SoZ transformer

Greetings All
Question for the more knowledgeable on this forum. I am in the process of building a Son of Zen amp with a 25 watt output. I have seriously underestimated the size of the transformer as well as the amount of heatsinking this project requires. The present transformer is a 1000VA Plitron with dual 32volt secondary, apparently way under sized
I have the option of purchasing a second identical transformer and build a dual mono amp, or using a1500va 2to1 step-down transformer before the Plitron and have an amp of about 8 watts output.
Comments, opinions, advice all welcome
Gustavo
 
Yes, saving up for another Plitron is probably the way to go.
I am building a SOZ also, and am finally starting to believe all the warnings regarding the amount of heatsinking required.
The weather dipped into the 40's this last month here in San Francisco, (I know, I'll get very little sympathy from everyone in the colder parts of the world!) Anyway, I set my space heater to 600watts and was awfully impressed with how much heat THAT is.

I, like you, was planning to dissapate 500 watts/ch, now I might back off a bit!


HERES the question: Like Grasshopper here I ended up with the wrong transformer size. For testing I have the variacs, but my transformers also have 220/120 inputs. IF I wire the transformer for 220 and use it with 120 I assume that the output voltage drops by half. This would give about 8 watts /ch - a good size to start with. OR if I reconfigure the amp for 4 ohm speakers(Nelson Pass say reduce voltage by 30% and all resistors by half)
this gives me about 18 watts/channel-perfect

OK HERE's the real question: What happens to the VA rating of the transformer? The voltage output is half, the amps are the same? so half the VA? BUT wait!! the trsansformer is the same, so can't it handle a similar load? Also All the Plitrons of the same VA are the same price and size and weight, regardless of voltage.
MAybe the wire gage is different in the different models?



Any insight appreciated,

Mark
 

paulb

Member
2001-06-01 4:53 pm
Calgary
While it is possible you may be able to get the same VA total, I wouldn't count on being able to draw any more than the rated current from the transformer. Wire gauge will definitely be different for different amperage.
This is a better question for Plitron - suggest you phone their tech support. Since you're already a customer, they should be able to help you out.
 
Paulb has a good idea. If I had to answer it though I would say you'd be able to use your original va rating. VA is just another term for watts (volts x amps). You can easily remain inside your va spec and still get into trouble due to the size of your wire in your winding. The NEC rates a #12 thhn wire for 120v outlet use at 20 amps. This is conservative though. Elsewhere in the code you can put almost 60 amps on that same wire for 15 min. given certain criteria. I have a 625va toroid from plitron with at least # 14 size wire and I would not have any problem with putting 20 to 25 amps on it if the va balanced out by lowering the voltage.

Your idea of 240 connection with 120 is good. Transformers don't know what they are doing, they are just wire wrapped around a core. You could even reverse wire them and step voltage up (though the current would go down). The only thing you don't want to do is exceed the voltage rating of the winding.

The way to figure secondary voltage is to determine the ratio of the transformer. The ratio is simple, If you have a 480v primary and a 120v secondary then the ratio is 4 to 1. The voltage will change by the ratio, regardless of how you wire it. If you have a 240/120 primary and a 2 x 30/60 secondary then you have a 4 to 1 ratio. 240/60 = 4, 120/30 = 4 . By wiring for 240 and applying 120 on it, you would have a 2 x 15/30 on the secondary.

It would be a good thing, as paulb said, to check if there's any doubt about the current demand. You could possibly look up the data on their website. I think Plitron posts this info, I don't know about others. Good luck
 
How to wire the famous 1010 VA toroid

OK guys, you have helped me with about every piece of the son o Zen so far. Lucky for you it doesn't have many pieces!

Here is one of my final yet most important questions. Grey Rolllins seems to have a grip on this transformer , the 1010 VA one sold by Apex jr. for the amazing price of $35 so I would appreciate his feedback among any others. If one can wire it as a center tapped
device, it would be able to drive 2 channels of an Aleph, so this info should be helpful to many in the Pass Amp catagory

I have now determined various ways to deal with the voltage that is higher than I need (the best suggestion was probably that given to another person: make an Aleph 2 or 4!

I probably will in the future.

So... the only remaining problem is how to wire it as a center tapped transformer so I can have + and - rails. As it comes, there is no center tap.

It has the 4 input wires for 120 or 240-no problem there

Then it has a total of 8 wires for the low voltage side.
The wires are grouped with4 different colors on one side, and the same 4 colors come out on the other on the other.

To me this means that there are 4 identical parallel windings.

So, now I'm looking at the thing so it is symetrical with 4 wires on the left and four wires on the right.

I will connect the orange and black wires one side together
to increase the current capacity. Then I will do the same on the other side

I will connect the yellow and red together on one side. Then do the same on the other.

I now have orange/black and yellow/ red wires so we are in effect down to 2 parallel coils.

NOW I take the left orange/black as my - leg

THE right yellow/red is my + leg

I CONNECT the left yellow/red to the right orange/black to produce the center tap.

I'm VERY concerned about some kind of phase problem

It seems that all the coils arewrapped in the same direction.
So it seems to me that both legs wil be putting out a pulse of current at the same time in thesame phase. Is this what centertapped trans do?

Will I create the equivalent of a center tapped transformer this way?

PLEASE try to read through this tortured description!

Thanks,
Mark
 
Mark,
Assuming that I understood the question correctly...
Beginning with four identical windings, you can use them in any combination you like. Just to make my eyes happy, I'd use the two yel/or windings in parallel; likewise for the red/bl--but it's purely a question of cosmetics. The way the transformer winding come off, it's certainly easier to group them red/bl & yel/or. Whatever suits you.
You're quite correct in your initial strategy: two pairs of windings in parallel, then those two in series to create a center tap.
You're also correct to be wary of getting them out of phase. I don't suppose that you've got an oscilloscope... Oh, well. I'd begin by testing them in series. One way will give you double the voltage, the other will give zero. (Your meter is essentially an infinite load, so you won't be drawing any current.) Once you've got the phasing identified, the rest should fall into place fairly easily.

Grey
 
Zappy times are here again

Buwahahahahaaaaaaa!!!!

(is that right?)


thanks Grey,
I now have the info to fire this sucker up (I'm still figuring out its mechanical construction though-looks count!)

I feel pretty confident that I can handle the aesthetic considerations of grouping the colored wire, but thanks for your suggestions!! :)

I'm pleased that I figured out that it could be wired up wrong, and even more pleased that it will be quite obvious if it in fact is
wrong, i.e. no volts.


Mark
 
Yep, a Variac will work. You'll be able to "dial-a-wattage" if you use one, and it will take care of any inrush problems you might have, but they're more expensive than fixed transformers. If you're lucky, you might be able to find one used or surplus and save a few bucks.
Two notes--make sure the Variac has sufficient current capability, and be sure not to run the knob up past the limits of your circuit. If you've got 35V caps and get a wild hair and dump line voltage into the circuit life will get interesting. I'd put a little dot on the scale to represent the maximum for the circuit, then place the Variac in a location where no one can accidentally bump the knob.

Grey