Ground Isolation for Daisy-Chains

[Rob Strand]

If you don't like the amount of filtering in the circuit shown, try adding another inductor in the ground lead between C1 and C2. This inductor works on smoothing the ground current. Pedal circuits often have zero rejection of both power supply noise and ground noise. You may have to smooth both of them.

This has to be done with some care. The DC resistance of the inductor will cause a DC offset so the resistance time the pedal current has to be low. Things get funny when you add impedances to "ground", so tinker carefully.

I suspect it will actually make things worse because the digital fx pedal has low impedance path from +9V in through the digital FX pedal then through the analog signal ground (coax connection) then back through the analog fx ground.

With the inductor in the positive rail the digital effect current pulses on the ground are kept local between the cap C2 and digital FX pedal.  The inductor in the positive path is preventing current pulse feeding C2 and so the current pulses don't actual pass through the ground between C1 and C2 hence do not flow through the analog ground (not much anyway).

If you want to break the signal ground path I was suggesting a small resistor in the ground leg of the analog pedal power (but keeping the digital FX filter with the inductor in the positive path.)

I still have the opinion that adding a power supply just for the noisy offending pedal may be the simplest and easiest solution.

That was suggested in a previous thread (by the same poster) for this same issue about a month ago.

The filter solution is just another way to achieve a similar result.  However, it is a more complicated solution and requires you to get things right.  The two power supply solution should be plug and play.

In either case, if you need to power two noisy fx then you really need the signal lines of the two fx to be cascaded.  If you were to put noisy effect 1 at the start of the chain and noisy effect 2 at the end of the chain you really need three power supplies or two separate filters, one for each effect.
Here's a crude simulation which confirms the suspicion,



Probably should try some lower resistances to see if it still holds but to me in principle it shows the idea.
This one is slightly more accurate:

Schematics:


Analog supply voltage


Ripple Current through Analog signal wire ground:


The inductor in the +ve rail is still showing up as the better option.

[Baran Ismen]

Just wanted to confirm something; should I connect this filter as 9VDC -> Filter In -> Filter Out -> Pedal or vice versa

I can't see the images that Rob shared, that web-site is blocked in Turkey unfortunately    So if its drawn there, I can't see it 

[antonis]

Does it appears to you, γείτονα..??

[Baran Ismen]

I have uploaded this video.

https://youtu.be/RNSyOUP1LCE?si=nAW8T8R4JFOS4aox

Now, i have made the filter, also added another 1n4148 in series to Vee and another 2200uf parallel to 1000uf's. Result is as above. Helped a bit with the high pitch sound though, but not completely. For example it completely cuts the one that comes from the tuner.

Thing is, when i plug in and out the cables on/from the pedals, frequencies change. I think each pedal has a different something that generates a pitched sound and some mask each other, or boost. This is also preset when the audio cables are not connected and pedal is solely powered.

I suspect of the crystals inside the circuits. Is it possible of this being the sub harmonics of 32khz or times of it?

Damn i dont want to invest on an iso brick, its expensive

[Rob Strand]

The reason the voltage drop keeps dropping is because you chose a large value inductor and a small package.  The DC resistance is too high.
https://www.diystompboxes.com/smfforum/index.php?topic=131639.msg1279658#msg1279658
https://www.diystompboxes.com/smfforum/index.php?topic=131639.msg1279665#msg1279665

It's still possible the whine is coming directly from your power supply.   Kind of supported by the fact that filtering output from the PSU seems to help.    Maybe the reason is spreads is because of poor layout in the digital effects.

If I ignore the entire thread and look at the video I would conclude you have a switch mode PSU with a high current rating and you don't have enough load on it.   You should add a dummy load using some power resistors.

[Baran Ismen]

The reason the voltage drop keeps dropping is because you chose a large value inductor and a small package.  The DC resistance is too high.
https://www.diystompboxes.com/smfforum/index.php?topic=131639.msg1279658#msg1279658
https://www.diystompboxes.com/smfforum/index.php?topic=131639.msg1279665#msg1279665

It's still possible the whine is coming directly from your power supply.  Kind of supported by the fact that filtering output from the PSU seems to help.    Maybe the reason is spreads is because of poor layout in the digital effects.

If I ignore the entire thread and look at the video I would conclude you have a switch mode PSU with a high current rating and you don't have enough load on it.  You should add a dummy load using some power resistors.

The voltage drop problem is solved, the inductor I used was 820uH, but a friend of mine told me that it probably has a thin wiring in it and it causes so much inductive reactance. I have luckily found some thicker and lacquered transformer wire around 30cm and wound it, afterwards replaced that with the 820uH one and the voltage drop problem is solved but god knows how much MH is it now 

For a dummy load, what resistor shall I use and what should its wattage be? I suppose it should be higher than 1/4 w right?

Also as a side note; I had tried with all of my pedals with a bigger type of adjustable power supply (see below) to see the total current that I need and had the same result. It's adjustable up to 30V and output is up to 5A, but I don't know if it works the same logic as regular SMPS supplies and requires a dummy load.

https://www.uni-t.com.tr/unit-utp3315tfl-ii-dc-guc-kaynagi-30v-5amper-tasinabilir-guc-kaynagi-kalibrasyonsuz

I'll try to find another 9V supply and check with it.

[antonis]

For a dummy load, what capacitor shall I use and what should its wattage be?

You probably mean "resistor"..
Its power rating should be calculated via P= V*I = I²*R = V²/R

I had tried with all of my pedals with a bigger type of adjustable power supply (see below) to see the total current that I need and had the same result. It's adjustable up to 30V and output is up to 5A, but I don't know if it works the same logic as regular SMPS supplies and requires a dummy load.
https://www.uni-t.com.tr/unit-utp3315tfl-ii-dc-guc-kaynagi-30v-5amper-tasinabilir-guc-kaynagi-kalibrasyonsuz

It indeed is a switch mode PSU (like the vast majority of benchtop power supplies of the kind..)
I'd try an external load of about 100mA current draw..
(a 10 - 100 μF electro and a 1 - 10 nF ceramic in parallel shouldn't make any harm..)

[Baran Ismen]

For a dummy load, what capacitor shall I use and what should its wattage be?

You probably mean "resistor"..
Its power rating should be calculated via P= V*I = I²*R = V²/R

I had tried with all of my pedals with a bigger type of adjustable power supply (see below) to see the total current that I need and had the same result. It's adjustable up to 30V and output is up to 5A, but I don't know if it works the same logic as regular SMPS supplies and requires a dummy load.
https://www.uni-t.com.tr/unit-utp3315tfl-ii-dc-guc-kaynagi-30v-5amper-tasinabilir-guc-kaynagi-kalibrasyonsuz

It indeed is a switch mode PSU (like the vast majority of benchtop power supplies of the kind..)
I'd try an external load of about 100mA current draw..
(a 10 - 100 μF electro and a 1 - 10 nF ceramic in parallel shouldn't make any harm..)

Thanks for the correction komşu

You mean 100uf + 10nf caps soldered parallel, can be wired between positive and gnd tips and create a minimal dummy load?

[antonis]

Parallel caps are optional..

Dummy load should be a resistor, the value of which should be calculated according to voltage and current..
e.g. for 9V output and about 100mA current (through it), a resistor of 82R to 100R (2W) should be fine..
(5W should be more than fine..)

[R.G.]

[much stuff...] Helped a bit with the high pitch sound though, but not completely. For example it completely cuts the one that comes from the tuner.
Thing is, when i plug in and out the cables on/from the pedals, frequencies change. I think each pedal has a different something that generates a pitched sound and some mask each other, or boost. This is also preset when the audio cables are not connected and pedal is solely powered.
I suspect of the crystals inside the circuits. Is it possible of this being the sub harmonics of 32khz or times of it?

Good guess. I have seen cases where digital pedals with their own internal switching converter power supply interact with the switching ripple on a noisy switching power supply to make sum-and-difference frequencies. It's possible.

I may need to go re-read this thread - have you tried this setup in a different building? That is, with a different electrical power supply? I is also possible that something else in the building is generating interfering RF.

Damn i dont want to invest on an iso brick, its expensive

Try a separate (and much less expensive) 9V power supply for the offending pedal. If this works, it's also much less expensive than an iso brick. Is it possible for you to take the setup to a music store and try to replicate the noise while trying out a separate smaller 9V supply?

[Baran Ismen]

[much stuff...] Helped a bit with the high pitch sound though, but not completely. For example it completely cuts the one that comes from the tuner.
Thing is, when i plug in and out the cables on/from the pedals, frequencies change. I think each pedal has a different something that generates a pitched sound and some mask each other, or boost. This is also preset when the audio cables are not connected and pedal is solely powered.
I suspect of the crystals inside the circuits. Is it possible of this being the sub harmonics of 32khz or times of it?

Good guess. I have seen cases where digital pedals with their own internal switching converter power supply interact with the switching ripple on a noisy switching power supply to make sum-and-difference frequencies. It's possible.

I may need to go re-read this thread - have you tried this setup in a different building? That is, with a different electrical power supply? I is also possible that something else in the building is generating interfering RF.

Damn i dont want to invest on an iso brick, its expensive

Try a separate (and much less expensive) 9V power supply for the offending pedal. If this works, it's also much less expensive than an iso brick. Is it possible for you to take the setup to a music store and try to replicate the noise while trying out a separate smaller 9V supply?

Separating the power for the digital pedals works indeed, yes, which also supports your idea to feed them separately.
This problem is also present in the studios where we rehearse.

Today I bit the bullet and ordered this Joyo's noise blocker apparatus. I saw some comments and videos of the people who experienced the very same problem that I have, and it somehow became a solution for them. If it works, I'll disassemble it to see what's inside creating this magic 

[Rob Strand]

https://www.uni-t.com.tr/unit-utp3315tfl-ii-dc-guc-kaynagi-30v-5amper-tasinabilir-guc-kaynagi-kalibrasyonsuz

I'll try to find another 9V supply and check with it.

That lab supply is fully linear which means the noise is coming from one or more of the pedals.
(No need to think about dummy loads.)

Good guess. I have seen cases where digital pedals with their own internal switching converter power supply interact with the switching ripple on a noisy switching power supply to make sum-and-difference frequencies. It's possible.

Separating the power for the digital pedals works indeed, yes, which also supports your idea to feed them separately.
This problem is also present in the studios where we rehearse.

That's the only solution left.   The fact putting the filter on the Mooer alone didn't solve it means that pedal is putting out an extreme noise.  (It's still possible your filter didn't work correctly.)

It would be interesting to see a power supply schematic for the Mooer because it's a good example of how not to do it.

[R.G.]

It would be interesting to see a power supply schematic for the Mooer because it's a good example of how not to do it.

It's almost a Darwinian thing. EEs that are good at designing low noise power switching systems don't usually go get good at DSP code, or user interfaces, or power cabling, or microcontrollers, or RF, and vice versa. Professionally, it means that once you've gotten capable in one field, you'd have to start over in another area as a beginner. That's not generally a smart career move.

Mooer (if that's who did the pedal in question) may not have had a staff with switching power supply experience or systems level switching power interactions experience, or RF experience, or for that matter, low noise PCB layout experience. And pedal shops often don't do a systems-level test of how their pedals will work with the whole range of other pedals and power supplies on the market. It's a tough job figuring out how anyone, anywhere, may cable up your pedals. Even if there was some testing, the variations in amps, cables, connectors, EMI/RF environment, and sensitivities to specific RF frequencies can bite you HARD.

I understand that all these scars I have amount to the education left over after I've forgotten the names and dates. 8-)

[Rob Strand]

It's almost a Darwinian thing. EEs that are good at designing low noise power switching systems don't usually go get good at DSP code, or user interfaces, or power cabling, or microcontrollers, or RF, and vice versa. Professionally, it means that once you've gotten capable in one field, you'd have to start over in another area as a beginner. That's not generally a smart career move.

Today that's even more the case.   Not much good electronics design going on with those arduino users.   Older engineers tend to have a wider and deeper knowledge, even when they were young.   Partly because the education system made you think more and follow recipes less.   Personally I was right on the cusp of the education downfall which means I've had to use my own time to fill in the gaps.

Mooer (if that's who did the pedal in question) may not have had a staff with switching power supply experience or systems level switching power interactions experience, or RF experience, or for that matter, low noise PCB layout experience. And pedal shops often don't do a systems-level test of how their pedals will work with the whole range of other pedals and power supplies on the market. It's a tough job figuring out how anyone, anywhere, may cable up your pedals. Even if there was some testing, the variations in amps, cables, connectors, EMI/RF environment, and sensitivities to specific RF frequencies can bite you HARD.

Yep, absolutely the case.   Unless you are in fields which force you to test and verify, like military/medical, the testing culture and methods are pretty bad.   Testing some products can require more expertise than designing the product itself.   There is also a culture of burying problems when someone finds something because it's usually found well into development or production and no one wants to take responsibility for stopping the show.

[Baran Ismen]

I had ordered this product just out of curiosity and arrived yesterday. Gave it a try, and guess what? It works!

Holy moly!

At first, I tried it on the main DC bus, but seemed not to help, then tried it on noisy pedals, and saw that it's actually working and cutting the noise!

I don't know what's inside, but it tends to get locally warm within minutes, I believe there's a regulator or inductor I'm not sure, yet I'll definitely tear it apart and see what's this magic about.

[PRR]

...I believe there's a regulator or inductor I'm not sure, yet I'll definitely tear it apart and see what's this magic about.

[Baran Ismen]

...I believe there's a regulator or inductor I'm not sure, yet I'll definitely tear it apart and see what's this magic about.

Can't see the image 

[FiveseveN]

It's of an isolated DC-DC converter. Also curious to find out what's inside but if I had to guess it would be one of those.

[Elijah-Baley]

Just yesterday I was looking this: https://www.muzique.com/lab/9v_iso.htm



To solve the problem when some pedals can't share the same PSU, like in a daisy chain, for example.
I'd like of build something like that.

[antonis]

Can't see the image