Mid-fi Demo Tape Fuzz, just...no fuzz.

[tracer03]

Building a Mid-fi Demo Tape fuzz today, and I get no fuzz. I've tried with a good JRC4558 and a TL072 (both pulled from verified working builds) and I get nothing but hum.

I've X-acto'ed the grooves, checked continuity across the tracks, checked the components, reflowed my solder joints, etc. And still nothing.

Voltages (from the TL072)
1 - 7.76
2 - 1.5
3 - 4.25
4 - 0
5 - 6.29
6 - 8.5
7 - 1.37
8 - 8.5

Top:


Back Side:

[Addy Bart]

Are you sure the input and +9v wires are not shorting? Looks like a possibility with the frayed wires poking out a bit on the top side. Tinning the ends of wires helps prevent this.

Your components look like they're in the right places but the solder side picture is too small to be of much use. But if you're getting nothing but hum you probably have a short somewhere.

[PMowdes]

I agree with Addy, hum normally means you have supply voltage bleeding through into the signal chain.  Check for shorts

[Marbles]

Could it be that the cut is not complete on the 9v row? It's hard to see, but maybe the bottom of that cut is not complete.

[tracer03]

Marbles wrote

Could it be that the cut is not complete on the 9v row? It's hard to see, but maybe the bottom of that cut is not complete.

I've run an xacto over all the tracks, but I will certainly give it another go. Could just be my luck th9s weekend - four builds (including this one) and only one has worked right off the bat...

In the meantime, here's a better pic of the solder side.

[Marbles]

Yeah, I would definitely check that cut. It looks like the bottom has a tiny line of copper still connected. That would also explain the other guy's comments:

[Hozy31]

Looking at the holes on the copper side, a lot look like they aren't complete with copper still present. Take a larger drill bit (i use 4mm) and use it to remove these and you may find it suddenly fires up.

[tracer03]

Hooked it up to my test rig this morning and found that now I got NO sound, not even hum.

So, I checked the soldering, re-cut the holes and cut the tracks with an xacto, and checked everything with my meter on continuity setting. I then hooked it up with an audio probe...and found that the signal died on the 1U cap at the far left. they measured fine at 1U, so I reflowed the solder joints - no luck.

Decided to swap out those caps (used the same kind for all 3 of the 1Ufs), and went over all my joints AGAIN with a magnifying glass and Xacto. I hooked it up to my test rig, and....Signal! Just not a lot of fuzz. Swapped the TL072 I started with to a JRC4558D, and didn't notice much difference. Granted, I'm using a Blackstar Fly practice amp for testing, but it just didn't get as fuzzy as the sound in the clips.

Any ideas?

[Marbles]

Your IC legs look like they not have been soldered in completely. Did you reflow those too?

[Addy Bart]

You could also double check that you used a 470k resistor in the feedback part of the chip... In the photo, that big cap is in its way.

Are the bass and treble pots working?