Help needed with a Keeley 4-knob clone

[LloydDexter]

Hey guys,
I built the Keeley 4-knob clone based on the effectslayouts design. I made one, almost had it and something shorted out and I couldn't figure it out, so I decided to make another one. It too, gives me a bypass (clean) tone, but no effect tone. Two things I did note this time, though:
1. Turning up the LEVEL pot, increases background noise, so the LEVEL knob is sort of "working," and
2. the SUSTAIN pot crackles as I turn it. The other two pots have no effect.

OK, so a few technical notes:

• I had to use an NTE996 chip, as I could not find either a CA3080 or an LM13700. People reported that the 996 chip worked well in a Ross compressor, which is what this Keeley is based on, so I went for it.
• I have tested ALL of my component connections and they all check out; no broken/cold joints
• I tried audio probing and what I found was that the signal gets to the first 3904 and then no further, however, I have swapped out ALL of the transistors and the main IC without any success.

The pin values are:
1   0
2   3.81
3   3.82
4   0
5   0.63
6   2.66
7   8.87
8   0

If anyone has any ideas, I'd really appreciate it.

[willienillie]

• I tried audio probing and what I found was that the signal gets to the first 3904 and then no further,

You're checking for output at the emitter, not the collector, right?

[LloydDexter]

Thank you guys, for taking the time.

So what I noted is that with the audio probe (which I admittedly am not good at using), I was able to follow the sound of the CLEAN signal UP TO the middle pin (base) of the first 3904. After that, I get nothing. The emitter does NOT produce any sound, clean or effected.

I have replaced all the transistors several times, as well as the IC itself.

Also, if you have any tips on how to audio probe better, I'm all ears. I know I have it connected correctly, because I get a clean sound at the input and then for a few more steps in the schematic. I have tried using it to troubleshoot several pedals and I basically get the same results, meaning, It doesn't get too far before I lose the signal and yet that component doesn't seem to be faulty. Everything online makes it seem like audio probing is easy and the key to understanding your circuit, etc. but I can't seem to figure that out.

Thanks!

[bluebunny]

What are the voltages at the transistor?

[ElectricDruid]

Also, if you have any tips on how to audio probe better, I'm all ears. I know I have it connected correctly, because I get a clean sound at the input and then for a few more steps in the schematic. I have tried using it to troubleshoot several pedals and I basically get the same results, meaning, It doesn't get too far before I lose the signal and yet that component doesn't seem to be faulty. Everything online makes it seem like audio probing is easy and the key to understanding your circuit, etc. but I can't seem to figure that out.

You've got the basics, so don't worry too much. I would say that "understanding your circuit" needs to come first, not after. Unless you have a reasonable idea about how what you're looking at works, it's difficult to know where to probe a circuit and what to expect to hear. This is exactly the same when testing voltages with a =multimeter. You need to know what you *expect* to see to know if what you *do* see constitutes a problem. Probing the wrong spot will give you nothing, and might well confuse you worse.

For example, I've often seen people probing the -ve input on an inverting op-amp and then saying that they think the fault is there because that's where the signal disappears. Inverting op-amps *never* have signal at the -ve input - that's how they work. You need to test the output instead.

There are about a million other simple ways to screw-up too. That particular circuit you're looking at contains several of them and would confuse the hell out of me. One further example to watch out for is current outputs instead of the more typical voltage output. Current outputs are common on OTAs and VCAs, and probing them directly doesn't work. That turns up in this circuit where the 3080 produces its output. Better to test the other side of the transistor at C6.

HTH,
Tom

[LloydDexter]

Hey Bluebunny,

Sorry about the delay, but I have Transistor values for you:

T1 (the one in question): E=0,       B=0.01,     C=8.78
T2:                                E=2.1,    B=2.34,     C=6.72
T3:                                E=0,       B=0,          C=7.82
T4:                                E=0,       B=0,          C=7.82
T5:                                E=8.31,  B=7.82,      C=8.87

Anything you can tell me about what these values tell you would be greatly appreciated.

One more thing: Oddly, I plugged it in just to see, and while there is no sound when the effect is on, when I strum my guitar hard, there is a "crackly static" sound made, so something IS coming through the circuit, just not what is expected.

[willienillie]

You should have some voltage on Q1e.  Power off, pull Q1 out of the socket and check to make sure there is 10k ohms between the emitter connection and ground.

[LloydDexter]

Just checked it. 9.89K!

[bluebunny]

You seem to have B-E shorted (and grounded) on three of your transistors.  This isn't a good sign.  Take a good close look at what you've built vs. the layout.   (My eyes and brain are too tired now to look.  Perhaps tomorrow morning...)

[Slowpoke101]

You seem to have a connection that is in need of some solder. Refer to the follow image;



Resolder it and see if you get some volts to Q1's base.

[antonis]

T5 doesn't seem to feel happy, also.. 

[LloydDexter]

You guys did it! I re-soldered that connection, checked everything else (didn't see any E-B shorting going on) and tried it and it worked.

The only thing is that now, I need to order a 125B. The 1590B I was trying to mount it in is just too tight. I get it working and every time I try to close the case, it shuts off. I think that off board wiring is just too cramped in there.

THANK YOU SO MUCH! I still have A LOT to learn about these things, but I feel like every time I get one to work (I have managed to complete a chorus, a JCM800 simulator, a Diesel VH4 and a couple of Fuzz Factories, as well as a basic headphone amp), a little more light shines on the science of it.

Really appreciate the help!

[bluebunny]

It's amazing what a good night's sleep can do.