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Old 2nd November 2012, 12:30 AM   #1
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Join Date: Nov 2012
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Default ISO: Guitar-Synth DIY Project Help.

Hello and thank you to all who take the time to read this.

So, I'm building a "Guitar-Synthesizer" project from the terrific website Music From Outer Space. About a month ago I initially "completed" the project but it did not work properly. I had power at all the IC chips but one in particular (U6) was VERY hot. I've had two stages in the process of testing that I feel should be mentioned. First when testing one time, I had hooked up the -12V lead from my bench top power supply, but I accidentally had the +12 and GND leads in each others' terminals Next, about a week ago, I discovered that I had installed a diode backwards (yes, it was between U6 and U7), and I felt both a a bit of relief and pretty stupid at the same time. After properly orienting the diode and replacing U6 I was able to get an audible signal, and the one chip was no longer hotter than the others. Today, I replaced the rest of the IC chips, plugged it in, and it wasn't any different. Now I'm just at a loss, one thing I'm wondering is if hooking up the supply wrong could damage transistors, bi-polar caps, etc.

Any input is greatly appreciated!
Thanks again.
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Old 2nd November 2012, 05:02 AM   #2
Enzo is offline Enzo  United States
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How about schematics and links to what you actually built? It is asking a bit for us all to have to research it just to check it out.

COnsider if you built it from scratch and already have run into misconnected power wiring, misinstalled diodes. It would not be unlikley there are other errors in the construction. I am not picking on you, we all have made construction errors. And yes, certain other parts could have been dmaged, but your problem might also be unrelated to that. If it were a commercial product, we could assume the basic thing worked at one point and something failed. A new home built product, we cannot make that assumption.

I am not sure what the problem is you are chasing. You say you are getting audible signal. Is that not the idea? If it is not right, what is wrong about it.

I'd verify ther is the correct power supply voltage at each IC power pins. I would look at each output pin for unwanted DC. If an op amp ought to have about zero DC on its output, then finding 12v there is a bad sign, and it can do that without getting hot. ICs that get real hot are probably bad, but all bad ICs don;t get hot.

You apparently have +12 and -12, whwich makes sense for audio, but since it is a synth, may I assume there are also logic circuits? And do they run on +5? Or do they borrow off the +12?

DO you have a scope and know how to operate it?
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Old 2nd November 2012, 01:23 PM   #3
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Thanks Enzo, you're right I should have included this...

http://www.musicfromouterspace.com/a...THAUG2007.html

Thanks again for any input.
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Old 2nd November 2012, 04:48 PM   #4
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Also forgotten was the detail that while I do have a clean signal there is no modulation effect from the VCA or VCF. Please forgive the noob nature of this post.
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Old 3rd November 2012, 12:57 AM   #5
Enzo is offline Enzo  United States
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OK, so then it basically works as a pickup and amplification system, but you are missing some of the effects.

I see the whole thing runs on just +/-12, no +5 or anything else.

When you reversed +12 and ground, it may not have harmed the op amps, but it would put reverrse power on the logic chips, the 4013s, the 555. I'd say that makes them suspects.

This is fairly complex, and he broke it down into sections. I might read the theory of operation text and follow along through the unit trying to verify each section for function.
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