Fuzz face turret layout w/ negative ground and PNP germanium transistors?

[Jussi]

Hey,

I'm going to build a fuzz face pedal to a turret board with PNP germanium transistors (ASX12D), negative ground, dc jack and a trimmer pot for bias. I've drawn a layout based on this . I don't have much experience or knowledge about these things so I'm asking if anyone could check if it looks OK? I don't want to kill my rare transistors   The DYILC file can be downloaded from here if you want to modificate it or something.



This is the schematics of pnp fuzz face with negative ground (so you can use power supply and daisy chain it with other pedals):

[LucifersTrip]

there's one at turretboard.org that you can compare to:



flip the electrolytic caps and power supply for npn

[Pyr0]

You have the jacks wrong, the input and output should be wired to the tips, power switching via the ring and ground to the sleeve.

[Jussi]

Thanks for the replies. I've updated the layout picture and added a pic of schematics. I'm not sure about the dc jack wire wich should go to ground (the pink wire). I think there is something wrong with all the grounding stuff but I don'get it.

You have the jacks wrong, the input and output should be wired to the tips, power switching via the ring and ground to the sleeve.

I fixed the tips now but are you sure about that ground to sleeve, because isn't it to the ring in this layout?

[Madkatb]

Actually it isn't. The negative of the battery goes to the ring of the input jack and the sleeve goes to ground. So when you push in a mono jack it completes the circuit to ground for the battery by connecting the ring contact and sleeve contact. In that way the jack acts as a switch, interrupting the ground wire of the battery and turning it "off" when no jack is inserted. 

[Jussi]

Thanks, I think I get it now. I've fixed the layout picture again. It is starting to look right  

[smallbearelec]

If you do make this work, and you may well, please don't post later on asking what to do about the motorboating noises (thump...thump). This is a known issue with PNP negative-ground FF builds, and it can be intractable. Beyond that, a germanium FF is a poor choice for a first build, made worse when you hard solder. If you want your best shot at winding up with a working pedal, BREADBOARD IT FIRST, POSITIVE GROUND. There are many sources out there for this kind of tool:

http://www.smallbearelec.com/servlet/Detail?no=374

and learning to use one is something that you'll do at some point, anyway. If you do this right, you'll satisfy yourself that the devices and other components are good before you solder. Then build for real, and either use sockets for the transistors or take major care with heat-sinking.

Good Luck!
SD

[Jussi]

Thanks for the tips and yes I'll breadboard it first. I need to get some sockets too.

If for some reason oscillation does occur, a quality low esr capacitor from the positive supply to ground will solve the problem everytime since it effectively places the power rails at the same ac potential. Put the capacitor on the pc board if possible. Also keep the positive and negative power wires as short as practical. I've used this method with two different fuzzface derivatives for years with no problems and one of them has a quite long positive power supply wire.

In this layout I have added a 220 uF filter cap. Gonna place it in a better way but is it even in the right place?


If it will sound crap I'll try with more original circuit. No led, no dc adapter, positive ground:

[Chris Brown]

that 220uf should probably be going across the power rails aka from the + to the - of the power jack

also... Instead of flipping the power for pnp/negative ground you can use a bipolar power supply... I've done both and it gives much better results. PNP with negative ground is nothing but trouble imho.

[Jussi]

So you haven't tried with the 220 uf cap? I will try both on breadboard and report back.