continuously.
If one assumes 95% efficiency, then that requires the primary to be rated slightly higher.

600VA for a 50W amplifier is 12times factor, we would expect it to be cool and quiet with that rating.
 
#20
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