[m1abrams]

I have an image of my voltage readings.

My output reading across V+/V- is 23.56

My Vin+ is 39.5 !

Thank you for the help.

Sigma11 Voltage Readings on Flickr - Photo Sharing!

 

[digger945]

The schematic you linked to in your other thread has schematics but no model number or specified output voltage.
Is that your question, the difference between the input and output?

Your not far off from the 24V operating points

 

[m1abrams]

Quote:

Originally Posted by digger945 /img/forum/go_quote.gif The schematic you linked to in your other thread has schematics but no model number or specified output voltage. Is that your question, the difference between the input and output?

Not sure the ?. However if you need the model # of the tranny is Standard 017012201.
2x115VAC input I have wired in parallel for 115VAC input.
2x12VAC output I have wired in series for 24VAC.

 

[digger945]

Is everything on the S11 as specified in the BOM?

It states in the S11 troubleshooting section at amb.org "Your actual measured voltages will vary somewhat from the shown values (due to parts tolerances). "

I would think it looks pretty good actually, and gives you the voltage out that you want.

 

[grenert]

Quote:

Originally Posted by digger945 /img/forum/go_quote.gif I would think it looks pretty good actually, and gives you the voltage out that you want.

Exactly. What is the problem? Are you concerned that you get a reading of 23.5V instead of 24V? Dude, that is a 2% difference! Easily within the tolerances of parts, meter accuracy, etc. Use it and enjoy!

 

[digger945]

The reason why all of your measurements are not spot on is because your input is not spot on so the other values are compensating to make the output what it should be.
It's doing what it's supposed to do, make the desired output voltage.

 

[m1abrams]

Quote:

Originally Posted by digger945 /img/forum/go_quote.gif The reason why all of your measurements are not spot on is because your input is not spot on so the other values are compensating to make the output what it should be. It's doing what it's supposed to do, make the desired output voltage.

Ok do you have any clues as to why my input is so far off?

 

[digger945]

The transformer secondary values are usually given with a certain load or full load, and you have little to none now if it's not connected to anything but the S11. As you load the plitron the values will go down some. I am sure Ti had this in mind when he designed this PS.

FWIW my S22's have 37V from some 30V transformers(entering the S22), unloaded. It will vary with the transformer and manufacurer or specs.

 

[m1abrams]

Just to be clear that 39.5 Vin+ is AFTER the bridge rectifier. The VAC input is ~30.4VAC. I understand that the voltage on the output of the transformer would be high when unloaded, I just did not know if a 0.5V difference on the output of the sigma11 is to be expected.

I need to get hold of a power resistor so I can test it loaded.

 

[digger945]

The AC from the trasformer is RMS. It is only an average if you will. The rectified DC will be approx. 1.414 times the AC, theoretically(there are other variables to consider, one of them would be rectifier diode selection, another would be the circuit immediately after the diodes).

From the Sigma 11 website: "The output voltage is determined by D5's zener voltage and the gain setting of the error amplifier (and can be varied by changing the value of R10)."
The exact value of the components will determine the exact output voltage. You could buy lots of extra parts and measure them to arrive at EXACTLY 24v but it would make little difference for an amplifier. The output here is not determined by the input, but the parts values used in your S11.


Another quote from the S11 website: " WARNING: Due to σ11's lack of current limiting protection and very high output current capability, short circuiting its outputs could result in damage even if there is a fuse on the AC mains."

Here is a link to a free power supply calculator to play with.

 

[m1abrams]

Ok thanks for the help everyone. I expected some variance due to tolerance in the components just thought it would be closer to 1% and not 2%.

 

[digger945]

You could play with R10 and probably get it to output exactly 24V, but would it make a difference in your application?
What exactly is it your going to be using this for(sorry if I overlooked it before)?

 

[Ferrari]

Quote:

Originally Posted by m1abrams /img/forum/go_quote.gif Just to be clear that 39.5 Vin+ is AFTER the bridge rectifier. The VAC input is ~30.4VAC. I understand that the voltage on the output of the transformer would be high when unloaded, I just did not know if a 0.5V difference on the output of the sigma11 is to be expected. I need to get hold of a power resistor so I can test it loaded.

Don’t worry too much about the ~0.5V (440mV) difference on the output of your σ11 PS.
With or without load, the σ11 PS will output the same DC voltage (~ target voltage).

The question if the variances of the σ11 PS output voltage is to be expected? Yes, parts tolerance can definitely play a role.
For example, the 12V zener diode (BZX55C12) can have a value of Vz = (11.4V… 12.7V).
The Vz of the zener diode you have on your PS is probably on the lower end.
If you have a handful of BZX55C12 on hand, you can try to swap it untill you reach the 24V you want.

BTW, already asked by digger945, but I would like to know it too…
What exactly is the application you are going to use this PS for. Does it really need to be within 1% accurate???

 

[amb]

I don't see a problem at all. The output voltage is a trifle lower than 24.0V because your D5 zener diode is a little lower than spec'ed at 11.78V, but well within its specified tolerances.

24V * (11.78V / 12V) = 23.56V

But so what. Most audio circuits don't need super-accurate supply voltages.

 

[m1abrams]

Great thanks for the responses. I just wanted to make sure my build was operating as expected. Sounds like I am good to go.

This sigma11 will eventually power a M3. So no the slightly lower voltage output is not an issue for that application.