Big Knob question

mjbphotos

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I've got a Mackie Big Knob positioned handily on my desk , outputs from my Scarlett 8i6 to it, then monitors hooked up to the BK, all via balanced cables.

I had used this previously to switch between 2 sets of speakers (I also had 2 computers, and used a switch to do that, so I only needed one keyboard and mouse that way). With my new place, I no longer needed the BK (only 1 set of monitors), so set it aside.
When I started doing a lot of Zoom music events, I found it was useful to put the BK close at hand for volume adjustment and muting when I play (to prevent Zoom sound issues).
Everything was fine, but I noticed I was sometimes cranking the BK volume all the way up when some people in Zoom meetings were particularly low volume, so I turned up the volume control on the 8i6 a little.
The other day, when I was 'mastering' some mixes, to get the overall volumes up, I heard distortion on some of the peaks that were getting very minor limiting.
Listening with headphones plugged into the 8i6, I didn't hear the distortion. Turning down the volume control on the 8i6 seems to have removed the distortion (but I crank the BK knob up).

So... is the 8i6 overdriving the inputs on the Big Knob? As its a passive (no power) device, I would not think that would be an issue.
 
What does the input meter on the BK show? I haven't experienced that issue myself.

Probably not related but I did however once have a dirty switch on the BK that was causing some crackling. The MONO button to be exact. They pull right up with pliers. sprayed some contact cleaner in there and that fixed it.
 
Being a passive device, the BK will likely lose some signal going through it and looking at the block diagram in the manual suggests its inputs are not balanced which may lose another 6 dB or so from the balanced out of the 8i6 even if TRS cables are used. I'm kinda thinking the 8i6 may not have the headroom to drive the monitors with the attenuation of the BK between the 8i6 and the monitors and limits/clips. The 'Dim' button appears to pad the signal another 20dB. I assume that's not enabled(?). It might be interesting to try the monitors with and without the BK at the same volume setting on the 8i6 and see if there's a notable difference.
 

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What does the input meter on the BK show? I haven't experienced that issue myself.

Probably not related but I did however once have a dirty switch on the BK that was causing some crackling. The MONO button to be exact. They pull right up with pliers. sprayed some contact cleaner in there and that fixed it.

There is no input meter - this is the BK Passive, not the BK Studio.
 
Being a passive device, the BK will likely lose some signal going through it and looking at the block diagram in the manual suggests its inputs are not balanced which may lose another 6 dB or so from the balanced out of the 8i6 even if TRS cables are used. I'm kinda thinking the 8i6 may not have the headroom to drive the monitors with the attenuation of the BK between the 8i6 and the monitors and limits/clips. The 'Dim' button appears to pad the signal another 20dB. I assume that's not enabled(?). It might be interesting to try the monitors with and without the BK at the same volume setting on the 8i6 and see if there's a notable difference.

There's plenty of volume. I had turned the 8i6 up to about 12 o'clock; before (and now), I have it around 10:30. Didn't realize that the inputs (and hence outputs) are actually unbalanced.
 
Hi Mike this is a can of worms! I have both an 8i6 and a BK Passive (but the BK is driven from my KA6 which is left at max output and no problems)

I have just checked the input resistances of the BK and was astonished to fine the ring to sleeve measures an almost exact 1,000 Ohms! The sleeve to tip is O/C so there must be a capacitor in that path*.

Now, I suspect the outputs of the 8i6 are 'properly' balanced i.e. an amp per 'leg' and the one driving the ring circuit is not happy with a the 1k load. This would certainly be the case if they use the TL072 type of op amp. Perfectly good amp at these levels but starts to distort at loads below about 2k.

You could try cutting the ring connection on a pair of cables and just drive from the tip. Now an unbalanced feed but since the input is unbalanced?? Note, the output IS 'balanced' sort of, they have fitted series resistors in the the ring and tip path thereby impedance balancing the output.

*Unusually for me I did not have the BK apart! I shall label all my cables up and do so now! Once I have gathered more data I shall see what the top bods at SoS think about this and then maybe ask Mackie Co some pointed questions!

Dave.
 
Interesting, Dave. I contemplated not using the BK while mixing, then re-plugging it in when I'm doing Zoom events, but that is a PITA. I'll try a couple of TS cables between the 8i6 and BK, but its frustrating to try to troubleshoot as the distortion only seems to happen during the loudest peaks in a certain frequency range (I'm sure there an electrical reason for that).
I never noticed any issues when I was using my Tascam interface.
 
Interesting, Dave. I contemplated not using the BK while mixing, then re-plugging it in when I'm doing Zoom events, but that is a PITA. I'll try a couple of TS cables between the 8i6 and BK, but its frustrating to try to troubleshoot as the distortion only seems to happen during the loudest peaks in a certain frequency range (I'm sure there an electrical reason for that).
I never noticed any issues when I was using my Tascam interface.

No Sir! A TS cable won't cut it the ring will be shorted to the sleeve and thus still impose the 1k load. Sorry boss, you gotta butcher a couple of TRS cables!

Do NOT forget to label them!

I have had the BK apart and it is nicely made (pickies in due course) for the price. Found the 1k Rs, so not an aberration but actual physical resistors..FFS why? there are also some wee bits that LOOK like resistors but are actually shorting links. Some ceramic caps as well, RF filters? Yes, two electrolytics feeding the 'top' of the rather uninspiring stereo pot. 10uF, a value that won't enamour the box to the audiophools but I doubt anyone could hear any LF distortion at these signal voltages.

Plenty of space in there so I might 'Activate' mine with balanced inputs and output drivers.

Dave.
 
No Sir! A TS cable won't cut it the ring will be shorted to the sleeve and thus still impose the 1k load. Sorry boss, you gotta butcher a couple of TRS cables!

Do NOT forget to label them!

I have had the BK apart and it is nicely made (pickies in due course) for the price. Found the 1k Rs, so not an aberration but actual physical resistors..FFS why? there are also some wee bits that LOOK like resistors but are actually shorting links. Some ceramic caps as well, RF filters? Yes, two electrolytics feeding the 'top' of the rather uninspiring stereo pot. 10uF, a value that won't enamour the box to the audiophools but I doubt anyone could hear any LF distortion at these signal voltages.

Plenty of space in there so I might 'Activate' mine with balanced inputs and output drivers.

Dave.

You're right, of course. No changes with TS cables. So I said F this, plugged the monitors back into the 8i6. Holy deafness, Batman! SO MUCH volume. I had forgotten that I had cranked my JBLs up all the way on their rear volume controls. The BK is knocking down the volume by at least 50%. So I'll leave it unplugged except for my zoom meetings (right now that is only once or twice a week). I liked having the volume control and mute being so close, will have to see if I want to move the 8i6 to the edge of the desk as right now it requires leaning and stretching forward to get to it.
 
Some more info Mike and some smudges.

I checked the input impedance and insertion loss..MO as per,

1kHz out of my ZED10 (hefty level.low z) and then into 'A' input. With VC at max, the loss was 1.9dB. Just audible on an A/B but hardly a bother?

My test kit situation is dire at the moment so an input Z test took the form of reading the volt drop across a 5k6 in series with the tip circuit. Bit o 'rithmetic gave me 10.53k very close to the pot value as would be expected.

That means that the output resistance could be as high as almost 3k and so cables to monitors should be as short as reasonably possible. Mine fortunately can be and are less than 2mtrs.

rock on,

Dave.
 

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Hi Dave, you kind of lost me on all that. My electrical engineering stuff was all 40+ years ago (how did that happen?)

I definitely experienced a big signal loss with the BK in place - 1 meter cables between the 8i6 and it, 2 meter cables from the BK to my JBLs. Still have the BK out of the circuit, besides turning down the JBL pots from full to noon, I also had the outputs in the Focusrite software cranked to full, so reduced them 5% - now at least I can turn the 8i6's volume control more than to 8 o'clock! Last night with a mix that was peaking around -8dB on the master track (someone else's initial tracks, I was just recording some new tracks), turning the 8i6 up to about 11 o'clock was very loud.
I will hook up the BK again later today, as I have a Zoom event tonight. Will experiment to see if the distortion is still present.
 
Mike, at one time I think you may have mentioned JBL LSR series for monitors(?). If you are using these, is the sensitivity switch set to a position (4dBu or -10dBV) that would need more signal coming through the BK from the 8i6 ? The -10bBV setting would need less signal and possibly the 8i6 wouldn't need to be pushed as much through the BK and less prone to distortion.
 
Mike, at one time I think you may have mentioned JBL LSR series for monitors(?). If you are using these, is the sensitivity switch set to a position (4dBu or -10dBV) that would need more signal coming through the BK from the 8i6 ? The -10bBV setting would need less signal and possibly the 8i6 wouldn't need to be pushed as much through the BK and less prone to distortion.

That ^ Mark and...I think we have established Mike that the 8i6 has a dual amp, balanced output? You therefore get 6dB more signal (will check the 8i6 spec in a mo) but, ONLY into a proper balanced input and the BK is not that! To add insult to injury the Mackie is loading down the ring signal and that is, I ma certain, upsetting the drive chip.

My tests indicate that the unbalanced path i.e. the tip signal is only attenuated by 2dB and thus should not give any really noticeable loss in the monitors (well, you will still lose the 6dB because I assume the monitors have a proper balanced input)

So, if you modify two TRS cables by cutting the ring connections I am sure the BK will work quite well, not AS loud as a straight through connection but loud enough?

Dave.
 
I have a question Dave? When did creating cables to make consumer products work right become a thing?

I do not have these issues myself, but wonder why there is an issue to begin with...

Serious question because it seems like a big pain in the ass IMO.
 
Hey Dave, the input jacks as shown in the BK diagrams seem to be remiss of the sleeve connections like as they are shown on the output side jacks. This would suggest the BK is using the ring connection of the input jack as the signal low and 'ground' internal to the BK. Probably done this way to accommodate both TS and TRS type cables(?) This 'ground' connects through to the outputs where as you note the ring is connected through a resistor to create an impedance 'balanced' connection. I kinda think if the ring wire in the cables were lifted the signal low may not have a path to the output jacks since it appears the sleeve of the input jack is not used. Maybe you can ohm this out to verify the non-connection of the sleeve in the input jacks? The other potential problem lifting the ring wire which kind of provides a ground and signal through path is that the sleeve of the input jack on my JBL monitor is connected internally to AC mains ground on the IEC connector block. This could provide a not so good ground signal path between the monitors and the 8i6 or it may present some sort of undesirable ground loop.
 
I have a question Dave? When did creating cables to make consumer products work right become a thing?

I do not have these issues myself, but wonder why there is an issue to begin with...

Serious question because it seems like a big pain in the ass IMO.

In the specific case of the BKp you would have to ask Mackie. In general, 'interconnection' for audio has always been a bit of a lottery. Sur le continent XLRs were I understand the other way? Ins were male and outs female. Very few people understood the wiring regime and reason for the DIN standard and when Americo/Japanese gear started to come here there were all sorts of bothers with weak, noisy signals or overload or just no 'king sound at all. We still have 'A' and 'B' jacks and if you plug the former into the latter you bugger it. There were long and short reach RCA plugs and things did not switch if you use shorty...

Mark, a 'block diagram' is not a schematic. But do not worry, the sleeves of all the jacks connect to each other via the chassis.

When I get a mo' I shall fire up my 8i6 and give it a 'do'. Is there a default, 'factory' setting for mix control?

Dave.
 
I have a question Dave? When did creating cables to make consumer products work right become a thing?

I do not have these issues myself, but wonder why there is an issue to begin with...

Serious question because it seems like a big pain in the ass IMO.
It seems that Mackies manual even states that if using TRS cables the 'ring' needs to be tied to the 'sleeve', which essentially makes the cable a TS cable to fudge the unbalanced connection for the BK :facepalm:

And yes Dave I fully realize a block diagram is not a schematic, but if the input jack sleeves are grounded (and it sounds as if they may be through the chassis), the block diagram provided lacks consistency as they've shown the output jacks properly with the sleeve connection and neglected to do the same for the input jacks.
 

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"And yes Dave I fully realize a block diagram is not a schematic," SORRY Mark! That came across as rather snotty when I see it again. My meaning was sort of "FYI" no slight intended.

Shorting the ring of an output to sleeve is always a bad idea since you rarely know what the source configuration is. As we have seen, if an output has a 'hot and cold' active stage as it seems does the 8i6, you would be shorting an op amp's output. This probably won't destroy it but it will be in a permanent state of current limited clipping and will almost certainly 'upset' the other half of the IC.

There are sophisticated 'quasi-floating balanced OP stages that deliver the full 6dB boost if one pin is shorted but these are only found on very upmarket gear.

I can only conclude that there are more compromises to making a passive controller than I had imagined. In MY setup the BKp works faultlessly and does what I bought it for. Anyone contemplating a controller would, IMHO do well to save their pennies for a Drawmer CMC2, one of the best for around $300.

Dave.
 
Mike, at one time I think you may have mentioned JBL LSR series for monitors(?). If you are using these, is the sensitivity switch set to a position (4dBu or -10dBV) that would need more signal coming through the BK from the 8i6 ? The -10bBV setting would need less signal and possibly the 8i6 wouldn't need to be pushed as much through the BK and less prone to distortion.

Yes, the JBLs are on the -10 setting. As I mentioned, plenty of volume when they are hooked up direct to the 8i6. Since turning down the Focusrite software output from full and the JBLs from full, the distortion (when using the BK) seems to have disappeared. This is with the 8i6's output volume control at about 1 o'clock. Plenty of volume for listening/mixing, but have to crank the BK's knob way up, of course.
Interesting that the TRS input of the JBLs isn't really balanced - of course, this doesn't matter when using the BK, as that is not really balanced either! I guess if I decide to not use the BK in the future I should get TRS-XLR cables for 8i6 to JBLs. If I ever get noise in my current configuration, at least I will have some possible solutions.
Of course I could hook up both ways, and use the Focusrite software to mute the 8i6-JBL path when using the BK path and vice versa.
Thanks for all the help, guys.
 
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