Switching PSUs noise elimination and protection

[alchemist]

Hello,

 

I am following that thread, and I am quite lost. Wouldn't be a good idea to provide sample schemas for 5v/9v/12v outputs, DC or transformer input(s), and the best options regarding the number of core and SID modules?

[Shuriken]

Unfortunately it is not that easy. It all depends on what regulator you use and so on. For the 78xx regulator the following table applies:
 
 

Output-voltage	Outputcurrent	Transformervoltage
V	100 mA	1 A	2 A	V
2	78L02	-	-	5
3,3	78L33	7833	-	9
5	78L05	7805	78S05	9
6	78L06	7806	-	9
7,5	-	-	78S75	9
9	78L09	7809	78S09	12
10	78L10	-	78S10	12
12	78L12	7812	78S12	12
15	78L15	7815	78S15	15
18	78L18	7818	78S18	18
24	-	7824	78S24	21 of 24

 

 
 
The parts need to be adapted to current and voltage. With a low voltage (below 5 V) C1 can be decreased to 1000 µF. With voltages above 15 V en 1 A, C1 needs to be 4700 µF. With currents above 1 A moeten the diodes need to be replaced by 1N5401's.
C4 needs to be applied if the wiring between powersupply and appliance exceeds ±15cm
 
Partlist:

• C1 = 2200 µF/35 V (see text for remark)
• C2, C3 = 100 nF
• C4 = 10 µF/35 V (see text for remark)
• Br1 = 4x 1N4002 of 1N5401 (see text for remark)
• Vr1 = 78xx
• T1 = trafo

Edited July 29, 2014 by Shuriken

[Hawkeye]

Great post, Shuriken!

 

That clears up all the confusion of the possible combinations! :-)

 

skunks, regarding your question

 

Hawkeye, I just looked at your calculations again and wondered, why 9V AC input for MB-6582 in PSU Option A is considered OK even with plain 7809 (non-LDO) ?

I make an assumption that it worked in your case because your transformed was good enough (25VA) to sustain 9V AC under load.

 

You are right, skunks, in the MB6582 Power Option A, the 9V AC are rectified and then directly sent into the 7809 - this differs from TKs "optimized circuit" with many MBSID modules.

 

Also, you and Shuriken are right - under certain circumstances (e.g. the AC wall voltage being low), the 7809 non-LDO vreg might deliver a bit lower voltage than desired, when fed by 9V AC + recitifer diodes. But, I think, in this special case, this is ok for the analog part of the SIDs (only opamps and stuff), and a slightly low voltage (e.g. 8.5V) would still sound good.

 

Also, the dropout voltage of a vreg depends on the amps being drawn - and probably the 9V rail is not very demanding (only a few opamps), even in a fully loaded MB6582 with eight 9V SIDs.

 

But Shuriken´s recommendation to normally feed a 7809 with 12VAC + rectifier diodes is solid - or to use a more modern LDO vreg.

 

Many greets,

Peter

Edited July 29, 2014 by Hawkeye

[alchemist]

Thank you, Shuriken !

 

Now I have to chose the best output, then the switchers for the 2 other voltages.

[skunks]

Hawkeye, thank you for giving your complete view on "why 9VAC worked" from different perspectives.

It's more clear now for me.

 

Shuriken,

 Did you provide power with a transformer?

 

I tried both, transformer and switching PSU (from dead printer).

As you advised I set LM2596 output voltage to 8v. And it helped. Thanks :-) Now LM2596 presence is not audible. And it's input doesn't have to be regulated, at least why care about it's input if you have to regulate it's output anyway.

 

Shuriken, you assembled so much useful info in one post!

Is transformer voltage in that table AC?

 

C4 needs to be applied if the wiring between powersupply and appliance exceeds ±15cm

 

Where it's better to apply it? In powersupply box or after that long wires?

 

 

Now I have to chose the best output, then the switchers for the 2 other voltages.

 

According to my tests you may even choose cheap LM switcher but have to use 78xx afterwards in order to cut noise.

[skunks]

Hello,

 

I am following that thread, and I am quite lost. Wouldn't be a good idea to provide sample schemas for 5v/9v/12v outputs, DC or transformer input(s), and the best options regarding the number of core and SID modules?

 

I just remembered one thing to add to Shuriken's post. Especially if you are dealing with multiple separate MB CORE and SID modules (not MB-6582 where there are easy pre-built PSU Options).

1. Bypass bridge rectifiers if you are using DC as input (more about it in this ) in order to avoid shifted grounds

2. Avoid ground loops (grounds must not be connected more then once)

I found a little improvement on my noise level when removed ground connection coming in ribbon cable between Core and SID module and put a separate thick wire.

[Shuriken]

I cannot take credit for the table. It's an article on a dutch website (circuitsonline.net) The pcb is also there.

 

Yes the transformer voltage is in AC (haven't yet seen DC transformer :wink:)

 

C4 needs to be applied in powersupply box.

 

 

As for the LM2596, you could experiment with faster diodes (MUR120) to rectify. And a big capacitor in front of it.

[skunks]

There were actually 2 big capacitors (2200uF and 1000uF) in front of it.

Thank you for faster diodes idea.

[jrp]

the 7809 non-LDO vreg might deliver a bit lower voltage than desired, when fed by 9V AC + recitifer diodes. But, I think, in this special case, this is ok for the analog part of the SIDs (only opamps and stuff), and a slightly low voltage (e.g. 8.5V) would still sound good.

 i cannot recomend this. Linear regulators will be very unhappy in such a case. It is not that the regeulator can adapt in a mannor: "Ok, i need to drop 3V, so i just adjust myself to 8.5V."

The Voltage will drop, yes, and the regulator will be fighting and sweating, not being able to do what it´s supposed to do: Stabilize voltage and get rid of any ripple.

It will lead to hum and possible failure.

For non demanding circuits (not this one!) it would then be better to go without a regulator altogether. Don´t try this with your sid though.

 

Also, to be safe it is common practice to account for 10% mains variations.

 

If you measure voltage and the regulator is a little of, just check the voltage at it´s input. These Parts have tolerances, so you might be getting 8.7V from 12v. That would be fine.

Edited August 8, 2014 by jrp