Alien Screamer Noise Box question

[snivelsnot]

Hi all, I've just completed my first Alien Screamer Noise Box (http://www.musicfromouterspace.com/forums.html?MAINTAB=SYNTHDIY&PROJARG=ALIENSCREAMER/ALIENSCREAMER.php&CATPARTNO=ALIENSCREAMERPCB), but it doesn't work properly - it just produces low-frequency beat without any sighnificant high frequency modulation on it (http://imageshack.us/a/img201/9100/asnb.jpg), so I have a couple of questions:
1)Aluminium non polarized capacitors of a 1uF value are not available in the element stores, so what would be a better replace:
- 2 aluminium non polarized capacitors of a 2.2uF value, connected sequentially;
- a ceramic capacitor of a 1 uF value;
- a film capacitor of a 1 uF value?
2)A LM386N3 chip also doesn't appear to be available to buy (LM386N4 neither), so can I use a LM386N1 chip instead? As I have figured, it wouldn't affect the circuit in any way except lowering the speaker volume, which can be compensated by using a speaker with lower resistance (< 8 ohms).
I would appreciate any advice or correction, thanks in advance!

[elmegil]

Good luck finding a ceramic at 1uF!

I would use ( and have ) the back to back electrolytics....

I don't usually work with LM386 chips at a detail that cares about N1/N3/N4 so perhaps someone else will be able to answer that.

[snivelsnot]

Thanks a lot for the advice about capacitors, but do you think using the right ones can solve the modulation problem? Is the schematic presented on the web (http://www.musicfromouterspace.com/forums.html?MAINTAB=SYNTHDIY&PROJARG=ALIENSCREAMER/ALIENSCREAMER.php&CATPARTNO=ALIENSCREAMERPCB) correct after all?

[elmegil]

I have done a lot of troubleshooting of various Ray Wilson designs, and I have yet to find a mistake in his schematics.

You say "the right one", but you have not described what "the wrong one" might be, so I have no idea as to the cause of your beating problem.

In what ways have you deviated from the schematic?

Are you using Ray's PCB?

[snivelsnot]

I've actually assembled the noise box twice - for the first time I was using a breadboard and wires and for the second time I printed a circuit board myself according to Ray's schematics. Both times the deviations from original circuit included using 1uF ceramic capacitors instead of non-polarized electrolitic ones (C4 and C12) and a LM386N1 chip instead of a LM386N3 (or 4) one. I've also simulated the work of the noise box in MicroCap9 but without the amplifier part (LMN386 chip is not present in MC9), the problem seems to be the same - the output signal appears to have no high frequency component. I'm attaching the pictures of the circuit I've built in MC9 and the output signal:
http://imageshack.us/a/img191/7821/asnbcircuit.jpg
http://imageshack.us/a/img201/9100/asnb.jpg
Once again thanks a lot for your interest in my little experiment!

[analog_backlash]

[wayoda]

Hi,
this post here
http://www.diyaudio.com/forums/parts/117452-non-polar-electrolytic-vs-polypropylene-film-capacitors.html
suggests that film-capacitors are an improvement to non-polarized elcos at least in audio circuits.

I also can't think of any (pyhsical) reason why a film-capacitor should not work here

[analog_backlash]

Right. Finally got round to it. I breadboarded the circuit and it seems to work fine. There's an mp3 file attached. There are a few glitches, because I'm working on a breadboard and I've used preset pots, but basically, it seems OK. I tried changing the capacitors C4 and C12 and it worked on everything I put in, i.e.

1uF multilayer ceramics
2.2uF non-polarised electrolytics (I didn't have 1uF)
220nF mylar (ditto)
Two back-to-back 2.2uF polarised electrolytics (i.e. 1.1uF)

The example that I've posted uses the final combination, although all seemed to work pretty well.

I've also posted some waveforms. The left-hand side 3 traces are of the LFO waveforms (from the common of S2). These are as shown in Ray's schematic. The right-hand side traces are of the output waveform (from C12). The top one is unmodulated (a ramp), the middle is squarewave modulated and the bottom one is in sync mode.

These outputs are all before the amp stage. I had an LM386-N1, so I tried that and got quite a loud output, especially when I added the 10uF capacitor across pins 1 and 8 of the amp.

I think that this confirms that you have a problem in the VCO part of the circuit as you are only getting the low frequency output of the LFO. I'd check that part very carefully, as I don't think that there should be any problems with the components that you have used.

Gary

EDIT

Forgot to say that if you use a standard brightness LED, the output is a bit pathetic. I changed it the a bright blue one (not one of the really high brightness ones) and I got much better results. Also:

[snivelsnot]

Thanks a lot for such a detailed answer, from now on I'm sure the schematic is correct. I'll try check the quality of my components and soldering itself!

[stolenfat]

I under stand this is an older topic but I recently built up this circuit on Ray's PCB and had a very similar problem (low freq only, LED flashed). There is a node on his PCB silk screen labeled ground... which I naturally soldiered to the ground of the battery. Turns out its actually at 4.5v (so kinda like a false or half ground which im sure is to help the opamps work propperly) As soon as I unsoldered the node labeled ground and just left it free floating... it worked fine.