How to wire a dual winding or multi-winding transformer

[Scratchy]

It is important to "phase" the windings of a dual winding transformer or you can end up shorting the transformer.
Here is a document showing how to correctly connect transformer windings in series or parallel:
http://www.hammondmfg.com/5CHook.htm

Additionally here is a design guide for rectifier use:
http://www.hammondmfg.com/pdf/5c007.pdf

[mr-busy]

This makes it clear: use a SMPS if you can (and pretty cheap these days).

Unless you can get hold of reaally cheap transformers+caps+bridge.

Antek transformers seem low-cost, but I believe they're cheap: made for US (60hz) and designed on-the-edge.
That's why EU ones are more expensive: they're just a lot better.

PS
Never confuse cheap and low-cost: 41hz amps are low-cost, but NOT cheap (-stuff).

PS PS
>Scratchy: do (all) your amp-constructions conform to your post?

[Haggis Basher]

Additionally here is a design guide for rectifier use:
http://www.hammondmfg.com/pdf/5c007.pdf

Dear Scratchy,

I have downloaded the file on power supply design. How timely of you to put these links on the Forum, as I am about to solder a “beastie” together; full wave capacitive load, 500VA transformer with two secondary windings at 35Vac, to be used on my TP-2. This “beastie will replace one of the PSU1-PS power supply with fried diodes and fried bulk capacitors.

On each channel I will use one rectifier bridge (1000V, 35A), following Skippy’s (Rod Eliot’s) advice regarding inrush current and voltage peaks; followed by two smoothing capacitors in parallel (10,000uF, 63V, 105deg C) ; followed by the output leads. This lot will be fixed through a glass fibre board and hard wired using 16AWG insulated wire or maybe even 2.5 square mm insulated domestic ring mains wire, if I can find any lying around.

I have deliberately chosen the rectifier bridge at 35A, as I managed to stop myself going even higher, as it is “pennies” in the difference in cost! Having been given a hard lesson, attempting to use a 1kVA transformer and a 750VA transformer, I have become quite sceptical.

Also, I have removed the vaporised 100 Ohm 5W resistors from the PSU-SS boards, the initial offenders which caused these disasters, and replaced them with 47 Ohm 25W chassis mounted aluminium coated wire-wound resistors bolted to the bottom of the case next to the soft start board, with heat-sink paste to help distribute the heat. For a “few dollars (pennies) more”, I could have used 50W or even bigger!

Do you think I am now on the right track? I will post again when I have made all the other necessary alterations to the soft start boards, the power supply boards, and the Truepath boards and re-tested and powered up both my Truepath systems. All this backtracking is finicky and very time consuming, so please, don’t “hold your breath”.

However, I am still concerned that the choke in the RF filter rated at 4A and 250V on the soft start board could be another point of disaster, and I would not like to see a transformer of 1500VA attached to the circuit! I also wonder how much abuse the nice "little boy in blue" varistor (S20K250) across the mains on the soft start board, will tolerate?

Ken.

[Scratchy]

@Mr Busy - AKA FFF - I'm not sure what you mean by this:

PS PS
>Scratchy: do (all) your amp-constructions conform to your post?

I do clean my PCB's with ISO and Power up with load limiting resistors if that's what you are asking.
The may be some final soldering done just before or after testing to some isolated components in which case I do not reclean the PCB - (see my AMP9 Polyfuse post).

@Haggis Basher
It really sounds like you are on the right track now Ken.
Thanks for sharing your findings so far.

[mr-busy]

It's just what it says. Take it easy.
Problem with tranny is you have high inrush currents, high voltage under low load, and at high load, when you want Power and therefore high voltage, it drops.
A smps is constant within specs, which is good for a long amp-life.

No friends anymore?

[Haggis Basher]

A smps is constant within specs, which is good for a long amp-life.

Dear mr-busy,

Which switch mode power supply would you suggest to replace the above power supply?

Ken.

[mr-busy]

It's just me Ken: FFF (that account is bit broken, and this one too).

You want mucho power....
2 of these maybe? http://meanwell.nl/products/Meanwell...DR-480-48.aspx
Can handle peaks to 720W, but max Vdc is 55V.
2x 140 = 280 Euro = 960W, peak 1440W. but will work perfectly, reliably, anywhere+compact. plug & play.
A 1500VA tranny+caps+bridges+...= maybe more?

But look for yourself on meanwell.nl -it lists them all conveniently.

[Scratchy]

Ken,
SMPS are great if you are starting out, but since you already have some "big iron" (no, not the golf club) I would stick with what you already have.
I guess I'm a linear PS kind of guy - oldskool, and FFF is a switched PS kind of guy - latest and greatest.

[V-bro]

SMPS are great for a compact amplifier, but a well soft started linear supply doesn't make the amplifier live a minute shorter... In fact, SMPS are put together from a whole lot more parts and are prone to break down much quicker than a linear supply.

A very good quality SMPS based supply (especially for big amplifiers such as the TA3020 amps) is also MUCH more expensive, unless you live in China or find some at a surplus or outlet store...

Hence my preference for steady big transformers...

Then with toroidal transformers winding some small current windings on top is easy...

Yet I would love to build a 1HU high Truepath amplifier one day and it will probably be done with SMPS. Or when the availability is there I would still choose one of those pancake toroidal transformers....

[mr-busy]

HB only wanted an idea of an smps option, that's all. When you've already GOT the toroid.... diff game.

There is one other BIG advantage of those smps's I noted: 3yrs guarantee.
You don't get that if you build a PSU yourself. Maybe only on toroid, if it fries. rest of PSU: 1hr. maybe.
And PSU is least interesting part of the amp, really.