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 Forum index » DIY Hardware and Software
LFO, Noise, IC trouble
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bigcat



Joined: May 13, 2013
Posts: 3
Location: Amherst, Mass

PostPosted: Mon May 20, 2013 8:59 am    Post subject: LFO, Noise, IC trouble
Subject description: Failing M.F.O.S. LFO and Noise unit.
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I'm trying to build a LFO unit and a noise unit to control the output of my oscillator. The oscillator I built was a kit from technologywillsaveus.com. I'll admit to being something of a novice with electronics. I majored in physics in undergrad so I have a very basic understanding of electronic circuits, but the inner workings of ICs confuse me and I think that's where my problem stems from. The schematic, which comes from Music From Outer Space, for the LFO, Noise, and power supply are attached. The original schematic calls for LF444 op amps. I read that the NTE 859 has the exact same pinouts and can be a suitable replacement. I purchased the latter as my local electronics store doesn't sell the LF444. The pinouts are shown here:

http://www.nteinc.com/specs/800to899/pdf/nte859.pdf

THE PROBLEM: The output from both the LFO and the Noise unit dies off in about one minute. Seen on a scope or put through a small speaker you notice the signal begin to fizzle and then flatline. After disconnecting the power and reconnecting the same thing happens but in a much shorter time period. Repeating one or two more times results in no signal at all. When left for a day the circuit returns to normal.

The time sensitive nature made me think I had a problem with the capacitors but experiments with discharging them helped me realize that that wasn't the case. I thought perhaps I had provided to much voltage and threw a number of different resistors in front of the input, following the +9V of the battery but that has had little or no effect. Either the resistance is too high and I get no signal or it's too low and the usual fizzle happens. One notable difference with the LFO is that instead of simply flatlining, the frequency of the signal slowly starts to drop. You can see the waveform on the oscilloscope stretching until it eventually flatlines and begins to respond just like the noise unit.

Any suggestions other than buying myself a book on Op Amps? Also is there any information that would make trouble shooting this thing easier?

thanks, Chris


synthkit_lfo_noise_power_001.gif
 Description:
original schematic
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synthkit_lfo_noise_power_001.gif



noise unit.jpg
 Description:
a camera phone picture of the noise unit on breadboard using the NTE859 in lieu of an LF444
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noise unit.jpg



power supply.jpg
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power supply
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power supply.jpg



dying out.jpg
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output beginning to falter
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dying out.jpg



flatline.jpg
 Description:
Output flatlines. Note that the readout on the scope is tracing over itself, in this image you see both the start (on the right) and abrupt stop (on the left) of the signal.
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flatline.jpg


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elmegil



Joined: Mar 20, 2012
Posts: 1475
Location: Chicago
Audio files: 14

PostPosted: Mon May 20, 2013 11:43 am    Post subject: Reply with quote  Mark this post and the followings unread

You don't mention if you've tested the battery or replaced it with a known good fresh one? That behavior sounds like power supply problems.
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bigcat



Joined: May 13, 2013
Posts: 3
Location: Amherst, Mass

PostPosted: Thu May 23, 2013 5:30 pm    Post subject: Reply with quote  Mark this post and the followings unread

At first I felt really patronized upon reading that. And then it turned out to be the batteries. I guess you really do have to triple check them. They weren't drained but one had a substantially lower voltage than the other and that potential difference is what made the circuit act all screwy. Thank you for the suggestion.

Chris
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elmegil



Joined: Mar 20, 2012
Posts: 1475
Location: Chicago
Audio files: 14

PostPosted: Thu May 23, 2013 5:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

My apologies, I did not mean to sound patronizing. I have done EXACTLY the same thing, so we're all in the same boat Very Happy
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bigcat



Joined: May 13, 2013
Posts: 3
Location: Amherst, Mass

PostPosted: Fri May 24, 2013 10:57 am    Post subject: Reply with quote  Mark this post and the followings unread

Oh not at all man, I was only half serious. It's just one of those things that's so obvious you just assume you're smarter than to forget to check the batteries, then it's totally embarrassing when that is in fact the one thing you missed. That you suggested it was a good thing because I never would have thought of it otherwise.
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