Mackie Big Knob - mods?

[AusTex64]

The Mackie Big Knob has a nice feature set, at least for me. But I have read that the sound quality leaves much to be desired. So has anyone ever looked into modding a Big Knob with better opamps, caps etc. to improve sonics? I need to ability to feed headphones from a separate stereo send from my DAW while monitoring the 2 bus and other sources,  along with talkback, so a simple passive monitor controller isn't going to cut it for me. Your thoughts?

 

[Andy Peters]

But I have read that the sound quality leaves much to be desired.

Is that assertion based on personal experience, or did you read that on Gearslutz?

 

[AusTex64]

Guilty as charged! 

I've never done any A/B testing. Perhaps I should not be lazy and do that.

 

[j.frad]

Well my personal experience tells me it Is not a satisfactory device. Neither is the spl monitor Controller.
Something sounds wrong, blurred.
When we put in the dangerous monitor st I felt like i was hearing right again.
That's just me

 

[AusTex64]

Thanks for those comments. I have a QA401 audio analyzer, so I'm going to do some measurements when I have a spare moment to see what's going on with the Big Knob. Will also pop it open and have a look around inside. Wonder if Mackie will send me a schematic?

 

[RuudNL]

No rocket science inside...
(If you need the schematic, just send me a PM)

 

[Monte McGuire]

I poked at one recently, and one major problem is that the power supply sits right above the analog board, and spits out some terrible hash. Basically, you get every multiple of 60 Hz up to a MHz or so, and a pretty healthy pile of it. My friend actually used the box for a while and found the noise to be an annoyance if the gain structure wasn't exactly ideal, so this would be a great thing to change.

Basically, removing the stock supply and putting it in another box would quiet the Big Knob down immensely. We tried playing with caps around the diode bridge and in other sundry places, but concluded that the hash radiated from the PSU coupled directly into the audio PCB, so little bypasses and the like affected only those 60 Hz harmonics that are completely supersonic, and not even close to "just above 20 kHz".

I put the Big Knob on an APx-555, and the attachment is an FFT of the analyzer residual with a 1.01 kHz +6 dBV tone as input. We used 1.010 kHz rather than something simple like 1 kHz to get the harmonics to not line up with multiples of 60 Hz, so you could see them directly. The graph is truncated to 5.5 kHz, but the harmonics keep going... and going... and going... as you look at higher frequencies. With higher frequency inputs, the distortion spurs became larger than the hum/buzz spurs, so there is definitely room for improvement, regardless of the atrocious hum.

You could play with metal screening between the PSU and the audio PCB, but get it wrong and you burn the house down. Again, the easiest plan was to move the PSU into an outboard box, but neither of us wanted to deal with that hassle, so we ignored it altogether.

I'm sure there are a bunch of chip swaps that could help, but the device is extremely cost reduced, so it'd be like an "interior gut" of a nasty house, and then you're stuck with the PCB layout and basic circuit. Maybe not such an awful thing to do, but it didn't seem worth my time or my friend's.

Best of luck!

 

[AusTex64]

Monte,

That's really good info, thank you for posting. I had not made it to any testing yet. Ruud sent me the schematic. Eight opamps from DAW input to monitor output, along with a bunch of coupling caps. Not good. Add that to the power supply problems and I agree, it's not worth the effort to improve. I'll probably buy a product until I can find the the time to build something optimum for my needs.

 

[chefducuisine]

I've been through this myself... most commercially available 'Monitor Controllers' are not up to what you'd expect unless you spend a huge amount of $$$...

I finally ended up building this kit and couldn't be happier:
http://www.soundskulptor.com/uk/mc624.html

Together with a beefy headphone amplifier for the artist fed by 2 separate channels from your DAW you get what you asked for.
My recommendation: http://lake-people.de/produktdetails/G103-P.html

 

[AusTex64]

Chef,

Thanks for that info. How do you deal with talkback to the headphones?

 

[chefducuisine]

I am using an RME Madi Card together with RME's TotalMix for talkback.
See explanation here: https://www.youtube.com/watch?v=aeKpM13Eb1M

If you are using a different interface check for the possible routing options or have a look if this can be done via your DAW.