I did a post on how to modify circuit from using NPN to using PNP transistors, and as a bonus I added a quick note on how to do this for Fuzz Face. Now it’s time to actually do it. I’ll breadboard a Fuzz Face clone, and then I’ll swap NPN transistors with PNP transistors.
I go through schematic and some extra details here, but if you prefer just seeing the video – go straight to it.
Schematics
Schematic is the same that I did earlier, if you want to know more about the circuit be sure to have a look at the build page for the effect, or you can jump straight into more detailed look at it.
The schematic here is slightly adapted so it is easier to see/explain the differences. Here are side by side NPN and PNP version of the effect:
Spot the Differences
As with LPB-1 conversion, the diagram layout is practically the same. Here are the differences highlighted:
It is clear that I have to replace transistors – I went from BC109C NPN transistor to BC559C PNP transistor. BC559C is PNP complement to BC549C that I tried out before. These are high gain transistors, if you used lower gain transistor for NPN version, and you like that sound maybe look for a lower gain PNP alternative.
The power rails for the amplifier part are swapped, as well, but that the same as when I tried out LPB-1 in PNP version.
The only difference is that C2 has to be rotated, because polarity changed. And this is important because if we don’t wire up electrolytic capacitors correctly – they might be damaged or destroyed (and in extreme cases they could explode or catch fire). C2 has to be reversed (note that positive lead is at 9V), but C1 should be left as is – because polarity for it did not change.
Breadboarding Them
Here’s an example of breadboarded circuits:
I organized it so the changes are minimal and clear. Replacing transistors, swapping two wires (I made them a bit thicker on the diagram above) and rotating C6 is all there is to it.
Trying it Out
I did a (relatively) short video covering this:
There you have it. I’m still undecided whether PNP versions sounds better ?.
5 replies on “Silicon Fuzz Face – PNP Version”
apparently low gain silicon transistors should be the aim,as the best sound is supose to be from germainium transistors eg AC128 s I have measured the hfe of typical audio transistors such as the BC108 npn and BC178 pnp to find they have hfe of over 250 .I looked at a higher power teansistor such as BFX88 BFX89 they have hfe of around 90. I have not tried them but they should work.
hey Neil, there are good articles on fuzz central: https://fuzzcentral.ssguitar.com/fuzzface.php and GEOFEX: http://www.geofex.com/article_folders/fuzzface/fftech.htm those are probably the best sources. Modern silicon transistors do have high gain by design. There are some like BC547B for example with slightly lower gain, I saw in the datasheet BC547A as well but never found the part, they still have gains like 200-450 for B and 110-220 for A … You might need to experiment with component values if using those high gain transistors are not sounding to your liking.
Hey! This was very helpful, Im trying experiment with clipping diodes in this circuit. I tried asymmetrical hard clipping and its ok, but I want to try soft clipping, although I’m not exactly sure where to place it.
Hi Breezee,
Are you trying it with this Fuzz Face circuit? I haven’t tried it with it, I’m not even sure if it’s possible with this topology.
Yes I am using this this circuit, different transistors so values have changed. I settled with a switch in the output section to turn clipping on/off and added another gain stage for make-up