issues with the AR

[fonik]

Hi all,
I have some problem with the AR:
The attack and the release times are VERY long, independent from the times set by the pots.

I suggest a faulty cap C3 and i want to replace it. Should it be a tantal and why? Could i use a electrolytic instead (and why not)?

At pin5 ic2-b i got the voltage rising from approx. +0.1V, which is okay, i think. At pin7 ic2-b the voltage rises from -9V!?

Could it be, that the trigger pulse from C1 is missing? (I only have a softwarescope which is a mess to handle with)

Any comments appreciated

Cheers,
Matthias

[Uncle Krunkus]

I'd check that the pots are connected properly first. It's easy to get something like that mixed up and use one end as a wiper (which would give you those exact symptoms)

[fonik]

Thanks for your suggestions.
Well, as to say for the SL the Wipers and the CWs of both pots are connected correctly to the timing Cap C3 and pin5 of IC2. Meanwhile i replaced the tantalum by a electrolytic cap. No difference.

[mosc]

For ARs and such, virtually any type of capacitor should do, but watch the polarity, of course. Electrolytics are used where you need a lot of capacitance in a little space, like power supply caps, but they aren't all that stable - so you might expect there value to change more rapidly than something like a ceramic or mylar type.

Random story: I built a 5V power supply one time and wired up the electrolytic cap backwards. It worked fine for about two years, then one day it blew up. If I would have had the misfortune to have been working with my face close to it at the time, I might not be here today. Fortunately nobody was hurt, but I was completely freaked out. It was a big explosion - could have been really bad in the wrong circumstances.

[fonik]

Okay, i checked the polarity of the timing cap. I then checked the trigger pulse at C1/R4 and as far as i could tell from the softwarescope its really there. I checked the pot wiring again and found it is as it should be. I checked the pot themselves (1M) and they are working.
Seems there is no way for me to localize the malfunction so i will check versa netlist...

[State Machine]

We can take another approach and based on the fact you gave that both the attack AND release times are longer than expected, check any circuit that is common to both functions.

First, check the value of R6, 500 ohm resistor. Also, check its wiring. This is a common charge and discharge circuit path. If this resistor is >> than 500 ohms and >> R10/11, then you would get the very symptoms you are observing.

Does the circuit behave in both triggered AND gated modes?

If so, then go to the bare minimum of circuitry to operate and set the circuit in GATE mode, NO REPEAT, and use the manual pushbutton. Make sure pin 2 of IC1 is switching to 9 volts when pushed and 0V released.

I will stop for now until you check these items ...

Good luck ...

[State Machine]

[fonik]

hi bill,

thank you very much for these hints. they help me understand the circuit and locate the problem.

unfortunately i am rushed up to my ears in stuff to deal with these days, but i hope to check your sugstions tomorrow.

i should add that the pots seem to have no influence on the attack and release times anyhow - strange.

again thank you very much for taking care

matthias

[State Machine]

[fonik]

hi bill,

i checked the value of R6 and i suddenly noticed that the D10 diode behind the attack pot was reversed.
i must overlooked that before, i guess, diodes don't change their direction by themselves naturally;-)
the diode is panelmounted and hidden by a cable tangle of panel to board wiring - nevertheless awkward. didn't wanted to waste your time.

thank you very much again

cheers,
matthias

[mosc]

Ah, the old backwards diode problem.

Anyway, glad you found the problem. The one trait of a technical wizard - they never give up.

[Uncle Krunkus]

Congratulations,
there's only one thing more rewarding than a circuit that works perfectly first time. That's finding out why it didn't!
There's no better way of learning how to troubleshoot something than to do some troubleshooting!

[mosc]

Before I studied engineering at school, a friend, George Gibson, thought me electronics. He said the most important lession is, "Never expect it to work when you first turn it on." If you just keep that in mind you'll go far.

[Uncle Krunkus]

Very good advice Mosc.
Complex circuits really do demand a certain level of respect.
It makes sense that the chances something will behave exactly as expected decrease exponentially with component count.
Therefore, "If it works first time, you're not trying hard enough."

Maybe we could write a book, 'Zen and the art of electron flow'

[mosc]

That rule has served me well in programming too. A corollary:

If it works the first time, you haven't found the problem yet.

[State Machine]

[State Machine]

[fonik]

[State Machine]

[Uncle Krunkus]

Something interesting I noticed the other day.
Even though I'm pretty well organised, component wise, I keep finding 2K resistors in my 1K slot and vice-versa. The difference between the brown and red which they use on the 1% metal film resistors can sometimes be nothing at all. (sometimes the red looks brown and the brown looks red! ) And, no, I'm not colour blind.
These days I check anything borderline with a meter just in case.

[fonik]

[Pehr]

[mosc]

[State Machine]

Uncle "K" says: