Hold my volts.

[Kipper4]

So Hypthetically.
I want to make an envelope detector.
What's the best one?





Seriously though.
I'd like to build an envelope detector who's output voltage is above 4v7 (turn on point for my vca)
and if possible goes to the plus rail. (The more volts above turn on the vca gets, the louder.)
Can I just put a zener diode on the output of the envelope detector.

here an example
zener not included


I hasten to add this is not on the breadboard I just did a lucky dip and this was the first to crop up in the eagle storage file.

Thanks
Rich

[EBK]

So Hypthetically.
I want to make an envelope detector.
What's the best one?

There is a risk of being so clever.  Some people may not read past that part.   

Are you looking to simply scale and shift the output of an off the shelf envelope follower?

[Kipper4]

Currant thinking is envelope detector to a comparator ic as a trigger generatir. Trigger to bootstrapped ramp generator.
Ramp between 4v5 and 8v ish

[samhay]

Have you studied the envelope detector the Engineers Thumb compressor uses?

[Kipper4]

Studied. No.
IIRC it has a diode and bjt  in the feedback .

[samhay]

U1b is a precision half wave rectifier biased to 4.5V. You can bias this to any voltage you want between the supply rails via the input signal.
With the diodes oriented this way, the envelope will swing from 4.5V downwards. If you reverse the 2 diodes, it will swing up until the input signal hits the positive supply rail.

U2a is a precision current source. You probably don't want this, but you do need to buffer the output of the envelope detector, so you can replace this with e.g. a non-inverting op-amp buffer.

[anotherjim]

You won't want a 358, it can't output to the +rail. In fact, it's the probably the worst possible choice. It kinda sacrifices positive swing in order to go all the way down to 0v.
You could follow a 358 based, works to 0v detector, just like that one; DC coupled to a rail to rail device wired for inversion, with some bias voltage set on its +input (to give 4v7 out while envelope = 0v) and gain set to give the required swing. Plenty of CMOS opamps will work off input to zero and go very close to positive rail. Then again a lot of CMOS amps can do just as well at working to 0v as the 358 anyway, so a quad version like TLC274 can do the whole job.

[Kipper4]

You guys are mint.
I'll breadboard some trials later thanks