Not sure it will fix your problem (especially if it is DC induced), but you may want to make friends with someone at an industrial motor rewind shop. They typically have a large tank which they use to draw a vacuum first to get rid of all air, and then thoroughly impregnate the TX with varnish. Your TX is probably of insignificant size compared to the tank, and if you wait until they do a motor, they may put it in for nothing or a small cost.
Good idea, Ron AKA, It's an awful job without the right gear! I worked with rewinders nationally for years and that certainly was the case. Better that way than be disappointed by failure after days of trying with expensive varnish.
Tiefbass.. your Oz Altronics reference is the same amplifier, issues and fix - Silicon Chip 20W class A amp. in my previous post.
Apologies for an error too, its 2 x 16VAC windings for 22V DC rails.
Tiefbass.. your Oz Altronics reference is the same amplifier, issues and fix - Silicon Chip 20W class A amp. in my previous post.
Apologies for an error too, its 2 x 16VAC windings for 22V DC rails.
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Mechanically noisy transformers are a pain. I have a 1kVA torroidal that I bought from RS a few years ago and it hums like a buzz saw. I am thinking about using it on my new amp but I am definitely going to have to try to varnish it myself if I do. I'll probably just run the transformer at full load for an hour or so and then dip that into a container of varnish. I also had a transformer specially wound for my 250W amp a few years ago (cost an arm), and it is superb. Its rated at 1kVA, but weights almost 18Kg - no noise whatsover. I got it from Airlink Transformers in the UK
Just put a simple filter before the transformer, I found 1R 11W in series with 220nf from live to neutral reduced 80% of the hum from my RS torroid. Gotta stick your head in the box to hear it now. (capacitor must be rated adquately for use between live and neutral and of sufficient voltage for your your country's supply).
I have a 650va toroid from RS bought some years ago (when I built D Selfs amp back in 93 ?) and that was always noisy (growly lol). Been meaning to have a play and try various DC blockers etc to see if that is the problem (and cure). I noticed mine was worse at certain times of day and scoping the mains showed the appearance of "data" showing as tiny pulses superimposed on the waveform... some kind of mains signalling maybe although we live in purely residential area. Really made it noisy though.
There is apparently a lot more to Toroidal manufacture and performance than you read in electronics articles. I have similar Antrim and Talema 300VA types from Northern Ireland that are about 30 years old and one growls and the other is beautifully silent. I have swapped them about in amplifiers many times with little change.
Having read Nico Ras' transformer manufacturing anecdote in another thread, I am beginning to wonder just what is involved here - If it makes so much difference, why don't we hear more about it?
http://www.diyaudio.com/forums/soli...oidals-summary-most-interesting-comments.html (post #9)
One thinks of soft silicon steel, grain orientation and defined winding tensions and density for the core and windings, Is there much more?
Having read Nico Ras' transformer manufacturing anecdote in another thread, I am beginning to wonder just what is involved here - If it makes so much difference, why don't we hear more about it?
http://www.diyaudio.com/forums/soli...oidals-summary-most-interesting-comments.html (post #9)
One thinks of soft silicon steel, grain orientation and defined winding tensions and density for the core and windings, Is there much more?
One important thing to note is that in many toroidal power supply transformers core saturation often occurs when line voltages are high. This is one of their drawbacks, especially when the toroid is already an "economic" type with some 1,8T.
When also low frequency DC components are present in the line voltage saturation of the core already occurs at the nominal line voltage.
Saturation causes mechanical resonance, and as toroids are not wound "tight" because of their shape, things can only get worse.
For this reason I don't understand why toroids seem to be the "standard" in quality audio equipment, however, as already stated, there are good ones.
A good quality EI core, or even better C-core, transformer can fight possible core saturation by applying a minor airgap (already always "there" in an EI type). I wind power supply transformers with maximum 1,2T to stay well under the safety limit when odd things are there.
Advantage of EI and C-core types is that the coil is straight and can be wound tight, especially when interleaved; when vacuum impregnation is applied there is a solid basis for a quiet transformer.
Thanks for your information, pieter t. It occurs to me that there are usually a couple of core size options when ordering toroidal transformers and of course, I always opt for the cheaper, smaller one.
We would then likely have the higher !.8T density you refer to, so I guess that should be considered with the next custom trafo. I don't recall seeing the flux listed though, so how would we ask about this from a non-technical sales person?
We would then likely have the higher !.8T density you refer to, so I guess that should be considered with the next custom trafo. I don't recall seeing the flux listed though, so how would we ask about this from a non-technical sales person?
Well I think that the non-technical sales person should ask his technical colleagues what options are available, and first of all should be able to provide you with the correct specifications of the standard option.
When you ask for a toroid with a flux density of 1,2T you will have a larger core (and in the end of course a larger transformer), because to lower the flux density of a given core more primary windings are required. More primary windings (and therefore also more secondary windings for the same primary to secondary voltage ratios) require more winding space, which requires the larger core.
Other advantage of the low flux transformer is more friendly inrush current behavior.
By the way I don't quite understand your "copyright" remark. Putting an induction right after rectification is (at least in power supplies for tube amplifiers) not uncommon as a good alternative for "capacitor input" power supplies; it is called "choke input" power supply.
It only refers to the magazine project article, which can't be read in full from the website and I don't post it, that's all. You're right about it being well known technology, however and anyone experienced could adapt it to their needs from the basic details given, if they wish.
Few seem to adopt these relatively simple measures, though. Maybe they just like using a sledgehammer first to crack the nut.
I used to do that all the time. It was not cheap though. There'd put it in with the big motor windings. It's called potting.
I have a Crown D-75A that has transformer buzz. I tightened two of the screws that hold the laminations together but it still buzzes. I wonder if the main filter caps are leaky, causing too much current draw at idle? I need to check that.
EDIT: I just checked the current draw of the amp with a metered Variac and it's drawing an insignificant amount current from the wall at idle. I need to investigate further.
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