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how to get the propper transformer??

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antoniodilen

New Member
hey hi again....

My problem is i do not know how to calculate the proper transformer for my circuits...
if i'm not making my self clear here's the examples-

1.I'm planning to design a subwoofer with the IC lm4702 with pwr transister's
max out put 100W
Q-What must be my transformer secondary current??

2.i'm planning to design an amp with an STK Ex-(stk4050) Which will do 200w max
Q-my transformer is going to be 30V how can i calculate the secondary amperage needed ??

Thank you to all the friends @ electro-tech-online
you guy's have been very helpful in my previous treads too
Thanks again
Dilen
:)
 
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Nigel Goodwin

Super Moderator
Most Helpful Member
Suggested supply is +/-66V for that chip, with +/-80V required for 200W - why are you trying to use 30V?.

But I would suggest at least a 2A transformer (so a 320W transformer for +/-80V).
 

Nigel Goodwin

Super Moderator
Most Helpful Member
So how did you suggest a 320W transformer??
is there a way of calculating that??
Crudely! :D

Amplifier is 200W with a +/-80V supply - so drawing 1A the amp would using 160W, and probably outputting 100W to the speaker. Drawing 2A it would be taking 320W, and outputting 200W to the speaker.

Rough, but probably near enough.
 

antoniodilen

New Member
thanks...yeah its a rough calculation,
now i know how to get the Transformer for the STK but i'm still puzzled in how to find the proper transformer for any other amp for an egsample the one below

so if i'm going to use +/-60V for the lm4702 hoping it will do 100W with the proper transistor's
How must i calculate???

sorry...i'm not that good @ theory yet....
 
Last edited:

antoniodilen

New Member
Is this a correct way to guess the amperage??
since recommended voltage is 66V
And the speaker impedance is 8ohm
The current at the secondary should be 8.25A???

Is this correct??
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Basically just spec your transformer for roughly 1.5 times the output of the amplifier, so for 100W output, use a 150W transformer. For a high level use PA amplifier, even bigger would do no harm, but for a lighter use home amplifier you could get away with a smaller one (and manufacturers often do).

Bear in mind, the previous example is +/-66V, so a total of 132V - NOT 66V.
 

antoniodilen

New Member
Basically just spec your transformer for roughly 1.5 times the output of the amplifier, so for 100W output, use a 150W transformer. For a high level use PA amplifier, even bigger would do no harm, but for a lighter use home amplifier you could get away with a smaller one (and manufacturers often do).

Bear in mind, the previous example is +/-66V, so a total of 132V - NOT 66V.
thanks nigel...finaly got it...good that You told it was 132V...i was thinking 33V-0-33V....
Thanks again
 
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