Sonic Boomer build report

[RickL]

I built this from the layout at Topopiccione http://topopiccione.atspace.com/PJ09EHSonicBoomer.html several months ago and couldn't get it to work. Today I found a wiring error I'd made, but more importantly there seems to be an error on the layout.

The schematic shows R3 and R4 connected, then going to pin 3 of the op amp. The mic element connects through C1 to this junction. The layout has R4 connected to the wrong end of C1. When I corrected this the SB started to work. Note that the site says the layout has been verified.

I also found that I had to drastically reduce the Sensitivity pot from 1M down to 10k to get any usable range. A 5k or even 2k might work even better. I still can't get the Trigger input to work. I rewired the jack using a switched mono jack to disable the mic input when the Trigger jack is used thinking the mic might be interfering but no luck. I was trying to trigger it with the output of a guitar, but I wonder if it needs a 5 volt pulse.

It sounds cool! Everything from super deep bass drum sounds to high pitched plinks. Watch the Sensitivity and Resonance pot settings though, it's easy to send this thing into uncontrolled feedback. Some frequencies seem more sensitive to this than others. Resonant frequency of my guitar amp (JC 120) maybe?

[Zero the hero]

 
Me so stupid. Teh error in the layout. I go and see my llayout...teh correction as soon as I can!


Thanks for pointing out this mistake, unfortunately, I've dismantled my prototype ao I cannot check what I did. I think I've built a corrected version of this layout and, while trying to compact the layout, this mistake has been added.
By teh way, what op-amp did you used? And what kind of mic?

[Mark Hammer]

Possible the wiper of P1 goes to C1 and not to ground as shown in the schematic?  That would seem to make a helluva lot more sense....well, to me anyways.

[Zero the hero]

I post the schamatic of the original unit, in order to clarify everything...
http://img.photobucket.com/albums/v368/zero_thehero/schematics/SonicBOOMER.jpg
Actually P1 wiper goes to ground, why Mark in this way does not make sense to you? P1 is configured as a variable resistor, so a different wiper connection affects only the pot rotation (CW or CCW for less sensitivity), or am I missing something?

[Mark Hammer]

I am not going to insist that I am right, because there is a LOT that I don't know, but there are a few things that are making me think the schematic is incorrect.

1) There is no way shown to adjust the gain of IC1a.

2) There is no way to adjust the input voltage of the crystal/piezo mic or the trigger except for loading them down via P1.  In other words, there is no way to *divide* the voltage from these sources.

3) Rick had to drop the value of P1 a considerable amount, and when he did the trigger input would not work.

4) If you rotate the wiper to one end, then the junction of C12 and C1 is grounded.  Why would they do that?

5) C12 and P1 form a highpass filter as they are shown right now.  If Rick reduces the value of P1 to 10k and turns it down a bit, the corner frequency can be 20hz or higher.  That just seems wrong fro accepting either a trigger pulse or a piezo signal.

[RickL]

Okay, I tried it Mark's way (1M Sensitivity pot wired as a voltage divider, wiper to C1). It also works but there's still not much usable range on the pot. It's all bunched towards one end, although it is easier to control than the way the schematic shows.

The Trigger still doesn't work. I can get it to work a bit if I feed it a 9 volt pulse (connect a battery ground to a short patch cord, insert the patch cord into the jack and quickly touch the + of the battery to the tip of the cord). It doesn't work very well and I can get it to ring by turning up the Resonance like I can with the mic element. Strangely, tapping the mic at this time gives me about the same response. The mic is disconnected by plugging the patch cord into the jack.

I'm using a TL074 and an unmarked condenser mic capsule that is about 1/4" in diameter. I got it in a package of 10 for a couple of dollars.

[Zero the hero]

It seems that I was missing many many things!
Thanks for pointing out all those possible source of error.
I tried to stay as close as possible to the original, while drawing the schematic, that's  why I didn't add any control to set the gain of IC1a.
The only difference between the schems is the resistor divider which supply the condenser mic: I chose to drive it with half the supply voltage and I thought that no further adjustment would be needed.

[TELEFUNKON]

mic mismatch (polarity?)