MXR Micro Amp Problem

[soupbone]

My MXR Micro Amp started sounding wrong all of a sudden.I've had it for 7 months and never had a problem with it.It sounds that a busted speaker,or almost a fuzz know.I always keep the knob at 12 O' Clock.I checked all the resistors,and it doesn't look like anything's wrong.Does anbody know what might be causing this?

[jefe]

Off the top of my head... Did you clean the flux from the board after you were finished soldering?

[petemoore]

Does anbody know what might be causing this?
 Yepp, it's a bug in the microamp !
 See "Debugging'' super-sticky.
 ...not too bad, simple...build another and compare !
 Audio probe tends to point you in a much more specific problem related direction than 'bug in the amp', gives much more to work with.
 Wiggle the board around ? Slightly bend-stress or push the wires 'in', or pull lightly. Tap-slap the box on all 6 sides in case something got lodged in there.

[Thomeeque]

Does anbody know what might be causing this?

schemo

- defective opamp (IC1)
- wrong bias (R7, R8, R2, C4, cold joint)
- interrupted negative feedback (R4, cold joint)
- defective decoupling cap (C1, C5)
- insufficient DC voltage (J3, D1, cold joint..)
- or maybe something completely different

Measure DC voltages at all IC1 pins and post them here.

T.

[soupbone]

Cool.Thanks everybody for your responses!I'll send you that info thomeeqe.

[soupbone]

Hey Thomeeque,When you say measure the pin voltages from the IC,Do you mean measure the IC pin's to ground?

[soupbone]

What should the voltage's read?

[petemoore]

What should the voltage's read?
 It is natural that they will read what they read.
 An out of the ballpark reading would be good, unreasonable bias voltage would be a good reason for it not working.
 The Sticky Thread: Debugging..when it doesn't work.
 Read [and follow] that and you can help fix the Microamp.
 Re-reading is also recommended.
 Include freshly measured battery [with circuit load on it] or supply voltage so we have a reference potential with which to analyze the pin voltages with.

[Thomeeque]

Hey Thomeeque,When you say measure the pin voltages from the IC,Do you mean measure the IC pin's to ground?

Yes

More debugging know-how here: DEBUGGING - What to do when it doesn't work

T.