Shin Ei FY2 Fuzz; or look, I broke something new!

[moid]

Thanks Mark - that's a great idea. I'll try some different resistors as soon as I have some fuzz sound back to test volume level against.

[moid]

More weirdness - measuring the transistors (DMM set to AC) gets sensible numbers sometimes then bizarre numbers the rest of the time (like almost nothing on all legs of the transistor). I also noticed that my DMM reads 0.49V all the the probes are touching nothing but air... I bet that's not a good sign. I did the measurements with music playing into the pedal.

Q1 MPSA18
C - 2.5V
B - 2.125V
E - 0.031V

Q2 2N3904
C - 2.180V
B - 2.166V
E - 0.031V

Thanks

[moid]

I've had some sleep and have re read everyone's suggestions but they seem to be contradicting each other? Or I haven't understood them (quite likely). If I move the trimmer from its current position to where Duck suggested I no longer have any way of controlling the volume coming from SW2. I could remove the ground connection as Cozybuilder suggested, hopefully that would restore the fuzz? Duck and Mark Hammer - your suggestions would allow me to control the volume of the audio coming from SW1 (difference between non scooped and scooped audio), but the loudest variation in volume is the audio coming from SW2 into the volume pot, and that's the one that needs to be quietened down the most if the audio is to remain similar-ish when SW2 is flipped on. I may well add those suggestions to the SW1 non scooped output though.

Should I try just removing the ground from the 50KB trimmer first? Would this remove the voltage dividing issue and allow me to hear fuzz and not clean audio?

[duck_arse]

when you take voltage measures on a transistor (or opamp) circuit, we want the quiescent voltages. and DC, allays DC. so, meter to DC volts, AND NO SIGNAL. this tells us what the transistor will/should do when signal is applied and rules out the trannie as the bumm part of the circuit.

disconnect your SW2 section for the moment, prove the circuit werks then wreck it again and then we can sort out the extra.

[moid]

Thanks Duck! DC it is! I haven't had a chance to disconnect the SW2 section (that will have to wait until everyone here is asleep). I did check the transistors and got very odd readings depending on whether I was using mains power or battery power.

Mains power

Q1
C -0.70mV
B -0.53mV
E 0

Q2
C -49mV
B -381mV
E 0

Negative voltage seems very wrong to me? I then switched to a 9V battery

Q1
C 1.85V
B 591.8mV
E 0

Q2
C 0.896V
B 567.8mV
E 0

[Cozybuilder]

Another schematic found on the interwebs:

[Mark Hammer]

That's my handiwork.  Well, my modification of someone else's handiwork.

The 3-way gives you scoop, lowpass without the highpass component (i.e., 1000pf disconnected), and a full-bandwidth bypass to supplement the bass component.  Three different tones with roughly equal volume level.

[Kipper4]

I haven't built it.
Those volts look way off. It looks like the transistor isn't even turned on.
I may have to breadboard it tommorow.
I'll try a quick sim but it's not my strong point.

Simmed Q1
C 4v7
B ~500mv
E 0v

Q2
C 1v2
B as above
C also

I didn't include the 2200pf

[PRR]

> my DMM reads 0.49V all the the probes are touching nothing but air...

Fix that first.

Then find the shorts or mis-connections on your build.

[moid]

Thank you for all the suggestions everyone. PRR - that comment about the 0.49V on the probes was because I had them set to measure AC not DC. I still thought it was odd, so I've swapped the batteries in the DMM for new ones and now if left on AC it measure 0.069V when the probes touch nothing... but the number fluctuates between that and 0.037V. I would've expected it to be 0, but perhaps my DMM isn't that accurate? If I set the DMM to DC and don't let the probes touch anything the value falls to 0. I tested the old batteries (AAA size 1.5V) and they both register as having 1.5V of power in them, despite them being the original batteries I bought with the DMM three years ago!

Just for everyone's reference I tested the voltages of the breadboard version of this circuit (which works fine, but doesn't have the exact same switch setup due to me running out of parts) and the voltages for the breadboard version, powered by a 9V battery are:

Q1
C 1.31V
B 593mV
E 8mV

Q2
C 1.33V
B 601mV
E 8.1mV

Which is similar to the values I got when I powered the effect pedal using a battery. So that made me suspicious of my wall power plug again. I swapped that out for another 9V DC power plug I have and I got values that were almost the same as the battery; when I plug in the 9V wall supply I was originally using, the numbers go weird again. I've tested both wall plugs by sticking the black probe of my DMM inside the barrel of the plug and the red probe to the outside of the barrel and both read values close to +9V, but only with one of them do I get weird negative readings... the only sensible answer is that some of my electrical equipment has been possessed by the devil and the only solution for this requires a priest, holy water and trial by fire

I'll try to get desoldering to see what happens when I remove some of the components as Duck asked. I'll answer everyone else soon too, just need to do this before I fall asleep.

[moid]

OK I removed SW2 from the circuit but it's had no effect on the sound - I can hear guitar playing through the circuit, the volume knob can reduce this to nothing if I turn it, but the fuzz knob does nothing. I have just looked at the original schematic for the circuit (and my modified one) and noticed that two audio lines go into that fuzz pot, but they go into lugs 3 and 2. Lug 1 is the output of the fuzz pot. Should lugs 2 and 1 be swapped over? So that the wiper becomes the output and the two input audio lines go to lugs 3 and 1 and the wiper blends between them?

Cozybuilder - I notice on the schematic you posted (thanks!) that the fuzz is wired up the way I suggested above - perhaps this is the issue?

[moid]

That's my handiwork.  Well, my modification of someone else's handiwork.

The 3-way gives you scoop, lowpass without the highpass component (i.e., 1000pf disconnected), and a full-bandwidth bypass to supplement the bass component.  Three different tones with roughly equal volume level.

Thanks Mark - should I follow this schematic instead of the original one I used? Your fuzz knob is wired in what I would think of as being the more normal way to wire it.

[moid]

I haven't built it.
Those volts look way off. It looks like the transistor isn't even turned on.
I may have to breadboard it tommorow.
I'll try a quick sim but it's not my strong point.

Simmed Q1
C 4v7
B ~500mv
E 0v

Q2
C 1v2
B as above
C also

I didn't include the 2200pf

Thanks Kipper  - my new values are similar to your sim with the exception of Q1's collector.

[moid]

OK I switched fuzz lugs 2 and 1 but there's no audible effect I'm going to try my DMM on my breadboard circuit and compare DC voltage with the perfboard version to see if I can find if there's a place that's obviously not doing anything.

[Mark Hammer]

That's my handiwork.  Well, my modification of someone else's handiwork.

The 3-way gives you scoop, lowpass without the highpass component (i.e., 1000pf disconnected), and a full-bandwidth bypass to supplement the bass component.  Three different tones with roughly equal volume level.

Thanks Mark - should I follow this schematic instead of the original one I used? Your fuzz knob is wired in what I would think of as being the more normal way to wire it.

I have an original FY-2 and find that I have more variation in fuzz intensity available to me the way I wire it, compared to the original.  Keep I mind when the original was produced.  Nobody was particularly interested in being able to achieve less fuzzy sounds.  Wiring it as a kid of blend (more/less fuzz) control is also more in keeping with its cousins like the Fuzz-Rite.

Personally, I find the sound coming directly from the wiper of the fuzz control to the volume pot a more desirable sound.  I applaud anyone striving for authenticity, but if you're only making a one-off for your own personal use, the unscooped one is the serious fuzz to be reckoned with.  Louder, throatier, and SO much easier to make.

[duck_arse]

is there a chance you have shorted Q2 C to supply? power off, meter to ohms range, check resistance between C and the +9V line. you can pull the transistors out for this test. [it wouldn't hurt to do the same check on Q1. and the base-to-collector resistances. and the emitter to ground resistances, while the meter is still set.]

also, just for fun, can you set your meter to the dreaded AC volts, and measure the output of each of those AC adaptors at the plugs?

[moid]

Thanks chaps I'll try this tomorrow, having to look after a sick child at the moment; he's picked up a horrid bug from one of the kids he was playing with earlier this week and is in need of a lot of attention.

[Kipper4]

Thanks chaps I'll try this tomorrow, having to look after a sick child at the moment; he's picked up a horrid bug from one of the kids he was playing with earlier this week and is in need of a lot of attention.

Much harder to debug a child.....good luck.

[moid]

Thanks Kipper, he hasn't been sick for about 12 hours now so that's a good sign... and the poor thing has conked out on the sofa, so I can 'quietly' measure the resistance values that Duck asked for

DMM set to ohms

Q1
I placed the black DMM lead on the lead of the 22K resistor closest to the Q1 socket and placed the red probe into the Collector socket = 4.7ohms

Red DMM probe into Base socket, black probe into Collector socket = 2.243M

Red DMM probe to Emitter, Black probe to PCB Ground (where the ground cable leaves the PCB) = 3.1 ohms


Q2
I placed the black DMM lead on the lead of the 22K resistor closest to the Q1 socket and placed the red probe into the Collector socket = 2.8ohms

Red DMM probe into Base socket, black probe into Collector socket = 1.272M

Red DMM probe to Emitter, Black probe to PCB Ground (where the ground cable leaves the PCB) = 3 ohms



Measuring the three power sources I have - I placed the black probe inside the barrel of the plug and the red probe on the outside sleeve of the plug. I set the DMM to AC

9V battery = 0.005V
Eagle 1 spot plug = 0.045V
Old 1 spot plug = 0.043V

The Eagle 1 spot was the one that seemed to generate weird values when used previously.

I hope some of this causes you to shout Eureka, (possibly hang on to your clothes!) and run around in an excited fashion. If you want me to re measure using different techniques / settings please say so. If it helps I can compare to voltages on the breadboard version, although that does have a lot of ground hum, and I'm not sure if that would cause issues. Thanks again.

[duck_arse]

welly, welly , well well. I think. I'm not 100% sure of your nearest to reference, but if you are measuring from the 22k to Q2 collector, you've lost all your resistance. your resistors is futile. (the collector-base readings look ok.) from the (+) of the battery clip on your schem to the Q1 C should be 22k, you say only 4R7. and from (+) to the Q2 C should show 147k, thereabouts. also, seeing as yr meter shows ~3R for emitters to ground, we have to assume your collector resistors are also 0R.

on ohms range, join your black and red probe tips, tell us what your meter reads for a dead short/0R please.

reading error? retelling error? meter error? board error? you'll have to work from the (+) point along the resistors to find which is disappearing your ohms. and - the AC readings on the DC adaptors check out OK/as expectable.

best wishes to the boy.