Obsidian Overdrive Feedback Problem... still

Started by robbiemcm, March 25, 2005, 09:27:14 AM

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robbiemcm

It should only be about 900kb in size... I don't want to hear about how I suck at guitar, how my tempo increases randomly, how I'm hitting the wrong strings, how my guitar's not tuned. We're talking about the pedal people!!!

Tis really quite an odd problem... usually I can get a bigger change in pitch when I change from 1 to 2 on the volume knob on my guitar, which is what I'm going from in the vid, lol. I can also get a sort of feedback free section ocassionally when the volume knob on my guitar is at around 5. The big volume change is when i turn my amp up during the vid. Anyone have any idea whats wrong here? Scuse the filming between the legs.

http://phpdevil.sparkysnet.com/robbie/obsidian.wmv

robbiemcm

Bah! So nobody knows why I get this odd feedback-ama-jig stuff? You don't even have to watch the video (might be better for my self esteem if you don't) maybe just suggest what could be causing this?

triskadecaepyon

Once I accidentaly bridged a solder joint to another, and I got that problem.

robbiemcm

I'll have a look but I'm pretty sure they're all fine... What if one of my pots was attached to the case via a solder joint?

Oh yeah, and would not having the circuit correctly earthed cause this problem? I can't solder it to the sides so its just sort of stuck there with a tiny bit of tape, about a 1cm gap.

robbiemcm

It seems to have two different modes. Extreme feedback mode (which has massive gain!) and no feedback mode (which has what I expect is meant to be the normal amount of gain from the obsidian overdrive). To switch between these two modes i have to move the circuit board in and out of the enclosure. My wires are too long you see, could it have something to do with the connections of my wires?

I audio probed around when it was on the 'extreme feedback' mode and the feedback is heard directly from the input, yet I never get it through bypass... so maybe it has something to do with my input signal wire's connection or soemthing odd. But then again, it could not be earthed properly... bah I just don't get why it's so screwed up!

Sure I could just try and screw the enclosure up and hope it's in the right position (happens sometimes) but a mere knock can set it out of place... fixing it is obviously a better solution.

RDV

Try shortening your wires and try to make everything go at right angles. I've had the same problem and it was cause I did a bad sloppy wiring job.

RDV

vortex

Hey Robbie,
Great video, I laughed my ass off!

I've had the same oscillation problem with my recent Bosstone pedal. I only have the problem when the preamp pot is in the most extreme positions. It is kind of fun actually.
I am sorry I don't have the answer for you, I too am working on a similar problem.
I assume it has to do with 1) either a ground or shorting problem 2) a layout problem, (ie input and output wires too close together etc.)
I recently read a thread here where someone cured the problem by using a coax wire for the input and grounding the coax ground wire to the circuit ground.

I hope you get this solved!

robbiemcm

Quote from: vortexHey Robbie,
Great video, I laughed my ass off!
I bet I can guess why :roll: I have plenty of time in my life to get good at playing though :P Oh yeah, and the pedal is fun to play around with at first. But uh... yeah... gets annoying.

I'm gonna try RDV's solution... but cause I have 3 pots, input + output signal, powere on/off switch, bypass switch and all there must be like... 20 wires in there. I don't want to have to do this lol. Especially if it doesn't solve my problem... well... has to be done.

robbiemcm

Alright, I shortened the wires, it all seems to be perfect there now. The problem is when I move the wires attacthed to the pots, I guess I must have done a bad job soldering them... but ther'es such a huge change in the output when I wiggle those wires. Maybe someone can suggest a good way to attacth my wires to pots, or any help you may wanna give me...

I'll give you a couple of pics of my crappy first attempt at a stompbox. Hey I just realised something... I suck at playing guitar, building stompboxes... is there anything I'm actually good at?


http://i2.photobucket.com/albums/y13/robbiemcm/oo1.jpg -Everything
http://i2.photobucket.com/albums/y13/robbiemcm/oo2.jpg -Wires + Pots
http://i2.photobucket.com/albums/y13/robbiemcm/oo3.jpg -PCB

Joe Davisson

Try these things:

-Make sure the drain voltages are somewhere between 4 and 5 volts.
-Put a 100uF cap across the + and - rails. That should stop the oscillation.

robbiemcm

Drain voltages are 3.86 3.94 3.97 are these close enough? So are you sure a  100uf capacitor will stop the problem? Because I don't really have any capacitors on hand, lol. It just seems odd I can get it to work fine when wiggling wires around.

Oh yeah, and it hasn't been noted in this thread but I'm using 2N7000 transistors instead and changed polarised caps and battery to suit.

Joe Davisson

After listening (watching? :shock:) I'm inclined to think the 100uF cap will fix it. Can be any large value, actually.

robbiemcm

Alright i'll pop down to the store and get one some time. Actually might aswell get a few, they're commonly used right?

vortex

Quotevortex wrote:
Hey Robbie,
Great video, I laughed my ass off!

I bet I can guess why Rolling Eyes I have plenty of time in my life to get good at playing though Razz Oh yeah, and the pedal is fun to play around with at first. But uh... yeah... gets annoying.

No, No! It's not the playing I am laughing at! I just had a similar experience while debugging the Bosstone. Letting the pedal buzz away on my little test amp while I tried solving the dilemma. I like that you took the time to document the problem on video. It makes me laugh to see that I am not alone in my troubles!

BTW, thanks for the oscillation/cap tip Joe.

vortex

I just had a look at the way you are wiring the pots. Is there a reason that you don't solder to the lugs? Perhaps you are getting a short to the casing of the pot...

robbiemcm

When I twist the wires around the little metal prongs it slips off before I can solder it on, so I pushed them through the whole on the pot and soldered on the other side. Is that bit of metal not connected in the same way or something?

vortex

Hi Robbie,
I am not saying that you are doing any thing wrong. In my experience, the pots I use generally have a hole in the lug which the wire is inserted. Often, the pot lugs benefit from a quick sanding with a file to get rid of oils etc. You can then  either wrap the wire or just insert it and solder. A squeeze with pliers before soldering will give the connection extra integrety.
Frankly, looking at your pics I am not sure where you are soldering ,but it looks a bit higher than I have ever attempted! It may not be the answer to your problems but I thought Iwould offer my two cents.

Hal

Quote from: vortexHi Robbie,
I am not saying that you are doing any thing wrong. In my experience, the pots I use generally have a hole in the lug which the wire is inserted. Often, the pot lugs benefit from a quick sanding with a file to get rid of oils etc. You can then  either wrap the wire or just insert it and solder. A squeeze with pliers before soldering will give the connection extra integrety.
Frankly, looking at your pics I am not sure where you are soldering ,but it looks a bit higher than I have ever attempted! It may not be the answer to your problems but I thought Iwould offer my two cents.

there's no problem, though.  I also use PCB mount pots becuase thy're cheap from futurlec.  They don't have solder lugs, so I wrap, and occationally put in the hole on the board.  It works well there - stong, and on isolating pheno board.

robbiemcm

Can someone maybe show me a pic of how they solder their wires to pots, I get the idea that's what I'm doing incorrectly.

robbiemcm

Well... it's still not fixed. I don't know how to get rid of the noise. I havn't tried the capacitor method, but someone told me the Obsidian already has a blocking cap in it... and I did build it like it said...

I used an audio probe, the sound is BARELY (or not at all maybe?) there at the first input, but gets amplified after each transistor... this could help someone in figuring out what's wrong, does a 2N7000 amplify oddly? If it makes any difference... I screwed up with the transistors first time round and had to reuse one of them, so only 2 are new. I pulled it out and put it back in... would that make this sort of problem?