Building a Fuzz FactorX

I'm building a Fuzz FactorX off a schematic I found on a french website. I got my hands on some old germanium AC128 transistors for the build.(and some extras for a Fuzz Face)

I have a multimeter that measures hfe, but I noticed as I hold the transistor in the multimeter socket, the hfe measurement seems to rise.

Whats the best way to get a reading? Do these type of transistors need to warm up?

Also I know I'm looking for low gain, but what hfe is good?

Also for a Fuzz should I be looking for a specific hfe in Q1 and Q2?

And lastly... I see two wiring diagrams, one appears to send out to ground when bypassed, the other just appears to bypass the effect out, but not ground it. Is it important to send out to ground when bypassed?

I'm building a Fuzz FactorX off a schematic I found on a french website. I got my hands on some old germanium AC128 transistors for the build.(and some extras for a Fuzz Face)

I have a multimeter that measures hfe, but I noticed as I hold the transistor in the multimeter socket, the hfe measurement seems to rise.

Whats the best way to get a reading? Do these type of transistors need to warm up?

Also I know I'm looking for low gain, but what hfe is good?

Also for a Fuzz should I be looking for a specific hfe in Q1 and Q2?

And lastly... I see two wiring diagrams, one appears to send out to ground when bypassed, the other just appears to bypass the effect out, but not ground it. Is it important to send out to ground when bypassed?

You can't get an accurate measurement of the gain of germanium transistors from a multimeter's transistor setting.

Germanium is very temperature sensitive and it affects the gain of them as you noticed.

Have a look through this article by R.G. Keen. It will answer most of your questions. http://www.geofex.com/article_folders/fuzzface/fffram.htm

Also have a look at a page Steve Daniels of Small Bear Electronics made up.
http://www.smallbearelec.com/HowTos/FuzzFaceFAQ/FFFAQ.htm

Just to underscore Jeff's response.

Read the R.G. Keen article as it explains a lot not only about the FF circuit, but about germanium transistors as well. You can't test them with a modern DMM that has an HFE tester. Your readings will not be accurate since germaniums have so much leakage.

The article also discusses the "best" gains for Q1 and Q2.

If you do intend on using them, you should set up a tester as R.G. describes. As you've discovered, they are temperature sensitive. When you test them, you'll need to let them adjust to room temperature on the tester - this may take 5-10 minutes per transistor.

I just went through a batch of 100 AC 128s and tested them for leakage and gain. I don't have my testing results spreadsheet in front of me, but offhand, I can say that I found about 20 or so that have enough gain to be used as Q1 in a FF circuit. I don't have any that have high enough gain for Q2. The remainder have gains under 70 - a lot around 40-50. Only a few had unacceptable leakage.

Steve at Small Bear has an interesting article on using 2 lower gain germaniums in a Darlington circuit to make up the desired gain. I haven't tried it yet, but that may be a way to use those lower-gain transistors.

-Kevin

Hey guys, need a little input here. All my transistors look like they have good gain in the DMM, but I wanted to test for leakage as recommended. I decided to go with the small bear method linked above, because it look simpler, and I actually have the 1M resistor I need for that test.

So I breadboarded up a little transistor testing rig.

battery voltage = 8.84
leakage voltage = 8.84(sometimes 8.83)

Now that seems like a lot of leakage... is that even possible? Does it just mean I have a batch of duds? When I bias the base... well, I get 8.84... which means I don't see a difference when it is biased for most of them. Back in the DMM they look good.

Just to be sure I put in a 2N3905, and tested that.
battery volatge = 8.84(still)
leakage current = 0
collector current = 8.83 (when I bias the base)

So my rig seems to work, the collector current still seems way high though with a 1M resistor in there.

I'm hoping I'm doing something wrong, and you guys can tell me what so I can pic out two good ones and get this baby built today, otherwise I'll have to toss all of these and order some from byoc or small bear. Which will take a little more time.

You may not be measuring the right way. You need to measure leakage current first, and then do the math to get your gain. You can't just take one reading and have it be accurate.

On Steve's diagram it's here:

http://www.smallbearelec.com/HowTos/FuzzFaceFAQ/Leakage.gif

Put your meter, set to Ma, low scale, from the collector of the transistor to the negative terminal of the battery. That reading is your leakage current. If it's less than about 300 ma, your transistor passes the leakage test. Note the reading and write it down.

THEN you add the 1 meg resistor from the negative side of the battery to the base as he has it here. Again you are measuring current, not voltage:

http://www.smallbearelec.com/HowTos/FuzzFaceFAQ/Gain.gif

Note that reading and write it down.

Then take the first reading and divide by the second.

As an example, let's say your first reading (leakage) is 200 ma. And your second reading is 5 ma. 200 divided by 9 is 40. That is your gain. In this example, we have a transistor with 200 ma leakage and a gain factor of 40.

Hope this helps.

-Kevin

Thanks Kevin, I think you are correct, I must be measuring something incorrectly. I'm going to try again tomorrow.

I decided to get everything soldered together, the box drilled etc.... I also grabbed two random transistors and put them in.... guess what? no sound. I think they may be incorrectly oriented in the board as well... how do I know the orientation?

Everything fits very nicely. I have to say this is why I picked this as my next build, it just looks so well designed. It is only my second build and it looks great... I just need to get the transistors figured out.

check it out

http://i1200.photobucket.com/albums/bb321/bitracer/806d67cd.jpg

here is a gut shot... not bad for my second build... now to get some sound out of it.

http://i1200.photobucket.com/albums/bb321/bitracer/737e0154.jpg

I decided to get everything soldered together, the box drilled etc.... I also grabbed two random transistors and put them in.... guess what? no sound. I think they may be incorrectly oriented in the board as well... how do I know the orientation?



Looks like a tidy build.

Is this a commercial board? There should be markings for the correct orientation. From your testing you should have them - the tab is near the emitter. The base is in the middle and the collector is the remaining lead.

Did you solder the transistors to the board? Did you use a heat sink? If not, they may be damaged. Germaniums are very heat sensitive - you should use a sink on the leads if you solder them. A lot of folks (me included) use sockets for them. I once ruined one NOS GE transistor and that was it for trying to solder them!

-Kevin

I'm stumped. when I connect + to the collector, and measure from the emitter to gnd.... I get the same voltage as the battery.

I'm sure I'm doing this right now. Maybe they are duds, maybe I fried them somehow. I'm buying a pretested set from byoc and dropping them in. the ones I'm testing are not even soldered in to anything yet.

Made the board myself, found it on a french website. The layout shows the tab on the transistor, but no "E B C" I guess I just assume base is in the middle?

I'll get some transistor sockets as well. Thanks for the advice.

I'm stumped. when I connect + to the collector, and measure from the emitter to gnd.... I get the same voltage as the battery.

I'm sure I'm doing this right now. Maybe they are duds, maybe I fried them somehow. I'm buying a pretested set from byoc and dropping them in. the ones I'm testing are not even soldered in to anything yet.

Made the board myself, found it on a french website. The layout shows the tab on the transistor, but no "E B C" I guess I just assume base is in the middle?

I'll get some transistor sockets as well. Thanks for the advice.

Yes, if it has the tab, we know that's the emitter. And the base is in the middle.

It's a good idea to get known good transistors. If you put them in and it works, you have a baseline to work from since you know the circuit works.

Let us know how it turns out!

-Kevin

I will, and I'll post some more pics as well. I'm pretty excited to hear this pedal, opinions seem pretty polarized about it, either love it or hate it. I'm hoping I love mine,

Hey Aballen,

Fuzz Factory user here(and big fan too), just wanted to say hi. Your pedal looks great, hope it works out and I'm definitely curious as to your impression of it!

Here's a link to a Fuzz Factory setting list,

http://www.thegearpage.net/board/archive/index.php/t-176319.html


Are you planning on painting it? If so, how?

I think I'll test some 3904 and 3905 transistors... I know the sound wont be right but I can make sure the rest of the circuit is right, and be sure of the EBC layout on the board.

I wish it was clearer. I don't speak French so I don't know if I should have mirrored the board, but I know the schematic is good, I've seen others make this one

http://membres.multimania.fr/davpseudo/ffactorx_fichiers/image018.jpg

I'm not sure if I'll paint it. I will mark the knobs somehow, but I don't want to make it look too much like an authentic pedal. I'm only making one, for myself and it looks nice in polished aluminum.

I'm really stumped here guys. I got a nice set of germanium transistors from byoc, but I dont want to put them in until Im sure I have the pinouts correct.

I socketed all the transistors and I'm putting in transistors like this
Q3: 2n3904, emitter on the bottom(according to the diagram below)
Q2: AC128, emitter on the bottom
Q1: AC128, emitter on the left

the odd thing is that I have to bend the middle lead on the AC128... like the triangle is .

when I'm in bypass mode, I get clean sound, but when I activate the circuit, no sound at all... and I have it wired exactly like this

http://membres.multimania.fr/davpseudo/ffactorx_fichiers/image020.jpg

can I try playing with 2n3905s just to get sound out of the damn thing, I'm thinking this will at least ensure the pinouts are correct. Is there anything else to troubleshoot or test? I've seen people claim this is a good circuit... I'm stumped.

It may be my first batch of ac128s are bad, but I'm worried about putting these new ones from byoc in the wrong way, and ruining them.

What to do?

I got it working. After procrastinating for awhile, I just decided to roll the dice and put in my nice Sony germanium AC128s from BYOC.

I usually like to put a "learn from my mistakes" section in my threads, so to wrap it up, here it is.

1) Q1 and Q2... well the pinout appears to be backwards for the container I have, rest assured the emitters are marked correctly. I kept thinking the transistor would fit more easily from the other side of the board. This led me to think the board needed to be mirrored.. the base may appear to be on the wrong side of the transistor, but the leads are easy enough to bend.
2) Not sure why, but when I tightened the nuts down over my pots, the pedal would go dead. I was a very tight fit, and I'm sure I was tweaking something when I tightened it all down. The solution, I put the washers inside the box, that seems to give me enough clearance to keep whatever it was from getting grounded, short circuiting... whatever it was. I had maybe 1/8" clearance for the battery, I could have drilled the pot holes a hair farther ups for an easier fit. I did put electric tape on the inside of the box where the bottom of the board rests, and snip all the leads as short as possible, so they would not poke through. Make yourself a nice template before you drill, space is really tight.
3) If you use the same small case I did, you will not be able to put a 3pdt in there and fit a battery. You can go with a bigger case it you want a 3pdt and more clearance in the box. I'm told a battery can last years without the led so I skipped it. With a battery lasting that long, there is no real need for a power jack either.

Overall an easy build, but if you want to get it in a tiny case like this one, it can be tricky. I have to say though it is a very eloquent design.

I have not had much time to play with it, Christmas eve, and I'm making cookies with the kids. I'll try to post a vid using the settings from the zvex site for comparison. I do get some fuzzy noises out of it... so I'm good for now.