Fried amps and a DIY bazz fuss

[ckc14]

So I am brand new to this and so far have only successfully built two Noisy Cricket amps.  My current project is a bazz fuss.  It worked fine on the bread board and sounded pretty good when I soldered it together it sounded fine for a minute then fried one of the noisy cricket amps I was using to test it.  At first it made sort of a flapping sound like a blown speaker which didn't surprise me because I was using lousy speakers from an old radio.  So I decided to test bazz fuss with my Vox Valvetronix, oops  ...  Anyways, now the Vox makes no sound at all except when attached to a cable there is a low pop when I turn the amp on then total silence.

So I went back to the noisy cricket and began my investigation there.  I used alligator clips to test the speakers on the broken noisy cricket with my functioning one and they work so that tells me it is something with the circuit.  I started testing the resistors and capacitors with my ohmmeter and I have one electrolytic cap and one resistor that are suspect, (C1 and R3 on the following schematic http://pedalparts.co.uk/wp-content/uploads/2012/12/rubycricket.pdf).  I don't think it is the IC or the transistor because I swapped those out independently and together and the amp still made the same sound, although now it sound a little more like steady human flatulence like from the camp fire scene of Blazing Saddles.

My goal is to fix the noisy cricket amp and use what I learn from that to give the guy that is going to look at the Vox a better idea of what might be wrong.  Any tips or suggestions are appreciated.  Also any ideas on what might have caused the bazz fuss to do this to my amps would be good to know.  Are there any precautions I should take in the future when testing pedal builds to make sure this doesn't happen again?

Thanks

[Mike Burgundy]

I can think of no way at all that the BazzFuss I know (no schematic or link) would be able to blow up/damage a cricket.
You'll need lots more data and measurements, for all you know your guitar cable has a tiny break on the copper... Good luck!

[ckc14]

I can think of no way at all that the BazzFuss I know (no schematic or link) would be able to blow up/damage a cricket.
You'll need lots more data and measurements, for all you know your guitar cable has a tiny break on the copper... Good luck!

The BazzFuss I built uses the same parts and layout as this one at Poodle's Pedal Parts, http://pedalparts.co.uk/wp-content/uploads/2012/06/BazzFuzz.pdf.

I can take some measurements tonight and post them here if it helps.  What measurements would be most useful, voltages on the IC and transistor?

Also, just to clarify it is not my instrument cables, (even though most of mine are lousy) the cricket makes the sound even when there is nothing plugged into it and I tried the cables in another amp and they work as good as ever.  The sound from the cricket is a constant low pitched sound something between a bumble bee and a fart that increases when I turn the volume knob.

I am not sure if I mentioned it above but the Bazz Fuss still isn't boxed up, I just have it loose on a perfboard and the power was hooked up using aligator clips and 9 volt.

Thanks for the response.

[ckc14]

Could it be possible that the alligator clips attached to the battery touched something they shouldn't have and sent 9 volts right into the cricket amp?  I just built up the courage to try the Bazz Fuss again on my other noisy cricket and it worked fine but instead of using alligator clips to attach the pedal to the battery I used the rails on my bread board and a battery clip with no problems.

The voltages for the pins on the transistor (MPF 102) are as follows:

D: 3.2
S: 2.6
G: 0

For the IC (LM 386-N3)

1: 1.2
2: 0
3: 0
4: 0
5: 1.2
6: 3.0
7: 1.4
8: 1.0

(If these seem way off as in I did them wrong, let me know I am a newbie)

[mistahead]

Someone correct me if I'm wrong, but pushing 9V down the signal channel of a LM386 amp will pretty much always melt the 386.

They also have ZERO tolerance for polarity issues (as my daughter's family of "chip creatures" to play with attests to).

[Mike Burgundy]

LM386 max input voltage is +/-0.4V. That's much lower that I expected.
It's protected from DC as per the schematic, but if you feed the cricket a LARGE signal an crank the volume, that could easily exceed maximum ratings. If you don't have a bypass switch, it's quite easy to lose reference with clean volume so you might slam a signal into the amp that's a lot bigger than it's supposed to be. Trace the signal to the IC, if it stops there replace (or just replace anyway)
No idea about the Vox, or what's in there.

[GibsonGM]

Odd, huh?   Yup, the 386 will fry under those conditions, no doubt. Just replace the chip, but watch your polarities and output from pedals, etc.

But, 9VDC going out to the VOX should be FINE.  Not that it's a 'nice' thing to do to something expecting to see pure AC, but it should not harm it.   Once the cricket works again, I'd measure the DC output at its jack, to be sure the output cap is ok and not allowing 9V thru.    The only other thing coming to mind with that, is that maybe there's an input cap in the VOX that is rated low, and the cricket caused it to blow??   I'd hope VOX built them with better parts than THAT, tho!!!   
Interesting problem
   
I suspect a combination of things here....blown 386, perhaps a bad cable, which i would definitely replace with a new or known good one.

[ckc14]

So I went down to the shack and got some new 386's and put one in and that seemed to fix it mostly.  Earlier I pulled an extra 386 and tried that and that one must have been fried too because I got the same bad sounds.  I fiddled with it some more and have decided that the speakers (which I pulled from a small radio) are breaking up more than they had and cutting out on low notes when I strike them hard so they are probably not as good as they once were. 

Thank you to everyone for the input. 

Also I got my Vox back today and they guy I took it too said it was working fine, I tried it and it is.  Not sure what went wrong there when I was trying the bazz fuss.  I swear I did everything when it stopped the other day... pedal, no pedal, different guitars, adjusted settings yadda, yadda.  Probably some combination of being a newbie, nerves about the broken cricket, and  Gremlins for sure.  Good to know that 9volts shouldn't and didn't cook something in my good amp.

Thanks again.