Attack Decay

[Kipper4]

Something I'm working on
Appreciate some input.

[EBK]

Quick observation: Pins 5 and 6 are shorted together.

[Kipper4]

Yer I tried both to the ni  input and it seemed more stable. Less ripple wired this way
I'll sim it later.

[EBK]

I'm very ill today, and I got almost no sleep last night, so there is a chance I'm about to write something that is incorrect, but:

By tying the op amp's inputs together, I think you've essentially turned it into a hyper-passive* device that simply doesn't care what the input voltage is (assuming it is safely within the rail voltages). There's no differential voltage to drive the output one way or the other.  I believe the result would be the same if you simply erased the op amp here. 

*I just made that word up.


UPDATE: Got an official diagnosis.  Influenza.     Yes, I was vaccinated. 

[anotherjim]

If both inputs tied together, an op-amp becomes non-inverting unity gain. It is still "active" when wired like that. I think that 1k R15 is the dominant load on the input.

Not sure what you have there. It looks like an envelope follower but you want to hear the ripple as the signal?

[ElectricDruid]

Something I'm working on
Appreciate some input.

I'd turn the 1K resistor into a wire, so that it's a simple non-inverting buffer. You'd also need to put the input into pin 5 and drop the 1M bias resistor.

What are you feeding in? A pulse or audio? It'll make a decent ASR envelope if you feed a pulse through it. With audio, you might want some rectifier before it.

Tom

[Kipper4]

I'll try some of those lads

It works well in that depending on the pot settings it goes from dark to brighter or light to darker.

I'm feeding it a guitar signal.

I'm away from the bench for a week so it'll be sims only.

What I did find intresting in the earlier sim is the response when fed a square wave. The results are quite severe..
I did wonder about maybe one day investigating the possibility to use lfo fed vactrols in th place of the pots.

Also I did try a charge pump rectifier on the breadboard before the AD pot arrangement.
It was ok but didn't really bring anything to the party with guitar so I decided to leave it out.
For now.

Thanks guys.

Edit
Ps it is not tended as a stand alone it will some effect or another

[Mark Hammer]

Frankly, Rich, I'm not sure what you're trying to do here.  Is this intended to control something else?  Is it supposed to provide rise and fall envelope on its own (something I'm not entirely convinced it is able to do).  Does it having nothing whatsoever to do with envelopes but is intended to simply monkey with rising and falling edges of waveforms?

Details, man, DETAILS! 

Oh, and Eric, get better quick, buddy.  While I normally get a flu shot, being an older cardiac patient, I skipped it this year because I'm not sitting on crowded buses or going to work anymore.

[PRR]

What does R12 do for you?

Do you want "Decay" to decay to zero, or to the negative side of the wave?

Context might reduce stupid questions. At my house, "attack" and "decay" have other meanings. (The little dog attacks the big dog, meanwhile old trees decay in the woods...)

[Kipper4]

I can't yet give it context as I'm not sure what to do with it yet.
I guess it a bit of an experiment.
Every envelope/peak detector I've built has needed some adjustment to suit the needs of the parameters it controls.

This is no different. Except as such it seems to stretch further than I think it will ever need it to.
At certain settings the led takes many seconds to relight to full strength with little apparent ripple to the naked eye.
Not much of a gauge the naked eye ,but the meter says the same the voltage slowly rising is fascinating to watch.


R12 sets up my high z for guitar. If I make it a wire does it make the impedance infinite?
Do you suggest another value or have a good reason for asking, I'm intrigued.

I'm sure it will evolve into something probably never to be built by anyone.

I'm fairly certain I can make c4 into a pf value, I did this once before to steady the led. Can't remember what build it was.

So.
Sorry I can't make it easy for you.
Oh and round here you're the big dog PPR. Watch out for those puppies. 

[anotherjim]

Is there a peak/hold intention then Rich?

BTW, R12 isn't setting your input impedance, R13 is. You may have intended to input via C1 to R12/pin3, but that isn't what we see. And I suppose R13 should go to Vb or 0v with another C1.
In audio, there isn't often any good reason to add an input resistor like R12 is drawn, when all it is doing, is the reference voltage supply for an op-amp +pin. It can be a wire to Vb.

I think the suggested "wire" is to put a link between pins 6 & 7 in place of R15 and remove the path from pin 6 to C7 so that the 2nd amp is a non-inverting unity follower/buffer.  That, though will stop it being a peak-hold thingy.

I would expect the  voltage on C7 tends to be Vb and the LED will be therefore be lit from that voltage most of the time.
As you have it drawn it, signal might kick the volts on C7 one way or the other. It may be then that the second opamp, via R15 actively "holds" the peak envelope stored on C7 and drifts back slowly due to tendency for the second amp output to "hold" the last peak change.

[Kipper4]

You're right Jim. I should pay more attention.

How it started was not how it finished.
I originally wanted all stages to be non inverting and did quite a few swaps before ending up with the diagram drawn from what was on the breadboard without reviewing it.

I should go back to my sim and check what's going on with the charge cap and review some of the other stuff too.
But right now I'm chilling with my good lady after a big holiday meal.
Looking forward to a lemon cheesecake pudding.

[Kipper4]