Green mic pre Buzz and phantom power hum

[Rob Flinn]

Here quadrupler is used to rise/convert  15VAC to about 60VDC.

Right, sorry I didn't study the circuit too much.

 

[amaurythewarrior]

So that's still things I need to figure out. I mean I kinda understand the +48v power rail, for the most part, how diode multiply the voltage, but why do I measure 35vac (which should be 30, right, center tapped?)
And then  something lower after the diodes. If I start with something higher... And end with something lower...

 

[Khron]

Because the output is a lower-than-the-input amount of AC, superimposed on whatever-amount-of-DC you have there?

The 35 vs. 30 may well be a combination of slightly-higher-than-nominal mains voltage and/or whatever regulation factor your transformer has (the voltage in the specs is measured at full rated load current; at lower loads, the voltage will be slightly higher).

https://sound-au.com/articles.htm#psud

 

[peterc]

Here is a page that explains the voltage doubler quite well
https://en.wikipedia.org/wiki/Voltage_doubler

Quite often, transformers will read higher than their specified voltage, and will reduce as the load is increased. So at the maximum load they will deliver the specified voltage, if the load is less the voltage might go up.

Also depends on your line voltage from the wall as this can vary depending in consumer laod.

 

[amaurythewarrior]

I'm making a note of all that, and I'll probably order and try a few things when I buy the parts for my next project (should be an ez1290 - which is well documented).
I'll also read more about PSU as I understand they should always be more or less similar, and might start by just the JLM PSU kit, but that will be another thread).

I won't touch the green too much until I get stuff like proper solder lugs, shielded cable (even though it's not really necessary, I'll eventually have to get some as the ez1290 asks for some). And then maybe I'll take a closer look at getting +48, after all there's no many parts on this part of the circuit, and other voltages are fine... Well all that is done, I guess I'll addess what noise may be left.

Thanks again to everyone, expect to see me around here when I attempt the 1290...

 

[seymourgler]

You should be using a TL783 for the 48v rail (i.e the reg in the top left corner in Whoops pic), The LM317 is a bad choice, if it gets shorted it will blow. The TL783 can handle a lot more voltage across it.

Great tip. Do you replace just that one LM317 with TL783, or all of the LM317s?

 

[Rob Flinn]

Great tip. Do you replace just that one LM317 with TL783, or all of the LM317s?

Just the one.

 

[seymourgler]

Just the one.

Gotcha, thanks again for clarifying.