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 Forum index » DIY Hardware and Software
transformers...explanation for a newb?
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sounddoc



Joined: May 31, 2006
Posts: 3
Location: boston, usa

PostPosted: Mon Jun 26, 2006 9:18 am    Post subject: transformers...explanation for a newb? Reply with quote  Mark this post and the followings unread

hi folks!

over the weekend i picked up a noise generator from the 70s-80s at the local thrift store. it's essentially a white noise generator and has two settings - "rain" and "waterfall", plus volume and tone control. i opened it up, and it looks like it's being run only off a few transistors - no opamps or other ICs in sight!

anyway, my plans are to give it a new home (the large and gaudy exterior in which it came can be used for other synths at another time) and also to have it hopefully run off a 9-volter. right now it's 120v ac, with a big transformer which as best as i can tell brings it down to about 12.5v on the board.

i snipped the transformer off, and now the current configuration is as follows: 1 trans. lead goes to the board, in between a couple diodes, the other lead (both of them red, so no grnd i'm assuming) goes to the volume / on/off pot. there's a ground off the board, but it was screwed to the base of the housing.

how can i "bend" this into a 9-volt configuration? i've tried every hookup combination except splitting the pos leads to the former transformer lines. i'm not sure weather i should use the housing ground as the neg. on the battery. i also don't know how to tell if the power is ac or dc on the board itself.

would appreciate anyone who can start me in the right direction. i'm familiar with small electronics, i.e. building little 555 timers and such, but when it goes beyond 9V dc, i get a little confused.

thanks!

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toppobrillo



Joined: Dec 10, 2005
Posts: 766
Location: oakland, ca
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PostPosted: Mon Jun 26, 2006 3:08 pm    Post subject: Reply with quote  Mark this post and the followings unread

hey i just wrote a real detailed response to your problem then my computer choked how annoying is that??

ok simply, if you have 12.5VAC on the 2ndary, it is rectified into around 17.5VDC so if you want to power this off batteries use 2 9Vs in series. if you have a voltmeter verify that this is true and determine where to apply DC. you will bypass the rectifying diodes, of course... to make it easy, look for the biggest cap on the board and your ground is it's negative side.

so how does "waterfall" sound different than "rain"? be aware that one of these things that look like transistors might actually be an integrated circuit, but, probably not if it's older like you said.

hope this helps

josh
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sounddoc



Joined: May 31, 2006
Posts: 3
Location: boston, usa

PostPosted: Mon Jun 26, 2006 4:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

hey josh, thanks for the reply!

to the best of my knowledge it is 12.5 (ac/dc?) running through the board, i.e. that's the voltage coming out of the transformer.

well, i just tried 2 9 volts in series, left out the pos. connection going into the 4 diodes (is that the ac-dc conversion?) and voila! at 17.5 dc across the board i get sound. it's a little bit weaker that the house current, but i think one of the 9v is in need of recharging.

so i guess now it's up to playing around to see what i can do to strip away needless components. here's the only relevant info i could find on the web:

http://home.gate.net/~saj/movingsale/id2.html

it's the 2nd item from the bottom. the circuit itself is very simple, employing a few 2n4401 transistors and a 2n2906 for each 'rain' and 'waterfall' sounds. the difference is that the rain incorporates the higher frequencies, but it's essentially a noise generator. i'll post pics of the circuit board itself if anyone's interested.

so far i've found the resistors that pick up the volume a little for each sound, but ultimately i wonder if it's possible to have it be real sample and hold and reduce the clock frequency...but something tells me that this isn't possible with a few transistors...also, running off a single 9volt would be nice. i suppose this thread will have to move to the circuit bending forum soon enough!

thanks again!

-p

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