Egodriver Problem

[tenwatt]

So I assembled my first Mad Beans board and it went well...BUT...for some reason when i turn the gain knob up to about 1 o'clock and beyond it stutters and doesn't stop.  It sounds like somethings shorting it out and causing a stuttering sound of full volume to no volume, full volume no volume....  This happens when you get to about 1 o'clock turning clockwise.

I took it back apart and checked all my joints.  I reassembled it and made sure nothing was touching.  After doing this the problem continued.  What should I check next?  Any ideas what the problem might be?  

[tenwatt]

I should specify that I used the A1M for the gain pot.

[stecykmi]

check to see that the pot isn't faulty, first off.

after that, i would use audio probe to see where the fault first arises. so check after each gain stage, after the clipping stage and after the filter stage.

[stecykmi]

also check that your supply voltage is stable (ie battery isn't dieing, 9v adapter isn't acting funny).

[tenwatt]

Crap...I guess I have to order parts to build a probe now.

[gtr2]

You most likely have what you need to build one.
http://diy-fever.com/misc/audio-probe/

A couple things could help us help you...
IC voltages and transistor voltages, plus pics are helpful

I don't believe your problem is in the gain pot.  It's being used as a variable resistor in this circuit.  When you turn the pot clockwise it is limiting the current flowing back into the negative feedback loop of the IC.  By restricting the signal here it creates more gain out of pin 1 of IC1A.  The IC is being used as a differential amplifier.  Wiki it for some "throne" reading.

You may have a resistor value mix up somewhere?  A little more info will help.

Josh

[tenwatt]

If the cap for the probe wasn't 63V I'd have it all.

I used this IC:
http://www.mammothelectronics.com/TL082CP-JFET-Op-Amp-p/400-1117.htm

and these transistors:
http://www.mammothelectronics.com/2N7000-N-Channel-60-V-D-S-MOSFET-p/100-1043.htm

When you ask for the voltages are you saying I need to messure the voltage they're pulling?

I'll post pics when I get home.  I'm at the lowest level of noob there is so thanx for bearing with me.

[tenwatt]

I just double checked all the resistors.  They all seem to be correct but I am confused with the value of the R1 resistor.  R1 is supposed to be a 1M.  What I have in it's place is coded Brown, Black, ?, Yellow, Brown.  I can't tell the color of the third stripe.

Here are pictures of both sides of the board.

[gtr2]

You don't need a 63v rated cap, anything rated 18v or above is fine.

For the voltage measurements: Put your DMM on the V setting.  Place the black probe on the power jack ground and then touch a pin on the IC with the red probe.  Record the voltages for each of the 8 pins.  Do the same for each transistor leg.

For IC pins and transistors utilize the data sheets.  The first two are free    Google is your friend for datasheet locating.

http://www.datasheetcatalog.org/datasheet2/6/0ed6f5j6u9r503itwtq3d7f38cky.pdf
http://www.fairchildsemi.com/ds/2N/2N7000.pdf

R1 is fine.  It's a bit strange because it's a 1.08M but it's fine.

Also verify that your getting 9v from your power source.  Do this prior to anything else.

Josh

[jkokura]

Can't tell from the pic. Is D1 backwards?

Jacob

[tenwatt]

You don't need a 63v rated cap, anything rated 18v or above is fine.

For the voltage measurements: Put your DMM on the V setting.  Place the black probe on the power jack ground and then touch a pin on the IC with the red probe.  Record the voltages for each of the 8 pins.  Do the same for each transistor leg.

For IC pins and transistors utilize the data sheets.  The first two are free    Google is your friend for datasheet locating.

http://www.datasheetcatalog.org/datasheet2/6/0ed6f5j6u9r503itwtq3d7f38cky.pdf
http://www.fairchildsemi.com/ds/2N/2N7000.pdf

R1 is fine.  It's a bit strange because it's a 1.08M but it's fine.

Also verify that your getting 9v from your power source.  Do this prior to anything else.

Josh

Again, showing my noobness, I'll have to pick up a multimeter tomorrow.  I only have an old radio shack cheapo with a needle.  I'm using a Voodo Lab Pedal Power Plus that's powering everything else well so I assume it would be fine.

Once I get the readings from the IC and transistors and compare them to the datasheets what do I do if they differ?  I guess we'll cross that road when we get there...

Can't tell from the pic. Is D1 backwards?

Jacob

D1 is installed correctly.

[gtr2]

I'll rephrase it, make sure you are getting 9v to the board.  Measure with the red probe on the 9v pad and the black on GND.  You probably are but it's always good to check.

Second, I agree with Jacob.  It looks like the polarity of D1 is wrong.  The diode band should be orientated like the silkscreen on the pcb.  To me it looks like the orange/red band is facing the opposite direction.

Josh

[tenwatt]

Second, I agree with Jacob.  It looks like the polarity of D1 is wrong.  The diode band should be orientated like the silkscreen on the pcb.  To me it looks like the orange/red band is facing the opposite direction.

I think the picture is a little deceiving (or maybe I'm the one that's deceived).  I believe it's in there correctly.  I used this diode:  http://www.mammothelectronics.com/PhotoGallery.asp?ProductCode=120%2D1017  From my understanding the BLACK band is what needed to be lined up with the silkscreen on the PCB.  Was I wrong?  There is a close-up of how I have it installed below.

Thanx for all the help guys.  Having such a helpful and welcoming community is a real blessing.

[gtr2]

Ok, D1 looks correct in that pic.

[tenwatt]

Checked the boards voltage and it's getting 9.26V.

The IC's readings were:

1 - 4.44V
2 - 4.44V
3 - 4.24V
4 - .1mV (sometimes dropped to 0)
5 - 4.44V
6 - 4.44V
7 - 4.44V
8 - 8.86V

The transistors readings were:

Q1
D - 4.42V
G - 4.44V
S - 4.44V

Q2
D - 4.44V
G - 4.44V
S - 4.44V

What do I need to compare these numbers to on the datasheets?