MagneQuest Forum

RE: here is a great article to read and keep....

151.197.209.119

In Reply to: RE: here is a great article to read and keep.... posted by gluca on March 09, 2008 at 12:31:28

Hi gianluca:

you wrote;

:::Hey Mike, I cant remember well now but it seems to me you stated somewhere you prefer unshielded trannies even if they can be much more easily offended by hum. Did you or am I wrong?:::

A long time ago I wrote an article for Sound Practices on why not to pot large signal output transformers.

small signal ac transformers often require shielding and even pretty aggressive shielding to prevent noise from overwhelming the AC signal.
But--- this becomes much more critical at 0 dbm levels and below.

now on to power tranneys--- what the author states is probably about spot on. First and foremost keep the flux density low. Second, whenever possible mount the transformer vertically (long axis up and down for chimney effect).

third-- space is your friend--- nice spacious chassis layouts--- perhaps (and I realize that there are pros and cons) consider separate power supply chassis and signal chassis. Four chassis arrangements like my pair of Heath W2's I suspect have some merit.

All the above said--- potting power tranneys with the proper potting compounds and the cans used as shields probably does help a bit. But I'd rather take the bucks you'd spend on the can and potting materials and just build progressively a better and better power transformer.

Paul Joppa had done some studies (as I recall) of several preamp power tranneys--- measuring a host of parameters including radiated magnetic fields and etc. IIRC--- a laydown power trans made by Peerless did quite, quite well in this evaluation.

So I think that you can build some really good power transformers to an really high level of performance without potting them.

I wish I could easily find the article I wrote for Sound Practices on how to be a good consumer of power transformers. As I recall--- what I wrote some ten or more years ago still would have relevance today.

DIY'ers tend to treat especially power transformers as mere commodities--- they shop on price and on very limited data that is generally not qualified well at all.

sometime over the next few weeks I'll be putting up a paper written by Ercel B Harrison in 1944. It covers a wide range of interesting transformer topics including power tranneys and outputs and etc.

If you dig through the Peerless archives you will find some really tasty power transformer designs--- that were designed balls to the walls for just high performance--- not cost. Some of these are really neat--- they migh have astatically balanced coils, or the hv ct windings were balanced (very strictly), and they were built on some weird lams like UI's and some single C-cores and etc. But these would be expensive critters to build.

I'm often reminded--- and this is yet another reminder moment--- of just how much is in the Peerless archives that has not seen the light of day in fifty plus years--- some really state of the art design stuff. And the same can be said (but to a lesser extent) with some of the Freed power transformer components--- for instance they too had a power trans in the same league as the Peerless R-080.

msl

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