Hawkeye, that’s how I measured it previously (I can do other tests if you have another ideas). I didn’t connect extra capacitors except that was on board of LM2596 I’ve bought and Core8 board. I connected LM2596 from SID module’s 7809’s output to Core module 7805’s output (bypassing 7805 and therefore 2200uF cap, but 10uF and 100nF were working). SID module was fed with 9.2V AC.
LM2596 was set to output 5v.
This was noisy.
Then 7805 was inserted between LM2596 and Core, I mean I connected LM2596’s output to 7805 input.
LM2596 was set to output ~6.3v.
This was a little better, but also noisy.
Then I thew away LM2596 and connected 7809’s output to 7805’s input directly.
It was MUCH, MUCH better.
I can upload mp3’s if you wish.
BTW, this way of cascading 78xx is a little more noisy then using separate transformer’s outputs. I can’t guess why.
Subtract ~ 2V for the rectifier diodes ~ ca 10.6V input to the 7809 - which is a bit close for a non LDO (low-drop) 9V linear regulator. You might go shopping for a LDO 9V vreg.
Under load, the 7809 may drop below its 9V target, as the input voltage will be lower…
edit: you have 9.5V ac, which might be just enough!
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.
OK, I’ll try it. Hovever shouldn’t it sound good even without 7805?
In theory yes, but it depends alot on the components in front of the circuit. Did you provide power with a transformer?
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.
a 7809 can never pull more load then 1A, so highly unlikely. It’s probably more todo with the amount of AC coming out of the wall socket. If the transformer outputs 9VAC at 230V and you only have 225V or less coming out of the wall…
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?
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
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.
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.
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).
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.
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.
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