Finding the ground issue… sushi box fx black eye

[Locrian99]

Hello,

Im having what I can only imagine is a ground issue.   

https://youtube.com/shorts/4TZqOF-4C7w?si=11EJmjC_yJAkFy_i



I had built the pedal mainly played late at night with the output low and hadnt really noticed it.   Loaned it to a friend of mine and he was running it turned up with humbuckers and getting lots of oscillation at higher volumes.   It is present if plugged into the same outlet or different outlet as amp.   It has done this in two different houses, different amps, different guitars, power supplies etc.   so im confident its the pedal.   I am using a 2 amp 9v supply with only this on it.   The pedal is pulling 480ma.  I have continuity with the enclosure from both jack sleeves and the ground pads for them on the board.   DC jack ground has continuity as well.   Hoping someone might have an idea of where to look

Build docs with schematic

https://drive.google.com/file/d/1AZtIS7IiQWQchlRfPitWsgdChZKbrSuD/view






I did go through and reflow all the solder joints after taking that pic...

Thx

[antonis]

If the purpose of those LEDs behind the tubes is purely aesthetic (e.g. for tubes illumination) get rid of them..

[Locrian99]

If the purpose of those LEDs behind the tubes is purely aesthetic (e.g. for tubes illumination) get rid of them..

They basically act as the indicator, I'll try that...

No change with the leds removed

[JTEX]

Do you have continuity from the pedal box to the AC outlet ground pin? The 9V power supply won't provide this, so you need an earth connection via the pedal's  output cable shield going to the amp's ground, then the amp being earthed via its 3-prong power cord.

[Locrian99]

Do you have continuity from the pedal box to the AC outlet ground pin? The 9V power supply won't provide this, so you need an earth connection via the pedal's  output cable shield going to the amp's ground, then the amp being earthed via its 3-prong power cord.

Ill check when I get home.   Continuity between output jack sleeve and the amps ground plug  of the amp basically.

[R.G.]

Kudos for doing the testing on different AC power (i.e. houses), amps, guitars, and so on.

JTEX makes a very good point - does the outside box get grounded to signal ground solidly and reliably? His suggestion of using a continuity tester is a great next step. The build documents don't show any explicit grounding path, so I'm assuming that grounding the box is done

The audible quality of the noise reminds me of fluorescent light buzz, but it would be odd for that to happen in different houses. It's not the more solid bass-y hum of ordinary AC mains hum. Seems like there is some 120Hz and higher in the buzz, as well as some line locked spike-iness.

My next step would be to get out the scope and see what the signal looks like. And then my very next thought is that the buzz will vanish when you clip the scope probe to the circuit ground. I hate it when that happens.

[Locrian99]

Yea theres continuity between the amps ground plug and the enclosure.   Hmm.   

One thing that also seemed odd to me.   And is what made me measure the current pull.   I plugged powered it off a battery last night just to see.   Battery measured 9.6v in checked because i was confirming polarity on my adapter to go to the dc jack.   Turned around turned my amp on, got my cables etc probably 30 seconds to a minite and the pedal wont turn on, no leds etc.   measure the 9v battery its now 7.8v.  And i hooked the battery turned

[drdn0]

Yea theres continuity between the amps ground plug and the enclosure.   Hmm.   

One thing that also seemed odd to me.   And is what made me measure the current pull.   I plugged powered it off a battery last night just to see.   Battery measured 9.6v in checked because i was confirming polarity on my adapter to go to the dc jack.   Turned around turned my amp on, got my cables etc probably 30 seconds to a minite and the pedal wont turn on, no leds etc.   measure the 9v battery its now 7.8v.  And i hooked the battery turned

It's pulling hundreds of mA for the tube heaters - most pedals are less than 10mA.

Or course it's going to cook a battery in next to no time

[Locrian99]

Yea theres continuity between the amps ground plug and the enclosure.   Hmm.   

One thing that also seemed odd to me.   And is what made me measure the current pull.   I plugged powered it off a battery last night just to see.   Battery measured 9.6v in checked because i was confirming polarity on my adapter to go to the dc jack.   Turned around turned my amp on, got my cables etc probably 30 seconds to a minite and the pedal wont turn on, no leds etc.   measure the 9v battery its now 7.8v.  And i hooked the battery turned

It's pulling hundreds of mA for the tube heaters - most pedals are less than 10mA.

Or course it's going to cook a battery in next to no time

I get its going to go fast but 480 ma draw on a 400mah battery 1 minute seemed fast.    Migjt be normal but in case it wasnt seemed worth mentioning.

[drdn0]

Yea theres continuity between the amps ground plug and the enclosure.   Hmm.   

One thing that also seemed odd to me.   And is what made me measure the current pull.   I plugged powered it off a battery last night just to see.   Battery measured 9.6v in checked because i was confirming polarity on my adapter to go to the dc jack.   Turned around turned my amp on, got my cables etc probably 30 seconds to a minite and the pedal wont turn on, no leds etc.   measure the 9v battery its now 7.8v.  And i hooked the battery turned

It's pulling hundreds of mA for the tube heaters - most pedals are less than 10mA.

Or course it's going to cook a battery in next to no time

I get its going to go fast but 480 ma draw on a 400mah battery 1 minute seemed fast.    Migjt be normal but in case it wasnt seemed worth mentioning.

There isn't a linear relationship between battery voltage and total charge, nor do nominal capacities last while you are drawing massively, massively more current than a battery is designed for (you basically cook them). From some quick charts I saw, you basically halve the capacity of a battery pulling 500mA over 100mA. That 400mA is now 200mA or so, and most seem to stay around 8v output until they go off the cliff.

Seems totally normal