Output configuration of mono Volcas

[richlooker]

I have run into the frustrating problem of how to correctly interface the mono volcas to a mixer. I have the Keys, Bass, Kick, FM, Sample and Drum - plus a Mix, which I use for tempo/sync/start/stop only, as in my experience the mixer section is noisy as hell. My main mixer is a Behringer Xenyx 1202.

I have read boatloads of threads on various forums, and watched a handful of videos, explaining you need to use this or that cable, and connect to the mixer like this or that - even suggesting you need to use a stereo channel for the mono Volcas.

It would be much easier to devise a proper solution if I knew how the headphone jack is in fact connected internally. First I connected a 1/8" TRS cable to the output of my Keys, and measured the resistance between tip, ring and sleeve.

• Sleeve - Ring: 1.00K
  Sleeve - Tip: 1.00K
  Ring - Tip: 2.00K

The readings were the same regardless of orientation/polarity of the DMM probes, and also the same for Bass and Kick. I powered on the Keys, and redid the measurements. Now, depending on polarity, the value started out a little lower/higher before it stabilized. Then I measured DC millivolts, and found no DC on the outputs.

From these results, I assume the output stage is capacitor-coupled, and that each channel is connected to ground with a 1K resistor after the capacitors.

Then I found the Volca Bass service manual: http://www.ksadhu.niezba.org/sajty/korg ... ass_sm.pdf

At page 7, "HP AMP" section, I got my assumptions confirmed, and we can see that the same signal is sent to both inputs of the stereo headphone amplifier chip - a Texas Instruments TPA6111A2 - and that the two output channels are connected to the tip and ring, respectively. This means;

• If you use a single TS plug on either end of a connecting cable, you are in effect shorting one channel to ground, this will lead to excessive and level-dependent power draw, resulting in attenuation and compression in the other channel
• If you use 1/8" TRS to 1/4" TRS into a balanced mixer input, you will get the difference between the channels (not much, that is)
• If you use 1/8" TRS to 2 x 1/4" TS into a stereo input, you get the full signal, but are wasting a stereo input for what is essentially a mono source
• If you connect only one of the headphone output channels to a mixer input, you will get a weaker signal (6dB) than by using a stereo channel - but I suspect this is the best compromise

Conclusion; the only correct cable to use is a stereo 1/8" TRS to 2 x mono 1/4" TS - plug one of these into the mixer input and leave the other one unused - unless you have stereo mixer channels to spare, then you can use both to get a stronger signal.

[LM]

Conclusion; the only correct cable to use is a stereo 1/8" TRS to 2 x mono 1/4" TS - plug one of these into the mixer input and leave the other one unused - unless you have stereo mixer channels to spare, then you can use both to get a stronger signal.

That's exactly how I do it, except for Volcas which have a stereo output (e.g.: Sample, FM). When it comes to the Sample, you can still treat it as mono if you leave all the individual parts panned center.

[Cardindex]

Hi there,

I am tearing my hair out trying to get the root of a problem with my Volca Keys.

The unit is used, out of warranty and worked fine…until I tried hooking it up to an FX pedal (the RAT). For this, I used a 3.5mm TRS cable into the headphone out on the Keys and used a 1/4” TRS adapter on the other end into the pedal.

For a while, I couldn’t hear anything and turned the pedal on and off a few times, after which I got a weak signal in one channel. After disconnecting everything, the Keys now plays back a very weak, distorted signal through both the onboard speaker and the headphone jack.

I now know that I have to use a dual mono connection on the pedal side and leave one connection unhooked, but I’m not great at electronics and trying to figure out what might have been damaged.

Can anyone here tell me what the issue might be and how (if possible) it might be fixed?

Thanks so much!

[LM]

Are you running it on batteries?

[Cardindex]

I am, fresh batteries, but I’ve switched them out twice with the same issue. You’re thinking I should try a power supply?

[LM]

If you have one available, might as well give it a shot.

[Cardindex]

Tried it but had the same issue. Does anyone repair these? I tried both the Korg site and a few local music stores without much luck.