anyone tried a compressor like this?

[birt]

i just found this on the web. the way the compressor works seems really straight forward and it looks like it might be used in guitar or bas projects

[Johan]

that looks pretty typical of simple comressors, look at the O.S for example(using a FET instead of LDR ).
..but as drawn, I doubt it will work. there is no bias/groundreference for the opamp inputs.
j

[JDoyle]

...but as drawn, I doubt it will work. there is no bias/groundreference for the opamp inputs.
j

Actually, there is. You are falling into the common trap of looking at everything from our perspective of just having a 9V battery to work with and thinking of 'ground' as 0V and V+ as 9V.

In the rest of the world, 'ground' is a point normally halfway between V+ and V-.

In this case interpret ground as 1/2 V+ and the circuit will make a lot more sense.

[birt]

and it comes from an existing transmitter as far as i know.

[Johan]

...but as drawn, I doubt it will work. there is no bias/groundreference for the opamp inputs.
j

Actually, there is. You are falling into the common trap of looking at everything from our perspective of just having a 9V battery to work with and thinking of 'ground' as 0V and V+ as 9V.

In the rest of the world, 'ground' is a point normally halfway between V+ and V-.

In this case interpret ground as 1/2 V+ and the circuit will make a lot more sense.

Oh, I know that..  but what I meant was, I dont see any DC-path to ground from any of the inputs..they are both blocked by caps making the biasing suspect. there might be something about this in the app.note for the TDA2002, but thinking of it as a regular opamp, I dont see it...
j

[puretube]

NO regular opamp...

[JDoyle]

NO regular opamp...

Looks to be internally biased. Though that datasheet is SEVERELY lacking, from the test circuit I have to infer that it is internally biased, otherwise their test circuit wouldn't work at all.

NOT a regular opamp at all.

Regards,

Jay Doyle

[puretube]

Fairchild, page 2... 

[Paul Perry (Frostwave)]

Nice one, puretube........
those chips are $4.50 at www.jameco.com
But I am always VERY suspicious of chips when the data sheet helpfully provides PCB layouts - it always strikes me as a way of saying "OUR layout works.. can't guarantee YOUR one will!"
Oh yeah, 40 to 80mA quiescent current. No batteries for this bad boy, unless it's a CAR battery

[Mark Hammer]

If I'm not mistaken, this is similar in some ways to what Crate has done with some of their chip-based power-amp stages using TDA2030/2040/2050 chips.  The output drives a rectifier stage that controls a Vactrol on the power-chip's input.  I gather this is not to function as a standalone compressor, but as a means for keeping the power-chip as clean as possible under the circumstances.

[birt]

i was thinking about using this as an add-on to a chip amp

[BubbaKahuna]

Nice one, puretube........
those chips are $4.50 at www.jameco.com

They're only $2.10 at http://www.newark.com

Cheers,
- JJ