MXR Micro Amp Problem (First Build)

[david1991ross]

Yes it is another IC. Also, I thought I'd post the original wiring diagram which I've been following.

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

I will do as you suggested Fender3D and check back in.

[david1991ross]

Ok so I connected the PCB input to the input jack and the PCB output to the output jack. I connected these wires to the jack tips. I'm not sure if that was proper to do or not. Anyway, it played but without the LED light and without the potentiometer working. I also checked the voltages on the IC:
One other thing I should mention is that I am concerned that I cooked the PCB. I did use a lot of heat trying to get the original IC off the board and some of the PCB track did pop off when I did this although there is continuity between the components/traces. This is getting very frustrating. Should I consider buying a new 3PDT switch or a new PCB? I cannot seem to figure out the problems.

[italianguy63]

This is getting very frustrating. Should I consider buying a new 3PDT switch or a new PCB? I cannot seem to figure out the problems.

David--  I can at least offer some encouragement.  We have all been there!  And, there is a learning curve to this, and we have all had problems and ruined stuff.  I have a drawer full of my own F'-ups!  Stay with it my friend.  You will get it!  The people here are great and helpful.  Best resource ever.

MC

[bluebunny]

Looks like you still have a problem with your ground connection - all your IC pins are close to 9V.  Check continuity between all those places that ought to be grounded - the ground lugs on the jacks and on your switch, the GND point on the PCB, pin 4 of the IC, the -ve side of the battery clip.  You might also want to redo your ground connections to the jacks: it looks like the solder may not have flowed too well.

[Fender3D]

pin4 is not @ 0V
check tracks and/or solders
check C4's positive lug is @ ~4.5V

edit:
bunnies are typing faster than me 

[Ice-9]

The voltages on the IC are all wrong.  I would try to test the circuit by disconnecting all the wiring and just connect the power to he pcb. test the voltages on the ic and if incorrect you will need to trace where the problem lies.  Even try this with the IC removed as with 8v on every pin of the IC it could be fried.

Without the IC you should at least get the correct voltages on the power at pin 7 and 4 on the PCB. If you still have bad voltages here with just the power going to the PCB and no IC you have an error on the board, likely a short somewhere or another failed component.
Can you provide a picture of the underside of the PCB as well as the top.

[J0K3RX]

Dude, try this... This is as bare bone as you can get it. No LED, no switch, no DC jack just running from your 9v battery. If you toasted your IC then it won't work any way you try it but at least you should get different voltage readings around the IC. If you have another IC I would pop it in and see if it works.

[david1991ross]

Update: I just got it to work. I realized that there was a track between two grounds which was broken. I soldered the two together and the circuit now works. I also resoldered the ground connections. I made a mistake in taking the voltages of the IC. I had the probe on the sleeve and not the ground. Here are the voltages of the IC. I hope that they are realistic. How would one know that they are? What is the basis for figuring out what IC socket voltages should be?



I'm looking forward already to my next build. I'm thinking maybe a point to point Fuzz Face, maybe a wah. I also have plans to build a AA764 Fender Champ clone and eventually a Marshall JCM800 2204 clone. I'm pleased with the pedal and with the help you all have given me. Thank you very much!

[Fender3D]

If you really read those voltages ^^ circuit can't work!

You must have supply voltage @ pin 7, 0V @ pin 4 and (with IC in place) ~1/2 V supply @ pins 2,3 and 6. Other pins don't matter

[J0K3RX]

+1 What Fender3D said ^^^

Have you played through a "working" micro amp before?

I'm looking forward already to my next build. I'm thinking maybe a point to point Fuzz Face, maybe a wah. I also have plans to build a AA764 Fender Champ clone and eventually a Marshall JCM800 2204 clone. I'm pleased with the pedal and with the help you all have given me. Thank you very much!

You may want to build a few more pedals before you get all elbows deep into those!

[bluebunny]

I had the probe on the sleeve and not the ground.

The sleeve should be the same as ground.  Still not convinced that it's working, but if it sounds OK to you, then it's working; it could be that the voltage measurements needs a little practice.  As Fender says, those readings are completely wrong.

[david1991ross]

If you really read those voltages ^^ circuit can't work!

You must have supply voltage @ pin 7, 0V @ pin 4 and (with IC in place) ~1/2 V supply @ pins 2,3 and 6. Other pins don't matter

I did some checking and I believe the problem with my voltages was that I'm not grounded properly, so I took a piece of solder and wrapped it around a ground sleeve and then attached it to the enclosure. When I did this, it changed my voltages:

Pin 2: 4.14V
Pin 3: 1.92V
Pin 4: 0V
Pin 6: 4.11V
Pin 7: 8.33V

According to you my Pin 3 voltage is low with my other voltages being good if I understood you correctly. I am wondering if I need to run a wire from the ground sleeve and solder it to the enclosure or if the cables coming from the amp and the guitar create a ground? Also, should I have measured the voltages with the pedal plugged into a guitar and amp or does it not matter?

One other note is that based off of demos I've seen of this pedal, I am very confident that mine works the same as they do, although mine may still have issues.

[PRR]

> Pin 3: 1.92V
> According to you my Pin 3 voltage is low

Pin 3 appears to be biased with a *10Meg* resistor. Any meter-loading will make it sag.

The fact you have nearly 9V, zero, and 4.1V (half of near 9V) at the other expected places suggests your pin 3 is happy except when you try to measure it.

[david1991ross]

> Pin 3: 1.92V
> According to you my Pin 3 voltage is low

Pin 3 appears to be biased with a *10Meg* resistor. Any meter-loading will make it sag.

The fact you have nearly 9V, zero, and 4.1V (half of near 9V) at the other expected places suggests your pin 3 is happy except when you try to measure it.

Ok cool. What about my grounding worries?

[bluebunny]

Ok cool. What about my grounding worries?

Check continuity between all those places that ought to be grounded - the ground lugs on the jacks and on your switch, the GND point on the PCB, pin 4 of the IC, the -ve side of the battery clip.  You might also want to redo your ground connections to the jacks: it looks like the solder may not have flowed too well.

[david1991ross]

Ok, I've got it working correctly. Thank you for all of the help! One final question. I am interested in building a fuzz face pedal and have heard that using a breadboard is helpful in making pedals. Would a kit like this be a useful route to go?:

http://smallbear-electronics.mybigcommerce.com/breadboarding-the-fuzz-face/

[duck_arse]

it would indeed. everyone here knows of the sterling service and support provided by the bear. he will come chase you with answers if you post problems, too.