Tremulus Lune - Depth affects volume

[patrick398]

Greetings Comrades, and happy new year!
I built a tremulus lune (3 knob version without fine or spacing pots) before christmas which i was happy with but now in the cold light of 2018's bleak mid-winter i think i was just ignoring the issues i was having.

Basically it all functions fine except that when i adjust the depth there is a quite considerable change in volume. When the depth is at 100% it's near enough unity, when i turn it down to 50% it gradually gets quieter, and then on the way down to 0% it starts to get louder again.

I've tried adjusting the internal trimpot but this doesn't affect the volume change just changes the overall gain on the circuit.
Any ideas why the depth would alter volume? I've been looking at the schematic and i just can't see why it would.

Schem:


3 knob Vero:



Thanks

[duck_arse]

does the depth pot affect the depth? it's a fair chance you've miswired wiper and one end of that pot, but we won't know until your build photos appear.

[patrick398]

Yeah the depth pot works fine. I can live with it because at maximum depth and around 30-40% it's near enough unity, it's just frustrating me that there's this volume drop in the middle of the turn.

Ah...the build photos. I can upload some, reluctantly. It's by far the crummiest, messiest build i've ever done. Was in a mad rush and really just wanted to cram it in the box...i guess that's probably my issue haha.

So the depth pot is sweeping between 9v through 330R (which i'm guessing is 0% depth) and pin 1+2 of the LFO IC (which is 100% depth)?

Thanks for the reply Duck!

[duck_arse]

yeah - top o'the pot will be near full bright led, other end of the pot will be on/off/on of some shape. the led connected to the wiper voltage-dividers between the extremes.

and it's not good enuff telling us "oh, I fixed it, thanks", youse gots to show those pics.

[patrick398]

My god it looks even worse outside the box 
This is bad even by my standards haha. I'll try and talk you through this scramble of wires. Where there's tape i think the wires weren't long enough so length added. The footswitch was salvaged from another pedal which was soldered to a daughterboard (a nightmare to get off, i'm surprised it still works). The tape coming off speed pot is a diode for the ramp switch.

Pot wiring looks alright to me...

[patrick398]

OK, I still haven't got a particularly good technical knowledge but i think my hunches are becoming better. I realised i was using a 2k pot instead of 1k for depth, don't think this would have too much baring on my problem but thought i may as well whack a 1k resistor across it while i had it out. Also i was using a super bright LED in my 'vactrol' so thought maybe that could be sucking too much current. Swapped it out for a normal 3mm red and bingo, proper depth control with no volume difference.

Is this something to do with the super bright LED's compatibility with my LDR or the fact that it draws more current from the LFO...or am i groping around in the dark here?

[highwater]

Could just be that the super-bright LED was still lit-up a bit even when it was supposed to be off. Tweaking the resistor values could probably have gotten it working, but swapping for the red LED is by far the easier way to do it.

And don't worry about the messy build... the "PCB" in the originals was literally a piece of cardboard. I've never seen one myself, but I'd be willing to bet yours is a fairly clean build by comparison.

[duck_arse]

superbright or normal diffused, the led will only eat the current you allow it. and that's determined by the pot/resistor string. I think the 2k pot might have unbalanced those two 1k/1k legs. would need Mr Ohm to work that out properly.

and yeah, S/B w/ only 1k clr might get a little on the bright side.