Hi. First post on this site, so bear over with me.
I recently buildt a bc108 fuzz face based on the schematic on this site:
Fuzz Central -- Arbiter Fuzz Face
Everything seems to work, it it cuts out if I play a little soft, between notes or if I turn the volume down just a little. Does anyone know what's wrong or what errors to search for?
(switch is wired as suggested here:
http://www.diystompboxes.com/smfforum/i ... _next=prev
There's also a led with a 1 k resistor that doesn't appear in the schem), all the ground points are soldered together and to common ground.)
I recently buildt a bc108 fuzz face based on the schematic on this site:
Fuzz Central -- Arbiter Fuzz Face
Everything seems to work, it it cuts out if I play a little soft, between notes or if I turn the volume down just a little. Does anyone know what's wrong or what errors to search for?
(switch is wired as suggested here:
http://www.diystompboxes.com/smfforum/i ... _next=prev
There's also a led with a 1 k resistor that doesn't appear in the schem), all the ground points are soldered together and to common ground.)
That led will be drawing about 7mA, so if you're running from a battery you'll dramatically shorten its life.
The second link you give:
http://www.diystompboxes.com/smfforum/i
doesn't work for me, so I can't see how you've wired it.
Assuming that's all ok though, and that you haven't got a defective component, all I can think of at the moment is that you've perhaps got a wiring error - how is it constructed? Pcb? Vero/Strip board? Dead bug?
Maybe a close up photo would help, if you can take one and post it? Better still two photos, one of each side of your board, assuming your using one.
Check and re-check that you've got the right connections between the right value components in the right places and that you've got E, B & C correctly oriented on your transistors.
The second link you give:
http://www.diystompboxes.com/smfforum/i
doesn't work for me, so I can't see how you've wired it.
Assuming that's all ok though, and that you haven't got a defective component, all I can think of at the moment is that you've perhaps got a wiring error - how is it constructed? Pcb? Vero/Strip board? Dead bug?
Maybe a close up photo would help, if you can take one and post it? Better still two photos, one of each side of your board, assuming your using one.
Check and re-check that you've got the right connections between the right value components in the right places and that you've got E, B & C correctly oriented on your transistors.
Last edited:
Hi, thanks for the feedback guys.
@Simon B: Not running a battery (using a t-rex fuel tank). I assume you mean the link doesn't work, try this:
True Bypass - Why not ground the input AND the output?
the switch seems to work fine. It's constructed using a vero board (i think thats it, the type with holes and no strips a.k.a. test board) and I'm quite confident the solderjoints are good, though I woun't rule anything out at this point, and shouldn't that make it cut a bit at random?
@Wavebourn: I buildt the second one on the page, the NPN one, using bc108 tranies. Someone at another site suggested it might be 8.2 biasing resistor on Q2 being wrong? I'll see if i can't get some measurements when I get home.
@Simon B: Not running a battery (using a t-rex fuel tank). I assume you mean the link doesn't work, try this:
True Bypass - Why not ground the input AND the output?
the switch seems to work fine. It's constructed using a vero board (i think thats it, the type with holes and no strips a.k.a. test board) and I'm quite confident the solderjoints are good, though I woun't rule anything out at this point, and shouldn't that make it cut a bit at random?
@Wavebourn: I buildt the second one on the page, the NPN one, using bc108 tranies. Someone at another site suggested it might be 8.2 biasing resistor on Q2 being wrong? I'll see if i can't get some measurements when I get home.
Hi
I guess that the battery is sagging because of high current taken from it...
As suggested, it is likely the transistors bias should be checked. According to the site you should measure a collector voltage at Q2 of about 4.5 to 5 VDC.
They suggest installing a 10K trimpot in place of the fixed resistors for adjustment. I would not do that without keeping some fixed resistance to avoid possible direct short when trimpot is at minimum. I would use a 5K fixed and add a 5 or 10 K trimpot in series to adjust it.
They suggest installing a 10K trimpot in place of the fixed resistors for adjustment. I would not do that without keeping some fixed resistance to avoid possible direct short when trimpot is at minimum. I would use a 5K fixed and add a 5 or 10 K trimpot in series to adjust it.
My DIY kit has a 10k pot instead of the 8.2k resistor.
I had major frustration for months with (seemingly) intermitted times of low output. Eventually I noticed that placing any "buffered" type pedal between the guitar and the fuzz avoided the low-output problem. The input to the fuzz loads down the guitar pickups more than they prefer. Different setups will have different sensitivity to it. Try placing any Boss brand pedal (in "off" mode) between the guitar and the fuzz to rule out the loading problem.
I had major frustration for months with (seemingly) intermitted times of low output. Eventually I noticed that placing any "buffered" type pedal between the guitar and the fuzz avoided the low-output problem. The input to the fuzz loads down the guitar pickups more than they prefer. Different setups will have different sensitivity to it. Try placing any Boss brand pedal (in "off" mode) between the guitar and the fuzz to rule out the loading problem.
No. The low input impedance of a fuzz-face, and the loading of the guitar it causes is an essential part of its sound.
It is not a problem; without it, ie driving the fuzzface from something with low output impedance, will give you a horribly harsh sound.
I include a series pot in the input as an extra control, in case it's to be used after another effect, and I believe others do likewise - don't worry about it for now though, get your unit working first.
This is not the cause of your problem, many thousands of fuzzfaces have been built and used straight after the guitar.
Measure the voltages referred to by previous posters.
Hi everybody, thanks again for all the feedback.
Sorry for the delayed reply, got a bit hectic going into the holidays, but now I've measured the voltages at each transistor and they are as follows:
Q1: b- 0,475 e- 0,003 c- 1,95
Q2: b- 1,95 e- 1,28 c- 1,3
Now I'm sure the values of Q2 are off (not even close to the 4,5 shanx suggested), but no idea what's wrong, or how to remedy it.
Sorry for the delayed reply, got a bit hectic going into the holidays, but now I've measured the voltages at each transistor and they are as follows:
Q1: b- 0,475 e- 0,003 c- 1,95
Q2: b- 1,95 e- 1,28 c- 1,3
Now I'm sure the values of Q2 are off (not even close to the 4,5 shanx suggested), but no idea what's wrong, or how to remedy it.
View attachment 276601
Ok, getting there. What's the voltage at the other end of the 8k2 resistor connected to the collector of Q2? Where it meets the 330R resistor and the 0u01 capacitor? How much voltage is being dropped across the 330R resistor? Suggest you check the value and connection of that 330R resistor - is it 330R? Not 330k for instance?!
The collector voltage on Q2 is too low - the base-collector junction is forward biased - fits totally with what you've described sound wise.
Ok, getting there. What's the voltage at the other end of the 8k2 resistor connected to the collector of Q2? Where it meets the 330R resistor and the 0u01 capacitor? How much voltage is being dropped across the 330R resistor? Suggest you check the value and connection of that 330R resistor - is it 330R? Not 330k for instance?!
The collector voltage on Q2 is too low - the base-collector junction is forward biased - fits totally with what you've described sound wise.
Attachments
Last edited:
If the Fuzz pot is correctly wired and the capacitor on it is good, rotating it will not affect the bias of either transistor.
The voltage at the emitter of Q2 looks about right to me, feeding through the 100k resistor it gives about 8uA bias current into the base of Q1, which should be bumping along the bottom rather. Negative input half cycles get clipped first.
Q2 has reasonable forward bias across the base-emitter junction, 0v68, given the apparent lack of current flowing through it. I'd be looking at the 330R and 8k2 first of all.
Why should it be 0.63v? It gets fed a tiny bias current. 0.63v might be what you'd expect in a "normal" circuit. This just isn't one of those circuits. Anyway, it isn't "off", it's got 8uA flowing into its base.
Last edited:
Sorry guys, when i went back to check the value of the resistor i discovered i had actually connected one leads on the voltmeter to the wrong terminal 
(I didn't even know that would show results) rechecked the values and they are as follows:
Q1: b- 0,64 e- 0 c- 2,12
Q2 b, 2,12 e- 1,45 c- 1,45
sorry for the mistake
resistor is correct 330 (no K) and voltage between resistors is 8,68
(I didn't even know that would show results) rechecked the values and they are as follows:Q1: b- 0,64 e- 0 c- 2,12
Q2 b, 2,12 e- 1,45 c- 1,45
sorry for the mistake
resistor is correct 330 (no K) and voltage between resistors is 8,68
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.