Harbinger 1.5 - no modulation

[jessenator]

Another one of my "started sometime early last year" projects comes back to bite me.

So I've got it built for 9V operation, the lamp is illuminating controlled by the rate, and affected by the two trimmers, and the volume control works on the signal while engaged. I can "hear" the pulsation —albeit incredibly subtly— of the lamp when I bridge the end of an input lead, but no actual modulation is taking place on an audio signal—other than the volume adjustment working, it sounds otherwise completely clean.




No solder bridges I can see.

I could just start probing, but if anyone has insights as to where to start, I'd be much obliged! Thanks.

edit: the shield is taped on—I made a dum dum and soldered (and now clipped) the wire holding it in place before actually testing, so I clipped it off to make sure the lamp worked  :/

[3knobfury]

I would start probing the transistors (Q4-Q10) through the phasing section specifically the emitters of the odd numbered ones. You can also verify at the base of the even numbered ones. I just probed my recently completed harbinger 2 to verify my thoughts based on the schematic. Interestingly, a few of the pairs I probed gave less of a distinct modulated signal and am wondering if that correlates to the LDR they are matched with since my LDRs were not EXACT matches.

[jwin615]

We all good right here?

[jessenator]

We all good right here?

Yeah. The light caught that all weird, but yeah, no bridges. The missing bits are part of the 18V build option. I even sharpied out the silkscreen on the top so I wouldn't get confused lol

I would start probing the transistors (Q4-Q10) through the phasing section specifically the emitters of the odd numbered ones. You can also verify at the base of the even numbered ones. I just probed my recently completed harbinger 2 to verify my thoughts based on the schematic. Interestingly, a few of the pairs I probed gave less of a distinct modulated signal and am wondering if that correlates to the LDR they are matched with since my LDRs were not EXACT matches.

Interesting. I'll have to take a look. I managed to get some of the on-spec LDRs when SmallBear came back online. I'm hoping I didn't royally screw up by soldering in all of those transistors. I've gotten myself out of that mess before, but still.

[3knobfury]

Nice! I missed out on the real deals b/c I never really thought I would have the balls to undertake the harbinger 2. One other thought, is the lamp changing when you turn the intensity pot? If it doesn't might mean you're getting modulation just that the I testify is so low that you're not hearing. If it does, then it's probably still in the phasing section.

[madbean]

Here's a little trick you can try: turn the speed and depth all the way down, adjust the trimmers if needed so the bulb doesn't illuminate at all. With sufficient ambient light in the room play a chord and put your hand between the room light and the LDRs. Wave your hand up and down so you block out the ambient light in pulses like the lamp. You are now doing a mechanical LFO. If you still don't hear any phase shifting at all the problem is in the phase shift area of the circuit for sure, or the actual LDRs are problematic themselves.