Help! U Boat not working

[Kipper4]

Hey May.
Have you an audio probe?
If you check the op amp outputs you might find something.
The schematic shows what kind of signals you should expect.

[anotherjim]

I note this build has some differences from the Merlin original, so the build doc that May has needs to be to hand for the real schematic. That's kind of tricky here because I don't want to copy and repost the developers work without permission.

Now the next part of stage testing that we have rushed past...
The schematic doesn't actually show the bypass switching, and that's how I'd wire it up when I'm ready for sound test. That means wire the jacks T&S to the board without the bypass switch. Bypass switch wiring and indicator LED  can wait - you want a working pcb first.

Then, we have a mix control pot. Looks like this can be set to 100% clean at one extreme, so turn that to the middle.
There is a preset pot R22 that sets the effect signal level - set that half way too. The Track pot can also be set to midway.


Next, as Kipper suggests, it would be nice if you could follow the circuit through to find where you have sound or not with an audio probe. This circuit doesn't directly distort the signal, so only hearing clean doesn't mean it's all faulty.

In the meantime, all the op-amp (TL074 and LM833) input and output pins should have close to 4.5v on them.

[bifbangpow]

So I fixed the IC chip problem but now Im getting clean sound whether the effect is activated or not.  Adjusting the pots and the on/on switch don't have any effect.  I'm not getting any suboctave.  Any suggestions?

[bifbangpow]

I note this build has some differences from the Merlin original, so the build doc that May has needs to be to hand for the real schematic. That's kind of tricky here because I don't want to copy and repost the developers work without permission.

Now the next part of stage testing that we have rushed past...
The schematic doesn't actually show the bypass switching, and that's how I'd wire it up when I'm ready for sound test. That means wire the jacks T&S to the board without the bypass switch. Bypass switch wiring and indicator LED  can wait - you want a working pcb first.

Then, we have a mix control pot. Looks like this can be set to 100% clean at one extreme, so turn that to the middle.
There is a preset pot R22 that sets the effect signal level - set that half way too. The Track pot can also be set to midway.


Next, as Kipper suggests, it would be nice if you could follow the circuit through to find where you have sound or not with an audio probe. This circuit doesn't directly distort the signal, so only hearing clean doesn't mean it's all faulty.

In the meantime, all the op-amp (TL074 and LM833) input and output pins should have close to 4.5v on them.

Do you or anyone here have a link to a really good audio probe making and using video?  I'm still learning everything I know from the internet, and I need something basic and clear.

[vigilante397]

Geofex saves the day!



And since it doesn't mention it there, the open end of the 100nF cap becomes your "probe." Clip the other lead to ground, plug in a headphone amp or other small amplifier and probe away.

[bifbangpow]

Geofex saves the day!



And since it doesn't mention it there, the open end of the 100nF cap becomes your "probe." Clip the other lead to ground, plug in a headphone amp or other small amplifier and probe away.

HOw may volts does the cap need to be?

[Kipper4]

A small ceramic 100nf 50v is ample for +9v circuits.

[Kipper4]

There's a picture of a probe here

http://fuzzquest.blogspot.co.uk/2013_04_26_archive.html

[bifbangpow]

A small ceramic 100nf 50v is ample for +9v circuits.

So very strangely I am only getting signal on resistors 4-7.  all resistors before and after have no signal.  some of the capacitors show signal.  I'm really bad with schematics, so if someone wants to help me understand what that means I would be much obliged.  I mean, how am I getting no signal at r1, but signal at r4?

p.s. I have never taken a course on electronics.  I didn't grow up around it and I don't work in electronics.  My ability to build pedals is purely from internet learning and moxy.  Be gentle.

[Kipper4]

The reason your getting signal at r4 is because your dealing with two different types of voltages.
In the DC power supply r1 r2 caps 1-3. This powers the componants.

With your probe you are searching for the AC signal (guitar signal)

Sorry the guitar signal comes in at r4 and flows through the circuit to the output.
You will get varying degrees of ac signal strength through out.

I'm not familiar with the circuit. Maybe Merlin will fill us in.
When I have time I will take a longer look but mean time if you find some spots where there's no ac signal report back on those.

I hope that makes sense. I too am no electrical engineer. Totally taught by the kind guys here.
I still get loads of stuff wrong but I'm always improving.

[Kipper4]

Here's the build docs btw

http://diy.thcustom.com/download/uboat-v1-5-build-instructions/?wpdmdl=3224

[merlinb]

Maybe Merlin will fill us in.

I have been watching the thread but I've been reluctant to jump in as I fear we have a difficult customer! Fault finding is easy; people make it difficult.

Bifbang: Post your voltages again.

[bifbangpow]

Maybe Merlin will fill us in.

I have been watching the thread but I've been reluctant to jump in as I fear we have a difficult customer! Fault finding is easy; people make it difficult.

Bifbang: Post your voltages again.

Definitely not trying to be difficult.  Just trying to understand.  I apologize for my confusion.  I will try to post voltages when I get home.

[bifbangpow]

Here are my current voltage readings:


IC1:  (1)  1.13
         (2)  1.18
         (3)  4.0
         (4)  9.0
         (5)  1.0
         (6)  1.04
         (7)  1.08
         (  5.6
         (9)  3.7
        (10)  3.7
        (11)  0.0
        (12)  5.1
        (13)  5.1
        (14)  4.8

IC2:  (1)  8.4
         (2)  3.4
         (3)  3.9
         (4)  0.0
         (5)  4.2
         (6)  4.2
         (7)   0.1
         (   9.0

IC3: (1)  0.0
        (2)  7.7
        (3)  0.0
        (4)  8.4
        (5)  0.0
        (6)  0.0
        (7)  0.0
        (  0.0
        (9)  0.0
        (10)  0.0
        (11)  0.0
        (12)  0.0
        (13)  7.8
        (14)  7.8

IC4: (1)  4.0
        (2)  3.7
        (3)  3.7
        (4)  0.0
        (5)  3.7
        (6)  3.7
        (7)  3.7
        (  9

[bifbangpow]

The reason your getting signal at r4 is because your dealing with two different types of voltages.
In the DC power supply r1 r2 caps 1-3. This powers the componants.

With your probe you are searching for the AC signal (guitar signal)

Sorry the guitar signal comes in at r4 and flows through the circuit to the output.
You will get varying degrees of ac signal strength through out.

I'm not familiar with the circuit. Maybe Merlin will fill us in.
When I have time I will take a longer look but mean time if you find some spots where there's no ac signal report back on those.

I hope that makes sense. I too am no electrical engineer. Totally taught by the kind guys here.
I still get loads of stuff wrong but I'm always improving.

Thank you for your help and patience.  I'm examining the schematics now, and fear I have to ask how do you know where is AC signal verses DC signal? 

[merlinb]

Here are my current voltage readings:

Wow, they're all over the place! I hardly know where to start. Your reference voltage isn't even 4.5V and you seem to be getting different readings! Pin-10 IC1 and pin-3 of IC4 are connected together, yet you have two different readings?
Suggests maybe you have a resistor that isn't actually soldered? Have you missed a joint or two? (Easily done).

IC1 voltages are way out. Looks like the output of IC1A is saturating low, or is shorted to ground(ish). Solder blob maybe? I suggest you remove all ICs except IC1. Most of the pin voltages should be 4.5V. Do you get that when the other ICs are removed?

C10 on the circuit diagram in the user manual is backwards. I did tell THC about this a while back, but it looks like it hasn't been fixed.

[thermionix]

Thank you for your help and patience.  I'm examining the schematics now, and fear I have to ask how do you know where is AC signal verses DC signal?

Signal is AC.  Active components that amplify (tubes, transistors, opamps) need DC in order to operate.  Generally you don't want that DC passed from one amplifying stage to the next (or to the circuit output), only the signal.  But they are usually combined at the output of an amplifying component.  That's where capacitors come in.  They block DC but allow AC to pass through.  Take a look at some simple boost circuit schematics.  You can see that signal goes into the base of a transistor, but the amplified signal is taken from the collector.  There is also DC voltage at that collector.  Then notice there is a cap connected to that collector and it leads to the next stage or maybe the circuit output.

That's why an audio probe is made with a capacitor.  It blocks any DC you may encounter while probing around, but allows AC signal through and into the amp your probe is plugged into.