[Troubleshooting] Mackie Big Knob Passive - Noise floor bump with balanced signal?

I bought a Mackie Big Knob Passive as my preamp between my Geshelli Labs Enog 2 Pro DAC and Archel Pro Amp / powered monitors. I wanted something to toggle between my speakers and headphone amp (current has no passthrough and future has no preamp).

In preparation for my balanced headphone amp, I wanted to test how the Big Knob handles balanced signal. I noticed that there is an audible bump in the noise floor when I send balanced signal through the Big Knob. The Geshelli components are not to blame – as a control I hooked up the monitors directly to the DAC using RCA and XLR. There is no audible difference in noise floor between the XLR and RCA outputs (recorded test with UMIK-1). Has anyone else noticed such a phenomenon? It is consistent across two Big Knobs.

The only thing that would exonerate the Big Knob would be if the XLR to TRS cables are bad.

I can add more details if requested.

Equipment involved:

  • Geshelli Enog 2 Pro
  • Geshelli Archel Pro
  • M-Audio BX5a (x2)
  • Mackie Big Knob Passive
  • Stage right XLR (M) to 1/4" TRS (x2)
  • Stage Right XLR (F) to 1/4" TRS (x2)
  • Stage Right XLR male to female (x2)
  • RCA cables (x2)
  • RCA to single ended 1/4" TRS (x2)
  • RCA to 1/4" TRS adapters (x2)

I have nothing bad to say about the Big Knob unbalanced – it’s incredibly handy being able to toggle Mono/Mute/Dim in a 2x2 matrix. The knob is a butter boat, and in a great position. This is just a quirk I’ve run into.

I was looking into a similar setup for myself, got the Big Knob and want to control the volume of my speakers. Was planning to get the Enog and those Stage Right cables for hooking it up. Seeing this makes me a little cautious though.

So far I’ve only tested with SE in/outs, those TRS jacks make it a bit difficult without proper pro gear.

Are you still having issues with it?

Yeah, the problem didn’t go away even when I got another Big Knob. I’m not sure what the exact design issue is, but I can say that the Big Knob is perfectly clean while handling a single ended signal (using RCA w/ TRS adapters). So if you want to use the Enog 2 Pro’s RCA outputs I think you’ll be fine. There’s practically no benefit to using balanced over single ended when using speakers (unless the cable runs are very long).

When I do get the THX AAA 789, I’ll simultaneously output from both the Enog’s XLR to the THX (headphones) and the RCA to the Big Knob (speakers). I could use digital volume control (at 24-bit, you’ll never notice a signal degredation), but so far I like the physical volume control.

I was going to purchase 10’ cables, wanted to test the Big Knob balanced today but my local store only had 5’.

I did discover that the SE is slightly quieter than without the unit in line, even when at max volume, and the knob is only attenuating for L/R and not fully balanced. The unit has resistors on both input and output jacks, with the difference to balanced seeming to be more resistors. Interestingly, the input jacks all have capacitors as well.

I might go back to the store and get something that will work with it balanced to see what happens.

Hey, best of luck and let us know the results. I found that the noise floor bump was independent of input volume (digitally controlled and toggling through the Enog’s output voltages). I figured it’s something in how the Big Knob works? I’d be happy for it to be something else, as there’s not much on the market with a passive 2x2 matrix and good ergonomics for $40.

I know that this topic is over two years old, but I am in a quandary. I am on my second Big Knob passive and so long as I do not turn the knob past 1pm, it is quiet. However, if I run it up past there I start to hear hissing and crackling. The inputs on the monitors are XLR and if I connect either the Apollo or the Rodecaster direct to the monitors there is no noise at all. The Big Knob passive is supposed to be passive so I wrote to Mackie. Took them five days to say that I probably got two bad ones. Has anyone else been successful with this thing? What about the powered Big Knob units?

I am looking for a two in, one out device. The outputs on the Apollo are balanced TRS as are the outputs on the Rodecaster.

Thanks in advance


The nobsound NS-05p and Little Bear MC-2 have never given me any noise but they only have a single pair of xlr in/out and a single pair of rca in/out (the ability to safely convert rca to xlr is nice). The NS-05p has a better potentiometer in the knob and a solid metal case but both are pretty equal.

Thanks Jeremy. My challenge is the need for TRS female jacks. I use a couple of Nobsound XLR switchers and they are perfect for the tasks at hand. I just learned of the Behringer Studio M which is a clone of the Mackie Big Knob Passive so I’m going to pick one up tomorrow and see if it does what I want without all the noise.

Cheers mate

sounds like you got it figured out, but also there’s xlr to trs 1/4 inch cables out there to convert over if need be for pretty cheap. if the behringer doesn’t work out, might be worth a shot.