MXR Micro Amp Problem (First Build)

[david1991ross]

I recently bought an MXR Micro Amp kit from General Guitar Gadgets (all of the information on this kit is here: http://www.generalguitargadgets.com/effects-projects/boosters/mxr-microamp/) and I just completed wiring it up but it doesn't work like it should.

Here are some pictures from an album: http://imgur.com/a/k77Wb

If followed the layout as exactly as I could but I'm still having trouble. I did not make any substitutions to parts and I checked the values of each capacitor and resistor and placed the positive caps accordingly on the PCB. As far as the IC goes, the kit came with two. One was a TL071CP and the other one, not on the board, is a bit of a mystery to me as far as why it was included. Does the orientation of the IC matter on the PCB? I know the position of the caps matter for 3 of the 4 included. What about the resistors?

As far as the unit not working, when I run a cable from my amplifier (turned off) to the pedal, and from the pedal to my guitar, I am able to turn the pedal on and off as indicated by the LED. But when I turn on my amplifier, the LED lights up to about 50% when off, and 100% when on. When I press the switch on the pedal, there is a large popping sound. Any insight would be very helpful and greatly appreciated. Thanks.


6.What it does and does not do how it works; partially or not at all. For instance, if it lets no sound through; or if it makes a harsh, distorted sound only when you strum hard on the strings at full volume; or if everything is really, really low volume.

[strungout]

Yup, the IC orientation DOES matter! Wouldn't work if it wasn't oriented correctly!

Nope, resistor orientation does NOT matter.

If you have a multi-meter (you really should); gives us the voltages pin by pin for the IC. Meaning connect the black lead of your multi-meter to ground (the ground from your DC jack or battery), and give us the voltage you get from each pin of the IC. Makes it a lot easier for us to help. If you have an audio probe (you really should ), you can follow the schematic and tell us where the sound "dies".

[david1991ross]

Here is a link to the various voltages on the pins of the IC:
http://imgur.com/a/Bc7Fn

[J0K3RX]

Here is a link to the various voltages on the pins of the IC:
http://imgur.com/a/Bc7Fn

I think Frank {strungout) was trying to tell you that you installed the IC (TL071) backwards... The dot at one end of the chip should go to the square pad on the board.  correct that and if it still doesn't work then take voltage readings. You said you got an extra chip with the kit... might need it. 

[david1991ross]

Ah, OK. I'll give it a shot and report back.

[J0K3RX]

You may already know this but I will throw it out there anyway just in case...

The kit probably didn't come with a chip socket but for future reference I would recommend that you get them and use them for IC's...

1. if you stick a chip in backwards all you have to do is pop it out and install it the right way although you may have damaged it by installing incorrectly. At least you won't have to de-solder it and risk possibly damaging the board or the chip.

2. If you use a socket you don't have to apply heat to the component.

3. If you have a socket you can experiment using different IC's..   

[david1991ross]

The kit did come with a chip socket although I didn't know what it was for so I installed the actual chip into the PCB and am having a time trying to get it out. I think I'll have to cut it out and get a new one because desoldering it doesn't seem to be working. Live and learn I guess. Just so I'm clear, I have to install the IC socket into the board in the correct orientation, and the place the IC into the IC socket?

[strungout]

When I have to remove a socket (valid for an IC) I try to quickly melt the solder WHILE prying off the socket (or IC) with a small screw driver, quickly going from pin to pin, until it comes out. It's ghetto but it works for me XD. Otherwise you can use something called solder wicker, which is braided copper that when heated and in contact with solder will sort of swallow it up.

It doesn't really matter which way you put in the IC socket, all that matters is that the IC is put in the right way. The IC usually has a dot near pin 1 (upper left corner). This is how you know how to orient it.

So, again, you just have to orient the IC in the correct position. Even if you install the socket upside down, the IC will still fit right side up.

Don't despair, most of us have been there. Hey, that rhymes...

EDIT: And like Jim (JOK3RX) said, you should always use a socket for ICs and transistors, it makes it much easier to replace the part, you don't risk frying an IC/transistor while soldering it AND you get to try different ICs/transistors and find out which part's sound you like best. I always use sockets.

[PRR]

If "all" your IC pin voltages are 7V and up, you probably do not have Ground (negative) connected.

On most chips in most circuits, one pin will be at zero volts. Not finding that is a red flag to look how that pin connects back to the other end of the power source.

[Fender3D]

Maybe it's not just the chip:
looking at your pics, your footswitch looks like turned 90°...

[italianguy63]

Maybe it's not just the chip:
looking at your pics, your footswitch looks like turned 90°...

I think you nailed it. 

[duck_arse]

the pcb has a small square pad to indicate pin1 of the IC. that spare IC in your last photo is not really a spare IC. I'd say the best way to replace that backwards one is to carefully cut each leg away from the body of the IC. throw the remains of the IC away, and then heat each soldered leg as you either pull on it with pliers, or poke it through with a needle-like tool. then put the socket in, and buy a new TL071.

and your footswitch needs to be rewired, after it's turned to match the ggg dia, like ^ they say.

[J0K3RX]

cut each leg away from the body of the IC. throw the remains of the IC away, and then heat each soldered leg as you either pull on it with pliers, or poke it through with a needle-like tool.

In regards to the "needle-like tool" I found a stainless steel needle and stuck it in a precision screw driver with the sleeve that tightens on the the bit. I use it to clear holes on circuit boards... Works great since solder does not stick to stainless And, when I can't find it (most of the time) I have a box of toothpicks handy.

[david1991ross]

Ok so I switched turned the DPDT switch 90 degrees as suggested and rewired. I was also able to get the IC socket into the board. One thing I did do was change a capacitor. It is the same value and I do not believe it will hurt anything. It's on the left hand side of the IC. Anyway, the pedal is still not working. The sound is either full or at 1/4 volume depending on when I use the DPDT switch. The LED does not come on and the potentiometer does not work. I checked a number of components to see if the values were correct and they were. Additionally, the connections on the PCB check out and I'm not really sure what the problem is at this point. Any insights would be greatly appreciated.

[Fender3D]

Switch wiring's still wrong...

[david1991ross]

How so? I rotated it 90 degrees. What am I missing?

[Cozybuilder]

Its difficult to see, but are the PCB input and PCB ground connections to the 3PDT reversed?

[david1991ross]

He is the same picture but labeled. It is as the layout specifies. Apologies for the bad picture.

[Cozybuilder]

Have you tried verifying the footswitch is good? Its easy to overheat and ruin it when desoldering and moving wires & such.

[Fender3D]

Sorry, the GND bridge confused me....
that is ANOTHER IC, isn't it?

Forget the switch for a minute and connect PCB input to input jack and PCB output to output jack: does it work?
Then post voltages as suggested here: http://www.diystompboxes.com/smfforum/index.php?topic=29816.0