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  • I built a Fuzz Face and it Motorboated...[Pics added]

So finally I got back to building another pedal!!!

I have been wanting to build a fuzz face for ages now (since I made the PCB about a year ago) and finally did it this weekend. I used http://fuzzcentral.ssguitar.com/index.php as a point of reference and information and grabbed the original Dallas PCB from there as well.

Because of the lack of availability of germanium transistors (AC128) and also carbon composition resistors, I decided to go with the the BC109C NPN transistors (gain of around 500) and carbon film resistors and then just see how the fuzz face sounds and if to harsh, then import some AC128 or AC127's and substitute them in. Component values are all from the original NPN schematic (not the re-issue version).

Next up was testing it...
Signal chain: Gibson Les Paul Deluxe -> Fuzz Face -> Vox ACTV4

Tone: I found that the overall tone of the pedal is quite nice. It is a bit deeper than expected, found that it cuts some of the treble as opposed to when the signal is clean.

Fuzz: Not to harsh in my opinion, however I must still listen to some you tube video's to see how it compares to the originals with the AC128 transistors. The only problem I am having is that when I turn up the fuzz pot the pedal starts to motorboat...apparently this can be fixed with a large cap across the power rails (+-1000uF) so must try this.

Things to try...
First I want to get the motorboating issue fixed. Then I want to try the AC128 germanium, the 2N3904 silicon and the BC109 low gain transistors. Then I will try the "Roger Mayer/Jimi" mods and see how those sound.

Pics:


Pedal housing


Shot of the inside showing the white plastic preventing solder joints shorting on the case


Proper gut shot

Sounds: who knows when I will post recordings as I don't have decent gear to record with...
    that circuit looks really easy

    is this similar to the one that was used on black sabbath - paranoid, the dallas rangemaster ?
      Manfred Klose wrote: that circuit looks really easy

      is this similar to the one that was used on black sabbath - paranoid, the dallas rangemaster ?
      No, this is a fuzz pedal. The Dallas Rangemaster is a treble booster. I had one there at Sanctuary the other day but you missed it ?
        ah ok, must have missed read something there.

        what i know about fuzz pedals is dangerous ☹
          Nice neat build!

          AFAIK though.. Gains of 500 are muuuuuch to high for this circuit. What you are hearing is by no means the revered fuzz-face. If you don't want to spend in excess of R200 on transistors, you will need to get a bit creative. If you want a guaranteed win, I'd say buy a pair from Smallbear. If you want to do it on the cheap, scout around for the suitable alternatives to the AC128, there are many.

          As NOS, the AC128 (at least in its original and useful form) is VERY hard to come by. Trust me on this one, be very wary when considering to put your money on what somebody claims is an AC128. Also understand that the AC128 is an PNP transistor, and to guarantee success, you will have to rewire your pedal to positive ground. There are some cases where PNP's have worked in the NPN circuit by just swapping the collector and emitters, but its not advisable.

          I would thus suggest that when looking for suitable alternatives, make a point to find NPNs, just for the sake compatibility with your pedal chain. You need low leakage (preferably <300uA) and gain of between 70 and 130. The transistor test circuit is very useful and simple to set up. Google 'Technology of the Fuzz Face' for info.

          On silicons. Sure, try them; but realize that using them in the Fuzz Face topology, its not going to be one - but you may like the sound anyway.

          Also, carbon comps have little to no tonal benefits in this circuit. They're great for hype and aesthetics, but unless you like noise and thermal drift, stay away. Kit it out with metal films and it will be golden.

          Another very important factor is setting up the correct quiescent conditions in this circuit.. Do not assume that popping in transistors whilly nilly is going to get you in the right place. I would recommend starting with a 50k trimmer each in place of the 33k and 8k2 resistors. Starting with the original denominations, set the Q1 collector to 0.5V with the 33k's trimmer and then set the Q2 collector to about half your supply voltage with the 8k2's trimmer. Then check your Q1 again. Once you're in that ball park, fiddle around to your tastes and you will have pleased ear-holes. A trimmer in place of the 330/470 ohm can help you set your output level.

          Very exciting circuit and lots of fun to mess around with! You might enjoy a switchable positive feedback loop in there aswell ?

          Have fun ?
            Thanks makepeace...

            Some of the originals used the BC109C tansistors had gains in the 500's, but they aren't the most desired ones! I simply built with parts that were available locally. You can get AC128 and AC127 (the NPN version) from quite a few places...some claim to match and measure the hfe, and others just sell them. One place I have noticed that claims measured, matched pairs is http://www.banzaimusic.com/Transistors-matched-selected/

            Apparently the 2N3904 silicon with gain between 100-200 sounds very nice so I want to try them as well.

            The PCB I made is the original +ve ground version, but I simply wired it for -ve ground. So when I do get my hands on an AC128, I'll re-wire it.

            Next step is to build up a vero-board test circuit for the transistors and also build a vero-board fuzz face that I can just plug different transistors onto to make life a bit easier when I want to see what they sound like after testing. I'll try the 50k trimmer trick on this as well when I make the board.

            For such a simple circuit, there are just so many options to play with!

            Time to play!
              Oh my bad, I thought you would be after the (first) original highly desired germanium fuzz face tone.. ? :?

              Man this whole AC128 story is funny..

              http://www.analogman.com/fuzzface.htm

              Read the part about the AC128 here. I don't know how much to respect this guy's idea, but from what I know, he's quite a venerated dude in the boutique circles. There's a lot of conflicting information, so I guess there aren't any real answers but peoples own experiences.

              here's another opinion:

              http://www.jacquesstompboxes.com/ac128.htm

              And then you obviously get the opinions expressed on FuzzCentral and also GeoFex.

              When I first tried my hand at building one of these I ordered 4 'matched pairs' of AC128s from a respected seller on eBay with gains between 80 and 120. I have since thrown them into the banishment pile, as no combination of these proved to be useful. Maybe I just got a bad batch, but it certainly wasn't worth it for me to return them to the seller.

              Its also interesting to note that Steve Daniels at Small Bear doesn't sell such a thing as an AC128. He's a very widely recognized seller of pedal supplies, and I think he knows his stuff.

              Anyway, the whole things seems to be quite a mystery. I would almost go as far as to say that at least one person is making up stuff.

              Anyway, what my experience has taught me: my 'good' ones have been a pair from Small Bear (bought them a while back when they were a bit cheaper) and a batch of cheap NPN's with a range of gains and leakages in which I managed to find some gold..
                Just to give some perspective of the kind of tone I would like...Here is what I'm going for:

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