Hi, i built amplifier called av160 and its working, but there is one problem, humming toroidal tranfsormer 600w 2 x 40v secondary and primary 240v, tried to connect 0.1uF MKT X2 275AC rated capacitor on mains in parralel but that didnt worked, any suggestions how to eliminate humming, when amplifier is working and music not playing you can hear like from 2 meters that humming toroidal in silent room....
If it´s *mechanical* humming, meaning the laminations vibrate, no *electronics* effort will correct that.
IF it´s too tightly pressed against an iron chassis and stray magnet field makes it vibrate, you might add a disk of spongy material (EVA rubber or similar) between it and said chassis; if vibration is internal, as in lamination to lamination or to winding, answer invlves some surgery: you´ll have to pull the outer wrapping , put transformer inside a suitable Tupper type case or similar, cover it in varnish (ideally *transformer* varnish and let it sit there for a couple hours, until you are certain it´s impregnated thoroughly.
Then you hang it from the wires over the varnish pot until it drips off, then (say, tied to a piece of wood or a chair) for overnight or a day or until varnish is not sticky to touch.
Put an old newspaper under it in case of a stray drop ruining your floor.
This impregnation *should* have been done at the Factory, of course.
IF it´s too tightly pressed against an iron chassis and stray magnet field makes it vibrate, you might add a disk of spongy material (EVA rubber or similar) between it and said chassis; if vibration is internal, as in lamination to lamination or to winding, answer invlves some surgery: you´ll have to pull the outer wrapping , put transformer inside a suitable Tupper type case or similar, cover it in varnish (ideally *transformer* varnish and let it sit there for a couple hours, until you are certain it´s impregnated thoroughly.
Then you hang it from the wires over the varnish pot until it drips off, then (say, tied to a piece of wood or a chair) for overnight or a day or until varnish is not sticky to touch.
Put an old newspaper under it in case of a stray drop ruining your floor.
This impregnation *should* have been done at the Factory, of course.
Hi. Toroids can really hum. The usual cause is sound generated by magnetostriction in the core and it gets really bad if the core starts saturating. Designers tend to push the core right to saturation to achieve lower copper losses. It is easy to add a few extra hand wound turns e.g 20 in series with the mains primary. If you get the phasing right the extra turns will reduce the magnetsing current (and noise) enormously without causing much drop on the secondaries. Do not attempt this unless you really know how to keep the extra windings insulated to 4 kV flash standard to secondary or chassis.
From what you describe is it Mechanical Hum? This can be caused by several things.
1. Disconnect all secondary windings. Power it ON.
2. Is it still humming? If so you need to find out if the core is in saturation or just the windings are loose. By measuring the excitation currents (TX not connected to any other circuits). Plot currents from 200 -264 vac @ 50Hz. If current changes by 2x or more the transformer is a poor design. If excitation currents are <2x the windings are the best suspect. POT THE TRANSFORMER.
3. If not humming, the power supply maybe HALF WAVE RECTIFIED. NEVER HALF WAVE RECTIFY a toroidal transformer. They do not have any air gaps and the core will saturate and you will get HUM and other problems.
Good hunting Duke.
1. Disconnect all secondary windings. Power it ON.
2. Is it still humming? If so you need to find out if the core is in saturation or just the windings are loose. By measuring the excitation currents (TX not connected to any other circuits). Plot currents from 200 -264 vac @ 50Hz. If current changes by 2x or more the transformer is a poor design. If excitation currents are <2x the windings are the best suspect. POT THE TRANSFORMER.
3. If not humming, the power supply maybe HALF WAVE RECTIFIED. NEVER HALF WAVE RECTIFY a toroidal transformer. They do not have any air gaps and the core will saturate and you will get HUM and other problems.
Good hunting Duke.
yes it was in the package with the toroidal transformer, transformer is this one TST600/014 INDEL - Transformer: toroidal | TME - Electronic components used Indel 300w toroidal transformer before but wasnt humming, ofcourse that was different house with mains 220v in Europe, now i live in UK with mains 240v...
Power supply goes like this, but instead of 4 capacitors i used one 10000uF cap on each rail, and different diode rectifier bridge [url=http://www108.zippyshare.com/v/4CRiWXUQ/file.html]From what you describe is it Mechanical Hum? This can be caused by several things.
1. Disconnect all secondary windings. Power it ON.
2. Is it still humming? If so you need to find out if the core is in saturation or just the windings are loose. By measuring the excitation currents (TX not connected to any other circuits). Plot currents from 200 -264 vac @ 50Hz. If current changes by 2x or more the transformer is a poor design. If excitation currents are <2x the windings are the best suspect. POT THE TRANSFORMER.
3. If not humming, the power supply maybe HALF WAVE RECTIFIED. NEVER HALF WAVE RECTIFY a toroidal transformer. They do not have any air gaps and the core will saturate and you will get HUM and other problems.
Good hunting Duke.
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what about this dc blocking circuit http://sound.westhost.com/articles/xfmr-dc-f8.gif
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most of our european transformers are designed for a nominal 230Vac but all should comply with the"harmonised "voltage requirement for the EU.
The UK is on a nominal 240Vac and generally operates at roughly 20V higher than mainland Europe. This does exaggerate the mechanical hum due to running closer to saturation when demand is very low. It also increases the risk of hearing a hum due to DC increasing the saturation.
Adding 20 or so primary turns can make a big difference, but you must feel you are competant to carry out that conversion safely.
And you must also be able to check you have phased the extras turn in the correct direction, otherwise you make the problem worse.
There was a long discussion and many reports by another Member who did that. I seem to recall he dipped and dried it over more than a dozen repeats to get a quieter toroid.can i do the same process without taking the outer plastic off?
you will probably need much more capacitance.
4pairs of 4700uF would be my minimum. I just built up a couple of 6pair versions and they work well.
4700uF paired, has an impedance of 1.35ohms @ 50Hz
Just 600mApk of AC current through the capacitors takes the diodes to about 400mV of Vf for each. i.e. the diodes are just starting to pass AC current when the toroid draws 600mApk of current. I think that is too low to be effective.
The capacitors are prevented from reaching high voltages by the opposed diodes. You can safely use 6V rated capacitors for this.
Buy 50off 4700uF 10V
That's enough to do three or four transformers.
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If your transformer was designed to works for 230V primary winding, connecting it on 240V network can increase the 100Hz noise due to core induction.
If you dont have tap at 240V no real solution (from my point of view) exempt may be increase the load by a bleeder resistor but not a very good solution.
regards
Every retailer of mains transformers and other mains powered equipment MUST comply with the EU's harmonised voltage regulations.
That requires correct and safe operation over a voltage range of 216Vac to 253Vac.
Your right but do you the level of noise the manufacturer can warranty and at witch rated voltage? Does the manufacturer test the steel sheet before production? Generally he cannot buy directly to Nippon steel or Ugine acier and you know there is large variation in steel quality.
My experience at full rated power a transformer is less noisy but for small unit it is very very small variation
Regards
I don't think the regulators would accept "should".
They demand that all mains powered equipment be safe on our harmonised supply.
That to me is a "MUST" comply.
The level of noise is rarely mentioned in a specification. I can't recall seeing any specification for noise. There will be some that do specify, but they are maybe a special purpose.
The increase in current as saturation nears is enormous.
A few graphs of Iprimary vs Vprimary have been posted.
Earlier there was a rule of thumb that suggested a doubling of Iprimary (for 200Vac to 264Vac) was an appropriate limit.
BTW,
I would not test Iprimary @ 264Vac for a 230Vac EU transformer.
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