Tractor Beam power /LFO issue SOLVED

[wizestwizard]

I had the tractor beam working, but some of the transistor sockets were a little loose, so I desoldered them and soldered in the transistors. Now the effect no longer sweeps, it's just behaving like a fixed resonant filter. Some of the voltages are off now too : pin 7 of the OPA is about - 3.2V instead of 0 and while the source voltage of the JFETs is 0, the drain is sitting at around half a volt. Power in from the switching board is fine (+/-7.5 ish V). The schematic for this thing is a nightmare, so I was curious if anyone had any thoughts on what might have happened? No solder bridges anywhere and the only parts I changed were pulling out the sockets and putting in the transistors. Thanks in advance!

[jimilee]

Got my pics?


Sent from my iPhone using Tapatalk

[wizestwizard]

Sorry, I just saw this, I'm not sure why I didn't get a notification lol. I can show pics but I don't think they'll be helpful - all of the voltages are correct now (the V- wire had somehow come disconnected which is what was causing the weird readings before) , the parts are in the right places and orientations. It was working properly, I removed the transistors and sockets and soldered the transistors back in and now it's just behaving strangely. There's no modulation, which leads me to believe it's an issue with the LFO. By turning the "center" knob, it manually phases, sweeping the resonant frequency, and by turning the bias trimpot there's a point at which this also happens. I can't make heads or tails of the messy schematic to figure out where to look to pinpoint the LFO issue though, that's the major problem I'm having at this point. Something is causing the LFO not to oscillate lol

[wizestwizard]

Here are the pics, it's such a congested board that I don't think they'll be very helpful though lol. I'm guessing it's a dead component at this point rather than a soldering issue but any suggestions are appreciated

[jimilee]

Have you tried adjusting the jfet trimmer again?


Sent from my iPhone using Tapatalk

[wizestwizard]

Yes, when moving the JFET trimmer, there is a point in the sweep where you can hear the frequency/resonance changing, however, it doesn't phase on its own over time. Moving the "center" control also has this effect - essentially, you can hear phasing when manually turning either the "center" control or over a certain part of the JFET bias trimmer, but it will not modulate on its own over time, leading me to believe it's an issue with the LFO. When the JFETs are in the sweep spot on the trimmer, it acts like a fixed resonant filter.

[Aentons]

 Sounds like your lfo is not o-ing. Did you happen to pull the lm358 out when you pulled the sockets? Maybe there's a bent pin or a hair stuck in the socket

[wizestwizard]

That's my thought too, I just couldn't figure out where to begin troubleshooting because 1) I'm still somewhat new to building (I've built a bunch of pedals, ~50, but I still don't understand all the specifics of more complex effects like those that are time based) and 2) the schematic for this is particularly hard to read, plus nowhere in the build doc does it show the component numbers (which are on the schematic) matched up to which component they are lol. I didn't remove the LM358 but I can pull it out and check it /swap it for another

[wizestwizard]

Switching the LM358 didn't help unfortunately. No idea what's going on.

[wizestwizard]

Anyone have any additional thoughts? Lol

[jimilee]

Hopefully Brian or someone will be round to help.


Sent from my iPhone using Tapatalk

[wizestwizard]

That was my hope but since it's been a month I kinda lost hope. I just tried pulling and resoldering the transistors, checked them after I pulled them to make sure they were still OK and they are. Just fought with the bias trimmer again as well after putting them back in, still same issue. I feel like it's gotta be one of the components in the LFO but between my lack of knowledge and the crazy schematic idk where to even start lol

[wizestwizard]

One of the resistors (3k3 next to the bipolar cap to be exact) had somehow broken off from the lead right at the board. Replaced it, works great now!