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Quick question - do passive attenuators destroy tone? If so is it extreme? Like does slight attentuation make it sound rubbish immediately? I want to build a box with 3-5 passive attenuators that I can set by potentiometers, each with their own bypass switches, so that I can basically have a bunch of preset levels right at the end of my chain!
Furthermore, does anything like this exist already / anyone wanna actually build or design this for me? I see the EHX signal pad but that's just one preset and seems expensivo for such a basic circuit, and also takes up too much board space to buy 4 of them.
The signal pad is simply a passive volume pot set inside a true bypass switch arrangement. You could easily wire a bunch of these in series to create presets for different levels of output, but each subsequent pot would introduce more of the same problems that are introduced when you roll down your volume pot, i.e. lowered S/N ratio and increased "tone suck" (mainly low end loss). Buffering each volume pot will help avoid the tone suck, but you also have the problem of true bypass switching requiring you to turn one preset off and turn another on to switch "between" presets. A simpler approach might be to have a master bypass switch (I.e in bypass = full volume/no attenuation), and another single switch that flips between two buffered volume pots for two different attenuated levels. This would give three presets, minimal noise and tonesuck and the ability to flip between any two levels with a single stomp of the foot.
Last edited by Nocentelli on Fri Mar 25, 2016 4:13 pm, edited 1 time in total.
Adding gain stages will never improve your signal to noise ratio. There are however major problems with sending very clean signals at low amplitudes through a copper wire with equipment that is not designed to do that. Unity gain buffering can potentially solve impedance and capacitance problems. You can also add rf low pass filtering at every buffer. But there is no magic opamp that will buffer or add gain to a signal with less distortion on the output then the input. Another reason to add gain before something is to bring the level up relative to an environmental condition that has a limited amplitude. Or also to avoid using a lots of noisy gain closer to the amp.
Instead of having a bunch of volume controls in parallel and switching between them, why not set up one master volume control and then switch in/out different values of either fixed resistors or trimpots on one leg of the voltage divider? Like how in say a big muff gain control, you add a 1k to the leg of the gain pot that goes to ground to keep it from being completely off. Now put several in series, and use switches to bypass them. Or put several in parallel and switch them in and out. That way, with 3 switches you can get 6 different presets. Theoretically at least. Or with 2 switches you get 3 presets, plus your overall control.
If you have more than 2 switches i would use an arduino to a digital pot. This replaces a vca. The only difference is that the vca is voltage control, includes a buffer. While the arduino is software controlled, and the digital pot may or may not benefit from a buffer. You will never run out of headroom on a passive volume pot or an unbuffered digital pot. Clipping there is impossible with no gain stage and no buffer and no power rails in the signal path.
