[w62820616]

Hello everyone,
 
                     I found a transformer on digikey which is 10VA, 2X110V primary 2X12V secondary. The schematic is attached below:
 
                My question is, can I simply combine the two terminals of the output to make a ground?
                   Like this:
 
 
 
Lee

 

[Avro_Arrow]

The dots on the winding indicate the phase.
To make a center tap, connect it as you
have shown.
If you wanted to parallel the windings (as you will want to
do for the 110 volt windings, connect the dot to dot
and no dot to no dot.

 

[w62820616]

Quote:

The dots on the winding indicate the phase.
To make a center tap, connect it as you
have shown.
If you wanted to parallel the windings (as you will want to
do for the 110 volt windings, connect the dot to dot
and no dot to no dot.

Thank you ! So if I want to power my transformer with 110v AC, is what it looks like?

 

 

[Avro_Arrow]

Yes, that is correct for 110 AC.

 

[w62820616]

Quote:

Yes, that is correct for 110 AC.

Thanks ! Do you think 2X 12 VAC @ 584mA (7w) should be enough for normal headphone amplifiers application?

 

[Avro_Arrow]

Yes, that should be good for a headphone amp.
Something like a PPA but without the ground channel.
 
Did you have an amp in mind?

 

[w62820616]

Quote:

Yes, that should be good for a headphone amp.
Something like a PPA but without the ground channel.
 
Did you have an amp in mind?

Sorry for the late response, I was working on the schematic. Here is the main structure of the amplifier. It is still an OP+BUF arti. Please give me some suggestions.

Obviously it will not run for very long on a battery so I need to make a separate linear voltage regulator (lm317 and 337?)
 

 

[Avro_Arrow]

Here is a diamond buffer that replaces R5/R6 with LED CCS for better perfomance.
It also has Jung multi loop feedback and class A bias for the op amp.
You would need to re-jig the values for +-12 volts rather than the +-6 volts in the
schematic. I would also use 2N5087/2N5088 and BD139/BD140 or maybe
MJE172/MJE182.
 
In your schematic, because you have a low impedance ground, I would make
your bypass caps go from rail to ground rather than rail to rail.
In Sijosae's design, you don't need the rail splitter part.
 
Good start
Cheers!
 

 

[jcx]

unregulated 12 VAC xfmr supply could lunch some op amps - xfmrs are wound for excess V to exactly hit their rated power under load so the no load rectified V could easily creep up over 18 Vdc
 
 
Walt Jung's 1M "inner" feedback resistor around the op amp is pointless - Jung was initially playing with Otala's "flat loop gain" idea - Walt later came to the conclusion that "flat loop gain" didn't fix the problems Otala was addressing
 
the 10k resistor in series with the -in is also misguided the +,- input Z are much better matched with the 10k pot's 2.5k max R at midpoint without it

 

[w62820616]

Quote:

Here is a diamond buffer that replaces R5/R6 with LED CCS for better perfomance.
It also has Jung multi loop feedback and class A bias for the op amp.
You would need to re-jig the values for +-12 volts rather than the +-6 volts in the
schematic. I would also use 2N5087/2N5088 and BD139/BD140 or maybe
MJE172/MJE182.
 
In your schematic, because you have a low impedance ground, I would make
your bypass caps go from rail to ground rather than rail to rail.
In Sijosae's design, you don't need the rail splitter part.
 
Good start
Cheers!
 

Do you know what kind of LED I need to use? Do I need to pair it?
 

 

[Avro_Arrow]

You will need 4 matched LEDs.
Exactly what there are is not as important as they
should all have the same voltage drop.
The CCS will be designed around them.

 

[w62820616]

Quote:

You will need 4 matched LEDs.
Exactly what there are is not as important as they
should all have the same voltage drop.
The CCS will be designed around them.

Hmm it looks like that the voltage drop for same model LEDs are pretty much the same. I found some old LEDs and they all have a voltage drop around 1,83X V

 

[Avro_Arrow]

They would do just fine.
Just find four of them the same.
 
Measure the voltage drop with about 10 mA going through them.

 

[w62820616]

Quote:

They would do just fine.
Just find four of them the same.
 
Measure the voltage drop with about 10 mA going through them.

So here is the specification for my transformer :
 
Output: 2 x12V292mA
NO load:  2 x16.2V
Resistance2 x7.7Ω
Weight Cu = 36 g
 
 
I want to use LDO linear voltage regulators like LT3015 and LT 1963.
Do you think I need a 15V output transformer and lower the voltage to 12V? I know the voltage regulator need some voltage like 1.2V so I need a 13.2V transformer.
 

 

[Avro_Arrow]

Some LDO have a dropout as low as 0.5 volts...
You could just lower your rails to +-9 volts
and use 317/337.
9 volts rails will still be plenty.