problem with MGV (Guv'nor GGG) build - does not work

[radrobot]

Hello.

First post, but have been lurking for a while.

Got up the courage to build my first pedal - the GGG EA Tremolo.  It worked the first time I hooked it up.  This encouraged me to build another pedal.  I just finished assembling the MGV (Gov'nor) pedal from the GGG site.  The LED lights up but the pedal passes no signal on or off.  I've checked my connections to the input/output jacks and also the wires going to the bypass switch.  All looks correct.

Below is the voltage I measured for the IC pins -- the ( ) show what it should be.

9 volt power supply -- 9.06v (9v)

Pin 1 -- 4.52v  (4.5v)

Pin 2 -- 4.52v  (4.5v)

Pin 3 -- 4.10v  (4.2v)

Pin 4 -- 9.06v  (0.0v)

Pin 5 -- 0.00v  (4.5v)

Pin 6 -- 4.52v  (4.5v)

Pin 7 -- 4.52v  (4.5v)

Pin 8 -- 4.51v  (9v)


As you can tell, pins 3, 4, 5 and 8 do not fall within the 0.5 volt variance.  Pins 4, 5 and 8 are switched around.

I am new to this, so I'm not sure where I should start looking for a mistake.  All the resistors, caps and diodes seem to be in their correct places.


Here's a link to the layout as well as a link to the schematic.

http://www.generalguitargadgets.com/pdf/ggg_mgv_lo.pdf

http://www.generalguitargadgets.com/pdf/ggg_mgv_sc.pdf



Thanks for any help.

[ItZaLLgOOd]

Check to make sure that you don't have your power and ground wires mixed up.  That might cause the voltage issues.

[slacker]

Hi, welcome aboard

I think what you've done is get the pins of the IC wrong. They are numbered like this

1        8
2        7
3        6
4        5

Looks like you've reversed 5 - 8 that would explain how you've got 4.5 volts on pin 8 (really 5).
If that's what you've done then it also looks like you've reversed the wires to the DC jack/battery or your power supply is the wrong polarity. To check this put the red lead from your DMM on the point marked 9v on the layout and the black lead on the point marked G and measure the voltage. You should measure 9volts if you measure -9volts then something is wrong.
Unfortunately if you've somehow reversed the power to the circuit you've probably destroyed the op amp.

Hope this helps

[radrobot]

Hi, welcome aboard

I think what you've done is get the pins of the IC wrong. They are numbered like this

1        8
2        7
3        6
4        5

Looks like you've reversed 5 - 8 that would explain how you've got 4.5 volts on pin 8 (really 5).
If that's what you've done then it also looks like you've reversed the wires to the DC jack/battery or your power supply is the wrong polarity. To check this put the red lead from your DMM on the point marked 9v on the layout and the black lead on the point marked G and measure the voltage. You should measure 9volts if you measure -9volts then something is wrong.
Unfortunately if you've somehow reversed the power to the circuit you've probably destroyed the op amp.

Hope this helps

So basically pin 4 and pin 8 on the IC are reversed.

Pin 4 should go to ground with a voltage reading of 0.0v, but I'm getting 9.6v.  Pin 8 should go to + with a voltage reading of 9.6v, but I'm getting 0.0v.

I checked the 9v to Ground on the board and am getting 9.6v (which is correct - I think).

A ground on the board is going to the ground on the DC jack.  The 9v on the board is going to a + on the DC jack.

The IC is in correctly with the "dot" on the IC matched with the square input on the board.

Confused.


Also, like mentioned before, the pedal is not passing signal even when off (with no power as well).  Shouldn't the jacks at least pass the guitar's dry signal?

[radrobot]

UPDATE:

I made an audio probe and poked it around on the circuit (sort of fun).  I followed the schematic (to the best of my ability) and everything passes a signal until I got to the 9v input on the board.  No signal was being passed from here to pin 5 on the IC. 

Touched up the points with the iron everything worked!!!!

But then things started crapping out like there was a short somewhere.  I traced this back to the output jack.  I've built the MGV inside an old Horizon metal DI box.  I have to use the washer clip things (like to mount stuff to a studio rack) in order for the screws to attach the top and bottom of the Horizon box.  Apparently something on the output jack was touching one of the clips and causing things to short out.  I better insulated the jack and added some electrical tape to the clip and everything sounds great.

Anyway, I guess I should have done the audio probe first, and then I wouldn't have had to waste space on this forum.

A big thanks to this forum and all the great info on here.


BTW, pin 4 and 8 on the IC are still reversed.  Not sure if I'm reading the IC correctly.  Looking at the IC the dot is in the upper left hand corner.  I'm counting that pin as pin 1.

1     8
2     7
3     6
4     5


Is pin 1 by the dot or pin 5?  Because if you flipped the above order the readout would be correct.

5     4
6     3
7     2
8     1

[dxm1]

UPDATE:

I made an audio probe and poked it around on the circuit (sort of fun).  I followed the schematic (to the best of my ability) and everything passes a signal until I got to the 9v input on the board.  No signal was being passed from here to pin 5 on the IC. 

There is no need to probe the power or ground connections. If things are working right, you will have no signal on these traces.

Touched up the points with the iron everything worked!!!!

Congrats. It's nice when it finally works.

BTW, pin 4 and 8 on the IC are still reversed.  Not sure if I'm reading the IC correctly.  Looking at the IC the dot is in the upper left hand corner.  I'm counting that pin as pin 1.

1     8
2     7
3     6
4     5


Is pin 1 by the dot or pin 5?  Because if you flipped the above order the readout would be correct.

5     4
6     3
7     2
8     1

Either you are reading the voltages incorrectly, or you have assembled a positive ground opamp circuit.

Unless you are the victim of a _serious_ manufacturing defect, the dot should be on pin 1.  Attach the black (negative) lead of your voltmeter to the sleeve (ground) connection on the input jack.  Touch the red (positive) lead to the terminal on the DC jack that you believe is ground. It should read 0v. The terminal that you think is positive should read 9V.

If that's the case, then touch the positive meter lead to each place on the schematic that should be connected to ground. You should read 0V at each point (that includes pin 4 of the IC).

[radrobot]

Thanks dxm 1.

With the way you described checking things, everything reads correctly now.

For some reason I had the red lead connected to positive on the DC jack and was using the black lead to check the pins on the IC.

I've learned alot, have a pedal that works and look forward to my next build.

Thanks again.