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finding the correct power supply
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conglomco



Joined: May 21, 2007
Posts: 27
Location: texas

PostPosted: Tue Jun 26, 2007 8:46 am    Post subject: finding the correct power supply
Subject description: MFOS sequencer
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Hello everyone..

I have been posting about building the MFOS sequencer, and I am wondering how to calculate what power supply can be used.
I found a great case (vintage medical equip), that is perfect to house all the circuitry, and it even has a built in power supply +/- 15v (see pictures below)..
MFOS site says that this sequencer will work with +/- 15volts-->http://www.musicfromouterspace.com/analogsynth/SEQ16_2005/SEQ16_2005.html
, but the supply is only 100mA.. How can I calculate how many milliamps I would need to drive this thing? Will this supply work??

Thanks for all your advice and help in this forum, I couldn't build anything without you!
tyler

built in power supply:
Posted Image, might have been reduced in size. Click Image to view fullscreen.

tough case!:
Posted Image, might have been reduced in size. Click Image to view fullscreen.
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andrewF



Joined: Dec 29, 2006
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Location: australia
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PostPosted: Tue Jun 26, 2007 9:19 am    Post subject: Reply with quote  Mark this post and the followings unread

100mA 'should' be fine. if its not, you will find out pretty quickly Very Happy
I would try it before buying or building something else.
Probably the LEDs suck the most power but its unlikely all 16 or so will be lit up at once.

Nice panel, i've ripped apart a lot of old medical gear - it always has that hospital stink.
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goldenechos



Joined: Jun 06, 2007
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PostPosted: Tue Jun 26, 2007 11:15 am    Post subject: Reply with quote  Mark this post and the followings unread

You should get Ray to confirm the current draw of the sequencer.

Vintage power supplies are not the best idea. At the very least you might want to re-cap the supply. Depending upon it's age you might want to consider buying a new supply.

TR
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Photon



Joined: Mar 22, 2005
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PostPosted: Tue Jun 26, 2007 6:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

goldenechos wrote:

Vintage power supplies are not the best idea. At the very least you might want to re-cap the supply. Depending upon it's age you might want to consider buying a new supply.


shit.


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goldenechos



Joined: Jun 06, 2007
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PostPosted: Tue Jun 26, 2007 6:44 pm    Post subject: Reply with quote  Mark this post and the followings unread

That is old. You might want to re-cap it... Very Happy


TR
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andrewF



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PostPosted: Wed Jun 27, 2007 2:39 am    Post subject: Reply with quote  Mark this post and the followings unread

I suppose it depends on a components history and the degree of wear and tear it has endured, but I use power supplies from 70's Korg and yamaha synths with no probs.

Old caps, to me, means wax and paper affairs oozing gunk over tube gear....i chuck those.
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Photon



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PostPosted: Wed Jun 27, 2007 4:25 am    Post subject: Reply with quote  Mark this post and the followings unread

It was still in the box, never used. I have a feeling it will be fine.

Peter


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conglomco



Joined: May 21, 2007
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PostPosted: Wed Jun 27, 2007 6:55 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
you should get Ray to confirm the current draw of the sequencer.

Vintage power supplies are not the best idea. At the very least you might want to re-cap the supply. Depending upon it's age you might want to consider buying a new supply.

TR


I talked to Ray Wilson, and he said a 100mA supply would work fine, so that's good!

Also does recapping the supply refer to replacing the electrolytic capacitors?

thanks!
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goldenechos



Joined: Jun 06, 2007
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PostPosted: Wed Jun 27, 2007 7:53 am    Post subject: Reply with quote  Mark this post and the followings unread

conglomco wrote:

I talked to Ray Wilson, and he said a 100mA supply would work fine, so that's good!

Also does recapping the supply refer to replacing the electrolytic capacitors?

thanks!


Yup, the larger value electrolytics. The bypass caps.

You could just lift a lead and check the caps too... they might be fine. In my limited experience with those large cans, they have needed replacing.

If you have a scope, take a look at the +15V and -15V supply lines with a dummy load on them. This way you are less likely to damage your precious MFOS sequencer that you worked so hard on! A dummy load could consist of a a resistor and an LED (for each supply line). Something around 1k for the R and any general purpose LED would draw around 15ma. With the -15V remember to reverse the polarity of the LED.

TR
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conglomco



Joined: May 21, 2007
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PostPosted: Thu Jul 12, 2007 12:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

goldenechos wrote:

If you have a scope, take a look at the +15V and -15V supply lines with a dummy load on them. This way you are less likely to damage your precious MFOS sequencer that you worked so hard on! A dummy load could consist of a a resistor and an LED (for each supply line). Something around 1k for the R and any general purpose LED would draw around 15ma. With the -15V remember to reverse the polarity of the LED.


We tried testing the power supply with a dummy load and checked it out on the scope. We're just not sure how to read what the scope is saying..

Basically, with no load the DC voltages just show up as flatlines (at + or - 15V). Our thinking is that under load a properly functioning power supply will show little to no difference from the "unloaded" test. ---And that's what happened.

I would think that if there was anything wrong with the caps I would get some kind of squiggly line, but I can't be 100% about that.

We are just wondering what you should see when you perform this test - find out what a good supply will look like vs a bad one.

Thanks!
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goldenechos



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PostPosted: Thu Jul 12, 2007 12:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

Sounds like your supply is good! Nice find (the case with working supply).

TR
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