Little Angel problem

[Elijah-Baley]

Hi everybody!
I need help.

I built a Little Angel on veroboard, tagboard layout, V4, the version with all fixes and two switch modes. My harder circuit.

I tested it, unfortunately, without the diode (1N4148). May I have damaged something? Then I tested it again, with the diode, and the circuit sounds, but seems to me without any effect. Just a slight oscillating, maybe some variation speed turning the pots. The switch with capacitor change nothing, maybe a little the tone, and the switch with resistor take off the sound in "no resistor" position.
Some doubts about the wiring. I soldered together lugs 1 e 2 of each pot. (The Depth Pot is a 500k Linear instead a 470k Linear).

A picture:


Thanks!

[Kipper4]

What is this angel you speak off ? (best monty python voice)

[Elijah-Baley]

It is a chorus.
http://tagboardeffects.blogspot.it/2012/02/little-angel-chorus-rick-holt.html.
I built Version 4.

Anyway, I fixed some mistake, I don't know how exactly, but the circuit works now.
Just a little problem now, about one of the toggle switch: the Chorus/Vibe. When I exclude the resistor I get a background noise when I play. In the other mode no noise.
It could be the PT2399? The regulator transistor, maybe?

[Elijah-Baley]

Help... 

[...] about one of the toggle switch: the Chorus/Vibe. When I exclude the resistor I get a background noise when I play.

What this background noise is?

When I include the resistor the noise is just a bit.
If I connect the two free lugs in the Chourus/Vibe switch the chorus effect fades away.

Thank you! 

[vigilante397]

First of all, you should know that despite being awesome, the Little Angel is one of the more problematic circuits out there. Even if everything is done right there is a chance it won't work. I have built a couple of these and everything was built according to the layout, all the voltages checked out, and they didn't work. So I gave up and built a small clone

[Elijah-Baley]

I need some easy chorus. The effect is there, and it is nice and the mods get it more versatile.
Are there some clues about this background noise? I read could be some problem about pt2399, somebody needs try several to get the circuit works good. Could it br my case? At the moment I have just that IC.

Thanks!

[anotherjim]

Have you noticed that the link running under the PT2399 connects to pins 3 & 4 under the chip?

You could experience an "apparent" increase in noise in Vibe mode because that removes the clean/dry signal - so all you hear is the output from the delay. The noise shouldn't be so bad that it's unbearable, but there usually is some from most delay circuits, which is why most dedicated Vibe effects use phase shifters instead.

[Elijah-Baley]

Thank you anotherjim. Yes I noticed that link. I soldered three pieces of jumpers, and in those spotlights there are the junctions of the three jumpers. First time I made, but it should be correct.

Your explanation about the "noisy effect delay" could be right, is that the reason because I suspect my PT2399 maybe is too noisy. I had read different posts and comments in the web about this background noise, in this chorus as some delay effects. (I was planing to build a Cave Dweller Delay, PT2399 based!  )

This noise maybe is not too much unbeareble, but watching some demos of noiseless Little Angel I thought I can get better results. This noise is rather an annoyance.
I bought my PT2399 from Tayda, Model: Princeton Technology Corp (PTC).

I can add a thing. My Crate amp has a chorus effect on board and there's a similar noise when I play with it, exactly like my circuit of the Little Angel.

[anotherjim]

Ok, PT2399 is a variable part, but in general, they either work or don't.
Looking at the layout there's some things missing I wouldn't leave out.

There's no decoupling capacitor on Pin 2 (The analog reference voltage).
There's no high frequency decoupling capacitor on the 5 volts power except back across between in and out of the regulator IC.
Note that ordinary ali electro caps do not work efficiently with the frequencies the chip operates at, and need help with an added ceramic capacitor.
If it were mine...
The 100nF cap (should be ceramic), across the regulator I and O should connect from I to G.
Another 100nF ceramic from PT2399 pin1 to pin 3 or 4.
A further 100nF ceramic from pin 2 to 3 or 4.

[Elijah-Baley]

Wow, so many things!
But the layout is verified.

Ok, this is the layout:

If it were mine...
The 100nF cap (should be ceramic), across the regulator I and O should connect from I to G.

Ok, I didn't get it too much. Anyway, I followed the layout. You can see the picture above.

Another 100nF ceramic from PT2399 pin1 to pin 3 or 4.
A further 100nF ceramic from pin 2 to 3 or 4.

This components there are not in the original layout, right? Should I add them?

I had some doubts about the kind of the caps, so just some of them are ceramic. Again, see the picture above.

[bluebunny]

Rick's design is peculiar in that it wobbles pin 2, rather than the more usual pin 6.  Go check out Rick's original thread for details, but these "features" are intentional.

[Elijah-Baley]

Indeed I had imagined it.
I think this layout is plenty studied and verified, included the V4 with the mod.
And so?

[samhay]

^And so?

You could pull the PT2399 - I see it's socketed - and build it on the breadboard. If it still doesn't work, then you have learnt something.

I didn't get on with the Little Angel, so eventually designed a work-a-like, which doesn't wobble the Vref pin. It works great:
http://www.diystompboxes.com/smfforum/index.php?topic=106854.msg968863;topicseen

[Elijah-Baley]

Thank you!
I am almost sure that the problem is the natural noise of the PT2399. I'm reading the similar problem with the Cave Dweller Delay, and one solution to reduction the noise is rise up the value of the cap between pin 13 and 14. This mod could be cut off some high frequency, but limits the noise.
So... maybe I have to buy some of this chip and choice the less noisy.

At this moment I haven't enough components to try the Little Angel on my breadboard, and the schematic is pretty complicated for me.

Your chorus seems nice, and extreme , but I prefer work on stripboard, it is easy for me.

[anotherjim]

The layout is verified in so far that it works. That doesn't mean the design is optimal. It was originally purely a chorus - noise on the delayed signal is obscured by the clean signal when mixed about 50/50. the Vibe mod is a cheap add-on, but bear in mind the circuit wasn't designed as a Vibe, but as a low part/cost chorus.

Here's how the 78L05 regulator should have the ceramic caps added (not my design). The original LA didn't have any, never mind the one fitted across the regulator in that layout.



The way I read that LA layout, the 100nF cap across regulator I & O pins is giving any high frequency noise from the power supply a fast, no waiting route into the circuitry instead of bypassing it to ground.

You can also see a 47uF cap on pin2. This is the reference voltage bypass cap. LA can't use a large value capacitor here because the LFO wave needs to drive pin 2, but I think there should be some. 100nF ceramic won't affect the LFO but will cut HF noise on the reference. If you have one, a 1uF Tantalum cap might be more effective.

As said you can clean it up by increasing some filter caps on the audio side of the chip, but too much and it will reduce the chorus effect.

[Elijah-Baley]

Thank you, but sorry man, english and some tecnical terms put me in difficult.

You're seggustion to make (or try) some adding, right? Do you think I can use my layout with no problem?
Then I should understand exactly what kind od components, value and where I have to put them.

Thank you again! 

[anotherjim]

Yes, I do mean add components.

To begin, you can do the regulator caps.
Remove the 100n cap between I and O pins of the 78L05.
Get a 100n ceramic cap, bend the wires in so it fits a 2 hole grid. Fit it between 78L05 I and G.
I've just noticed the layout does have a 100n between G and O at the edge of the board. If this is a ceramic, leave it there. If it's not ceramic, change it for one that is.

It's good to have a ceramic cap as close as possible to the power pins of the chip, you can fit another 100n ceramic between pin1 and pin3.

Finally, to filter the reference supply on pin2, at the left edge of the board, you can fit one more 100n cap across the strips that lead out from pins 2 and 4.

That's dealt with the power supplies, which MAY NOT completely solve the noise problem, but at least you can be sure the circuit is now reasonably immune from radio interference or of causing interference to others.

Now attack the audio filtering on the other side of the chip.
Now I suggest trying some things out first. You can use any type of capacitor for testing, but Film type caps would be preferred. But, if ceramic is all you have and it works, use it.

On the back of the board, solder a 47n cap between PT2399 pins 11 and 12. If that works, you can replace the 10n already fitted there.
Standard design value with this chip is a 100n in this position, so try 100n if 47n wasn't enough.

Finally, if all else fails, try adding 10n or 22n between pins 13 and 14. This will make the delayed sound darker, and may spoil the chorus effect. You will just have to try it. If it reduces noise for the Vibe effect, but spoils the Chorus, you can add this extra cap using an SPDT switch and call it a "Dark" switch and think of it as an added feature

[Elijah-Baley]

Ok.
I have to make an order for this new components, but not much soon. I let you know my progress later.
Thank you! 

[anotherjim]

The more I think about it, the more I believe the 100n that is shown on the layout connected between I and O of the regulator is an error. That 100n was meant to go between I and G.
I would try fixing that, using the same 100n cap if that's all you have.

[Elijah-Baley]

Seems to me really weird this error.
The schematic is much discussed and the layout verified, and some builds it with less problem.