First Time Fuzz Face Build - Help Identifying Problem

[pastor_ron]

Hey! I'm new here. I've gotten some help at another DIY forum, but it's been offline for a while now, and I thought I'd look for some help here.

A quick history: I am building my first DIY pedal - a Dallas Arbiter Ge PNP Fuzz Face (no LED or DC Power). I bought a populated board off of eBay, and then purchased the enclosure, jacks and switch through PedalPartsPlus. It's been a major learning experience as there were no written instructions, and I'm not experienced with electronics other than changing pots/pickups on my guitars. I've learned a lot, but am still very green. I've made some mistakes (didn't know the correct pinout for my transistors and put them in wrong, had the polarity of the caps wrong, didn't have it ground properly) but have corrected all of the ones I've been able to identify. I have a good strong bypass signal but absolutely no sound when the effect is engaged (with a battery and input cable connected). I've checked the continuity of all of the paths on the board, and everything seems okay, although I only get a beep if there is an actual track. So for instance, there is no beep from the + to the - side of the polarized capacitors. I don't know if there should be continuity between components. Before correcting the pinout I tested the hfe's of the transistors in my multimeter and they both checked out okay, so I assume they are working correctly. At this point it is above my level of understanding to pinpoint exactly what is going on.

I've included some pictures. If any other shots are needed please let me know. A couple of other notes:

* The board came populated but the transistors were not attached. The eBay listing showed 2 NPN Ge MP38's (?), but the seller also sent a pair of PNP Ge 1t308b's (I think because the hfe's are higher; 50 on Q1 and 53 on Q2) That is why the transistors were put in wrong initially.
* I realized today that the polarized caps were installed for the NPN transistors and turned them around in the board.
* If you notice a lot of flux on the board it was probably me undoing something and redoing it. It was much cleaner when I got it

Here are the values I've measured:

Black lead at board - 8.31v
Red lead at ground - 0v

Q1:
C - .44
B - .14
E - 0

Q2:
C - 8.24
B - .44
E - .22

Hopefully that will help someone pinpoint what is going on here. I've been working on this for more than a month, and am starting to get discouraged  

[/list]

[LucifersTrip]

I have a good strong bypass signal but absolutely no sound when the effect is engaged

it is best to test the circuit without a switch...it eliminates the switch & possible wiring errors from the troubleshooting

I've included some pictures.

I do not believe the pics showed up...your links look like some type of mail attachment instead of a normal url

* The board came populated but the transistors were not attached. The eBay listing showed 2 NPN Ge MP38's (?), but the seller also sent a pair of PNP Ge 1t308b's (I think because the hfe's are higher; 50 on Q1 and 53 on Q2) That is why the transistors were put in wrong initially.

the difference between 50 & 53 is insignificant...the most important thing is you have the pinouts right...remember, many of the russian ones do not have a base in the middle

Q1:
C - .44
B - .14
E - 0

not bad

Q2:
C - 8.24
B - .44
E - .22

C is way off...remember, you're shooting for ~ 4.5 - 5

here's a set of normal voltages:

q1e: 0
q1b: 0.1     
q1c: 0.578   

q2e: 0.447
q2b: 0.578   
q2c: 4.51

If you were close to 4.5 - 5, I'd say just alter Q2 collector resistor to tune it, but it's far enough off that you probably  have a wrong component, a transistor that isn't going to work there or a bad/wrong solder joint.....or you measured wrong.

I still think you should have gotten some sound (albeit very bad), so there's more than 1 problem

start by eliminating the switch from the equation, then look for errors around Q2...and try a different Q2

good luck

[pastor_ron]

Q1:
C - .44
B - .14
E - 0

not bad

Q2:
C - 8.24
B - .44
E - .22

C is way off...remember, you're shooting for ~ 4.5 - 5

here's a set of normal voltages:

q1e: 0
q1b: 0.1     
q1c: 0.578   

q2e: 0.447
q2b: 0.578   
q2c: 4.51

If you were close to 4.5 - 5, I'd say just alter Q2 collector resistor to tune it, but it's far enough off that you probably  have a wrong component, a transistor that isn't going to work there or a bad/wrong solder joint.....or you measured wrong.

I still think you should have gotten some sound (albeit very bad), so there's more than 1 problem

start by eliminating the switch from the equation, then look for errors around Q2...and try a different Q2

good luck

Thanks for your help! When I've got time I'll work on the photos. I don't have a Flickr account or anything so I've got to find some other url.

I have tested the continuity from the board input to the board output and get no beep there. I do get a beep from the middle to upper left and middle to upper right lugs on the switch when engaged.

By wrong component do you mean a wrong value? I'm thinking I may have soldered something where I shouldn't have, or that I even may have been wrong about which hole in the board goes where (none of the holes are labelled). Of course pictures would help that . Can't do that until later today.

[PRR]

> Q2: C - 8.24

Two resistors from Q2 C to Battery--- what values? What voltage measuring end-to-end on each resistor? (I suspect one is way-wrong or shorted.)

> I don't have a Flickr account

Good. Flicker sucks. Try http://imgur.com/  The free/anonymous service is good enough for this.

[LucifersTrip]

By wrong component do you mean a wrong value?

yes, or one that is ruined.

[pastor_ron]

Okay, try again...










Reistance on the 2 resistors are 320ohms and 32.7k. On the 320 resistor I get 8.31 on either side. On the 33k I get 8.31 on one side and .46 on the other.

[PRR]

> resistors are 320ohms and 32.7k

What is the nominal "8.2K"?

[LucifersTrip]

I can't see the lugs of the transistors, but I'm pretty sure the pinout is ECB with the dot on top over the emitter, collector in middle and base on the other side

the 320 would be good for silicon, but will most likely give you too low output for ge.

[pastor_ron]

> resistors are 320ohms and 32.7k

What is the nominal "8.2K"?

Resistance is 8.21 and voltage is 7.6 and 7.68.

Were the voltage readings I gave before normal? I only got .46 on one side of the 33k.

I can't see the lugs of the transistors, but I'm pretty sure the pinout is ECB with the dot on top over the emitter, collector in middle and base on the other side

Yeah, I found the pinout online, so I'm sure that's right. I had to twist the collector and base around each other to fit it into the board, and I insulated the collector with some wire shielding to keep them from shorting out.

[PRR]

> I only got .46 on one side of the 33k

That's reasonable. We expect two Vbe drops plus some resistor drop. Vbe of Germanium may be 0.15V-0.25V depending on transistor.

> Resistance is 8.21

_K_??

> and voltage is 7.6 and 7.68.

The 8K2 connects to Q2 Collector. In your first post this was reported as 8.24V. Now the resistor connected to Q2 C is reported as 7.6V. Are they in fact the same (with maybe a dying battery), or different?

Something is not adding up.

[pastor_ron]

> I only got .46 on one side of the 33k

That's reasonable. We expect two Vbe drops plus some resistor drop. Vbe of Germanium may be 0.15V-0.25V depending on transistor.

> Resistance is 8.21

_K_??

Yes. Sorry

> and voltage is 7.6 and 7.68.

The 8K2 connects to Q2 Collector. In your first post this was reported as 8.24V. Now the resistor connected to Q2 C is reported as 7.6V. Are they in fact the same (with maybe a dying battery), or different?

Something is not adding up.

I'm embarrassed to admit this, and please bear with my complete lack of experience, but I just hooked up the battery and input cable, set the red lead of the MM on the ground lug (which I thought I was supposed to do for a positive ground pedal) and tried testing the resistors again for voltage, numbers were very erratic and after about 5 minutes the battery was smoking hot. I know enough to recognize that that is not good, and the battery is now fried. That's about it 

[LucifersTrip]

set the red lead of the MM on the ground lug (which I thought I was supposed to do for a positive ground pedal)

not a big deal...you will just get the negative (ie, 4.5 instead of -4.5)

numbers were very erratic and after about 5 minutes the battery was smoking hot.

most likely you have shorted (connected + to -) the battery....nothing to do with the wrong dmm leads

edit (next time before checking voltages):
first put the dmm leads across the battery...should get ~ 9v
then, put one lead on ground and the other lead on the junction of 33K and 470. should get the same

[pastor_ron]

edit (next time before checking voltages):
first put the dmm leads across the battery...should get ~ 9v
then, put one lead on ground and the other lead on the junction of 33K and 470. should get the same

Did that, and got 8v (old battery, only one I have right now ) on the battery and 8v on the path between the 33k and 330k (on my board).

What is the nominal "8.2K"?

The voltage readings on the 8k2 resistor (on the component side) are 7.84 and 7.9.

I hope these readings are valid and helpful.

[oldschoolanalog]

Measure the resistance between your black and red (power & ground) battery leads.
Report back.

[pastor_ron]

Measure the resistance between your black and red (power & ground) battery leads.
Report back.

17.55kohms With the battery and cable plugged in.

[pastor_ron]

 

[pastor_ron]

An update:

I picked up a 15 pack of PNP silicon transistors at Radio Shack. I figured I'd swap out the germaniums and see if they were the culprit. Also, my board has a 330k (?) resistor instead of the 470, which is supposed to be used for silicon anyway, right? After getting home I tested all 15 in my multimeter and the hfe's ranged from 268 to 332  . I put the 268 in Q1 and a 276 (IIRC) in Q2. Plugged it in and got a killer, albeit very quiet fuzz sound. The pots both seemed to do what they should, but the overall volume is extremely low.

Could this be due to the incredibly high hfe's on the transistors? I triple checked all of my soldering, looked for loose wires/connections. I re-soldered any joints that looked questionable. I'm pretty confident about the solder connections.

Any help is greatly appreciated. I'm incredibly excited to finish my first DIY build and use it!

[jrod]

You should replace the 330K ohm with a 330 ohm resistor. 330K is too high. Or just leaving the 470 ohm would be fine.

[pastor_ron]

You should replace the 330K ohm with a 330 ohm resistor. 330K is too high. Or just leaving the 470 ohm would be fine.

I'm sorry, it is a 330 ohm. I'm at work and don't have the pedal with me, and didn't bother to look at a schematic 

[jrod]

You should replace the 330K ohm with a 330 ohm resistor. 330K is too high. Or just leaving the 470 ohm would be fine.

I'm sorry, it is a 330 ohm. I'm at work and don't have the pedal with me, and didn't bother to look at a schematic 

Cool! Hope you get it working!