Mxr Micro amp problem (1st build) help

[Bearbadger]

Hi, I'm trying to get an Mxr micro amp clone from tonepad .com to work.


I have put everything together, have sound in bypass and very very faint sound when engaged which turns up slightly when pot is turned. I am stumped.

Ic reads

P1 - 4.36
P2 - 4.36
P3 - 4.34
P4- 0.00
P5 - 2.80
P6 - 5.46
P7 -5.46
P 8 - 8.70

[Mark Hammer]

One of the common bugs in novice builds is that people overheat their stompswitches and create discontinuities as a result.  Just for the heck of it, try wiring your circuit board directly to the input and output jacks, such that it doesn't go through any switch.  If you get a properly-functioning booster, then your problem lies somewhere in the switch, or the wiring to it (e.g., cold solder joint on a switch lug).

Although the voltages look a little wonky to me.  If you are using a single op-amp, whether TL061 or 71, or some reasonable replacement, your supply voltage should show up on pin 7, not pin 8.  Did you stick a dual op-amp in there somehow?

[matmosphere]

Go back and double check the values of the resistors. Looks like you're using solid wire instead of stranded, make sure there isn't any shorts anywhere in the wire.

[duck_arse]

hello and welcome to the forum, bear.

you have a problem with V+ somewhere. pin 7 should be supply (8V7 ?), possibly shorting to pin 6. pin 1 should be less than shown as well, I think, and possibly pin 8. power off and measure the resistance between each ic socket pin, and each pin - to V+ line and to ground line. R4 appears to be empty, is there a reason? and what are the colour bands on the left-most bottom resistor, and what does it measure?

can you post photo so we can see solder condition?

[Bearbadger]

Thanks for the replies. I tried wiring straight to the board and still get a really faint sound which increases when pot is turned. Could this be a problem with the Ic? I didn't think solid wire would be a problem, should I swap that out? Here are the solder points....    The bottom left resistor is a 22M. I was going off this diagram. http://www.tonepad.com/getFileInfo.asp?id=6

[matmosphere]

You should reflow some of the solder, especially around the IC to make sure you have a solid connection. You should also try and cut the leads down more, long leads can cause problems.

You probably don't have to switch the wires though, just a thought for future builds. I think generally solid wire are best places were things will not move at all (jumpers). Solid wire is actually much more delicate than stranded. Solid wire is way easier to solder though.

[Fp-www.Tonepad.com]

Nice looking photographs, although I must agree with the previous post, you need to reflow some of those joins.

First begin by using an old toothbrush and a few drops of alcohol for cleaning.
Get some liquid soldering paste and add a little to the worst parts.
Touch with HOT soldering iron until you get a nice Hershey's kiss shaped blob. Some will need you to add extra solder.
A magnifying glass and good light are essential.

Fp

[Govmnt_Lacky]

Your R1 resistor is WAYYYYYYY OFF!!

You have a 22 ohm resistor in there when it should be 22M  

Most of your input signal is going to Ground  

R1 color code SHOULD be Red, Red, Black, GREEN, Brown for a 22M 1% resistor.

[Fp-www.Tonepad.com]

Good eyes!

[Bearbadger]

Thanks for the replies. 'll tackle it now. 

[Elijah-Baley]

You could try as R1 a 2M resistor or some near value. That is a pull down resistor. With a 22M you might, but not necessary, a sort of bump when you engage the pedal.

I built the GGG version, slightly different, but 2M resistor don't give me any trouble.

[Fp-www.Tonepad.com]

22M has always seemed unnecessarily high, but that's what was called on the schematic.
2M or even 1M would be ok.

[Bearbadger]

Replaced the resistor, went over every solder joint, still no joy. Must be the IC? 

[Elijah-Baley]

Do you have an audio probe or something? Or some alligator clips?

[duck_arse]

bear, you know the resistor is a 2M2, and I know the resistor is 2M2, even g_lacky knows it's a 2M2, but what did your meter say it's value was before you put it in?

[Bearbadger]

I  replaced the R1 with this.  

[Crontox102098]

I  replaced the R1 with this.  

Besides that, apply little bit of thinner with a brush on the copper side 

[Fp-www.Tonepad.com]

Try removing it and test the pedal. If that's your problem it should work.

Also, it seems like you replaced R1 with another 22 ohm resistor.

[duck_arse]

use the meter. it still looks like fp-www says, way too low. use the meter.

[Govmnt_Lacky]

I  replaced the R1 with this.  

Is there a color stripe on that R1 resistor between the Black and the Brown?

It looks like the color code for the one you have in there now is Red, Red, Black, NOTHING, Brown.

It looks like there almost maight be a Blue stripe there BUT... I highly doubt it is a 220M resistor  

Whatever it is... I personally think you should remove it and use a meter to test it's resistance. I still think you are using the wrong resistor there.

You need a resistor that is color coded RED, RED, BLACK, YELLOW, BROWN.