Can circuits be damaged if a 9V power connector touches the output jack ?

[eh la bas ma]

Hello,

I might have done a terrible mistake.

I use multiple stompboxes in a signal chain. The other day, i swapped one of the stompboxes, to replace it with another one. All the circuits were connected to 9V by a daisy chain.

I disconnected the power supply from the circuit i was moving away. The patch cable from the stompbox, located before the one i was replacing, came in contact with the tip of the free 9V connector.

It made the status led of this next stompbox briefly light up, as if i switched it on and off quickly. 

The sound was cut by an other circuit further in the signal chain, but i guess there was some popping noise too.

Now, i notice that two circuits in the signal chain aren't behaving as usual. These 2 circuits are Aion's Spectron (Meatball) and an OC-7 octaver clone (Up DownDaddy, from Delyk).

Both were connected side by side, OC-7 before the Spectron. The 9V power plugg touched the Spectron's output patch cable (yellow).

The octaver became very noisy, with multiple loud popping noise, especially if i press the 3PDT and hold it down. The noises tend to disappear progressively by themselves, when i release the 3PDT footswitch. Sounds like the issue affects mainly the octave up control, because noises can reappear  only if i turn the octave up knob.

I opened the enclosure, changed one TL074, one TL72, all the transistors, took out a piece of hair stuck on a pot. Sounds like it works a little bit better, but i still have a weird noise when i switch the OC-7 on. Some brief crackling popping noise.

The Spectron also sounds like there is something wrong. With the Mix control fully CCW, clean signal only, there is a volume decrease, and the signal is slightly distorted. The enveloppe filter is still working, but it's much weaker than before, even with Mix fully CW. The circuit doesn't behave as it used to... Also, the Mode toggleswitch became noisy, with a loud pop when toggling. This toggle "selects whether the filter acts as high pass, bandpass, or low pass".

Is it possible that some parts have been damaged, because the patch cable touched a 9V power connector ?

If so, i guess i need to replace all IC and all transistors, one by one, to check which one could have been damaged.

Are there some other parts that i would need to replace ?


https://www.delykpcb.com/product/up-down-daddy-pcb/?attachment_id=1089&download_file=k0sve9jvlkveb

https://aionfx.com/app/files/docs/spectron_documentation.pdf

Every suggestions and observations are welcome !

[GibsonGM]

Wow.  I can only imagine a real problem happening from this if an effect did not have an input or output cap...if the cap was bad...or if the cap is rated 6.3V or something like that, and was destroyed by 9VDC.    It is for this reason that I typically use 16V caps in my builds, and often higher, allowing use at 18V if desired. 

One other thing occurs...if a pot was located before or after the in/out caps, and set low enough, perhaps the 9VDC input would damage it.

The short answer is "No, it should not hurt anything, IF there are properly rated, good in/out caps in place"...


Final thought...if the power supply GROUNDED itself, perhaps IT was damaged, leading to noise/instability?  Perhaps you should make sure it is ok?

[duck_arse]

as gibbo sez, both those circuits show input and output isolating caps. but - neither doc shows any connection to a bypass switch or the jacks, so no idea what circuitry might be inbetween. maybe if you listen to signal to and from the boards themselves, instead of to and from the in out jacks and whatever is between.

[eh la bas ma]

Wow.  I can only imagine a real problem happening from this if an effect did not have an input or output cap...if the cap was bad...or if the cap is rated 6.3V or something like that, and was destroyed by 9VDC.    It is for this reason that I typically use 16V caps in my builds, and often higher, allowing use at 18V if desired. 

One other thing occurs...if a pot was located before or after the in/out caps, and set low enough, perhaps the 9VDC input would damage it.

The short answer is "No, it should not hurt anything, IF there are properly rated, good in/out caps in place"...


Final thought...if the power supply GROUNDED itself, perhaps IT was damaged, leading to noise/instability?  Perhaps you should make sure it is ok?

Thanks for your reply !

On Spectron i guess the output cap is C3 :


On my build, at C3 i read : 10uF, 50V.

So it would be absolutely impossible to damage anything ?

If the cap was enough to stop the current, would i still see the status led or the effect indicator led light up, when the power connector touched the patch cable ?

I will try both circuits with a different power supply to rule out this possibility...

Edit : Looks like the power supply is ok, it works with other circuits. I still have the same issues with OC-7 and Spectron with a different power supply...

Edit 2 : On the OC-7, the output cap is probably C13, 1uF :


On my build I read 1uF, 100V.

Does it mean that i can rule out the 9V connector episode, to explain the sudden changes in both circuits ?

[eh la bas ma]

as gibbo sez, both those circuits show input and output isolating caps. but - neither doc shows any connection to a bypass switch or the jacks, so no idea what circuitry might be inbetween. maybe if you listen to signal to and from the boards themselves, instead of to and from the in out jacks and whatever is between.

Thanks !

Understood, i'll use an audio probe on both circuits, and try to see if anything sounds strange along the signal path.

I should mention that the daisy chain is connected to a TrueTone power supply, with 1700 mA.

Some transistors can take 25V, TL72 can take 45V according to datasheet, but what about amperage ?

[GibsonGM]

You're welcome, this is interesting and we like to help!   

Like Duck said - you will have to explore the circuits that you believe were affected.   You have identified the correct input/output caps.  They appear quite sturdy - unless they are already damaged somehow, I believe they would have blocked any DC from your active components.


If the event happened as you say, I see no path for the transistors or opamps to have received too much voltage....or current.  They are not supplied by the input jack tip.  If they ARE damaged, then something more like a reverse polarity situation could have occurred, and you should proceed (as Duck says) accordingly, by 'going inside' each that seems damaged.

As for current and transistors/active components....the current they draw is controlled by the resistances in series with their power supplies (sometimes, as with opamps, those resistances are internal to the IC).    They would not be damaged from too much current in this case - but reversed voltage, YES!   

[ElectricDruid]

Doesn't the status LED lighting up mean the power must have been the right way around?

I suppose it could have done both. It wouldn't be hard to brush the +9V barrel of a power plug against a jack and contact both the tip and the sleeve, sending 9V into the output and then into the ground. Even then though, if the pedals were powered up (and they must have been if they're on the same daisy-chain) then they had 9V on their positive power and 9V on their ground. I don't see how that destroys them, really.

Test them both with an audio probe to be sure, but I'm sceptical that a brief flash of 9V power damaged anything.

[R.G.]

Electrolytic caps have a low reverse voltage withstanding ability. In fact, in special cases, they can act almost like very poor quality diodes. Aluminum caps reverse conduct at an ill defined voltage that depends on their forming method and forming voltage, but in general it's ... um, a volt or two. Reverse current degrades the insulating oxide layer so that it withstands less voltage the "right" way.

In this instance, it is >possible< that the output electro caps were a little damaged and now have higher leakage. Or maybe not.

I'm happy to tear into any pedal/PCB, so if these were mine, I'd replace the output caps, just for luck. It's a guess. There is only a slim possibility that the ICs were hurt, as noted.

[eh la bas ma]

I'll try R.G's idea and replace the output caps first.

Just to be clear, if this doesn't work : during the audio probing test, i will need to give some special attention to all pots, transistors, ICs, electrolytic caps, and that's all ?

Are there any other parts in these circuits that could have been damaged ?

I guess  ceramic and film caps should be safe, just like resistors and diodes ?

When the contact occured, some circuits, before and after the one i was replacing (7th position), were powered from the same daisy chain and switched off. Two other circuits (BD-2 and Morning Glory clones), 3rd and 4th in the signal chain, were connected before the OC-7. Both are fine, or at least there is nothing noticeable. Same for the 1st and 2nd circuits.

[GibsonGM]

If you want to KNOW if they're damaged...power up one separately, insert 2 patch cords, and measure for DC on the input and output cable tips.  For curiosity's sake.

But if you're opening them up anyway, I'd do like R.G. and just change the in/out caps, it's a small matter to do so.  Poly and ceramic should be fine.

If 'noises' continue after that, address them in order...

[eh la bas ma]

If you want to KNOW if they're damaged...power up one separately, insert 2 patch cords, and measure for DC on the input and output cable tips.  For curiosity's sake.

But if you're opening them up anyway, I'd do like R.G. and just change the in/out caps, it's a small matter to do so.  Poly and ceramic should be fine.

If 'noises' continue after that, address them in order...

On OC-7 output jack's tip, i read oscillations between -1mv and -5.2mV. Same values on the Input jacks'tip. On both jack's sleeves i read -0.003mV.

It's almost the same for the spectron. Oscillations between 0V and -10mV on both tips.

I guess all input and output caps are fine ?

[GibsonGM]

The voltage readings SEEM ok, but you still can't really say, because you're experiencing, as you said, 'crackling and popping' noises.  Maybe the problem is so fast, the meter cannot resolve it.

Since the footswitch seems to cause 'crackle' that goes away, this DOES suggest damage to the cap(s)...so I would change them, as they are not expensive items.    Remove them from the list of possible problems.

If problems continue, I would 'walk' thru the circuits (do one PCB at a time) and observe where it seems to be normal, and where you encounter 'problems'.  I would even 'listen' to the bias/power filtering network to see if there are pops    

Try to aggravate the problem - make it happen, try to find where it is coming from.  Is there a cap associated with the bypass LED (to reduce switch pop)? If so check it.

I will be shocked if touching 9V to the input or output caused much damage; I hope that changing the in/out caps resolves this for you! 

[eh la bas ma]

Looks like i must audio probe them... I'll do that and report.

I changed Output caps on both circuits and it didn't change anything. I also replaced all ICs on Spectron, TL72 and LM358, still no luck.

Spectron internal leds are lighting up as usual, but the effect is weaker than usual.  There is a tiny bit of dirt added to the clean signal, with a noticeable volume loss. No unexpected noises beside the Mode toggleswitch, which became noisy when toggling.
I guess my victim(s) and culprit(s) can only be an electro cap, or a pot on the Spectron...


About the Input caps, if i read the schematics correctly they are either film caps, or ceramics. So they should be allright

OC-7 :


Spectron :



Would it make sense to replace the first following electrolytic caps in the schematics ?

Respectively C3 1uF on OC-7, and C4 10uF on Spectron ?

[GibsonGM]

I would first audio probe, because it's easier than desoldering/replacing!   

You may find the signal is good up to a certain point, which we can then try to find a fix for.

[PRR]

Electrolytic caps have a low reverse voltage withstanding ability.  ....they can act almost like very poor quality diodes.....

Maybe not a 1N4007, but electrolytic rectifiers were widely used for radio power for several years.

https://www.nature.com/articles/114462d0
https://simplifier.neocities.org/rectifier
http://www.sparkbangbuzz.com/els/borax-el.htm
http://no3m.net/2016/02/electrolytic-rectifiers/
https://chestofbooks.com/crafts/popular-mechanics/The-Boy-Mechanic-700-Things-for-Boys-to-Do/How-To-Make-An-Electrolytic-Rectifier.html

[eh la bas ma]

Something strange happened with the Spectron right now, a good thing but i don't understand what it is.

Ready to spend the day on audio probing tests, I recorded a loop, connected the loop station directly on the Spectron. No other circuits involved, audio probe connected to the amp.

I started by checking the volume loss and the distorted clean signal when the effect is switched on, but everything was fine this time. Even the Mode toggle was silent when i probed the output jack.

When i experienced these issues, the Spectron was connected as follow :

Loop station --> Meridian compressor --> Morning Glory --> BD-2 --> OC-7 --> Spectron

I disconnected the Morning Glory and the BD-2, put back the Spectron in my set-up. Still fine, the toggle was a bit noisy but quieter. I switched on and off to compare with the clean signal, tried an other power supply which accidentally touched the other power supply connected to the daisy chain, making a single brief popping noise. No led lighting up.

No more loss of volume or distortion on the Spectron , the toggle became silent as usual, the third or fourth time i switched the circuit on.

Then, I put back the Morning Glory and BD-2 exactly how they were before. Still ok, no issues anymore.

The output cap has been changed yesterday, but i still experienced the same issues after that. I did nothing else to the circuit.

No idea how i would explain this. Problem solved i guess, only time will tell if it's really alright for good...

Now i'll move to the OC-7...

[GibsonGM]

It doesn't happen often, but I have had this occur a few times. I'm sure everyone has.   Something you just have no answer for  
 
Hopefully it never comes back!

[eh la bas ma]

The OC-7 crackling and popping noises appear only when the Octave Up control is set somewhere CW. It happen when switching on, and randomly after that, as i turn the Octave up pot.
I changed the pot, but the issue is the same.

Both Octaves down sound terrible. I don't have all the IC necessary to replace them all, so I guess i will order them and wait.

I would gladly do an audio probing test, but on such a complex circuit i wouldn't know where to start, I don't understand what are the various sections, and what they are supposed to do.

Maybe I should check if the Octaves signals are crappy as soon as it is generated, or if it gets damaged shortly after in the signal path ?

Can you please show me on the schematics where the octaves signals are created ?





https://www.delykpcb.com/product/up-down-daddy-pcb/?attachment_id=1089&download_file=k0sve9jvlkveb

Edit : Here is an attempt at deciphering the circuit. I assumed both CD4013 IC are involved to make both octaves down.
Octave up created by TL74, LM324 and CD4013. 1= oct. up 2= 1st oct. down 3= 2nd oct. down :

[GibsonGM]

I believe you are close, ha ha. Yes, the circuit is a little complex, those 4013's.  Not my 'specialty', sorry.   I would be more interested in the voltages of each IC pin; someone with more experience in this 'octave method' may be able to decipher them better than I.  You certainly can 'listen' to the entire circuit if you like!  Maybe you will hear a clue, but I can't tell you exactly what to search for.

According to that schematic, there is DC on the octave pot (VR).  Unless I'm mistaken, I'd expect it to crackle when turned because of this.

For now, I'd post the voltage of every IC pin, clearly labeled based on the schematic you posted, as well as the JFET voltages.  You can also test any diodes.

There are a few other electro caps in there, too - I wonder how they fared if polarity was reversed a bit?

[eh la bas ma]

Here are my readings :

Circuit powered and switched off, no signal coming in.

Q1 J201

G= 9.46
S= 9.46
D= 4.60

Q2 2N5457

G= 5.36
S= 5.39
D= 0V

Q3 2N5457

G= 5.36
S= 5.39
D= 0V

IC1 TL72

1= 4.88     8= 9.46
2= 5.08     7= 9.46
3=4.68      6= 4.87
4= 0V       5= 4.78

IC2 LM324

1= 4.84  14= 8.27
2= 5.38  13= 5.15
3= 5.33  12= 4.87
4= 9.46   11= 0V
5= 5.34   10= 5.15
6= 5.38   9= 5.38
7= 5.30   8= 0V

IC3 CD4013

1= 5.70  14= 9.46
2= 3.8     13= oscillating from 0V to 9.46
3= 0V      12= oscillating from 4.50 to 7.50
4= 2.1     11= 3.8
5= 0V      10= 0V
6=oscillating from 2.5 to 5.38   9= oscillating from 0V to 9.46
7= 0V      8= 0V


IC4 CD4013

1= oscillating from 4.35 to 9.46   14= 9.45
2= 9.45   13= 9.45
3= 9.45   12= 0V
4= 0V      11= 0V
5= 0.5mV   10= 0.5mV
6= 0.3mV   9= 0.4 mV
7= 0.3mV   8= 0.3mV

IC5 TL74 (I read different results at pins 3, 5, 6, 7, 8, 14, depending on the TL74 i use, I guess there's something strange here)
Edit 2 : I was confused and probed IC2 instead of IC5. No wonder it felt  "strange"...


1= 5.31   14= 8.28 or 1.5V
2= 5.39   13= 5.18
3= 4.84 or 5.35   12= 5.38
4= 9.46   11= 0V
5= 4.84  or 5.33  10= 5.15
6= 4.88 or 5.38  9= 4.88
7= 4.81 or 5.35  8= 0V or 8.94

IC6 TL74

1= 5.36   14= 5.46
2= 5.37   13= 5.37
3= 4.93   12= 4.94
4= 9.45   11= 0V
5=4.92   10= 4.93
6= 4.93  9= 4.93
7= oscillations between 2.3V and 3.5V  8= 7.55

Edit : Sorry, i think i made a mistake with IC5 TL74.

1= 5.46  14= 5.46
2=5.46   13= 5.46
3= 5.42  12= 4.99
4= 9.45  11= 0.5mV
5= 5.02  10= 5.42
6= 5.45  9= 5.46
7= 5.45  8= 5.46

There are different readings when swapping IC, as mentioned above, but it is on IC2 LM324 replaced by a TL74.

I just tried the circuit again with a TL74 instead of the LM324 (by some lucky mistake) :  the crackling popping noises are gone, both octaves down  sound better. 2nd octave down might be a little bit quieter in volume, but it's not very noticeable. Sounds like problem is solved.

I probably should replace the LM324 ? Not sure if the TL74 is a perfect substitute in this application ?

Both have the same pinouts, but i guess BOM calls for LM324 for a reason ?