Passive monitor controller

[Tubetec]

Im just looking at passive monitor controllers ,
Behringer Mackie and RCF all do a competing product , all indentical feature wise , A/B source select , mute ,mono, dim monitor select and of course volume .
I was wondering how good interchannel balance is , pots dont tend to be great lower down in the travel range . I was wondering about fitting a switched attenuator of the budget DACT type , they typically have interchannel balance as good as 0.1db at any setting , the dim button typically attenuates by 20 db ,so even with a 21 position attenuator you get 42 volume settings . Interested in hearing peoples experience with these passive type controllers .

 

[pvision]

They always seem to me to have the wrong connectors - a mix of XLR, TRS, Dsub, etc. I think they'd be better (and more expensive) with all XLRs

 

[Tubetec]

The Mackie and Behringer has all jacks(bal,unbal) ,The RCF unit has combo/xlr/jack inputs and two pairs of xlr outputs .

 

[scott2000]

Pretty sure I've mentioned before that those ?Rockmann? SLC-1 monitor controllers used those "dact type" switches and they were very nice and accurate. Something about the way they sounded bugged me and the Alps Blue Velvet just seemed nicer to listen to. But it's been a long while.
No features like dimming on either though. Depending on your room,dacs,etc, not sure the sound differences would be as much of an issue as channel balance or features... even an active line amp/splitter is nice in some situations... could even mod them with 10 turns if feasible .. everything in the chain is janky at times..

 

[gyraf]

the DIM switch is there as the solution for poor tracking at low levels

switches for volume control most often makes for way too coarse control

every time I sit down and try to design a monitor control, it dies of feature creep

/Jakob E.

 

[Matt Syson]

A passive monitor controller is basically a bad idea all around really as there are significant compromises to be made with almost everything you do. Having it unbalanced is on the way to invite hum and interference pickup unless you are running into a stereo monitor amplifier (or amplifiers if you use more than one). Length of wire from the pot to the amplifier must be within about 1 metre (yard) if you have any pretence of 'high frequency flatness' with a 10K pot/attenuator. The HF response will also change depending on the level setting. A 10K attenuator (plus the power amp input impedance) MAY present a total load that is unsuitable for some sources and again is variable depending on setting. THEN it gets more problematic again when you add a 'Dim' control and a Mono control.
Granted a 'pot in a box' works but to attempt to claim it is 'better' than a properly designed active (with amplifiers) controller because you think simplicity is better can cloud the practical issues.

 

[Tubetec]

Im planning on sitting the control unit directly on top of my power amp ,so only 30 cm of cable to unbalanced input , 100kohms , 1.8 volts for full output . The B output can feed my active monitors balanced over a longer distance . On the input side the DAC can sit only inches from the controler

The budget dact attenuators with 21 steps are set up as a volume control , ie the steps are more coarse the lower the postion with off at the end ,
Ideally you want an even db step per position , and seeing as most passive monitor boxes have mute anyway you dont need any off position ,
So including the dim switch we could have 42 volume settings , maybe 1.5 db per step might make sense , so a little over 60db range , is that feasible ?

I found the schematic of Mackie's Big knob and it seems its only impedence balanced at the outputs not true balanced .

I saw the Khozmo passive preamps , around 90 euros for the mono 42 way attenuator , stereo is roughly double the price . its big and bulky , the box doubles the price .
I have made a couple of passive preamp attempts over the years with motorised volume pots for remote control to keep audio cable distances to a minimum ,
at higher levels on the scale it worked well enough ,at lower levels it was a bit all over the place as is the way with pots . I found the passive preamp under favourable conditions allowed me one step closer to the source compared my active pres.

The Heritage audio baby Ram ticks almost all the boxes ,but lets itself down on the connectivity side with all TRS/TS jack
a mini 21 pos dact with dim switch should do the same job for a fraction of the price .
In fact thats exactly whats inside the Baby Ram I bet , The RCF unit looks best for connectivity and button layout , I might try and pickup a Mackie on the used market for experimentation with the Dact pot.

 

[ccaudle]

The B output can feed my active monitors balanced over a longer distance .

The entire signal chain will be unbalanced after you connect one output to your unbalanced amp.
Matt Syson also pointed out the high frequency response changes you should expect to your active monitors. Be sure to use low capacitance cable for that longer connection.