Raygun Youth Fuzz Breadboard Issues

[patrick398]

Hello all,
Got a few problems with the raygun youth fuzz i have on the breadboard and it's proving to be a bit of a noodle scratcher. Hopefully someone can guide me in the right direction.


1.What does it do, not do, and sound like?
Signal is fine coming out of the first op amp and fine going into pin 14 of the CD4046BE (Signal In). It's fuzzing as is expected (maybe not quite as fuzzy as i'd like). I have signal coming out of pins 2, 3, and 4 all of which sounds like its been filtered which i believe is correct. I have nothing coming out of pin 13 (PH Comp2 Out) which is confusing me slightly and as such I have nothing going through the disorder pot and nothing going into pin 9 (VCO In). There's signal at pin 1 (PH Pulse) regardless of whther the rotary switch is on 1,2,3, or 4. Probing the output when selecting the different modes of the rotary pot i have the correct fuzz signal coming from the first Op amp at switch 1. Switch 2, 3 and 4 have the filtered fuzz but the disorder pot has no affect and therefore there's no craziness.


2.Name of the circuit = Raygun Youth Chaos Fuzz

3.Source of the circuit (URL of schematic or project) = http://www.parasitstudio.se/uploads/2/4/4/9/2449159/raygun_youth_doc.pdf

4.Any modifications to the circuit? N

5.Any parts substitutions? If yes, list them. N

6.Positive ground to negative ground conversion? N

DC Jack: 9.73v

IC1 (TL072)
P1 - 8.93v
P2 - 2.29v
P3 - 4.56v
P4 - 0.00v
P5 - 4.56v
P6 - 4.59v
P7 - 4.59v
P8 - 9.16v

IC2 (CD4046BE)
P1 - 9.16v
P2 - 0.00v
P3 - 0.00v
P4 - 0.00v
P5 - 0.00v
P6 - 0.00v
P7 - 0.00v
P8 - 0.00v
P9 - 0.00v
P10 - 0.00v
P11 - 0.00v
P12 - 7.63v
P13 - 0.00v
P14 - 4.12v
P15 - 0.00v
P16 - 9.12v

Pictures here: http://imgur.com/a/3xoZ9
Forgive the ugliness of the rotary switch, all the posts have been isolated with track cuts and continuity between post A and Posts 1,2,3,4 tested.

Thanks

[PRR]

> IC1 (TL072)
> P1 - 8.93v
> P2 - 2.29v
> P3 - 4.56v

P2 should be 4.5V. Or a bit less due to meter loading. However P1 should also be 4.5V. Instead it is slammed to the rail (as close to 9V as it can get). One possible reason is a short around C1.

However this does not agree with "Signal is fine coming out of the first op amp".

Rest of U2 looks OK. U1 just confuses me; maybe someone else can suss it.

[anotherjim]

Well, the first op-amp is working as a comparator. Open loop. Both inputs at +VR, with no input signal, it will sit with output high or low depending on slight difference in offset between the + and - inputs.

The 4046 can be tricky to trouble shoot if you don't have an oscilloscope.
To run at all, the inhibit pin (INH pin5) needs to connect to ground. I can't see anything there in the photo.
Edit second glance it looks like a black wire goes to pin4 in error - that is shorting the VCO output to ground.
If the VCO was running, you will get half of the supply volts on VCO output pin 4. That is a square wave output with equal 50:50 duty cycle and the meter will read the average voltage, about 4.5V.

The 4046 is wired to use phase_comp_2 (pin13) as frequency tracking control. With no signal input, the control to the VCO_in (pin9) will drift to 0v and the VCO is stopped, so you will only hear the VCO with something reaching the signal input pin14.
To force the VCO to run, for testing purposes, you could wire the junction of R12 & C6 to the +VR supply which will put some positive control voltage to the VCO control pin9.

[patrick398]

Thanks for the replies! I thought the voltage at pin 2 of the first OP amp was correct as it's getting +VR through a 1M resistor?

I think it just looks like the ground wire is going to pin 4 of the 4046 in the picture, it is in fact connected to pin 5, as well as 8. I just can't understand why there is no input signal at 14, it's connected to the 10k resistor coming off pin 7 of the TL072 and there is signal there. I put +VR at the junction of R12 and C6 and got some loud oscillating which changed in pitch with the disorder pot so i guess that means the 4046 is working? Just not getting the signal at 14 for some reason...
I also can't understand why nothing is coming out of Pin 1 on the 4046...

[patrick398]

I have internet at my flat again so i'm giving this a cheeky bump

[anotherjim]

If you disconnect feed to pin14, that pin should have about half power supply voltage on it : it has it's own internal bias.

Is that resistor to pin14 from the op-amp pin7 the right value? Is it making good contact? It looks set at quite a stretch in the pic.

Temporarily, try a capacitor in series to pin 14 - any nF or uF size will do - just to make sure the DC level on pin14 isn't getting dragged high or low too much so it can't see the signal wiggle.

[patrick398]

With the 10k resistor disconnected from pin 14 the voltage reads 3.47v, will it connected it reads 4.17v. The resistance of the resistor when removed from the circuit reads near enough exactly 10k but when measure in the circuit it's just below 4k...i'm confused 
Also tried a 10nf cap in series but the voltage remained at 3.47v

[anotherjim]

Yes, the 4046 pin14 input contains it's own Vref.
Make sure you don't measure resistance of parts in circuit with the power on - you'll confuse the meter.
Your measurement report calls it a CD4046 -  is it actually that? Because some try to use the 74HC4046 type and they are 5v parts and won't like 9v supply.

[patrick398]

Ok so the voltages at pin 14 are correct both connected and unconnected to the first op amp? Makes sense about not measuring things with power going through them, that's one to make a mental note of. Just checked and the chip and it's definitely a CD4046. I've already taken it off the breadboard and put it back together once but tempted to try that one more time. If the same problems arise i may buy a new rotary switch with solder lugs just to remove any chance of dodgey connections or bridges on the vero mounting. Beyond that i'm out of ideas