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WIGGLING 'LITE' IN GUEST MODE

CGS Power Supply noob
MUFF WIGGLER Forum Index -> Music Tech DIY Goto page 1, 2  Next [all]
Author CGS Power Supply noob
falafelbiels
Dear People,

I had a CGS66 Power Supply in the mail and I am building it tonight. Now I've run out of the parts I had around and am about to order some, among which are some 1n4004 diodes. Now my regular guy doesn't seem to have any around, but he does have the 1n4007. I wonder if could just substitute. I read the datasheet and it seems the forward voltage drop of the 1n4007 is higher and I think that would influence the workings, but would it?
Adam-V
They should be OK to use. I think the only difference will be in their maximum ratings (the 1N4008 has a higher reverse voltage rating than the 1N4004).

Cheers,
Adam-V
falafelbiels
Allright then, thanks a lot Adam.
falafelbiels
I changed the title of this thread from "1n4004/7 CGS Power Supply" to what it is right now because I am a bit unsure how to go about this next. The whole 230V AC thing gets me nervous I guess. Oh well...

SO allright, this thing wants a transformer and I'm considering building in this big plastic block type transformer, you know the type.



Thing is, I can't easily find a center tapped one. I do think I remember seeing an image on the net somewhere of ground being taken from a non-center tapped transformer like the one above, with the aid of some (high value?) resistors. Am I getting things mixed up here?
Luka
I used a toroid for mine
andrewF
You can use a non-centre tapped transformer but the resulting DC will not be as clean as that from a CT (centre-tapped).
have a look at wiki - http://en.wikipedia.org/wiki/Rectifier
for the difference between half wave and full wave rectification.
It is okay tho, it means you can just buy an AC wallwart and do not have to deal with mains voltages. You have to do a small mod of the rectifier diodes on the PCB, check the MFOS PSU for a how-to.

One way to get a centre-tapped transformer is to buy a multi-tapped, one with a range of outputs. Ideally for a +/-12V PSU, get one with 0,15,30 outputs (and whatever else it has).
The '15' becomes your centre-tap (0V) and the '0' and '30' are your 15VAC.
For a +/-15V supply, ideally you want a transformer with 0,18,36 taps, with 18 becoming your 0V centre-tap.
falafelbiels
OK I am now thinking about simply building that MFOS one on stripboard, but I need +/- 15 volts. I am going to build a new rack that houses some 15V modules I would like to build, such as the JH Living VCOs.

I suppose using 7815 and 7915 with this power supply should do, right?

The CGS board will just have to wait until I feel more confident, or bump in to an appropriate center tapped transformer. Who knows, it may even be a toroid. They sure look impressive, all in the dark in a cabinet where no one can see them...
andrewF
yep that'll work, certainly the best way to do it if you are not used to dealing with mains voltages. Keeping safe is #1
falafelbiels
andrewF wrote:
Keeping safe is #1


So I heard... Over and over until it really gave me the creeps!
falafelbiels
But still I just don't get it! Won't this "ground" that that MFOS circuit produces be something very different from the ground in other cabinets? In other words, won't there be any trouble?

Sorry guys, just attempting to learn...
Luka
ground is just a voltage reference level
they may differ between isolated systems but when you connect them they balance
falafelbiels
Oh alright then...

I believe I was mixing up AC and DC (in my head)
otherunicorn
Simple answer for using that transformer - one AC output goes to the "0V" connection of the PCB. The other AC output goes to one of the "18VAC" connections. The transformer would need to be 18VAC out.

From the page on building the CGS66:
Can this PCB be used with a conventional AC-wall-wart (two AC wires out)?
A center tapped transformer is better, though it is possible to use a wall-wart between CT (the 0V connection on the PCB) and one 18V AC connection. The required pads are marked with large white circles. The result will be half wave rectification. If you use larger caps (3300uf) and limit the loading, you will be okay. My test bench power supply had been running like this for years. Watch the output with a CRO if you can, to find the limit. If you really wanted to, two wall-warts could be used, each between one of the 18V connections, and commoned at the CT connection. You'd have to make sure the phases were right though. With the one wire from each of the wall-warts connected together, measuring across the other two wires should give you something like 36 volts. If it gives you 0 volts, you will need to swap the wires from one of the wall-warts.
falafelbiels
d'oh! It actually says it.

What can I say? I'm just no good at reading build docs all the way down.

Thanks for pointing me there...
otherunicorn
falafelbiels wrote:
d'oh! It actually says it.

What can I say? I'm just no good at reading build docs all the way down.

Thanks for pointing me there...


Hits you over head with rolled up web-page.
falafelbiels
this one is a bit much eh?

otherunicorn
it is a bit much. You'd be putting 30 volts into your regulators, and that will generate a lot of heat.
dude
someday i hope to have these problems and questions.
falafelbiels
otherunicorn wrote:
it is a bit much. You'd be putting 30 volts into your regulators, and that will generate a lot of heat.


Too much though?
I'd like to hook up 2 CGS66 boards in parallel (one that I will build on srtipboard since I have plenty parts anyway) to it. Make this a 6U cabinet while I'm at it.


Someday I hope I will finish this thing; My Living VCOs are populated and awaiting power (and likely debugging) as of tonight w00t
otherunicorn
The regulator chips will handle it IF you have sufficient heatsinking and don't draw too much through them.
Suggestions: add a few power diodes in series with each coil. The diodes will need to be connected so that current can flow both ways:

-->|-->|-->|-->|--
--|<--|<--|<--|<--

Have two strings of diodes like this, connected together at the ends. The idea is to allow the current to pass in both directions, and for the diodes to drop voltage across each. 8 diodes per low voltage coil like this will drop the voltage the regulator sees by 3 or so volts, bringing it in line with an 18V transformer.

Consider adding a fan to the heatsinks. Run the fan on a lower voltage than it is meant use to slow it down and make it quieter.
falafelbiels
Fan? F* that! I'll not turn my synth into an Xbox! thanks for the tip though...

I just had this thing around and thought oh why not. Well that's why.
I just found the correct part at Conrad and ordered 2.
otherunicorn
Using the correct part is always the best option.
falafelbiels
huhuh, you have plenty of patience with your customers Ken thumbs up

nice quote there...
falafelbiels


Can't say it's definitely not a bodge job, but it sure works! -15, 0 and +15 volts, all at the same time...
otherunicorn
I trust you will cover the mains wiring so nothing can fall against it or touch the bare fuse connections.
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