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#### mart_1986

##### New Member
im going to make this circuit

a few questions

1. i want to know instead of using the 7812 can i use 78s12cv?

2 instead of using the 100n can i use a 0.1uf capacitor

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Yes, you can use 78S12CV
Hmm,
0.1uF=100nF

Yes, you can use 78S12CV
Hmm,
0.1uF=100nF

would you just use the 100n then i dont have any of those at the moment

i found this on a site 0.1uF = 100nF = 100000pF (MMFD

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yes 100000pf is the same as 100n according to my chart.

and is the same as 0.1uF

The regualtors will get extremely hot if the transformer is 18V-0-18V and the output voltages are 12V.
Use a 12V-0-12V transformer instead for less heat in the regulators.

The 2200uf main filter capacitors should be 4700uf each.

yes its the same.

my transformer is 12volt 50va it has 2x 12volt outputs

You need at least 2 volts more on your transformers for 12v regulators (pretty sure this is correct, read data sheet)

You need at least 2 volts more on your transformers for 12v regulators (pretty sure this is correct, read data sheet)
No.
A 12V transformer winding has a peak output of (root of 2) x 12V= 17V. One of the diodes has a drop of 1V max so the main filter capacitor charges to 16V if it is big. The 4V extra for a 12V regulator is fine for a regulator that works with only 2V extra.

You need a 0.1uF or 0.33uF capacitor on the output for good transient response but the regulator takes care of low frequency and DC regulation.

Here is my transformer calculation:

nominal output voltage=12V
idle output=1.3 to 1.4 times the nominal output voltage (15.6/16.8V)
rectification * sqr2 (22.06/23.76V)

minus 1.4V (worst case) for double diode voltage drop using a bridge rectifier (20.66/22.36V)

Transformers deliver their nominal output voltage at the rated current they are designed for. Currents lower than nominal always result in a higher than rated voltage output.

The filter caps should be rated 35/40V

Low quality audio equipment uses cheap transformers and low capacitance filter caps, just rated for low consumption. The quality becomes clearly visible when the VU-meter lamps start blinking at low frequency peaks (basses).

Boncuk

my bad. I always thought that 2volts higher to be safe and sure of the required regulated output voltage.

my bad. I always thought that 2volts higher to be safe and sure of the required regulated output voltage.
Yes.
Ordinary regulators need an input DC voltage that is at least 2V higher than their output voltage.
But a 12V transformer has a peak voltage of 17V and it makes an unregulated DC for the input of the regulator of 15V if there are four rectifier diodes or 16V if there are two rectifier diodes.

As Boncuk says,
when a transformer has a light load then its voltage is much higher.

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