Transistor troubles!

[fuzz/volume-full]

hi, i'm attempting to build my own fuzz face clone and i thought buying 4 AC128 (pnp germainum), however no matter what order i put them in it either sounds terrible or just doesn't work.

Now i know the transistors are the problem so, i wondered what would be a good modern pnp alternative for a fuzz face pedal, that are easy to get hold of?

[Scruffie]

It's likely they are crap (read this article by the way - http://www.geofex.com/Article_Folders/ffselect.htm ) but are you altering the bias on them? You need to adjust Q2s collector via the 8k2 resistor untill you get approximatley 4.5 - 5.2V on it (assuming you have a DMM, if not... buy one)

This is an invaluable article on the Fuzz Face - http://www.geofex.com/article_folders/f ... fftech.htm

Russian Germaniums are supposedly fairly consistent as they're more recent in production, you can buy a matched pair though which will sound good through either -
http://www.smallbearelec.com/Categories ... ransistors

Which will come with the resistor values included to make it sound good or buy them from our own Culturejam here -

http://www.forrestwhitesides.com/shop/i ... a0509b5bc3

Both sites will provide you with good Ge's for a Fuzz Face... One other thing, did you solder the Germaniums? With excess heat they can fry so socketing is usually reccomended for first time builds.

[fuzz/volume-full]

so, would it be worth replaceing the 8K2 resistor with a trim pot to bias it before i dive into buying more transistors, i'll have a go at doing that tommorow and i'll get onto reading the articles now, thanks for the help.

[culturejam]

Pn2907 is a great sub for the old PNP germaniums. They have a gain of around 120 to about 160. And they are cheap!

so, would it be worth replaceing the 8K2 resistor with a trim pot to bias it before i dive into buying more transistors,

Yes.

[fuzz/volume-full]

Pn2907 is a great sub for the old PNP germaniums. They have a gain of around 120 to about 160. And they are cheap!

so, would it be worth replaceing the 8K2 resistor with a trim pot to bias it before i dive into buying more transistors,

Yes.

thanks! I'll pick a few of those transistors up and a trim pot next time I go into town, i'll post back into the thread once i get this thing working (hopfuly in a couple of days)

[devnulljp]

hi, i'm attempting to build my own fuzz face clone and i thought buying 4 AC128 (pnp germainum), however no matter what order i put them in it either sounds terrible or just doesn't work.
Now i know the transistors are the problem so, i wondered what would be a good modern pnp alternative for a fuzz face pedal, that are easy to get hold of?

I had good luck with Matsushita 2SB172s in a fuzz face (replacing crappy AC128s). AC125s are pretty standard issue too...

[nbabmf]

Make sure you have the legs oriented correctly and that you are powering the effect according to the transistor type (negative ground for NPN, positive ground for PNP). If you have a meter, anchor one lead at a ground point and use the other to take DC voltage readings at each leg of the transistors. Post them here.

[fuzz/volume-full]

Make sure you have the legs oriented correctly and that you are powering the effect according to the transistor type (negative ground for NPN, positive ground for PNP).

yep their pnp so they have positive ground

If you have a meter, anchor one lead at a ground point and use the other to take DC voltage readings at each leg of the transistors. Post them here.

so, attach any lead to the ground, along with the positive part(i don't know the correct term for them, probe?) of the mmultimeter to ground and the negative ground to either leg, and record the results?, i'll get rigt on that now and write them up and put them here.

[nbabmf]

I use an alligator clip to set one multimeter lead to ground, so I only have to worry about keeping one lead in contact. In the case of a PNP circuit, the red lead goes to ground. Take a voltage measurement for each leg of each transistor and report back.

[fuzz/volume-full]

right i've recorded the results (the battry was a 9 volt that was giving off 7.60V)
T1 | T2 | T3 | T4
e 7.52 | 7.43 |7.42 |7.41
b 0.461 | 0.645|0.520 |0.650
c 7.5 |7.26 |7.25 |7.19

there are the results and i'd just like to say ahuge thank you to everyone helping me out here, cus i'd still be a bit stuck without some help!

[nbabmf]

If you took those voltages with the transistors in the circuit, you would have only had two... And Q1's emitter would have read 0v since to goes directly to ground.

I'm thinking you don't have the ground right. Post the layout you used and a picture of the actual circuit if possible, and I'll help you get it working.

[fuzz/volume-full]

ok, i didn't think i did it right either, im very bad with technology so sorry about that but,
i connected the positive side of the multimeter to the positive battry lead and one of the legs of the transistor i wasn't testing, the lead i was testing was connected to the negative lead and the the negative side of the multimeter and the third leg wasn't connected. i can't post pictures btw, sorry about that


EDIT:seeing as i'm going into town soon would it be worth picking up a couple of these to try out?
http://www.maplin.co.uk/Module.aspx?ModuleNo=33802

http://www.maplin.co.uk/Module.aspx?ModuleNo=33879
and which ones specificly?

EDIT 2:to add a trim pot i connect the second and first lugs to the resistor that is 330 ohms and the 0.01 cap and the third to the collector of the second transistor right? http://www.google.co.uk/imgres?imgurl=h ... x=66&ty=93 i'm useing that scematic btw if it makes what im asking anyclearer

[nbabmf]

Nope, not right at all. The transistors are in circuit and only one leg is tested at a time.

Hook the battery up to the circuit. Connect the positive multimeter lead to the positive terminal or your positive ground (any of the points that connect directly to it with nothing in between).

The other lead will measure one leg of the transistor at a time.

Q1
C
B
E

Q2
C
B
E

Leave whichever transistors are in there now, and I'll have you swap them around if we can't get this working as is.

[fuzz/volume-full]

ok then i'll get onto checking them as soon as i get home.
Thanks for all your help for a slow minded noob like myself btw

[fuzz/volume-full]

right, i did it right this time, the battry's original voltage was 8.17 volts
Q1
e 0.2 mV
b 65.7mV
c143.8mV

Q2
e0.4mV
b142.5mV
c17.4mV

am i right in guessing that the m means micro (and hence 10^-6) as it can't possibly mean mega.