Are you sure its not the old "DC on mains" problem ? although if you are running them at 400va loading then you may be hearing the harmonics as the bridge comes into and out of conduction. Worth looking at though.
Wouldn't like to say on potting compounds. Over the years we had this type of problem on numerous ferrites and HF transformers (TV Trade) and there is so much energy involved that encasing the coils wasn't the success you might have expected.
Wouldn't like to say on potting compounds. Over the years we had this type of problem on numerous ferrites and HF transformers (TV Trade) and there is so much energy involved that encasing the coils wasn't the success you might have expected.
Put them in a box that is non magnetic cover with sand and fill with melted paraffin. Potting compound still mechanically couples the noise.
I am using 3 x 33000uF per rail. (12 caps in total).
I might try some larger transformers if I can get them in the chassis.
try a DC block. They are relatively inexpensive. Only mod I would make is to add a parallel film cap of the highest value you can find.......point of marginal return would be around 250uf on the film bi-pass caps.
The ESP images have been removed as Rod Elliot specifically asks that any reference to his work be linked directly to his site.
http://sound.westhost.com/articles/xfmr-dc.htm
The ESP images have been removed as Rod Elliot specifically asks that any reference to his work be linked directly to his site.
http://sound.westhost.com/articles/xfmr-dc.htm
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Yes it works... the trouble is its been copied out of context and the diode and resistor are part of a worked example explaining the theory.
http://sound.westhost.com/articles/xfmr-dc.htm
Good question and I haven't got the answer. I suppose the question really is what voltage is allowed to develop across the caps. If the reactance is low enough (and hence no or little voltage developed across the cap) then the diodes never come into conduction anyway. Its what happens at the moment of switch on under worst case conditions that counts.
Putting my "practical empirical" head on for a moment I would say that as we usually specify a hefty bridge rectifier for this application (because if you look at the circuit its just a matter of shorting the appropriate connections on the bridge) it becomes a non issue as the surge current of these things is huge. The voltage rating is unimportant as it never sees more than a volt or two.
Putting my "practical empirical" head on for a moment I would say that as we usually specify a hefty bridge rectifier for this application (because if you look at the circuit its just a matter of shorting the appropriate connections on the bridge) it becomes a non issue as the surge current of these things is huge. The voltage rating is unimportant as it never sees more than a volt or two.
1000 VA need a soft start and in particular if those are toroidal transformers.
extract below says if you do not use a soft start device (like an NTC inrush limiter) diode current requirements go up. I was surprised to see the 25A and 35A rectifier recomendation. IMO, It's much cheaper to use an NTC inrush limiter and the smaller diodes.
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The circuit shown above satisfies all criteria. There is more than enough capacitance, and the diodes specified have a continuous current rating of 3A and a peak current rating of 200A (non-repetitive). After this circuit is included, the no-load current falls back to 16mA, and the visible signs of asymmetrical saturation are gone. As transformer load increases, the diodes will take over from the caps, preventing the peak voltage across either capacitor from exceeding 1.3V - even during the inrush current period.
Note that if no soft-start circuit is used, larger diodes are highly recommended. Regardless of whether soft-start is used, a 25A or 35A bridge rectifier assembly is a simple and relatively inexpensive way to obtain very high current diodes, already neatly packaged and insulated. When using a bridge, remember that + and - must be shorted together to obtain 4 diodes in anti-parallel (as shown in Figure 3).
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