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Audio Biasing

On my previous post about the MAX4571 which I didn't get an answer if the device is DC or AC. All testing point to it being DC but datasheet doesn't mention it and its circuits do not show any biasing(they show a function generator directly inputing to the switch). The app notes also say that the switch(but not specifically for the MAX4571) will pass current in both directions.

I'll go ahead and assume its a DC device cause all the evidence seems to be support that(although I'm still confused about the app notes).

In any case I have biased it using resistors and it works accept for some attenuation.

I'm curious as to other biasing methods though. There resistor divider method introduces some components that add noise to the system and also need to be chosen optimally.

An idea I had was to use a dual supply or a +- supply that gives -2.5, 0 and

2.5V(or equivalently 0, 2.5, 5). These voltages work perfectly for my devices because I have a uC that runs off 2.5V and the analog switch IC runs on 5V.

I was thinking that I could just bias the audio signal by grounding it to the 0V and treating the -2.5V as ground for the uV and switch. This way the audio signal can swing from -2.5V to 2.5V without any need for extra components. I believe this should work and if my power supply is extremely regulated it would probably work out better? Of course the power supplies introduce there own noise issues and it probably isn't worth it?

The thing is, I want to be able to run the device off batteries. The uC doesn't really come into the picture because its rarely used and the switch itself only consumes power when switching. So I assume that probably 99% of the time I'm only drawing a few uA's.

This is essentially a pro audio application so I want to maximize SNR.

The other method is clamping where I can use a cap and diode but this doesn't seem to be that good.

Any ideas?

Thanks, Jon

Reply to
Jon Slaughter
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Please do not answer this asshole. You will get nothing for your trouble and he will argue with you without any basis for his position.

He appears to be a troll in drag.

Jim

--
"If you think you can, or think you can't, you're right."
        --Henry Ford
Reply to
RST Engineering (jw)

Function generators can apply a signal with a DC bias. No cheating going on there. Yeah, the switch works in both directions, but probably only for voltages above ground.

There are two ways to go single supply audio.

1) create a pseudo ground at mid rail, then AC couple the audio into and out of the box 2) create a negative rail and process the audio normally (maybe three ways if you go into differential schemes)

I think you have the hang of it. You need to insure you drive the logic levels rail to rail. if you go the pseudo ground route, you need to insure it can sink/source current as need be.

Reply to
miso

On a sunny day (Thu, 22 Nov 2007 00:26:20 -0600) it happened "Jon Slaughter" wrote in :

Good. The attenuation is die to the swith on resistance I think. They give some examples how to use it where the current through the switch is zero. audio ------ \\ --- \\--------- + | switch out ----------- | | --- - | /// | | opamp | | | | | -------------- from micro

Exactly, that is why 74HC4053, ..51, ..52, are so nice, as these have a negative supply input, and you can work referenced to ground. Those MAXIM chips ae not very usefull for a big audio project in my view.

Well, you will have to look in the datasheet what logical input level the MAXIM chips need. If you put the uc at +2.5, maybe the switch will not want to go off. Check it, else you do indeed level conversions, as I mentioned before. better get some74HC4053, I have a whole lot of those, and use thse for many things, cool chips, cheap, can get those everywhere, been around long too.

Makeing a + and - stabilised supply is not much harder then makeing just a +. Plenty of ideas have been posted here. Then use normal good audio opamps.

Reply to
Jan Panteltje

Actually, you did get an answer from me and it appears that I was right.

Your problem comes from the fact that the inputs have clamping diodes to the supply rails. Reading the data sheet properly would have furnished you with that fact.

--
The Force is dark on one side, light on the other and holds the world
together.

Hmmm, just like Gaffer Tape then.
Reply to
Hot Jock

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