Your Stripboard looks good to me! I don’t understand what the opamp with all the diodes is doing, probably a kind of precision rectifier, but with more diodes and no resistors…
So the circuit works but the amount pot does nothing? Can you send in not a kick, but a constant voltage and see what happens with that?
This is what I Imagine what it should look like:
Edit: I mean the waveforms, not the circuit. The wiggles of the kick should be made only positive and then control the led.
Edit2: maybe you should add a resistor as in my picture (R2), because in Juanito’s version the opamp operates in open loop mode when the diode is not conducting, so differences between opamps might be important ( how fast they are etc.)
My first suggestion, change the pot, but im sure you have tried that.
oh I see it’s fixed while I was replying, nice
@sebastian it is a strange inverting rectifier, I was intreged and decided to simulate it. This is a plot for a 1kHz sinewave input, and a link to the simulation.
Hm, I did a simulation too, just up through the rightmost diode.
Except I assumed the input signal was synth level so used a 10 Vpp sine, in which case the first op amp output is almost always ±12 V, and what comes off the pot wiper is a near square wave. (Note the pot is configured like a voltage divider, but there’s current through the wiper when the voltage is above ~700 mV.)
I think what’s happening is:
When the pot wiper voltage is negative the leftmost diode has only a small leakage current. That current has to come through the top left diode, so the second op amp output must be a diode drop above -(the wiper voltage), and the output is a diode drop below that.
When the pot wiper voltage is positive so is the inverting input on the second op amp; it has no way to change that, so the op amp output is -12 V. Then the output is three diode drops below the wiper voltage.
I don’t really see the point of the rightmost diode other than to reduce the output by a diode drop; it’s always in conduction (for ±12 V out of the first op amp).
Why they’re going through all that just to drive a vactrol I don’t know, it’ll presumably just smooth this out into an envelope, so it’s kind of an envelope follower but seems an oddly obfuscated one. On the other hand just this part of the circuit, without the vactrol and with a coupling capacitor to remove the DC, might make an interesting distortion.
Well, after eating, i come back to my build, and the Amount pot works like this morning test, but when i touch (or near) the pot : the led bright up !?
With my finger on the pot to have the problem led light up
and with a wire connected to the gnd i looked for where to connect the other end so that the led goes out
i found it but it’s still strange
it was my standoff near the pot
very strange because the standoff dont touch the led, the knob, the pot …
on the other side there’s 2 lines without short between the rest of the circuit
i put a wire on the standoff line on the board, connected to gnd
and all is ok now (ouf!)
the standoff surrounded by the led and the gnd can become an antenna ?
always weird stuff for me
@analogoutput Thanks for the explanation, however, I still had to think this through for myself, it took a while to realize the second opamp is effectively bypassed when the wiper is positive, and an inverting buffer when negative. This is a nice low component active full-wave rectifier, if like in this module, the inconsistant diode drops and non-lineararities are not of importance, I might try this for driving signal led’s
Nice to know im, not the only one using Circuit labs, I only found it a couple of weeks ago. I’m still only a few chapters into the tutorial, but find it really useful.
Conclusion of the day, I have the impression of having isolated something, as if I was isolating my wooden panel !!!
I have a little trouble thinking about that
I come back to this, in fact I think I understood this story from another world
When i test my news modules, i made it on my old little 5W Marshall guitar amplifier on my work table.
And i see some problem on my jack in, move a lot and grounding problem.
“zzzzzzzzzeeeee” when i touch the jack socket !
So some strange parrasite issue on this capricious module, which I never would have had, if I had noticed it sooner.
@Dud
First of all: thanks a lot for your stripboard layout.
I built it and it showed the same strange issue as you mentioned. Touching some diodes made the circuit act better. The amount pot acted strange. When I my louleamp (with the leds of) around the circuit the sound almost totally faded away.
Like something was acting as an antenna.
That started me thinking that the biggest difference between Juanito’s build and you stripboard is the dimensions. Juanito’s parts are really close to each other. So I moved the D1 diode from the pot to the stripboard as close to the other diodes as possible.
Result: circuit works perfect and no audible interference at all etc…
=> So for future builders: move the diode as close to the other diodes and you should get out of trouble.
)
