DOD YJM 308, farts out!!!

user · November 22, 2006, 10:11:33 AM

I built the DOD YJM 308. Was working fine, except for the sound. When i play, the sound remains good for like 2 seconds, then it farts out and gets dimmer and dimmer until when it completely disappears. Then if i touch, the metal section on the top of a particular Electrolytic cap (whose negative lead is grounded), the sound revives. This cap is situated in the section which is supposed to connect the +9volt to the input that goes into the 3rd lead of the JRC4885 dual opamp that i have used. Please Help!!

jonathan perez · November 22, 2006, 10:13:18 AM

awesome! yngwie doing what he does best!

grab yer DMM and start poking around, it sounds to me like you got a short.

user · November 22, 2006, 10:15:08 AM

Quote from: thebattleofmidway on November 22, 2006, 10:13:18 AM
grab yer DMM and start poking around, it sounds to me like you got a short.

DMM? wots that? please explain . thanks for replying.
And yes, im using a JRC 4558 opamp. Hehe got mixed up.

R.G. · November 22, 2006, 11:25:55 AM

That capacitor was supposed to have a resistor from +9V and another resistor to ground from its + lead. The resistor to ground is open.

user · November 22, 2006, 11:40:51 AM

Quote from: R.G. on November 22, 2006, 11:25:55 AM
That capacitor was supposed to have a resistor from +9V and another resistor to ground from its + lead. The resistor to ground is open.

tungngruv · November 22, 2006, 12:09:47 PM

Quoted from the the Wah Dr. (Paul Marrosy)

QuoteThe YJM308 schematic linked above appears to have one error: the 100 ohm resistor should be between the power supply and the opamp power supply rather than in series with 22K resistor at the voltage divider network.

Dirk_Hendrik · November 22, 2006, 12:46:27 PM

Quote from: thebattleofmidway on November 22, 2006, 10:13:18 AM
awesome! yngwie doing what he does best!

Oh My! You've just unleashed the f-in fury...

user · November 23, 2006, 09:57:15 AM

The problem persists. Wot a farting pedal...
And yes, ive corrected the power supply as shown here

QuoteThe YJM308 schematic linked above appears to have one error: the 100 ohm resistor should be between the power supply and the opamp power supply rather than in series with 22K resistor at the voltage divider network

I wouldve posted the voltages, but i dont have a multimeter yet...Can anybody please help me?

petemoore · November 23, 2006, 10:05:31 AM

...we just did. And will again...
Good news is DMM's are super useful and not too expensive...and will help you...er enable you to help us help you and all that...you gotta getta meter.

tungngruv · November 23, 2006, 10:23:31 AM

What layout did you use? Are you 100% positive that all resistors are the correct value? A pic of both sides of the board would be great also. Check your pm.

Also, if you used Nabos layout, you need to cut one of the connections (between the 10K and .001uf, circled in red):

user · November 23, 2006, 10:33:07 AM

Thanks, i am really positive that im using the correct resistors...i dont have my camera rite now..cant post pics..looks like im getting hopeless for you all....

tungngruv · November 23, 2006, 10:39:06 AM

You could rebuild it using the above layout. It's verified to work.

jonathan perez · November 23, 2006, 10:41:06 AM

Quote from: user on November 23, 2006, 10:33:07 AM
looks like im getting hopeless for you all....

without a DMM, or Camera, and without telling us which layout you used, id say yeah.

check your values. triple check them.

user · November 23, 2006, 10:50:47 AM

Quote from: tungngruv on November 23, 2006, 10:23:31 AM
What layout did you use? Are you 100% positive that all resistors are the correct value? A pic of both sides of the board would be great also. Check your pm.

Also, if you used Nabos layout, you need to cut one of the connections (between the 10K and .001uf, circled in red):

Yes ive used exactly this layout...
OMG!! i hadnt done this..I will do it now..

user · November 25, 2006, 05:56:17 AM

Ok guys, i probed around today. I still dont have a DMM.

The last output i get is at the 1st pin of the JRC4558. And no further.
The only modification that ive done is that ive used a 22pF capacitor instead of a 25 pF as shown in the layout.And one more thing, ive swapped the places of the 22pF cap and 1 meg resistor shown above the 1 and 2 pins of the opamp in the layout/ But the 0.047 cap still gets its input from the 1 meg resistor. The bloody thing is farting all day..please help.

petemoore · November 25, 2006, 09:09:49 AM

Not sure I follow allt he changes made.
IF the sound stops at pin 1 [the output of Opamp 'A'] then the opamp is probably misbiased.
Set that thing down until you can get your hands on a DMM

slacker · November 25, 2006, 10:10:13 AM

As the problem seems to be around the 10uF cap, try taking it out. If the rest of the circuit is correct then it will work without that cap.

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DOD YJM 308, farts out!!!