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Toroidal transformer secondaries question..
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mubase



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PostPosted: Thu Oct 27, 2011 6:58 am    Post subject:  Toroidal transformer secondaries question.. Reply with quote  Mark this post and the followings unread

Hi again. Been using and listening to E-M a lot lately Smile
I have a question about a power supply that was included in an interface box I bought on ebay to use as a housing for an analog baby 10 sequencer/sound generator project I am building...

http://electro-music.com/forum/topic-50071.html

The transformer inside is toroidal ( see picture )
The secondary wires output as follows: Black and red: 7VAC
Pink + Purple: 5VAC
Pink + White 7.6 VAC
and Purple + white: 13 VAC
now, could anybody tell me if I could make a +/- 12V supply out of this with an extra 5VDC output as well???
I've been looking at PSU circuits ( Ken Stone CGS/Ray Wilson etc) .

Is this possible, any help much appreciated,
Thanks again.
Steve.


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Transformer showing secondary wires...
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vladosh



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PostPosted: Thu Oct 27, 2011 10:57 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi MuBase .. i made this PSU with torus http://www.nutsvolts.com/media-files/11/January%201998%20Thomas%20Henry%20-%20Power%20Supplies%20for%20Electronic%20Music.pdf just changed 15v regulators with 12v ones and it's working great
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mubase



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PostPosted: Thu Oct 27, 2011 2:09 pm    Post subject: Secondary. Reply with quote  Mark this post and the followings unread

Thanks for the Doc. its a nice circuit & from T.Henry. I have his 8038 linear vco breadboarded and designed a stripboard version..... very nice...

So can I use this transformer to get +/- 12 V using the pink purple and white wire outputs using the right regulators??????

I've set up the rectifier part of the Thomas Henry PSU circuit using 4002's and the output gives a steady 13.6 V AC. Is this enough for +/-12V??
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Uncle Krunkus
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PostPosted: Fri Oct 28, 2011 12:46 am    Post subject: Reply with quote  Mark this post and the followings unread

No,
Unless you can find a pair of wires which have 24VAC across them, and one which is in the middle, you won't be able to get +/-12DC out of this transformer.

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mubase



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PostPosted: Fri Oct 28, 2011 2:06 am    Post subject: transformers Reply with quote  Mark this post and the followings unread

Thanks again, krunkus.
so i could use it for the 5v i guess.
I ll have a look at buying one that puts out the right amount.

VERY GOOD Sah!
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mubase



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PostPosted: Fri Oct 28, 2011 4:41 am    Post subject: POWER 2 the people. Reply with quote  Mark this post and the followings unread

So Sah ! Would it be possible to use this??
I'm guessing yes scratch

HT transformer ( toroidal .)

Primaries:
0-10-120 : 0-10-120

Secondaries:
6.3-0-6.3 (12.6V centre tapped) @ 3A
0-210-230 @ 300mA
18-0-18 @ @120mA

120VA rated @ 70 deg C

Electrostatic screen, with mounting hardware. 110 x 60mm

Never used.


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Nice transformer ( ebay ) 5 quid.
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Uncle Krunkus
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PostPosted: Fri Oct 28, 2011 4:59 am    Post subject: Reply with quote  Mark this post and the followings unread

It'll give you +/-12, but only at 120mA per rail.
And regulating the 18-0-18 down to 12-0-12 DC is a bit of overkill really.
I'd go for a 15-0-15 if you can find it, with no other outputs. It will no doubt be able to deliver 1A per rail for the same size as this one.

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mubase



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PostPosted: Thu Nov 03, 2011 11:34 am    Post subject: V nice circuit but is transformer o.k for this??
Subject description: have transformer, will travel.
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Hi UncleK. Thanks for the advice on transformers. I've since acquired a 1A 230V primary, +/- 15 V centretapped for £5 from an ebay supplier. Im now looking at power circuits. I've posted a picture of a circuit from Delton Horn's Manual of synthesiser construction. This looks perfect for my needs,
+/- 12 V using 7812 and 7912 and 5 volt using a 7805. All from one transformer!. I have the Thomas Henry article on synth power supplies but this requires 2 transformers.
The attachment shows the Delton design. The BOM asks for 3A from the transformer but I'm asking if 1A would be OK.. ? ..
Thanks,
Hope all is good in KrunkWorld.
Steve.


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DTHorn power circuit
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Uncle Krunkus
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PostPosted: Thu Nov 03, 2011 2:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

If the BOM quotes 3A for the transformer, that just means that this set of components, in this configuration, can deal with 3A. (with the appropriate heatsinks on all the regulators)
If you use a 1A transformer, you can only draw 1A before the transformer would give up. So in that case the transformer would fail before anything else.
My advice is to make sure you have an appropriate fuse on the 240V input connections, AND if you want to avoid damaging the transformer, put a 1A fuse on EACH 15V line as it hits the regulator board. It may seem like a pain now, but when you short something and smoke starts coming out of your new transformer, you'll wish those fuses had been there.
Again, make sure you have reasonably sized heatsinks on your regulators. (Don't put them all on one heatsink, as this could cause a short, or use the correct insulation kits for them all)
If you haven't worked with 240V before, please get it checked by someone who has, even if it seems to work fine.

Apart from all that, I'd say it looks like a perfect PSU circuit to get started with. It's good to see someone putting the effort into a decent supply. It can make a big difference later to know that the PSU is a reliable one. Very Happy

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mubase



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PostPosted: Sat Nov 05, 2011 11:01 am    Post subject: cap vals
Subject description: 0.3 uf to 0.22uf??
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Ok! I've taken your advice and ordered the heatsinks and will incorporate fuses between the secondary outputs and regulators....Thing i'd like to ask now is that the circuit asks for 0.3uf caps on C3-C6 after C1 and C2 which are 100uF filtering caps. 0.3uF caps are hard to come by so I was wondering if I could use 0.22uF box caps instead. Would this have a seriously detrimental effect on the output to the regulator ics???
Thanks again.
Oh and Happy Guy Fawkes night!!
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Uncle Krunkus
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PostPosted: Sat Nov 05, 2011 2:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

That's fine.
Those smaller value caps near the regulators just help to stabilize the regulators when you have long wire runs on the output (AFAIK) In most situations you could do without them and not notice any significant difference.
As a general rule though, in PSUs, go for the next higher value in caps if you can't find the spec'd part. So I'd be going for .33uF (u33) or .39uF (u39)
If you've already got the .22uFs, they will work fine.

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mubase



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PostPosted: Sun Nov 06, 2011 10:43 am    Post subject:  Stripboarding and bridge rectifier Reply with quote  Mark this post and the followings unread

Hi Unkle, brilliant. I might try without the 0.3uF caps then...maybe.. Can you please tell me that I can use an RS 603 bridge rectifier ( single phase, 6A)? rather than the diode method. It would take up less space on the stripboard and look nicer. ( seems more pro to use a BR as well!!)
Thanks.

P.s. wish me luck on a bid for a Bullet SE 01 76477 experimenter board kit...
thumleft


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Rs 606 bridge spec.

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Uncle Krunkus
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PostPosted: Sun Nov 06, 2011 9:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yeah, that bridge rectifier is fine.
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mubase



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PostPosted: Tue Nov 08, 2011 5:24 pm    Post subject: Stripped Horn circuit
Subject description: Stripboarded power supply for 3 voltages......
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Hi! So I have come up with this design for a stripboarded +/-15V, +5 and +9V supply ( with heatsinks as kindly recommended by Unkle Krunkus amongst other stuff ) for modules requiring differing voltages based upon the DT Horn supply shown above.... Can any of the kind, experienced bods give me a heads up on this one???


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PostPosted: Tue Nov 08, 2011 5:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

It looks pretty good, except,....
Check the pinouts of your regulators.
The 78XX series have GND on the middle pin (which you have right) input on the left (looking at the part no. legs down) output on the right. Yours look the other way around.
The 79XX series has a completely different pinout, including the GND NOT being the middle leg.
I also think you might need more room for the caps. Remember they need to be roughly twice the voltage rating of what they are handling. That means at least 25V for the first two. They will be a bit bigger than your current spacing.

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PostPosted: Wed Nov 09, 2011 8:01 am    Post subject: Turn & turn again.... Reply with quote  Mark this post and the followings unread

Ah yes, thankyou again Unkle K.. Checked the regulator pinouts...Sorted! and then realised the difficulty of fitting the Bridge rectifier to the stripboard ( legs too thick ) and I wouldn't want to attach it to the box as it would take up more space ( the box is small and I am already wanting to fit an sn voice pcb and baby 8 sequencer stripboard inside...) so I went back to the diode method.. Embarassed
The caps are 1000uF @ 25V and 220uF @ 25V and I believe i have now accomodated enough space for them....
I think I might have the final version:: !!?!!

With respect,
Steve.


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Uncle Krunkus
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PostPosted: Wed Nov 09, 2011 6:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yeah, that looks pretty good now.
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mubase



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PostPosted: Thu Nov 10, 2011 1:40 pm    Post subject: The heat is on?? Reply with quote  Mark this post and the followings unread

Ok! I've started the stripboarding and have placed all the components ( caps/diodes/resistors) on the board. One more Q before wiring and testing: ).
I am putting the regulators on seperate anodised heatsinks ( small- about 1" tall).
Can I bolt the heatsinks to the back of the box which is metal ? or will this cause shorting problems???
Thanks .
Stevn.

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PostPosted: Thu Nov 10, 2011 3:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

Metal to metal means a short.
For the 78XX regs it would be okay, as all their baseplates are commoned to the middle leg which is ground, but the 79XX at least needs an insulator kit between it and the heatsink, or some other form of insulation between it's heatsink and the case. (You can get plastic/ceramic nuts and bolts, and spacers etc.)
This is, of course, assuming that you have the incoming mains earth connected to the case metal, which also connects to the system's 0V line. And yes, that's the way it should be done because it's safest that way.

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PostPosted: Thu Nov 10, 2011 4:37 pm    Post subject: Earth calling... Reply with quote  Mark this post and the followings unread

Yes, I see : The mains earth is connected to the case as is the 0V .Thanks for the tip on the plastic spacers/nuts bolts or I was thinking I could solder the 7912 bolted to the heatsink onto the stripboard @ the edge...?!? ( see pic..). The stripboard will be fixed to the box base via plastic adhesive holders.


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PostPosted: Thu Nov 10, 2011 7:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yeah, that's fine. Just make sure it doesn't touch anything.
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PostPosted: Fri Nov 11, 2011 6:08 am    Post subject: Good to go+ thanks. Reply with quote  Mark this post and the followings unread

Unkle Krunkus. Thanks for all your help. When I get some funds I'll send along a small donation to the site. ( probably enough for a round of cokes...Smile )

It is great to be able to get help from and contribute to this site.
I'll keep posted on the build(s)..
All the best.
Steve.

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PostPosted: Sun Nov 13, 2011 4:40 am    Post subject: here come the odd voltages..... Reply with quote  Mark this post and the followings unread

The board is built and has been tested. The negative supply shows -13.84V whilst the positive 12v shows 11.88V???
The 5V from the 7805 was showing just 3.8 so I removed the 2.2k resistor and got a full 5.00V.
I don't know whats wrong, I've upgraded the 1000uF 25V caps to 1000uF 50V but the readings are the same..Sad Is there a possibility of a faulty 7912 or could it be ground discepancies I don't know...
If I place a 220Ω resistor on the output of the 7912 and measure I get -11.48V which is nearer to the 11.88 of the 7812... I was thinking I could use the resistor on the 7912 and make due with 11.88 and -11.48V but hmm... ( BOLLOCKS!! )...

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PostPosted: Sun Nov 13, 2011 5:42 am    Post subject: 0.68uF Reply with quote  Mark this post and the followings unread

1 hour later after doing some research , I've placed a 0.68uF 25V cap between the earth and the output of the 7912. Reading now gives -12.02V Smile .
So all outputs:

+11.88V
-12.02V
+9.00 V
+5.02 V
Excellent. Smile

Now keeping her switched on to do a heat test...


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Stripboarded +/-12V 9V 5V supply for SN voice project.
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PostPosted: Sun Nov 13, 2011 3:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

That's actually pretty good for those types of regulators.
I think they are only spec'd for +/-5% anyway, and that's well within that.
The main thing is that the output (V) is no longer dependant on the load (A).

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