[sdiy] Kraakdoos output revisited

[The Peasant]

I have built a total of four Kraakdoos so far, here is what I have experienced:

The first two were the CrackleKats on my webpage. Both worked well right from 
the start, although one is noticeably louder than the other one. Actually, the 
loudest one is almost earsplitting, a very surprising volume level for such a 
small circuit. I attribute the difference to different speaker efficiencies, 
although I have no proof to back this up. Certainly the lm709 is not the 
culprit, as I built a socket into one CrackleKat and have tried different chips 
with no obvious differences found. I have also used the same 2N3904/6 
transistors in both, as well as the other parts.

I recently built a third Kraakdoos for a friend, but I used a 12 ohm speaker 
instead of 8 ohms (it fit the enclosure just right!). At first the output was 
so low that it was barely audible, so I tried some different 8 ohm speakers, 
with almost no effect. I ended up using a 10K - 8ohm transformer on the output 
before the speaker, which brought the sound level up to a reasonable level, but 
did make a minor change to the sound itself, damping the high frequencies a 
bit. Since I already was using a transformer (although it's wired backwards to 
what one would expect) I also included a line out jack, but I have not 
connected it to the PA yet to see how that sounds. Maybe tonight?

So I built up a fourth unit, but after many attempts all I seem to be able to 
get out of it is a clicking sound. Virtually every part in it has been replaced 
at least once, but to no avail. The 709 works fine in my CrackleKat, but not 
here. I will spend a few more hours on this one tomorrow, before I go on to 
other things.

It seems strange that out of four attempts at such a basic circuit they all 
gave different results. This would appear to be a fairly sensitive and unstable 
circuit (partially due to the "body" interaction). Usually when I build 
multiples of a circuit they function identically, even the complicated circuits 
on my Monster Drum Synth. If anyone has any suggestions on what might explain 
all this wackiness, I'm all ears.

Take care,
Doug
______________________
The Electronic Peasant

www.electronicpeasant.com


Quoting Metrophage <c0r3dump23 at yahoo.com>:

> I just got a lot of my junk back from the storage facility near my
> parent's house, and sorting through it found the little output
> transformers I wanted to use for my Kraakdoos output. I don't recall
> what they are supposed to be specifically, but for some reason I
> thought they'd be 8 ohm - 10k ohm (I know I've asked how to measure
> transformer windings before, I'll look it up later).
> 
> With the voltage divider which was suggested before (by Ian and Henry),
> the output was at a decent level, but my problem was that the output
> connection interacted with the Kraakdoos circuit. Example? I could have
> my fingers on the contacts to produce a certain oscillation, meanwhile
> I'd plug in the output to my amp, and the oscillations would change
> drastically. Sometimes they'd even stall. So, it was very much playable
> without the output being used, and slightly less so connected to an
> external device. The output changed the "action" of the circuit.
> Consider though, that the Kraakdoos circuit is an old-style op-amp
> which is induced to feedback and re-bias via finger contacts, it is
> designed to be very sensitive to the point of crazy.
> 
> I just removed the voltage divider and cap which I'd done before, and
> tried Godfried's method of simply connecting an 8 ohm - 10k ohm
> transformer to the same points in the circuit as the speaker. It is no
> better! Even with transformer output, plugging in an output cable to my
> amps, soundcards, etc changes the sound. I don't understand how this is
> working. I suppose I can live with it, but I am perplexed. I love the
> way the unit plays and sounds ordinarily, so am not inclined to change
> it very much. Weird though that none of the others who accounted their
> Kraakdoos building recently have experienced this. I'll try building
> another one later with banana-plug contacts (for electrodes, etc) and
> switchable caps, maybe it will be a different story.
> 
> Not really looking for any answers here, just thinking out loud.
> CJ
> 
> 
> 		
> __________________________________ 
> Yahoo! Mail - PC Magazine Editors' Choice 2005 
> http://mail.yahoo.com
>