Using a 45-0-45 toroid on a AMP5/AMP10

[PViegas]

Hi, to all

I've got a 45-0-45 , 750VA salvaged from a 500W PA and I'm thinking in trying the AMP5 / AMP10, but because they work with a much lower voltage (half this value), it occurred to me that I could use just one of the windings and split the voltage/current.

Also, in the future i could add another AMP5/AMP10 and make a quad amplifier (A and B monitors), because I still have another winding not been used on the toroid. Right ?

Now the problems :
I searched for a voltage divider and can only find the classic resistive divider, now, would not this design create a very nice toaster (at 750VA/2 = 375VA )?

Any suggestions for a divider (efficient for this current values, ~16A) ??
Did anyone tried a similar setup ?

Also, will I not have problems with this "virtual ground" on the line input side (created by splitting one of the 0-45V windings) ?

The idea :


-----) | (------ +45 V - AC -------------->> to voltage divider Module 1
( | )
Mains ) | )------ (center tab 0V) ---->> to voltage divider Module 1 & 2
( | )
-----) | (------ - 45 V - AC -------------->> to voltage divider Module 2


Module 1:
----------------- |-----------|----------> + 22.5V - AC (going to AMP5/10)
| |
From Toroid | Divider |----------> 0 (going to AMP5/10)
| |
---------------- |-----------| ---------> - 22.5V - AC (going to AMP5/10)


Suggestions welcome, regards

[FFF]

What you want, can't really be done.
Six options:
1- unwind halfway, cut+make connections, put windings on again+make connections: 4x 22 Vac !
2- use an AMP (or two) that CAN take it (AMP-7 -takes- 30 Euro more, but -gives- a LOT more back!)
3- you get a cheap 220>110V step-down transformer (about $40)
4- put it on eBay and get yourself a (for you) more usable transformer.
5- use a half-bridge rectifier (1 diode on each secondary, middle=gnd), this should get the voltage down. (but caps will build up to full voltage in time/low load) (don't)
6- try with reasonable big (10A, 600V) diode in primary (tranny wont like this) (don't)

Resistors (L, C or R) won't work because load changes.

[V-bro]

If it is a toroid I would unwrap it and unwind it a little to have it output max 42Vac and wrap it up again. You can make a "shuttle" for this job to unwrap the wrapping material (usually non-adhesive heat resistant tape, which I would certainly keep to wrap it up again!) Then still you need an amp like AMP15/7/Truepath....

To see how a shuttle works look at my "toroid winding tool" thread...

[V-bro]

No, D's in line are not very elegant and fast Schottky diodes which come in high power drop the voltage just minimally...

Unwrapping is pretty easy, but takes almost an hour. I've done it many times and for a large transformer which is expensive it can be well worth it. And believe me the manufacturer has wound the two windings in one draw as well, so they are side by side which makes unwinding simultaneously a piece of cake!

I would advise an AMP7 on that transformer. And even for that amp I would unwind it a bit because 45Vac is just too high...

[V-bro]

That is good to know!! Very usefull piece of info! I think most just don't know.

Then Unwinding+AMP7 becomes option numero uno, I'd say!

V, this might be useful for a new thread "Unwinding and winding transformers", in the Misc. forum? together with shuttle thingy and other related stuff.

Yes, I was also thinking of a video for this one too!

You could even wrap it all down to the level of an AMP5/AMP10.. The windings are not that numerous and you don't risk a shock because the mains windings are wrapped 'inside'.... Once the windings are not around the core any more they don't count, so you can measure every now and then on the ends "how far" you are....

For this reason I love toroidal transformer, also because you can wind extra windings quite easy....

This now my standard Truepath/AMP7 configuration. Even with the use of PSU1-SS, just wind the aux. voltage windings (5V/VN10) extra on the large transformer(s) and use NTC resistors, then bypass with either an AC relay or the delayed output of PSU1-SS. The latter having the advantage of always having softstarting, even with a quick power down and up... (the problem Krilli experienced here:http://www.41hz.com/forums/showthrea...10-of-the-time)

[Scratchy]

Rather than unwinding, you could try winding new secondaries over top of the existing to get dual 22VAC outputs.
As a test, take some small hookup wire and wind 10 turns, and then power up the primary (make sure your 45VAC sceondaries are isolated/insulated!).
Then measure the voltage on the 10 turns. From there you can calculate how many turns you need for 22V & how long the wire must be when unwrapping the 10 turns.

[V-bro]

For each turn you get roughly 0.33 Vac is my experience... That is for a 230Vac primary toroidal transformer...

[Scratchy]

For each turn you get roughly 0.33 Vac is my experience... That is for a 230Vac primary toroidal transformer...

Of course it also depends on how many turns are on the primary.

[V-bro]

Sure, this was with Amplimo transformers... Haven't tried other brands, neither all their sizes, but until now it's never been far off...