Good small monitor controller.

[Hugh Robjohns]

Ah yes, okay, that would work. I had speaker switching at the outputs in mind, but you could arrange to switch feeds from the left/right outputs across to the passive summing network instead.

Ideally, the switching should also ground the left/right outputs to prevent noise from the left/right speakers (and ground the summing resistors when not in use for the same reason) and you will still lose a bit of signal level through the passive summing, of course. A 4PDT switch would do it I think.

If you're going to use the passive attenuator schematic you linked above, i think it might be possible to use the input buffer resistors on each leg as the summing resistors too, but linking the two hot sides for both channels (and the two cold sides) to feed the hot (and cold) balanced mono output. The two sides of the volume pot would then be in parallel, halving the value, so the attenuation range would change, but I doubt that would be a major problem in the circumstances.

[ef37a]

Whichever way you cut it a passive controller is going to suffer from crosstalk, poor control law, level shifts, low input Z, high output Z, noise if the resistors get too high...All these factors can be traded off, one against the other but you cannot have it all good, all at once.

I knew all this of course when I bought the Mackie Passive but for my particular application, mostly source switching, it seems a good choice. What I did NOT know was how compromised it was in other respects and I still do not know the design rationale behind those compromises!

I continue to be amazed why some people are afraid a of a few op amps!

Dave.

[Hugh Robjohns]

Sam, I had a quick sketch of an idea for your passive monitor controller, using the line feed resistors as the mono summers, and bypassing half the volume pot so that the control law and impedance remains roughly the same in both stereo and mono modes.

The minor complication is that the stereo/grot box switch needs to be a 12-way changeover in order to mute the unused outputs properly at the same time as routing the sum signals appropriately. There are 12-way push buttons... or you could use relays.

Anyway, for what it's worth, here's my sketch:

[Sam Spoons]

Thanks for taking the time Hugh, I'll have a close look. I do have a couple of 4 pole double throw toggle switches I was planning to use but could consider other options.

[Hugh Robjohns]

I think I'd do all the switching with miniature sealed relays. It means the unit would need a small power supply, but you could use a ready-made wall-wart for that.

[Arpangel]

After all this talk I’m regretting ordering my TC, sounds like passive is verboten from what you all say!
All I want to do is turn my monitors down!

[Bob Bickerton]

The TC is just fine - simple big knob with a nice action and you won’t notice any problems.

Bob

[Drew Stephenson]

What Bob said. ^^^
It's the ideal tool for the job you want to do.

[Hugh Robjohns]

After all this talk I’m regretting ordering my TC, sounds like passive is verboten from what you all say!

You're really not good with decisions are you? Or technical descriptions, come to that...

A passive controller is absolutely fine when used appropriately. And inherently compromised when not used appropriately.

Your application is an appropriate use for a passive controller, and hopefully you can be trusted to install it correctly as previously advised.

The alternative is a well-designed active controller and that's going to cost you £200+ as a minimum....

[Arpangel]

After all this talk I’m regretting ordering my TC, sounds like passive is verboten from what you all say!

You're really not good with decisions are you? Or technical descriptions, come to that...

A passive controller is absolutely fine when used appropriately. And inherently compromised when not used appropriately.

Your application is an appropriate use for a passive controller, and hopefully you can be trusted to install it correctly as previously advised.

The alternative is a well-designed active controller and that's going to cost you £200+ as a minimum....

Thanks, I’m using short leads, as I said, so it should be OK.
I know it’s not a good idea, but there are Youtube reviews that have said it sounds very good, more transparent than the Mackie for instance, but who knows, I’m sure it’ll be fine.

[Hugh Robjohns]

Thanks, I’m using short leads, as I said, so it should be OK.

Yes, it should.

...there are Youtube reviews that have said it sounds very good, more transparent than the Mackie for instance...

I was very disappointed with the sound quality of the original Big Knob (I haven't listened to the later models). I found it a little noisy and veiled... but PW thought it was fine and used one for years very happily...

[Sam Spoons]

The original Big Knob is active, isn't the one discussed up-thread the BK Passive?

[Wonks]

The original Big Knob is active, isn't the one discussed up-thread the BK Passive?

One could say 'floppy'.

[Sam Spoons]

It's my age...

[Hugh Robjohns]

The original Big Knob is active, isn't the one discussed up-thread the BK Passive?

I've lost track... but it's hard to imagine a comparison with a passive BK involving comments about a lack of transparency. But I could see how that comment might be levelled at an active BK, and especially the early ones.

[Sam Spoons]

Both BK's were mentioned early in the thread with the discussion moving towards passive controllers later.

WRT my possible DIY job*, I'm trying to get a schematic drawn out and was wondering what app you used to draw your diagram? All the ones I can find for Mac seem to either be general drawing apps or for PCB design (or hugely expensive and/or complicated).

* Costed out at around £65 but if I can make it work I have some DT4P toggles switches, a large knob and a bucketload of XLR and phono sockets so just need a box, stepped attenuator and a bag of suitable resistors which ebay will provide for the princely sum of £36.56. That said a Big Knob passive would pretty much get the job done for £65 and save me the hassle

[Hugh Robjohns]

...was wondering what app you used to draw your diagram?

Coreldraw. Straightforward vector drawing program.

That said a Big Knob passive would pretty much get the job done for £65 and save me the hassle

So often the case! Unless you want something particularly unusual a commercial product will often work out less expensive than a custom DIY job.

[Sam Spoons]

Still pondering, the features on the BKP are almost spot on :-

Stereo balanced input - (X32 control room outputs)
Stereo unbalanced input - (Logitech BT receiver)

Stereo balanced output - (Quad 522/Kef 104bAs)
Mono balanced output - (Avantone Mixcube)

Volume control
Input switching
Output switching
Mute

BKP features not required on custom box :-

Mono (output 2 is mono)
Dim

[Drew Stephenson]

You could see how much John at Orchid would charge you?
Takes the fun out of it of course...

[Sam Spoons]

True, and at least I'd be sure he'd design it properly... But the fun aspect would definitely be a loss...