Service centre for the Little Big Muff

Little Big Muff P1020477Hello again. This blog refers of course to the original Little Big Muff pedal by Electro-Harmonix from the 1970s, and not the more recent version which is basically a Big Muff in a smaller enclosure. This pedal is much loved by its owners, including our customer Adam, for its rarity and its outrageous sound. The Little Big Muff circuit comprises four NPN transistor cascaded gain stages, with each stage filtering and shaping the guitar signal before sending it to the next stage. The “Tone” switch allows two only extremes of either treble or bass tonality. The circuit component values are very similar to the well known Big Muff pedal.

Little Big Muff P1020471Adam shipped his LBM down to us from up in Lismore, Northern NSW. The ongoing problem with his pedal has been massive amounts of hiss – the hiss is of a “whooshing” nature, and renders the pedal unplayable. This pedal has been the subject of attempted repairs at least twice previously. Our immediate impression from trying out the pedal was that there was some instability in the circuitry in addition to the excessive levels of white noise. Please note – there is always going to be some white noise with the LBM as the design is very similar to a vintage Big Muff with the “Fuzz” control turned fully clockwise.

Little Big Muff P1020470First things first !! There were several electro-mechanical issues with this pedal to be corrected before we concentrated on the circuitry/PCB. The “Tone” switch, bypass footswitch, and input jack were all going intermittent, very much confusing the issue. The input jack was also wired incorrectly (!). We replaced all three items plus the DC IN jack (3.5mm min. jack socket) and the battery clip. All were at the end of their useful life.

Little Big Muff P1020472The pedal was now working as intended, but still with mega amounts of white noise. Turning our attention to the PCB (printed circuit board), we found that the 1st gain stage had been modded. We restored this stage to original spec, which included replacing the BC239 NPN transistor. The BC239 hasn’t been manufactured for donkey’s years, so may be difficult to source, but we have kept a private stock for these repairs. If you substitute a higher-gain device for the BC239, then the pedal probably won’t sound the same.

Little Big Muff P1020473Still noisy ! We ended up replacing all four NPN devices with BC239’s. A number of signal path capacitors had been previously replaced and we weren’t happy with what we saw, so we replaced them again with known types plus a few carbon composition resistors that we suspect had gone noisy and drifted off value.

Little Big Muff P1020476Now the PCB needed a tidy up and repair. We can’t help but notice that some PCB repairs to vintage pedals these days are not working out very well due to the application of too much heat and definitely too much solder. Surely everyone these days is using a temperature controlled soldering tool ?? The tracks and pads are being damaged by too much heat, or else taking too long on each solder joint. Too much solder might create the impression of a long lasting solder joint but in fact is  creating leakage paths across tracks or even the occasional short-circuit. It’s important to clean up after a job like this, in other words all the solder flux residue on the PCB and excess solder. This particular PCB had so much flux residue we couldn’t clean up completely – much of it was probably from original manufacture, but various attempts at repair through the decades have added to the mess.

Little Big Muff P1020481So – in the end, how did it sound ?? Pretty awesome, no wonder these pedals are so collectable. We did a direct A/B comparison with a Big Muff clone, with the “Fuzz” (aka “Sustain”) control set to max clockwise, as per the description above and the level of hiss was very similar, as was the performance of the pedal – taking into account the different “Tone” settings. Our favourite was the very fat bass setting of the “Tone” switch. We hope that Adam is enjoying his Little Big Muff, the pedal is now as quiet as we could achieve. See you next week for the next blog. IR.

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