Is it wise to connect the ground lines of the 5v and 9v branches, to create a common ground?
If not then please also answer the following question:
I’m going to wire up 4 Core boards and 4 SID boards. On the SID both 2 voltages are used. Should I use the ground from the 9v branch, or the 5v branch?
And another one:
The MIDI and audio jacks, where should I ground them to? Is star-topology grounding an issue here?
OK, not really an answer I completely understand, but I gave it a shot and connected the branches just behind the 100nF caps, works fine!
The only problem now is that since I rebuilt the PSU board, the 9v I measured erlier now measures 8v. Right before the 7809 I still measure 10,5v, so this has not changed since the rebuild. Has the 7809 been too hot perhaps, bacause of soldering and desoldering, or do I need to seek the cause in a different direction?
Cheers, Alex.
[edit]
I’m going to post this question in the troubleshooting forum, as it isn’t a design question.
““Common Ground” is something that any decent Midibox should have. There might be some on the eBay and some on the “Request to sell”.. Please - don’t trust on these - If not approved by Thorsten -none of these have the “Common Ground” the Midibox has!”
““Common Ground” is something that any decent Midibox should have. There might be some on the eBay and some on the “Request to sell”.. Please - don’t trust on these - If not approved by Thorsten -none of these have the “Common Ground” the Midibox has!”
Do connect the grounds.
M
Damn, I just bought myself a bucket of common ground and put it in the box… Couldn’t you have warned me earlier???
Is this taking into account the voltage drop across the rectifier?
It’s ground, it doesn’t matter ;)
And by the way, the rectifier ups the voltage by about 41% (minus about 0,7v), it doesn’t drop it at all.
(When I started understanding the concept of ground a few days ago, it felt to me like suddenly the light was turned on, now I can’t imagine not undertanding it anymore )
And the 41% isn’t really the rectifier upping the voltage but that’s due to the 12V at the input of the rectifier being 12V AC. That means that the average voltage is 12V but the peak voltage can get much higher. For a sine wave you can just multiply the average with the square root of 2 to get the peak voltage.
The capacitors after the rectifiers will store the voltage you put in them. They will lift the voltage to the peak voltage they receive. That’s where the 41% comes from.
But I see everyone has fallen asleep so I’ll stop the useless technical explanations :
The regulators need about 2 volts more than their output to regulate correctly. So If you put in a 7809 you need a capacitor big enough to store enough electrons to keep the input of the regulator above 11V.
The regulators need about 2 volts more than their output to regulate correctly. So If you put in a 7809 you need a capacitor big enough to store enough electrons to keep the input of the regulator above 11V.
So for the big capacitors to be able to do so, you’ll need to supply them with at least 11Vdc. THat means, taking the 1,41 rule into account, that your Vac just before the rectifiers has to be at least 7,8 - plus the 0,7V the rectifier consumes, so 8,5Vac at least. 9,5 would be more comfortable, for example when your mains power is below average (which caused “unexplainable” readings on my box earlier )
Just a post to check if I understand correctly now, correct me if I’m wrong about anything
So for the big capacitors to be able to do so, you’ll need to supply them with at least 11Vdc. THat means, taking the 1,41 rule into account, that your Vac just before the rectifiers has to be at least 7,8 - plus the 0,7V the rectifier consumes, so 8,5Vac at least. 9,5 would be more comfortable, for example when your mains power is below average (which caused “unexplainable” readings on my box earlier )
Correct.
Another thing you should take into account is that your capacitors get 100 peaks (120 in the US) every second but the voltage in between peaks drops to 0V. The trick is making sure you dont deplete them too much in between peaks. When your supply just supplies 100mA you can use small capacitors because you’re not discharging them very fast. But when you’re building a bigger supply you need bigger capacitors so they can hold more charge.
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