Clock noise DC filter circuit for 9V guitar pedals - Page 1
Forum section: electronics / general

author: bsas
author_rank: Regular Contributor
timestamp: June 26, 2019, 10:37:37 pm
content: Hi all,I have this issue where one digital guitar pedal has a blinking LED (it blinks very slowly for example 60-90 times per minute, it is used for the delay tempo) that if it is daisy chain with any other pedal it leaks and audio click. So, the moment I plug another pedal and they are both on the same GND (via the audio cable) you can clearly hear a BOOP everytime the LED blinks.Since this is very likely to be some kind of clock noise leaking to the audio/analog GND, is there a way to filter that out? I am thinking about a very simple passive circuit on the 9V DC input of the pedal but I am not sure what technique is better to filter those slow 60-90Hz spikes. Capacitors + Inductors networks? Isolation transformers? I am open to any suggestion.Thanks!

author: Benta
author_rank: Super Contributor
timestamp: June 26, 2019, 11:06:07 pm
content: Get a better 9 V adapter. Or run the pedals on 9 V battery.

author: bsas
author_rank: Regular Contributor
timestamp: June 26, 2019, 11:26:40 pm
content: That is not an option and that is NOT the issue.It is not an 9V adapter, it is an 9V battery powered pedal board called Outlaws Nomad S128.And the pedalboard works perfectly fine with any combination of analog and digital pedals except the HX Stomp.Also, 9V batteries don't have enough juice for modern digital pedals like the HX Stomp that consumes 9V 1000-1500mA...

author: windsmurf
author_rank: Frequent Contributor
timestamp: June 26, 2019, 11:56:29 pm
content: Maybe the HX Stomp is pulling so much power that its dragging down the voltage when the LED blinks? I see the Nomad can supply 2000mA and HX Stomp pulls more than half that.Have you tried powering the HX Stomp with its AC adapter instead of the Nomad to see if that fixes it?Maybe all you need is a capacitor to attenuate the drop, but I'd defer to the EE's here for actual implementation

author: bsas
author_rank: Regular Contributor
timestamp: June 27, 2019, 03:27:55 am
content: I thought about that and I tried another power supply in daisy chain and the same thing happens.The "problem" obviously is that the Nomad S128 doesn't have isolated power ports, so, it works exactly like a daisy chain.So, anything daisy chained with the HX Stomp will have the noise. Then, my question is: how to build an DC circuit to "isolate" the other ports?Thanks!

author: windsmurf
author_rank: Frequent Contributor
timestamp: June 27, 2019, 04:49:01 am
content: So what does fix it? Using all separate AC adapters for all the pedals?At what point does introducing the Nomad cause the issue? Whenever Nomad is used to power the Line 6?BTW I see the Line 6 has a 3A power input... are you certain it only pulls 1 - 1.5A?You might contact Outlaw effects to make sure its capable of powering an HX Stomp.Isolate the 9v power source?https://www.edn.com/design/power-management/4437430/Understanding-isolated-DC-DC-converter-voltage-regulation-Get a 2nd 9v power source - maybe build your own power bank, modifying this for 9-10v:https://www.instructables.com/id/PowerBanks-How-It-Works/If isolating 9v power doesn't work to fix the issue... get an AxeFX

author: windsmurf
author_rank: Frequent Contributor
timestamp: June 27, 2019, 07:02:10 am
content: Neither of the below "isolates" it, but it cleans it up the 9v.https://www.logsdonaudio.com/shop/the-quiet-boxOr this DIY...

author: Pete66
author_rank: Regular Contributor
timestamp: September 30, 2019, 10:03:03 pm
content: I'm not sure how this pedal works but from my experience delay, chorus, phasor pedals use a low frequency oscillator that produces a square wave and triangle wave to control the clock. Usually the LED is tapped off the square wave and therefor will flash at the rate. This can cause a ticking at the rate just like you describe because of the sharp rising edges of the square wave. Its better to use the triangle wave to flash the LED or have some type of filter that softens the edge of the square wave. Im not saying that there is anything wrong with the pedal it could be that it just needs more power.