Bad filter on the whacky noise generator

LektroiD

Having a bit of a problem with my wacky sound generator, the filter is down until the last degree, then rises rapidly, I'm sure replacing the pot for a different value would cure it, but it's designed to be 1MΩ, so the problem must lie elsewhere in the filter section. I can't see anything obvious though. I've included a photo, maybe someone else may spot the fault?

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stolenfat · Posted: Mon Oct 20, 2008 5:20 pm Post subject:

this wont answer your question, but its on the same topic. I was interested in using the wsg filter in another project because i have alot of those parts lying around some where, does any one have a schematic of Just the filter? Or could some one tell me how using ray's schematic to cut out the filter to be used in other projects?

LektroiD · Posted: Mon Oct 20, 2008 7:49 pm Post subject:

The 741 end of the schematic is the filter.

I'd still like to know where I went wrong with my board, I followed everything verbose, or at least I thought I had!?

Pehr · Posted: Tue Oct 21, 2008 1:06 am Post subject:

Sounds like a bad pot, replace it would prob fix the problem.

Uncle Krunkus · Posted: Tue Oct 21, 2008 3:33 am Post subject:

You used linear (B) pots all round yeah?

LektroiD · Posted: Tue Oct 21, 2008 3:41 am Post subject:

Yep all linear (B), all brand new.

It's not a faulty pot either, it has a hard slope, rather than 'cutting in & out'. I know it's going to be something simple.

Uncle Krunkus · Posted: Tue Oct 21, 2008 2:04 pm Post subject:

It looks from the picture that you might have a 1M resistor for R4 and R13. R4 should be a 10M. Check these and make sure. If R4 was 1M that would explain the effect you described perfectly.

LektroiD · Posted: Wed Oct 22, 2008 1:44 am Post subject:

R13 was listed as a 1MΩ, not 10MΩ, unless this was changed and the component list not updated?

http://electro-music.com/forum/phpbb-files/whacky_list.txt

R4 is a 10MΩ (Brown, Black, Black, Green)

Uncle Krunkus · Posted: Wed Oct 22, 2008 2:52 am Post subject:

No, I only said R4 should be 10M. It looked like a 1M in the photo.

stolenfat · Posted: Thu Oct 23, 2008 9:18 pm Post subject:

stolenfat · Posted: Thu Oct 23, 2008 9:26 pm Post subject:

would this be a safe assumption of the oddness filter cut out from the rest of the schematic?

The red X's are areas highlighted that are cuts from the original wsg schematic and i think pin 2 of the 741 would be the input? Maybe?

Im not sure if the cuts will affect the filter or not...

Could i get a little revision from an expert? thanks!!

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LektroiD · Posted: Thu Oct 23, 2008 9:38 pm Post subject:

That looks like a slightly different schematic to the one I've been working from, I wonder if that's why I'm having the 'ramping' issues? Mine doesn't have a 'fine' pot for a start, and neither does mine have Resonance..

Uncle Krunkus · Posted: Thu Oct 23, 2008 10:24 pm Post subject:

LektroiD · Posted: Thu Oct 23, 2008 10:31 pm Post subject:

stolenfat · Posted: Fri Oct 24, 2008 12:02 am Post subject:

thanks for the help up there

get this! So i'm going through my old parts to build up this filter again and i get to the 10 meg resistor. I fumble through my bags and find the one labeled 10 megs. I grab the resistor and drop it on the floor, upon picking it up i look at it, huh brown black green? "I thought it was brown black blue," i say to myself... I check the bag ALL of the resistors in there are brown black green!

BUNG!

Looks like the two WSG's i've built in the past dont have any 10 meg resistors in them, only 1 meg!

I've always thought the filter was kinds harsh at times, that may be why! I've noticed some times the rezz knob often totally changes the sound of the wsg and not just add resonance, that could be it!

woah

Uncle Krunkus · Posted: Fri Oct 24, 2008 1:42 am Post subject:

Geez Stolenfat, for second there I thought you were Brainstormer! I had to go back to the start to check who it was who had the initial problem, that I told to check that he hadn't used 1M instead of 10M!! Laughing

It seems I successfully diagnosed a problem which you didn't even know you had!! Laughing

I recommend checking resistors a lot.
When I'm collecting parts for a build, I still check one of each "bunch" of resistors, just to be sure. It's amazing how easily our eyes will see what we want to see, and not what is actually there. And I'm short sighted too! I can't imagine what it would be like for so many people I know in there 40s who are long sighted and have to wear glasses to see things which are closer than an outstretched arm! Shocked

And,..... from my experience, most build faults due to incorrect parts are resistor values which have been mis-picked or swapped. Other components tend to look after themselves.

RF · Posted: Fri Oct 24, 2008 3:58 am Post subject: