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[Strat68]

Got this built but when engaged, I'm getting a periodic click once the Ratio control is turned above zero. It does not appear to do anything to the guitar signal. I am unfamiliar with the LM13700 IC. There are several questions beside the original:

1. Which lead should go ito the square pad: Cathode or anode. (I always have this problem).
2. There is no wiring diagram. So I soldered the 1-6 pads on the board to a DPDT ins the 1-6 order. The footswitch does control D1 as I think It should.
3. Where should one start to debug this?

have several Dead End FX boards waiting to be built and this was the simplest.

Attached is the schematic.

 

[Feral Feline]

3. Where should one start to debug this?

Start by posting pics.

USE LOTS OF LIGHT

Pics of front and back, pics of all connections.



Then while helpful forumites are looking at your build, you should be

- checking all your solder joints, looking for possible cold joints, cracks, dull-solder (indicates a possible cold-joint) — reflow as needed
- checking all cap & resistor values are as should be — colour-codes for resistors can sometimes be tricky reading, L>R or R>L — ex:

Brown Red Black Black Brown (120r)​

or​

Brown Black Black Red Brown (10k)​

1. Which lead should go ito the square pad: Cathode or anode. (I always have this problem).

Use your DMM to see which end goes where compared to the schematic — that will tell you which goes where.
DMM set to BEEP (continuity mode) and holding one probe in the square pad, what's it connected to? What's the schematic show?

2. There is no wiring diagram. So I soldered the 1-6 pads on the board to a DPDT ins the 1-6 order. The footswitch does control D1 as I think It should.

Here's a good example of why pics are necessary.

How do I know what the 1-6 pads on the board are? You haven't posted a pic/diagram of the board, only the schematic.

Is your 1-6 order the same as mine?

Some mistakenly think DPDT numbering goes:

1 — — 2​

3 — — 4​

5 — — 6​

Or other irregular ways of numbering the lugs.

DPDT Numbering should be:

1 — — 4​

2 — — 5​

3 — — 6​

 

[Strat68]

Yeah, I forgot about the photos. I inserted the cathode legs of the LEDs into the pad connected to ground. I assumed the switch lugs corresponded to the board's numbered pads and the switch is:

1 4
2 5
3 6

One more thing I forgot to mention was that the first time I turned it on it made all sorts of wild oscillating sounds related to the Ratio pot. And LEDs 3 and 4 were flashing in unision with the oscillation. It now only outputs the clicking noise with no flaching LEDs. I have not had a chance to trace the sound through the board.

Update: The LM13700 data sheet says the V+ (single-supply configuration) is 9.5V. By the time the the voltage gets to the PCB through the test rig it's down to 8.6.


Thanks for the help.

 

[Feral Feline]

I've not checked the resistor values, still can't quite make out the colour-bands — but everything else looks oriented properly compared to the build doc. I can't tell if D3 & D4 are oriented anti-parallel or not — so long as they're not facing the same way you're good there.

I'd go through it with a DMM and make sure there's continuity where there's supposed to be, and none where there's not supposed to be.
In particular, I'd be checking the IC sockets to make sure there isn't a hidden short underneath one of them.

Once all that's confirmed, I'd then try going through the circuit with an audio probe.

Also, once confirmed there're no shorts/solder-bridges and the IC-sockets are good... I'd reinstall the ICs and/or swap out for known good working chips. Might be you've got a dud or if there was a short blown out the 13700 — I don't know, I'm just a neophyte at this stuff.

Where'd you source your TL072s? There are some known fakes floating around. Maybe check the forum for related threads on fakes, to determine if yours are legit or not.



An aside:
How are you grounding the in/out jacks? I see the pads on the board aren't occupied...

 

[Strat68]

I’ll check the I/O grounding but they should be common with the power on the debug rig. I checked the parts and reflowed the soldering. I’ll try some part substitution. I’ve built over 100 pedals and this makes me wary of the other Dead FX I have on deck. They require some really obscure parts. This one is fairly simple.

I buy most common parts from Tayda.

 

[Strat68]

Before I get back to this should the guitar signal be traceable through all the various ICs? Or are some sections and pots used to control voltage and current into other sections where the signal travels. I’m not familiar with how this type of compressor works.

Got back to it. I replaced all the ICs and transistors with no change. I also wired up the I/O jacks so nothing going through the debug rig. With no input at all the unit outputs a rapid, periodic thumping noise. With a guitar plugged in I get the guitar and the thumping sound. The thumping noise starts when the ratio knob is turned up from zero.

 

[Strat68]

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