The Quackmire: A simpler vactrol LP envelope filter for 1590A

[jfrabat]

Bump... Any ideas what to try next?

[Fancy Lime]

Bump... Any ideas what to try next?

Hi Felipe,

sorry, I missed your last post. Wasn't too active here lately. Anyway... You tried the LED and it lit up and you tried the 10k parallel with the vactrol and that did not give you signal. That means that your problem is somewhere between the vactrol and the output. It is not the power supply pf the opamp, else the LED would stay dark. This suggests that there may be a cold connection or a short to ground somewhere on or between one or several of the following components:
LDR1 (resistor side), Range pot, R6, R7, R8, C4, C5

Can you check the voltages on either side of those components?

Cheers,
Andy

[jfrabat]

This suggests that there may be a cold connection or a short to ground somewhere on or between one or several of the following components:
LDR1 (resistor side), Range pot, R6, R7, R8, C4, C5

Thanks, Andy!

I cannot get continuity from these components to GND, so it seems this is not the case.

Can you check the voltages on either side of those components?

Looking at the ground issue, I noticed that I made an error soldering C5 (I have it in line 7 instead of line 6).  I will fix this tomorrow (I am kind of tired today).  Will let you know if that fixes the issue!

[jfrabat]

Looking at the ground issue, I noticed that I made an error soldering C5 (I have it in line 7 instead of line 6).  I will fix this tomorrow (I am kind of tired today).  Will let you know if that fixes the issue!

I honestly believed this would be the source of the issue...  But it was not.  I also had a lose solder joint in C4, which I corrected, but it was not that either.  I mean, both were issues, for sure, but I still get no sound...

Can you check the voltages on either side of those components?

LDR1 (resistor side)
Range pot
1: 3.83V
2: 3.83V
3: 3.42~3.44V

R6
1: 4.49 (at line 7)
2: 3.91 (line

R7
1: 3.43 (9)
2: 0.884 (10)

R8
1: 0.884 (10)
2: 2.2 (14)

C4
1: 1.328 (12)
2: 3.84 (

C5
1: 0 (at line 6; this may be the issue!  Now that I connected it to the right row, I get ground here!)
2: 0.884 (10)

[Fancy Lime]

What sticks out to me is the 0.884V between R7, R8, and C5 on row 10. It seems that this is the point that drags all the voltages down. Please check the section of row 10 on the right side of the cut (so columns 9-12) very carefully. Are there any accidental connections to ground? You say there is no continuity to ground, from which I assume you tested with the continuity function of a multimeter, yes? Try the resistor function, sometimes there is a very tiny solder bridge that has hundreds of ohms or even a few kilo. Are you sure C5 is good? Sometimes capacitors are faulty (very leaky) and act like a small resistor. This is not very likely for a ceramic cap, but if there are no erroneous connections around row 10, I would try changing C5 for a different capacitor of the same or similar value.

I think we are getting close,
Andy

[PRR]

> I made an error soldering C5 ....  I also had a lose solder joint in C4

I'm on a purple drug and not seeing/thinking clearly.

But an old technician says: bad solder/joints run like deer or turkeys: in packs!


If you see one deer or bird on the road, slow WAY down, because there are probably more that you have not seen yet.

[pinkjimiphoton]

>

I'm on a purple drug and not seeing/thinking clearly.

But an old technician says: bad solder/joints run like deer or turkeys: in packs!


If you see one deer or bird on the road, slow WAY down, because there are probably more that you have not seen yet.

mmmmmm. purple drug. been years. carry on!

+10000000000000 on solder joints in packs. best bet if in doubt, suck the old stuff out and reflow fresh.

don't use your lips tho

[akkar]

Will any NSL-32 work fine?
I see different ones one the bay... NSL-32SR3, NSL-32SR2...

[Fancy Lime]

Will any NSL-32 work fine?
I see different ones one the bay... NSL-32SR3, NSL-32SR2...

Vactrols generally have fairly wide tolerances, so using any type always comes with a big "YMMV". That being said, the Quackmire design attempts to mitigate this a bit by working in a range where many vactrols should work ok. The speed of the vactrol is no big concern here. The dark resistance is also not too critical unless it is below say 200k. As long as the bright resistance isn't too high (<1k is ideal but <3k or so should be fine), it should work as intended.
Beware of fake vactrols on the bay though. Just because it says NSL-32 does not necessarily mean that that is what it is. Some may not be vactrols at all or may be dead devices. If possible, I would recommend buying such specialized devices from a "known reliable source". It may be better to use a different type of vactrol (along the specs outlined above) than to chase an NSL-32 and fall for scammers.

Andy

[akkar]

Thanks for your suggestions!

Another thing, I'm not sure about the mode switch... is it a SPDT with a central off position?

It is actually connected like this?

[bluebunny]

Yes, it's an on/off/on switch.

[Fancy Lime]

Thanks for your suggestions!

Another thing, I'm not sure about the mode switch... is it a SPDT with a central off position?

It is actually connected like this?

Precisely so,  as the wise bunny already said.

[ElectricDruid]

Weird choice of values though, right?

We've got 1u+4u7 one way, 1u in the middle, and 1u+22u on the other side.

So those are roughly 6, 1, 23 ratios,  but excuse me if those seem like odd numbers to choose...

Maybe those values are great, and I'm just too twitchy about stuff like this. Those ratios freak me a bit because they don't fit any pattern, although I recognize there's actually no reason why they should.

[Fancy Lime]

Yeah, well, life's full of compromises, innit? I liked 1u for the shortest and 22u for the longest time constant. Wanting a small and cheap switch meant on/off/on was the way to go, leaving me with one more value somewhere in the middle. I only had 4u7 and 10u around and wasn't going to combine two caps to get anything more tailored (for simplicity and because electrolytics have ginormous tolerances anyway). Out of the two choices, I liked the 4u7 in parallel with the 1u better. That's all there is to it. If I were to put this in a larger enclosure, I would probably go rotary switch with 1u, 2u2, 4u7, 10u, 22u, 47u, or something like that.

Andy

[ElectricDruid]

Yeah, well, life's full of compromises, innit?

Yep! I guess it is!

I liked 1u for the shortest and 22u for the longest time constant. Wanting a small and cheap switch meant on/off/on was the way to go, leaving me with one more value somewhere in the middle. I only had 4u7 and 10u around and wasn't going to combine two caps to get anything more tailored (for simplicity and because electrolytics have ginormous tolerances anyway). Out of the two choices, I liked the 4u7 in parallel with the 1u better. That's all there is to it.

Entirely fair enough. As I said, I think I'm just twitchy about stuff like that. Trying it to see what sounds good is a very reliable and well-thought-of method to determine required values, after all..

If I were to put this in a larger enclosure, I would probably go rotary switch with 1u, 2u2, 4u7, 10u, 22u, 47u, or something like that.

Now that sounds like it might be overkill!

[PRR]

Weird choice of values though, right?

I read it as 1, 5, 25. 5:1 steps. 2+ octaves each, 5 octaves total, half the audible range.

Yes yes I am over-simple.  1, 5.7, 23; 4.6oct. Not that you can be so precise on 1st-order filters.

Anyway, "that's what was in my box!" You think I'm driving to the store for more theoretical or metaphysical values? Does Hogwarts U. teach a spell for cap-value tweaking?

I learned to drive on several 3-speed gearboxes. The ratios were barely logarithmic. "We have a 17-tooth sprocket design on hand, we are using it!" The '42 Plymouth has a loooong jump from 1st to 2nd. A later Honda 5-speed had more uniform steps. The new Toyota 8-speed I dunno what the steps are, it never stays in one very long.

[Fancy Lime]

[...] As I said, I think I'm just twitchy about stuff like that. [...]

Oh, me too, brother, me too! Bugs me to no end when I see this sort of nonsense in someone else's design. Being all reasonable and pragmatic instead of theoretically sound! Ugh! It's a lot easier for me to accept that the rules of neat design sometimes get broken, if I'm the one swinging the bat

Now that sounds like it might be overkill!

Right, like that has ever stopped the likes of us

[Fancy Lime]

Weird choice of values though, right?

I read it as 1, 5, 25. 5:1 steps. 2+ octaves each, 5 octaves total, half the audible range.

Yes yes I am over-simple.  1, 5.7, 23; 4.6oct. Not that you can be so precise on 1st-order filters.

Anyway, "that's what was in my box!" You think I'm driving to the store for more theoretical or metaphysical values? Does Hogwarts U. teach a spell for cap-value tweaking?

I learned to drive on several 3-speed gearboxes. The ratios were barely logarithmic. "We have a 17-tooth sprocket design on hand, we are using it!" The '42 Plymouth has a loooong jump from 1st to 2nd. A later Honda 5-speed had more uniform steps. The new Toyota 8-speed I dunno what the steps are, it never stays in one very long.

In hindsight, that's the smart answer that I should have given.