SOLVED Caesar Chorus troubleshooting

[immi]

Hello,

this is the first guitar pedal I built and I have some problems.
First of all the out of the four leds only two work. Of the two small leds, only the top one works (hard to see in the picture), and out of the two bigger ones only the right one works (constantly on). I get a Chorus effect with a very fast rate with all the pots turned down and nothing changes when turning any of them up. So the effect is always the same. Also when the effect is turned on, the bigger led is off.
Some additional info: I set the trim pot to around 6V and already resoldered most components.
Let me know if you require a detailed view of any component.

Thank you, I appreciate any help

 

[Bio77]

Try a TL022 or TL062 in the LFO. I'm not 100% sure that a 72 won't work as an LFO, but I've never seen one used.

 

[mybud]

Yes when the pedal is engaged I get a Chorus effect but its very fast and turning any pot doesn't change the sound.

Turning the trim pot also doesn't change the sound.

I actually don't understand what I'm supposed to be checking regarding the foot switch (Sorry if that's a dumb question). I understand that im supposed to check the continuity but between which lugs? I get continuity from the cables going from pcb to foot switch and the cables connecting the lugs inside the foot switch have continuity too.

I tried taking a better picture of the foot switch, could you explain based on that.

We want to confirm that you have connections between the horizontal rows so that in one position the switch connects between the top and middle row (pedal activated) and in the other between the middle and bottom (bypass). If this checks out (as it seems to, since you’re getting some kind of effect with pedal engaged), let’s try the next step, giving the board a thorough clean to eliminate any stray connections.

Try cleaning the board with isopropyl alcohol. There might be a stray connection or a fragment of solder causing a short somewhere.

If this doesn’t make a difference, it’s time to audio probe the circuit. Google this, a really basic way of tracing the audio path through the circuit.

 

[benny_profane]

Try a TL022 or TL062 in the LFO. I'm not 100% sure that a 72 won't work as an LFO, but I've never seen one used.

A TL072 will work; it’s usually avoided due to the higher current draw and potential to introduce noise.

 

[immi]

We want to confirm that you have connections between the horizontal rows so that in one position the switch connects between the top and middle row (pedal activated) and in the other between the middle and bottom (bypass). If this checks out (as it seems to, since you’re getting some kind of effect with pedal engaged), let’s try the next step, giving the board a thorough clean to eliminate any stray connections.

Try cleaning the board with isopropyl alcohol. There might be a stray connection or a fragment of solder causing a short somewhere.

If this doesn’t make a difference, it’s time to audio probe the circuit. Google this, a really basic way of tracing the audio path through the circuit.

I got it working, the only problem now is the sound. The sound is crackly sometimes and the sound is not really there / comparable to the original pedal. I know that turning the trimpot should solve that, when I set the trim to 0 I get no sound and slowly turning it up (bad crackling noise at this point) increases the volume until a certain degree (crackling gets a bit better). Turning the trim higher makes the crackling noises worse again.
Is this normal or am I still missing something?

 

[mybud]

First, good news on getting it working. It seems that the trimmer connection to the board might be faulty.

Try reflowing just there and see if that fixes the crackling (not normal). Otherwise, it may be worth replacing the trimmer if you see signs of damage to it. It may need replacing if reflowing doesn’t work.

If that fixes the problem, you’re good to go and you can mark this solved.

 

[immi]

First, good news on getting it working. It seems that the trimmer connection to the board might be faulty.

Try reflowing just there and see if that fixes the crackling (not normal). Otherwise, it may be worth replacing the trimmer if you see signs of damage to it. It may need replacing if reflowing doesn’t work.

If that fixes the problem, you’re good to go and you can mark this solved.

Definitely trying that, unfortunately I can't continue until friday because of Uni.

 

[benny_profane]

What did you do to get it working to this point?

There’s typically a narrow band on the trimpot that has the clearest effect. (One way of biasing is to mark the extremes where the audio drops out and find the spot between those.) Are there no points in the rotation where it’s fully clear?

Is there distortion if the blend pot is completely dry? That would tell you if one of the op-amp stages is introducing clipping. Have you traced the circuit with an audio probe (as mentioned above)?

 

[immi]

What did you do to get it working to this point?

There’s typically a narrow band on the trimpot that has the clearest effect. (One way of biasing is to mark the extremes where the audio drops out and find the spot between those.) Are there no points in the rotation where it’s fully clear?

Is there distortion if the blend pot is completely dry? That would tell you if one of the op-amp stages is introducing clipping. Have you traced the circuit with an audio probe (as mentioned above)?

I pretty much followed the instructions @mybud gave in his response.

Unfortunately there is no point where the audio is fully clear, the noise decreases a lot but never completely disappears (I guess that's the right spot minus the noise).

At the moment I can't answer the question about the blend pot but I will try when I'm home again.

I ordered the necessary parts for the audio probe, waiting for them to be shipped.

 

[immi]

Ok I got the pedal kinda working now.

I changed the TL072 to the TL022 and adjusted the trimpot again, that seems to have solved all the problems.
All of the Leds work, the Pots work and the chorus effect works.

The only problem now is the distortion I get.
The distortion is not present when the blend pot is completely dry.
Which components are the op-amp stages, so I can have another look at them.

 

[mybud]

Pins 1 and 7 of IC2 are the audio outputs (as far as I can tell). Try audio probing this section, but I suspect you may need to adjust the trimmer more exactly to find the sweet spot where you get most chorus and lowest noise.

The 022 is the oscillator and the 3102/3207 pair is the BBDs.

Best to test with no other pedals connected.

 

[immi]

Pins 1 and 7 of IC2 are the audio outputs (as far as I can tell). Try audio probing this section, but I suspect you may need to adjust the trimmer more exactly to find the sweet spot where you get most chorus and lowest noise.

The 022 is the oscillator and the 3102/3207 pair is the BBDs.

Best to test with no other pedals connected.

Yes you were right, I didn't think the adjustments had to be so small. Everything is working fine now.

Thanks for the help, couldn't have done it without you and all the other people that helped.

 

[mybud]

Only a pleasure and glad you got it working.

 

[mybud]

Only a pleasure and glad you got it working.

I am tempted to recommend some ways forward for you. Ignore these as you wish.

I know nothing of your background in electronics so please take my advice (as before) as well-intended and with the proverbial pinch of salt.

I speak of these things after a long and initially frustrating return to electronics some five years or so ago. I’m gradually getting better at it but still have a long way to go, so…

In no particular order:

Find some simple circuits and breadboard them. There’s an excellent repository of breadboard circuits right here, courtesy of the highly esteemed @BuddytheReow.

Understand the schematic and the flow of electrons through it. Learn to recognise basic building blocks of circuitry (RC filters, op amp configurations, biasing circuits, etc.).

Then build them on veroboard.

You’re developing practical skills of layout, soldering, and troubleshooting at the same time while understanding how the resistors resist, the capacitors capacitate, and so on. Make Electronics has some good projects as well.

Others differ but I swear by socketing transistors esp FETs and MOSFETs. These deserve special care as do ICs against static and using sockets eliminates destroying them through overheating.

Soldering hygiene matters for you and the board alike. Avoid fumes and common soldering faults (strive for volcanoes not blobs or dry joints).

There’s a lot to learn but it’s hugely rewarding when you build something that works and is beautifully made. Check out some of the great builders on this site who inspire us all. Now go build something and congrats