SOLVED Cepheid Chorus: No Sound but LEDs work

[fogboundrogue15]

I recently started my first PedalPCB build, the Cepheid Chorus. I've built a few overdrive pedals in the past from The Tone Geek, but wanted to try something new.

This is also the first time I've had significant issues with a pedal (surprisingly!), so I'm very new to actually troubleshooting.

The Situation Currently

• I've soldered in all components.
• I've offboard-wired the pots (because I was hoping to drop in the circuit to a bigger enclosure than the one pictured)
• The LFO LED is pulsing and changes rate as I change the rate knob, so that's good
• The only sound I get out right now is a ticking sound that looks to be the clock (it speeds up and slows down with rate and the LFO)
• The indicator LED does not turn on when the circuit is switched on
• When the circuit is off, the guitar signal gets through as normal

The Situation Recently

• There were a few minutes where the indicator light did work and instead of a ticking sound, there was white noise with a tiny bit of guitar signal coming through
• After moving my workstation, things reverted to the no LED and only ticking sound
• You'll see one photo attached where both LEDs were working (however as I mentioned, they no longer work now :/ )

Current Steps to Remedy

• I went through and checked that I have all the correct values where they are

Next Step (Ideas)

• I've measured voltages on the ICs and listed below
• I was thinking about going and resoldering joint by joint but would love some input before doing that. I'm guessing there are some cold connections somewhere, I'm just not very familiar with wiring diagrams and how to figure out where to start
• I was thinking about re-doing the wiring to the 3PDT because it's a bit messy
• Only other thought is that one or more of the ICs is bad, but I did order the V3207D and V3102D from CabinTech so they should be legit

Questions

1. Could the wiring to the pots be throwing things off? I'm guessing not since the rate knob works and the LFO is pulsing
2. Some of the values on the 3207 chip seem low (ie. pins 3, 6, 7)

Voltages on ICs

IC1 - TL022
1) 4-5 fluctuating
2) 4.5
3) 4-4.7 fluctuating
4) 0
5) 4.5
6) 4.5
7) 4-4.5 fluctuating
8) 8.95

IC2 - RC4558
1) 3.3
2) 3.3
3) 3.3
4) 3.3
5) 0
6) 3.3
7) 3.3
8) 9

IC3 - V3207D
1) 0
2) 4.3
3) 0.018
4) 8.45
5) 9
6) .008
7) .008
8) 4.62

IC4 - V3102D
1) 8.94
2) 4.3
3) 0
4) 4.36
5) 0.3
6) 8.58
7) 2.96
8) 8.37

 

[fogboundrogue15]

Quick update: Indicator LED is now working. It must have just been a dud because I replaced it with a new one that works

 

[Locrian99]

If there is one piece of advice I still follow religiously and have since my first pedal I’ve built is always rock it before you box. It really makes trouble shooting so much easier and really doesn’t change much in the process of building in my eyes. You eliminate the possible wiring errors being an issue or you know that is where the issue is.

Have you turned the bias trimmer and see if this has any change to your signal? I honestly don’t remember if you get signal when it’s way out of bias. And I’ve built the Caesar bit the Cephied yet (though I was planning on starting it tonight) I would put it around noon and see what happens. Or just pluck your low e while turning the trimmer to see what happens.

Your 4558 voltages look strange to me. I’m not going to say they are wrong but they look strange to me. Oops yes they are wrong. You have 3.3 at pin 4 this should be ground and be 0, you have pin 5 at 0 is this just a typo? Typically pins 1-3 and 5-7 are 1/2 supply voltage but that’s not written in stone. So I would expect to see around 4.5 there.

Reflowing all your joints is always a good place to start after verifying your supply voltages to your chips are what they should be. Quick look they all look ok to me.

Do you have an audio probe? If not look up how to make one. Probing likely will be the fastest way to figure this out if reflowing your solder joints or the bias doesn’t provide a fix.

 

[PJS]

My memory of BBD chorusing is that there is a very narrow band on the trimpot that will give you anything.

 

[Dirty_Boogie]

Any chance you have a short/solder bridge here?


I'd suggest getting some isopropyl alcohol and a toothbrush and thoroughly cleaning both sides of the board, and then reflow solder joints, as suggested above.

Also, since you haven't socketed your IC's, there's no easy way to switch out any of the chips to test if you have a dud/fried chip. IC sockets can be such a timesaver when troubleshooting.

 

[fogboundrogue15]

If there is one piece of advice I still follow religiously and have since my first pedal I’ve built is always rock it before you box. It really makes trouble shooting so much easier and really doesn’t change much in the process of building in my eyes. You eliminate the possible wiring errors being an issue or you know that is where the issue is.

Have you turned the bias trimmer and see if this has any change to your signal? I honestly don’t remember if you get signal when it’s way out of bias. And I’ve built the Caesar bit the Cephied yet (though I was planning on starting it tonight) I would put it around noon and see what happens. Or just pluck your low e while turning the trimmer to see what happens.

Your 4558 voltages look strange to me. I’m not going to say they are wrong but they look strange to me. Oops yes they are wrong. You have 3.3 at pin 4 this should be ground and be 0, you have pin 5 at 0 is this just a typo? Typically pins 1-3 and 5-7 are 1/2 supply voltage but that’s not written in stone. So I would expect to see around 4.5 there.

Reflowing all your joints is always a good place to start after verifying your supply voltages to your chips are what they should be. Quick look they all look ok to me.

Do you have an audio probe? If not look up how to make one. Probing likely will be the fastest way to figure this out if reflowing your solder joints or the bias doesn’t provide a fix.

I regret not doing that this time around and will plan on it in the future, that's for sure.

Trimmer: I tried adjusting the trimmer and no audio changes happen. I'm still only hearing a small ticking pulsing with the rate indicator

4558: I did mistakenly mix things up. Messing with the trimmer, I was able to get voltages on this chip to right near 4.5 and I've updated readings for this chip and the other 3 below.

Audio Probe: I don't have one, but looked up how to build one and just ordered some parts tonight! I'm hoping this will help.

IC1 - TL022
1) 0-8 fluctuating (this seems extreme?)
2) 4.2-4.8 fluctuating
3) 0-6 fluctuating
4) 0
5) 4.2-4.8 fluctuating
6) 4.7
7) 0-6 fluctuating
8) 8.95

IC2 - RC4558
1) 4.49
2) 4.5
3) 4.49
4) 0
5) 4.5
6) 4.5
7) 4.5
8) 9.11

IC3 - V3207D
1) 0
2) 4.3
3) 3.81
4) 8.73
5) 8.95
6) .0002
7) .0002
8) 5.1

IC4 - V3102D
1) 8.94
2) 4.3
3) 0
4) 4.32
5) 0.3-.32 fluctuating
6) 8.58
7) 2.96
8) 8.37

 

[fogboundrogue15]

Any chance you have a short/solder bridge here?
View attachment 42760

I'd suggest getting some isopropyl alcohol and a toothbrush and thoroughly cleaning both sides of the board, and then reflow solder joints, as suggested above.

Also, since you haven't socketed your IC's, there's no easy way to switch out any of the chips to test if you have a dud/fried chip. IC sockets can be such a timesaver when troubleshooting.

Thanks for pointing that out. I went ahead and cleaned both sides of the board.

I definitely regret not socketing the IC's - I ordered some sockets and may try desoldering them and then socketing them if audio-probing things doesn't work

 

[Locrian99]

I regret not doing that this time around and will plan on it in the future, that's for sure.

Trimmer: I tried adjusting the trimmer and no audio changes happen. I'm still only hearing a small ticking pulsing with the rate indicator

4558: I did mistakenly mix things up. Messing with the trimmer, I was able to get voltages on this chip to right near 4.5 and I've updated readings for this chip and the other 3 below.

Audio Probe: I don't have one, but looked up how to build one and just ordered some parts tonight! I'm hoping this will help.

IC1 - TL022
1) 0-8 fluctuating (this seems extreme?)
2) 4.2-4.8 fluctuating
3) 0-6 fluctuating
4) 0
5) 4.2-4.8 fluctuating
6) 4.7
7) 0-6 fluctuating
8) 8.95

IC2 - RC4558
1) 4.49
2) 4.5
3) 4.49
4) 0
5) 4.5
6) 4.5
7) 4.5
8) 9.11

IC3 - V3207D
1) 0
2) 4.3
3) 3.81
4) 8.73
5) 8.95
6) .0002
7) .0002
8) 5.1

IC4 - V3102D
1) 8.94
2) 4.3
3) 0
4) 4.32
5) 0.3-.32 fluctuating
6) 8.58
7) 2.96
8) 8.37

I ended up messing up mine but it’s good now (I put the 47u electro in backwards). Heading out to a poker game but I’ll do some voltage comparisons tomorrow. If you aren’t getting any thing. I’m worried about the lack of sockets on those bbd chips. The mn versions at least to me seem easily fried (I fried two today) heat may be an issue I’d look at one of the Caesar threads in the meantime and if the voltages match. They are nearly identical. There’s one that has all the voltages listed.

 

[fogboundrogue15]

I finally got the parts to build an audio probe and did some testing this morning. I'm still fairly new to reading schematics, so I tried to put notes where things weren't as fully expected (such as around R10, R14, C5, and IC 2). I marked the parts that work as expected with green checkmarks.

My first guess is that IC4 (the V3102) is fried, though I'm not sure what to expect when it comes to audio signal in and out of it. I'm hoping the notes on the attached diagram help someone that knows better than me to diagnose!

@Locrian99 , (and anyone else!) mind taking a look?

 

[fogboundrogue15]

Oh and if anyone can explain to me how to tell 1 vs 2 when it comes to legs on these resistors/capacitors, that'd be helpful! I noted left, right, top, or bottom leg in some instances based on if you were looking at the circuit board/diagram.

 

[Bio77]

The 3102 is your clock chip, you won't hear any signal from it. You can check pins 2 and 6 of the 3207 with the frequency setting on your multimeter to confirm the 3102 is working.

Looking at your diagram: do the green checks mean you can hear guitar signal? If so, you have a problem with the clean side of your chorus signal. You should hear guitar all along the top trace (R34 for example). You might have a short or bum part. Try replacing C5.

 

[PJS]

The V3102 is a clock generator. It generates the clock signal that make the delay chip work. Something would be very wrong if you had the audio signal on any of it's pins. It looks as if you are getting audio out of the delay chip, which I think means the clock is working fine. From your audio probing it looks as if either bad solder or broken traces on the board are more likely to be your problem. Chorus works (broadly) by mixing a clean signal in with a delayed signal. You have the clean signal at IC2.1 but you don't have it at R34 even though they are directly connected together - either bad soldering or a broken trace between them is likely. Reflow the solder and use a multimeter to check for continuity there. It looks as if you have delayed sound at C17, but not at R35. Again, they are directly connected so if you have sound in one part of that junction you should have it everywhere. Check you solder in this area and check for continuity.

 

[fogboundrogue15]

You are all lifesavers! I got it working! I'm not entirely sure what was wrong, but I did replace C5 and then replaced R34 and R35 (it may have been overkill, but I initially just resoldered both of those and it didn't seem to be working at the time).

I started checking continuities between IC 2.1 pin 1 and R34, then C17 and R35, then R35, R35 and IC2.2 pin 6. On checking continuity, everything looked right, so I plugged it in, and low and behold, it was working!

While I can't exactly pinpoint which exact piece of those two resistors and that one capacitor was the culprit, it must have been a part of one of those three.

Thanks again everyone for the help! I can't wait to drill the enclosure and get this thing all put together. It may be a bit, but I'll make sure to post a photo of the finished product when it's ready.

One last (unrelated) question: is it possible to wire up the LFO so that it only turns on when the pedal is on? I was actually hoping to use only one of the LEDs and I thought it would be cool to not just have the LFO pulse with the rate control but to also indicate whether the pedal is on/off. Right now, it pulses at all times, regardless of the pedal being off or on.

 

[fogboundrogue15]

I'd also add this has been a great, though at times frustrating, experience. I had never used an audio probe or even continuity mode on my multimeter before and it was wonderful having so many people reply so quickly to this thread and my questions, so again, thank you thank you!

 

[Locrian99]

Awesome you got the pedal working. To make it so the lfo rate indicator led only works when the pedal is on you just need to wire it so the cathode goes to where you would wire the sw pad of the indicator led. You’ll need to use a wire and remove the cathode from the pcb and run it over to the switch.

 

[fogboundrogue15]

As promised, here's the pedal! I was hoping to use a white LED but accidentally burned out the one I had. May replace it in the future. Also, not sure whether I like the LFO or would prefer just the indicator LED. I used a Gorva enclosure and drilled it with offset footswitch/LED. The inside is a bit of a mess with all of the wires you can see in previous photos I've posted.

Anyway, it sounds great! Better than the 70s Chorus on my HX Stomp (aka CE-1).

I recorded a little demo video here:

 

[fogboundrogue15]

Follow-up question(s) now that I've been playing around with it working for a bit:

I've noticed that I get a bit of clipping with the pedal when running any sort of drive (or even just a clean boost) before it. Playing with chorus effects on my HX Stomp, I get no clipping (or at least significantly less).

Is this normal? I'm using the V3207 and V3102 chipset running at 9v.

Would running the pedal at 12-15v (by finding a real MN3007) increase headroom and decrease clipping? Or is there another way to decrease clipping (would tweaking the trim pot help for instance)?

Thanks!

 

[Locrian99]

Follow-up question(s) now that I've been playing around with it working for a bit:

I've noticed that I get a bit of clipping with the pedal when running any sort of drive (or even just a clean boost) before it. Playing with chorus effects on my HX Stomp, I get no clipping (or at least significantly less).

Is this normal? I'm using the V3207 and V3102 chipset running at 9v.

Would running the pedal at 12-15v (by finding a real MN3007) increase headroom and decrease clipping? Or is there another way to decrease clipping (would tweaking the trim pot help for instance)?

Thanks!

Yes the trimmer can help with the clipping.

 

[fogboundrogue15]

Awesome, I messed with the trimmer and it helped! Sounding great now