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Passive switcher/volume control Saturation Plugins
Old 26th June 2007
Passive switcher/volume control

So, I'm handy with a soldering iron but crap with circuit design. I'd like to build the following but am having trouble knowing where to begin (I think it should be rather simple...):

Balanced stereo input to 3-way switch (off, monitor pair1, monitor pair2), plus left and right individual mute switches, mono switch and finally volume knob. Two pair of balanced outputs at the end of the chain.

Et voila:
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Old 26th June 2007
Gear Maniac
c.gymer's Avatar

You might find it useful to add a phase switch in there as well. The BBC used passive controllers very similar to the idea your proposing so it might be worth hunting down some of their schematics.
Old 26th June 2007

The mono part may be a bit tricky in a passive box - depending on how tolerant the DAW driving the box is of output shorts.

I'd start with something like this, as the volume control part is the most expensive and trickiest to get right:
NHT - Now Hear This ®


Old 26th June 2007
Lives for gear

On the basis that you should be 'terminating' (short circuit or low value resistor) the speaker set that should be 'Off', then you really need an 8 pole switch and 8 ple 3 way are fairly rare although the 'mini maka' switches should be available still (Farnell / Newark). Assuming the DAW is happy with a load of say 1K0 then some resistors for the 'mono' function should be reasonable.
If you are wanting accuracy then either 'goldpoint' attenuator or a 4 gang pot is needed to stay balanced.
What is your budget?
Matt S
Old 27th June 2007
Lives for gear
ulysses's Avatar
In order for a monitor controller to be worth a damn, it has to be totally transparent. It seems reasonable that a passive circuit is most likely to be transparent, but that isn't automatically the case. The devil is, as always, in the details. If you want to go with a passive circuit, you may want to consider how badly you really want a continuously-variable volume control. If you think about it, you really DON'T. Twiddling and micro-adjusting the monitor level is a terrible habit. Calibrated monitors that allow you to truly know how loud something is - that's a much better idea. How about a 6-position volume switch?
Old 27th June 2007
Lives for gear

A 6 position 4 gang switch is difficult to find unless you go for the 'mini maka' mentioned above, in which case you get a 12 position 4 gang switch which then is more 'user friendly' (more levels to play with).
I would add a 'plug' for Audio Gagets software (Glassware) which allows you to design attenuators but there is a design flaw in that it assumes your amplifier has very high imput impedance, which you don't as it will be around 10K.
Matt S
Old 27th June 2007
Thanks, everyone, for the thoughts. It seems like what looks like a good idea on paper may be more than I want to bite off in reality.

Justin, I'd be fine with a stepped switch for volume - I'm certainly not married to the idea of a continuously variable pot. I generally monitor at only 3 or 4 settings anyway.

Matt, as far as a budget, I was hoping to be able to do this for under $500, but if I'm dreaming at that price, I may look for other (pre-made) solutions.
Old 27th June 2007
Lives for gear

If you are not going for the goldpoint attenuators but a 12 way switch would suffice then you are looking at around 100 Dollars for the switches.
Now my interest is sparked I will look out some possible switches.
You could go for ELMA gold plated but they are serious money so for now yopu could build an 'economy' version and see how you get on.
The only real question is what level you get when in the 'mono' situation and the choices of resistors for it.
Matt S
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