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Synthcube Fuzzbucket build
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Author Synthcube Fuzzbucket build
jschussler
I've put together one of the Synthcube Fuzzbucket kits, and seem to be having issues. Calibration isn't working as specified in the build doc, and I'm wondering if there are any obvious errors in my build. Anybody built this and able to help?

Here are some pics:




teebeehex
First thing, clean up the flux. It’ll help you see the joints clearly. I’d also recommend reflow your ICs, and any joints that you feel look a bit suspect. I can see C5 appears to have a cold joint on the right side of the first pic.
joem
teebeehex wrote:
First thing, clean up the flux. It’ll help you see the joints clearly. I’d also recommend reflow your ICs, and any joints that you feel look a bit suspect. I can see C5 appears to have a cold joint on the right side of the first pic.


I second this advice. Cleaning up flux and reflowing anything that looks potentially suspect solves almost all of my problems when I have issues. Also, I think this module uses some no-longer-in-production or hard-to-find part, right? Did you get it from a reputable supplier, or did you just ebay it from some random person who might be selling bad or counterfeit parts?
ndf
What chip are you using for the schmitt triggers (U1)? It should be an HEF4093B or CD4093 quad 2 input NAND Schmitt trigger.
jschussler
Ok, flux fully cleaned. Here are some better pics in daylight.

This is a kit from Synthcube. Uses all their parts supplied.



ndf
Well it looks pretty much ok, although U1 looks a little off, perhaps re-flow the pins with a little flux paste to make sure they are all connected. Calibration is not totally necessary, you can check the basic operation first.

- set all controls and the trimpot to midpoint
- check that you have about +12V DC on the positive side of C6 and about -12V DC on the negative side of C5
- check that there is a square wave on the clock output, U1 pin 10
- check that the clock is also visible at test point 1 (also U1 pin 3)

If there's a working clock, skip the bias calibration and check the inputs and outputs with an audio signal.
jschussler
Fully reflowed.

Wrt your instructions:

I get +12 on the positive side of C6, and -11 on negative of C5.

No square wave on pin 10, it goes to -12 volts and stays there. The only pin on that IC that's outputting anything is 11, which is noise.

No clock on test point 1, or on pin 3.
guest
what is the voltage drop across R5? if its 1V, then that means there is 100mA flowing on the -12V rail, which would be lot. what are the voltages on all pins of U1? U1 looks like it might be cracked in your photo.
ndf
Sounds like U1 might be faulty. There's not much to the circuit, and all the passives look ok - so it would be worth swapping that out if you can.
jschussler
Voltage across R5: 1.1V
The IC isn't cracked, just scratched from the tweezers when I slipped.

Voltages on each pin of U1:

1: .1 mV
2: -6V
3: -7V
4: -7V
5: -.5mV
6: .1mV
7: -10V

8: .1mV
9: -5.5V
10: -5.8V
11: -5V
12: 1.5mV
13: -5.9V
14: 1.3mv
guest
U1 is most likely bad. there is also some chance that one of the output is shorted to ground some place (or through too low of a resistance). all of the outputs are stuck at -6V, and they should be at -12V. so, either the chip is busted, or there is a lot of current flowing on the negative rail through the chip. you can shut the power off, and measure the resistance to ground on all of the outputs. if that doesnt show anything less than 100ohms, then id reccomend just swapping the chip.
guest
by the way is U1 or any of the other ICs warm? with 100mA flowing through the negative rail, something should be getting warm.
jschussler
It was super warm at one point but after reflowing stopped being warm. Probably just dead now.

I've ordered a new one through Mouser.

Any suggestions for getting this one off? I'm a noob to SMT, and last time I tried to get an IC off I ended up lifting a bunch of pads and killing the board....
nigel
jschussler wrote:
Any suggestions for getting this one off? I'm a noob to SMT, and last time I tried to get an IC off I ended up lifting a bunch of pads and killing the board....

If you have fine enough cutters, you could try clipping all the legs off the chip (or clipping the chip from all of its legs, really), and then desolder each leg separately (grab it with tweezers, heat, lift).
ndf
Another approach is to bend a piece of solid core wire around the chip, then solder it into place with pleanty of solder so that it flows all over the legs. Then heat it up and drag the whole chip away. Then you can clean the pcb with some braid. Let me know if you'd like a photo instruction.

Good luck - make sure you use a static wrist band when you place the new one in smile
guest
if you have a heat gun, you can flux up the chip, and slowly bring the heat gun closer to the chip till you see it start to bubble up. then wait a bit for the solder to flow, and then lift the chip off. its a bit risky, as its easy to get too hot and do damage to the board or other parts without a heat gun designed for this purpose.

another method is to slip a thin piece of nichrome wire beind the legs, and pull the wire forward as you desolder each leg. the wire will slip under the leg, seperating it from the pad, but it wont stick to the solder. you might be able to do the same thing with an xacto blade.

you can also use a small screwdriver to bend each leg up as you desolder it.
jschussler
I went with the "clip the legs off first" method and that seemed to work pretty well.

New IC on order at Mouser, will see how that goes once it arrives...
jschussler
Ok, so replaced the U1 IC.

On first boot, with an audio signal on Input 1 and just output 1 hooked up, I get a faint sound that seems reasonable. The fuzz pot works, sound gets fuzzier, and the time pot does...something.

But over the course of a minute or two the sound gets fainter and fainter until all I hear is a little static and crackle. I can turn the time pot and hear an oscillator going from low to high, but just faintly.

So unplug it look at it quizzically, then plug it back in. Just static and crackle. And a little faint bit of osc if I turn the time knob.

Does that make any sense to anybody? Seems like the ICs are working and the basic circuit is working, but there's some critical element like a VCA that's unhappy....
thetwlo
holy shit did you not put the MN3005 BBD chip in a socket? WHY? Even in the '70's that's the the chip about everyone socketed! Even DOD...
swap that chip first. Much more likely to be faulty than an opamp, or too much heat from soldering.
jschussler
It is a kit from Synthcube, and they didn't provide a socket....
thetwlo
jschussler wrote:
It is a kit from Synthcube, and they didn't provide a socket....


that's weird. if it's a thru hole IC you should use a socket, especially a pricey one! only costs few cents.
ndf
Well it sounds like your clock section is functioning ok. But the effect you mention sounds like maybe the the bias or gate voltages going to the BBD might not be completely right. Does it do that every time you power it on? Or did it only do it once? It also sounds kinda like what happens when you have the feedback set to full. Try making sure both inputs are set to zero before starting.

Can you do the clock calibration now?

If your clock is running, and the flip flop is flip flopping, tracking down an error shouldn't be too hard. The Xvive BBD Synthcube supply is pretty seriously robust, so it should not be a problem - I have no hesitation whatsoever soldering it in place. Maybe defer swapping that out until you are sure it is the source of the fault.
ndf
Actually I just spotted one error on your build: R22 should be 22k. It looks like you might have a 100k in that place. With 100k there, your output level will be vey low even if it was all working otherwise.
guest
double check that the oscillator is doing its thing. check at both outputs of U2.
jschussler
I don't have another 22k on hand, but do have a 15k. I swapped that in and now it's louder.

Checked U2: have several pins that are doing oscillator-y things. Which pins in particular should I look at?

I've recorded what it does on first boot here: https://soundcloud.com/jschussler/fuzzbucket-broken

Notice that at the very beginning you can hear the source sound (a somewhat sparse output of an LPG). I then start twisting the the clock knob and you hear the whine change frequency. You also hear BBD behavior in the source sound (changes pitch and speed). Then I twist Fuzz, and it gets a little louder.

Then you hear the whine suddenly get much louder, and no longer can you hear the source. Twisting clock still gives some whine frequency change, but that's about it, and now lots of rice krispies.

Seems like it warms up and that's when the source goes away entirely. If I try it again after having had it plugged in, I can't hear the source sound any more.
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