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Author Topic: Custom LPF build is distorted  (Read 15769 times)

shinychrome0

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Re: Custom LPF build is distorted
« Reply #30 on: August 11, 2010, 09:59:59 AM »
I'm going to try to salvage this by integrating it into a tube preamp i built last year.  I figure i can run it off the spare 12v secondary on the transformer if i put in a small rectifier.  The tubes will give the extra gain i need.

Will a full wave rectified signal be good enough without extra smoothing caps since they will go through the 1000uf caps in the power section anyway?
« Last Edit: August 11, 2010, 10:07:25 AM by shinychrome0 »

shinychrome0

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Re: Custom LPF build is distorted
« Reply #31 on: August 11, 2010, 03:29:14 PM »
Alright that didn't work.  I had everything hooked up and it sounded good for about ten seconds.  Then my signal slowly gave way to a loud hum.  I'm done.  I have no idea what happened, what fried, whatever.  And i don't have the time to find out.  I leave for college again this weekend.  So the soldering iron is off till christmas.  But i'd still like to know where the hell i went wrong.  Any ideas?

J M Fahey

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Re: Custom LPF build is distorted
« Reply #32 on: August 11, 2010, 05:33:07 PM »
Your schematic is good, so the problem is in the actual gadget.
Triple-check everything, measure voltages.
Post clear pictures of what you did.
Aren't you counting the IC pins backwards?
There's a zillion small mistakes possibles.
After you find it, you'll knock your head against a brick wall, saying nooooooooooooooooooooooooo !!!!!!!!!!! , *that* was all the problem ?????
Don't worry, we've all been there before.  :-[ :-\

shinychrome0

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Re: Custom LPF build is distorted
« Reply #33 on: August 11, 2010, 07:54:06 PM »
Well thats the problem.  I HAVE triple checked everything, and can find nothing wrong.  Actually, before combing the LPF and the preamp, both worked fine, except for the volume drop that was a design error, not a build error.  The only problem that i can find is that there may be too much ripple in the dc supply, but is there really any way that could harm any components?  Its only like a +/- 6v supply.  Its not anywhere near the limits of the opamp, or anything else for that matter.

J M Fahey

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Re: Custom LPF build is distorted
« Reply #34 on: August 11, 2010, 11:18:32 PM »
No, ripple is not a *big* problem, only a nuisance.
Juat a thought: so far you have been posting the PCB software drawing, which is very specific.
1)Post a picture or two of your Protoboard.
2) Draw *by hand* the *real* schematic of what you actually have built, including input and output jack drawings, the power jack, wire colors, etc.
Forget the "official" schematic, draw with only the board before you.Also show your switching.
3)Last but not least, post the voltage on pin 6 on each op amp, as well as on pins 4 and 7. Also on pin3 of op amp 1, with and without the Pod plugged there. All referred to ground.
Also check continuity between input and output jack grounds as well as with the power supply centerpoint.
Well, that's all for now.
Good luck.

shinychrome0

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Re: Custom LPF build is distorted
« Reply #35 on: August 12, 2010, 10:11:01 AM »
its a dual package opamp.  Are those still the same pins you want voltages for?

And i'll try to get some pics and a drawing up later today if  i can manage it.
« Last Edit: August 12, 2010, 10:14:03 AM by shinychrome0 »

shinychrome0

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Re: Custom LPF build is distorted
« Reply #36 on: August 12, 2010, 02:21:27 PM »
http://www.flickr.com/photos/26826525@N05/4885957996/sizes/l/

here's the board.  I'm still working on drawing up a schematic.

J M Fahey

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Re: Custom LPF build is distorted
« Reply #37 on: August 12, 2010, 02:51:32 PM »
Hi shinychrome.
Then THAT is your problem !!!
The LT1001 is a SINGLE package op amp, with industry standard LM741 pinout !!!!!
What IC did you actually use?
Edit: Now I've seen your picture.
I see parts bent to different angles (to avoid shorts and problems they should basically be vertical, at least with this layout), plus you should try to find a cleaner wire layout.
I would get the thing going on regular plug-in ProtoBoard first, for easier debugging (and even pulling everything out in frustration and re-starting from zero) and only after satisfied I would put it in a Proto-similar PCB.
Wish you a pound of good luck and a ton of patience..
EDIT2: and what are those Germanium point contact diodes doing in your board????
« Last Edit: August 12, 2010, 03:12:45 PM by J M Fahey »

shinychrome0

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Re: Custom LPF build is distorted
« Reply #38 on: August 12, 2010, 04:01:30 PM »
Sorry i should have mentioned that sooner.  I used a TL082 opamp, but i just used a random opamp for drawing up the schematic.  I wish there was a cleaner wire layout, but with these stupid rat shack boards, it was the best i could figure out.  I know it sucks.  And i had already done the whole thing on a breadboard, except it was powered by a battery, and this was supposed to be the permanent build, not another troubleshooting phase. 

Here is the Schematic i've drawn up from the board.  I found and fixed two errors, one in the power supply (the 1k resistors were in series with the voltage rails, rather than with one end to ground) and another that should have stopped the whole circuit cold.  There was n connection from the output of the first opamp to the input of the second.  I have no idea how any got any sort of sound out of it before, but i don't anymore.  Fixing both of those things still has done nothing though.  nothing but hum city.

And the GE diodes were all i had around to build a bridge rectifier with.

http://www.flickr.com/photos/26826525@N05/4886278694/sizes/l/

J M Fahey

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Re: Custom LPF build is distorted
« Reply #39 on: August 13, 2010, 01:24:01 AM »
Now you see that drawing by hand what you actually built is better than any packaged solution.
1) The filter schematic is basically correct, just replace the two pots by fixed resistors, leaving both halves the same.
Make it work and then add the frills.
2) The PSU part is wrong.
a) As drawn the upper rail is negative, the lower one positive, the opposite of what you need.
b) *As drawn*, the upper electrolytic is reverse-biased, which being an electrolytic means it becomes some kind of short too.
You will hardly have more than 1V there, because reverse charged electrolytics have *very* high losses..
3) As drawn, the lower electrolytic is correctly biased ... but it supplies positive voltage into the negative rail.
4) Please replace those 1N34 with 1N4002.
Well, enough for today, good luck and post often.

shinychrome0

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Re: Custom LPF build is distorted
« Reply #40 on: August 13, 2010, 08:56:03 AM »
Ugh.  Stupid mistakes.  I'll try to get to them before i leave for school sunday.  But i can't guarantee anything.  It would be nice to get it working though.

joecool85

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Re: Custom LPF build is distorted
« Reply #41 on: August 13, 2010, 09:45:08 AM »
Ugh.  Stupid mistakes.  I'll try to get to them before i leave for school sunday.  But i can't guarantee anything.  It would be nice to get it working though.

It's ok, those stupid mistakes are the ones that always trip me up too.  By "school" I take it you mean college.  Where are you going/what are you going for?  I just graduated 2 years ago from UMaine with a BA in New Media.
Life is what you make it.
Still rockin' the Dean Markley K-20X
"New" amp: Fender Frontman 25 DSP (FM25DSP)
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shinychrome0

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Re: Custom LPF build is distorted
« Reply #42 on: August 13, 2010, 01:59:37 PM »
Yeah.  I'm at cincinnati christian, majoring in classical guitar performance.

bry melvin

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Re: Custom LPF build is distorted
« Reply #43 on: August 13, 2010, 03:48:29 PM »
Isn't Music a second major there? or has that changed?

shinychrome0

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Re: Custom LPF build is distorted
« Reply #44 on: August 13, 2010, 10:59:34 PM »
what do you mean?

 

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