Korg Forums

Dannyhammond · Joined: 08 Nov 2019 Posts: 9 Location: Ontario, Canada

Hey forum members and users....I'm new to this site and I have a question for Korg Kronos users.

I'm afraid I did the unthinkable to my Kronos!

Normally I use the main left and right balanced outputs as well as outputs 1&2 which are all fed to a small mixer as I like to separate the bass and drums on my sequences.

Unfortunately, I inadvertently fed phantom power (48volts) to output number 1 from the mixer. I noticed this after about 2 minutes and shut it off immediately.

Now, output 1 & 2 are still operating perfectly however I am now experiencing random loss of output on the main L&R outputs. In other words it sometimes takes an hour or two before it dies.....it is very unpredictable.

Could this be an issue with the op amp after it warms up due to the hit from FP even though the FP was on output #1??

Everything was working perfectly before I made this tragic mistake!!

Any help or advice would be greatly appreciated. Embarassed

Poseidon · Senior Member Joined: 08 Jul 2018 Posts: 373

Phantom power has the potential to damage equipment not designed for it, specifically devices with unbalanced outputs, as most unbalanced equipment does not have any protection from DC voltage and its output circuitry can be damaged.
Korg Kronos outputs are balanced, the question remains do Kronos OUTs have sufficient protection against DC ? It completely depends on the design of Kronos output circuit.

alland

Dannyhammond · Joined: 08 Nov 2019 Posts: 9 Location: Ontario, Canada

Thank you so much for taking the time to look at this for me.

Yes, I do lose the headphone signal/volume at the same time as I lose the L&R output.
Yes, I do lose both the left and right channels at the same time when it occurs.
And finally, no there is no cracking when I turn the volume control....it works perfectly.
I hope this gives you some clues when troubleshooting where the issue may be......cheers.

geoelectro · Posted: Sat Nov 09, 2019 2:38 pm Post subject:

Normally, phantom power will damage series capacitors or muting transistors in a keyboard output stage. The series caps are usually electrolytic types with voltage ratings around 15Vdc. Applying 48Vdc to those will cause them to fail. Failing could be partial or complete depending on the quality of the part and the time the phantom power was applied.

Muting transistors go from the output line to ground. It is on during startup and power down to prevent unwanted noise from the amplifiers. They may be connected directly to the 48V phantom power which can cause them to short. That short may be partial as a reduction of volume or a complete loss of volume. It could in fact cause the transistor to be damaged where it just fluctuates between working and shorted.

Whether you're running balanced or not, this voltage will be applied to either both sides of the balanced line (balanced mode) or one of the balanced lines (mono or single ended mode). In either case, the output will be affected.

48Vdc is applied between the signal lines and ground.

[/img]https://www.dropbox.com/home/Public?preview=phantom+power.jpg[/img] (alt+p)

Below in the Korg output schematic, the two transistors (muting) would be the likely suspect for damage.
BTW, they could be removed correcting the output level but would also allow the turn-on noise to be heard.

[img]https://www.dropbox.com/home/Public?preview=korg+kronos+outputs.jpg[/img] (alt+p)
_________________
Kronos 61 : 3GB RAM 120GB 2nd Drv.
Kronos 2 61
Synthesizers.com Custom Modular
N.I. Komplete 11, Omnisphere 2, VB-3.
HP i7 8GB Win 10
Yamaha P-80 Weighted Keyboard. NanoPad2

geoelectro · Posted: Sat Nov 09, 2019 2:41 pm Post subject:

Normally, phantom power will damage series capacitors or muting transistors in a keyboard output stage. The series caps are usually electrolytic types with voltage ratings around 15Vdc. Applying 48Vdc to those will cause them to fail. Failing could be partial or complete depending on the quality of the part and the time the phantom power was applied.

Muting transistors go from the output line to ground. It is on during startup and power down to prevent unwanted noise from the amplifiers. They may be connected directly to the 48V phantom power which can cause them to short. That short may be partial as a reduction of volume or a complete loss of volume. It could in fact cause the transistor to be damaged where it just fluctuates between working and shorted.

Whether you're running balanced or not, this voltage will be applied to either both sides of the balanced line (balanced mode) or one of the balanced lines (mono or single ended mode). In either case, the output will be affected.

48Vdc is applied between the signal lines and ground.

[img]https://www.dropbox.com/home/Public?preview=phantom+power.jpg[/img]

Below in the Korg output schematic, the two transistors (muting) would be the likely suspect for damage.
BTW, they could be removed correcting the output level but would also allow the turn-on noise to be heard.

[img]https://www.dropbox.com/home/Public?preview=korg+kronos+outputs.jpg[/img]

Geo

I don't know how to get the images to show, heck, I lost my avatar trying to change it!
_________________
Kronos 61 : 3GB RAM 120GB 2nd Drv.
Kronos 2 61
Synthesizers.com Custom Modular
N.I. Komplete 11, Omnisphere 2, VB-3.
HP i7 8GB Win 10
Yamaha P-80 Weighted Keyboard. NanoPad2

Dannyhammond · Joined: 08 Nov 2019 Posts: 9 Location: Ontario, Canada

Thank you so very much Geo.
This information is perfect and so very helpful to pass along to an authorized service person.

This is something I'll make sure never happens again...having said that I really don't understand why a voltage suppressor would not have been part of the initial design....seems to me that this is something that could easily happen when dealing with so many different sound technicians and mixers??

I truly appreciate you taking the time to define this for me Geo.

Many thanks from Canada.
Cheers