buzzing transformers....

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
Hi, I take it you mean mechanical hum. I have heard, but never tried this myself, that you can connect a large value electolytic in series with live and neutral connections BUT YOU MUST INCLUDE a pair of inverse connected diodes across each cap to limit the D.C. across each to around 0.7 volts. If you are at all unsure DONT TRY THIS. I can draw what you need but as to it's effectivness I don't know. This is to prevent D.C. component that may be superimposed on mains causing a problem. Do you have an oscilloscope ?
Regards Karl
 
rtate said:
I have 8 leach super amp mono blocks all built with toroid transformers, 10 amp with 80,000uf supplies
Some of the trannies have developed a hum or buzz that is audible during quiet passages.

Is there any solution to this problem??

I had the same problem as you with toroid xformer. Not the tightening - up to death! - and not the rotation resolved the buzz problem. After a discussion with my supplier, he told with each sincerity that the noise caused from the core if it is not tightened very strongly. The core of the toroid constructed from a soft iron flat plate which is formed by turning a piece of it around a cylinder for example 5 times. One secret it is there. The cylindrical folded core it is not absolutelly compact, and thus can cause crackling noise even without load. Most constructors use the tightening of the copper wires during the winding process to tight simultaneously the core. But this method it is not the better. A such maden xformer even if it is encapsulated with epox. rosin can cause buzz noise. After examining the problem with my supplier, now we have resolved it, with an additional cost of 10Euros per piece, for: After the forming of core and before the winding, the core is dipped on varnish first and stay for 2 days tightened for good drying. Then it follows a carefull winding proccess, and before the final winding of the mylar insulating tape, it is dipped again in the varnish and stays again to dry for another 2 days. Then the encapsulation it is useless. The only additions it is the filling of the centre hole of xformer with epoxy rosin with the mounting bolt fixed into (thus there is not need for use an upper plate for mounting), and an external metal foil around the xformer for electromagnetic shielding.
Finally, a little secret from my experience. After delivering the xformer, i leave it on the shelf (in room temperature) for two weeks at least so to i feel secure that the varnishes dryied absolutelly. Never i connect it in the mains before this. Thus, the xformer after all these it becames a compact device.

Fotios
 
I forgot to reffer the following. As many of us i use double binding post pairs for each channel and double cables from a common point of output for each post separatelly. Don't make the same with the Gnd connection. If you use also double cables to connect the Gnd in the black posts, then you have a nice "Y" open loop which is like an antenna. This is a true problem that i was faced in the past. For the gnd connection use only one cable arriving from th P.S. star point to one of binding posts and then simply bridge the other post with the first.
Another one trick ;) that i use for examining any buzz noise, it is the connection in the output of a professional speaker (i use a 12" woofer for this) which due to its high sensitivity it reveals by far better the existence of any audible noise instead of an oscilloscope.
I hope to resolve your problems. And i don't believe that you use a common supply for the two channels simultaneously, because then you will have a nice Gnd loop. For this reason used the individual power supplies in amplifiers with big voltage gain, to has each channel separate Gnd node from the other channel.

Fotios
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
Hi, This is the idea, but to be honest the switch on surge of all those toroids is massive. Do you power each one up one up separately ? Caps are large e.g. 10000mfd at 63volt although the diodes limit any voltage to -/+ 0.7 volts or so. You want 30amp diodes at least with a high surge rating, you can use the diodes in bridge rectifier and use all four diodes, two each way in parallel. I can't claim any credit for this, iv'e seen this technique a few times but would be interested to know if it works. Is your problem worse at certain times of day ? I know from experience having worked in a service dept, just how difficult it can be to stop tranny buzz and particularly line output transformers whistling, varnishes, epoxy resins, you name it, we tried it, even replacing with manufacturers new part did'nt always cure.
Regards Karl
 
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Hi Karl, Yes the buzz is deffinetly worse at different times of the day and different from amp to amp.I thought that running a dedicated circuit would eliminate dc caused by other small appliances on the line. I do turn the amps on one at a time and I'm sure the inrush is hard on the trannies,that is why I am currently building softstart circuits base on a design from the same siite(Thanks PER-ANDERS!!). The transformers are "Plitron's "and are there top of the line being potted and double insulated.
The trap circuit shows 3 diodes stacked to eliminate more DC, that is why i wanted to use individual diodes instead of a bridge rectifier.
Last night I measured the DC component in the supply circuit and got any where from 10 to 40mv dc both across the lines and from each to ground.

If I was going to try a trap is there a better side of the circuit to put it on i.e. Line or Neutral to get better results.I read somewher that it could be dangerous to trap on both hot and neutral although some circuits do show it on both.
 
rtate,

I've got a very similar problem... ~60Hz hum coming from my trafo. The differences are:

1. My Trafo is ~1kVA EI core ($20.00 Surplus)
2. I re-wound part of the transformer in order to attain the correct voltage and make a center tap. My windings are loose and poorly done. I've been meaning to fix some of my shotty work, but haven't got around to it yet.

I'm curious to hear how the DC trap works.

How do you determine the size and voltage rating for the caps? Is it necessary for the voltage rating to exceed the parallel voltage of the series diodes?

Cheers,

Ryan