LFO, Noise, IC trouble

bigcat · Joined: May 13, 2013 Posts: 1 Location: Amherst, Mass

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

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original schematic

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noise unit.jpg

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

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power supply.jpg

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power supply

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dying out.jpg

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output beginning to falter

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flatline.jpg

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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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elmegil · Posted: Yesterday, at 11:43 am Post subject:

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.